Transplasma membrane electron transport in plants

Journal of Bioenergetics and Biomembranes, Vol. 23, No. 3, 199l

MINI-REVIEW

Transplasma Membrane Electron Transport in Plants

Prakash C. Misra ~

Received July 30, 1990

Abstract

The presence of transplasma membrane electron transport in a variety of plant cells and tissues is reported. It is now agreed that this property of eukaryotic cells is of ubiquitous nature. Studies with highly purified plasma membranes have established the presence of electron transport enzymes. Two types of activities have been identified. One, termed "Standard" reductase, is of general occurrence. The other, inducible under iron deficiency and relatively more active, is "Turbo" reductase. However, the true nature of components par- ticipating in electron transport and their organization in the plasma membrane is not known. The electron transport is associated with proton release and uses intracellular NAD(P)H as substrate. The electron flow leads to changes in intracellular redox status, pH, and metabolic energy. The responsiveness of this system to growth hormones is also observed. These findings suggest a role for electron flow across the plasma membrane in cei1 growth and regulation of ion transport. Involvement of this system in many other cellular functions is also argued.

Key Words: Transplasma membrane electron transport; plasma membranes.

Introduction

Considerable work has been done over the past 10 years to understand the nature of transplasma membrane electron transport and its relationship to intracellular electron donors, associated proton release, cell respiration, and growth in plants. Conflicting claims have been made vis-a-vis studies with mammalian cells. Since a number of reviews have appeared on this subject in recent years (Crane et al., 1985; Moller and Lin, 1986; Bienfait and Lüttge, 1988; Crane, 1989; Crane and Barr, 1989), a comprehensive survey of the

Department of Biochemistry, Lucknow University, Lucknow-226007, India.

425

0145-479X/9[/0600-0425506.50/0 ~ [991 Plenum Publishing Corporation

426 Misra

literature is not intended. My purpose in this article is to sketch out a possible role for such an electron transport from the data these studies have provided. I begin by asserting that the presence of redox activity at the surface of plant cells provides an additional mechanism to control its metabolism.

Electron Transport

The presence of transplasma membrane electron transport in plants was reported by Craig and Crane (1981) as a preliminary demonstration of extracellular ferricyanide reduction in cultured carrot cells, and subsequently established to be an enzymatic process (Barr et al., 1985a). In the meantime, a number of laboratories provided evidence for the existence of such a reaction in a wide variety of plant cells including yeast (Crane et aI., 1982; Yamashoji and Kajimoto, 1986a), plant roots (Federico and Giartosio, 1983; Sijmons and Bienfait, 1983; Roemheld and Marschner, 1983; Rubinstein et al., 1984; Boettger and Hilgendorf, 1988; Buckhout et al., 1989), tobacco cells (Barr et al., 1984), Elodea (Ivankina and Novak, 1981; Marré et al., 1988), Anacystis nidulans (Craig et al., 1984), Lemna giba (Lass et al., 1986), sycamore cells (Blein et al., 1986), angiosperm parasites (Revis and Misra, 1986), mesophyll cells of Asparagus (Neufeld and Bown, 1987) and guard cells of Vieiafaba (Vani and Raghavendra, 1989). In most cases ferricyanide is used as electron acceptor because of its impermeability to the plasma membrane and the relative ease with which its reduction is monitored. Sijmons and Bienfait (1983) used extracellular Fe(III) • EDTA as electron acceptor at the root surface of iron-deficient bean plants. Further studies helped to distinguish two types of redox activities (Bienfait, 1985; Bienfait and Lüttge, 1988). One is induced by iron deficiency and is present in dicots and nongrass monocots (but see Rensch and Boettger, 1988) and is called the "Turbo" system. The second type, generally present in all plant materials, is constitutive in nature and is called the "Standard" system. The high reducing activity of roots as observed in bean plants, attained upon iron deficiency, is able to reduce many other electron acceptors (Sijmons and Bienfait, 1983; Buckhout et al., 1989). The use of ferricyanide as the sole electron acceptor in most of the studies appeared to be a serious limitation to Luethen and Boettger (1988), and they showed that hexachloroiridate(IV) could be used as a new electron acceptor for the plasmalemma redo× system in maize roots. The high redox potential for hexachloroiridate (E0 = 0.87) makes it a preferred electron acceptor under certain conditions. For example, the slower rate of ferricyanide reduction by yeast cells encouraged Yamashoji and Kajimoto (1986a) to use the catalytic action of vitamin K3 as a redox mediator for the reduction of ferricyanide by Sac«haromyces cells. Similarly,


Table I. Transplasma Ferri¢yanide Reduction by Plants

427

Cell or tissue

Rate of reduction (/~mol min- 1 g wet weight- l ) Reference

Anacystis nidulans 0.05 Asparagus (mesophyll cells)

Dark 1.55 ~ Light 22.9 a

Bean roots Fe-sufficient 0.05 Fe-deficient 0.17

Carrot cells 0.23 Corn roots 0.02 Corn roots 0.018 b Cuscuta (apical segment)

Dark 0.38 ~ Light 0.64 c

EIodea (leaves) 0.31 d Elodea (leaves)

Dark 0.05 Light 0.12

Rhodotorula 0.015 »

Saccharomyces O. 11 Saccharomyces 130 e Shizosaccaromyees 0.02 »

Sugarcane (protoplasts) 1.33 f Tobacco callus 0.03 Tomato roots

Fe-sufficient 0.02 g Fe-deficient 0.11 g

Craig et al. (1984)

Neufeld and Bown (1987) Neufeld and Bown (1987)

Lubberding et al. (1988) Lubberding et al. (1988) Cf. Crane et al (1985) Federico and Giartosio (1983) Luethen and Boettger (1988)

Revis and Misra (1986) Revis and Misra (1986) Marré et al. (1988)

Elzenga and Prins (1989) Elzenga and Prins (1989) Srivastava and Misra (unpublished data) Crane et al. (1982) Yamashoji and Kajimoto (1986a) Misra and Hoefer (unpublished data) Thom and Maretzki (1985) Cf. Crane et al. (1985)

Buckhout et al. (1989) Buckhout et al. (1989)

aRates are expressed as 109 cells 1. bRates with hexachloroiridate(IV) as electron acceptor. «Based on wet weight = 10 x dry weight. «Rate is average over 90min measurement. « Rate promoted by vitamin K 3 . fRate expresed as 104 cells -t. gRates with Fe HEDTA (N-hydroxyethylethyldiamine triacetic acid) as eleetron acceptor.

in yeas ts S h i z o s a c c h a r o m y c e s a n d R h o d o t o r u l a an a p p a r e n t n o n r e d u c t i o n o f

f e r r i cyan ide is c h a n g e d in to a s p o n t a n e o u s r e d u c t i o n wi th v i t a m i n K3, bu t

the use o f h e x a c h l o r o i r i d a t e is m o r e c o n v e n i e n t to d e m o n s t r a t e a m e a s u r a b l e

ra te o f t r a n s p l a s m a m e m b r a n e e l ec t ron t r a n s p o r t ( M i s r a and H o e f e r , u n p u b -

l i shed resul ts ; S r i v a s t a v a a n d Mis ra , u n p u b l i s h e d results). T a b l e I p resen t s

the d a t a for t r a n s p l a s m a m e m b r a n e e l ec t ron t r a n s p o r t by s o m e p lan t cells.

T h o u g h a strict c o m p a r i s o n o f t r ansp l a sma m e m b r a n e e lec t ron t r anspo r t

ac t iv i ty in d i f ferent sys tems c a n n o t be m a d e because o f va r i ed e x p e r i m e n t a l

cond i t i ons , still the va lues give s o m e idea o f the re la t ive act iv i t ies in d i f ferent

c o n d i t i o n s o f l ight and nu t r i t i on .

428 Misra

Sources of Electrons

There is substantial indirect and direct evidence indicating cytosolic NAD(P)H as a substrate for such an electron transfer. Stimulation of extracellular ferricyanide reduction by ethanol in carrot (Craig and Crane, 1981; Chalmers and Coleman, 1983) and yeast (Crane et al., 1982) is, prob- ably, the first indication for a role of cytosolic NADH in these reactions in plants. These cells possessed alcohol dehydrogenase activity, and the ethanol-stimulated ferricyanide reduction was inhibited by the alcohol dehydrogenase inhibitor pyrazole. Besides, glycolysis inhibitors, arsenite, malic hydrazide, and iodoacetate inhibited the transmembrane ferricyanide reduction (Craig and Crane, 1981; Revis and Misra, 1986). The dependence of vitamin K3-mediated transplasma membrane ferricyanide reduction on intracellular NADH level in yeast is also reported by Yamashoji and Kajimoto (1986b). These investigators recorded a marked decrease in the levels of intracellular NADH rather than NADPH upon ferricyanide reduction. NADH-dependent transmembrane electron transport is also suggested in guard cells of bean plants (Vani and Raghavendra, 1989). On the other hand, evidence is presented in favor of NADPH as a source of electrons for transplasma membrane reduction of ferricyanide and iron chelates by iron deficient bean roots (Sijmons et al., 1984b) and corn roots (Qiu et al., 1985). Additional support in favor of NADPH for such a role in Elodea densa leaves is presented by studying associated respiratory and metabolic changes (Trockner and Marré, 1988). Light-stimulated ferricyanide reduction in tissues capable of photosynthesis provided an indication of increased supply of NADPH under illumination (Dharmawardhane et al., 1987; Neufeld and Bown, 1987). Further work with iron-deficient plants established that not only iron-deficiency activated the electron transfer system in the plasma membrane but these cells also acquired a higher capacity to reduce cellular NADP + (Lubberding et al., 1988). On the other hand, the plasma membrane preparations isolated from iron-deficient tomato roots showed a marked increase in NADH-dependent Fe 3+ -citrate reduction compared to NADPH- dependent reduction (Buckhout et al., 1989). This suggested NADH as the preferential electron donor. Lowering of intracellular NADH and NADPH as a result of transplasma membrane ferricyanide reduction in Cuscuta has been reported earlier from the author's laboratory (Revis and Misra, 1988a), where a larger decrease in intracellular NADH than NADPH levels pointed to the major involvement of the former as an electron donor, though glutathione (GSH) levels were also lowered. Involvement of glutathione in transplasma membrane electron transport in carrot cells is suggested (cf. Crane and Barr, 1989). The role of ascorbate as an electron supplier is orte more possibility (Morré et al., 1986; Hassidim et al., 1987). From these data

Transplasma Membrane Electron Transport in Plants 429

it is difficult to generalize unequivocally what the true nature of the electron donor is.

Electron Carriers

In order to implicate the reduction of exogenous electron acceptors in transplasma membrane electron transfer, various electron acceptors have been used. NAD(P)H-dependent reductions of a variety of electron acceptors including ascorbate free-radical (Morré et al., 1986; Luster and Buckhout, 1988), cytochrome c (Lundberg et al., 1981; Buckhout and Hrubec, 1986; Sandelius et al., 1986), dichlorophenolindophenol (Buckhout and Hrubec, 1986; Sandelius et al., 1986), ferricyanide (Barr et al., 1986; Sandelius et al.,

1986), iodonitrotetrazolium violet (Buckhout and Hrubec, 1986), and various iron complexes (Sandelius et al., 1986) have been reported. Involvement of several other constituents associated with plasma membranes as possible electron carriers is also proposed. A blue light-sensitive cytochrome-flavin complex from corn plasma membrane was partially purified by Leong and B riggs (1981). Presence of light reducible cytochrome b in plasma membrane preparations from oat is shown by Widell et al. (1982). The possibility of cytochrome P-450/420 as a component of the blue-light reducible flavoprotein-cytochrome complex in plasma membrane is argued by Kjellbom et aI. (1985). Subsequent work in this line suggested a blue light-regulated photomorphogenesis in plants (Widell and Sundqvist, 1987). Recently, a flavin-mediated electron transport system sensitive to blue light in V i c i a f a b a

is suggested (Vani and Raghavendra, 1989). Whether the blue light-sensitive redox components are part of transplasma membrane electron transport system(s) is not clear presently. Plasma membrane preparations from S a c c h a r o m y c e s cerevis iae and A v e n a sa t iva roots have been analyzed by Ramirez et al. (1984) for the presence offlavins, cytochromes, and NAD(P)H dehydrogenase activities. The presence of a b-type cytochrome and flavin in plasma membranes isolated from soybean hypocotyls is also reported (Sandelius et al., 1986). The results of such studies are summarized in Table II.

Table Il. Redox Components Identified as Plasma Membranes of Plants

Flavin Cytochrome Plant sample (nmol mg prot- 1 ) (nmol mg prot- 1 ) Reference

Avena roots 0.21 0.22(560) ~ Ramirez et al. (1984) Glycine hypocotyl 2.4 0.5(561) Sandelius et al. (1986) Maize coleoptile 0.4 Yamamoto et al. (1985) Maize coleoptile 0.16(560) Widell et al. (1980) Saccharomyces 0.28 0( - ) Ramirez et al. (I 984)

~Values in parentheses represent wavelength of absorption of c~ peak.

430 Misra

The presence of a quinone-dependent NAD(P)H oxidase activity in the plasmalemma fraction from the Cucurbita hypocotyls is reported (Pupillo and DeLuca, 1982) and a role for quinones in plasma membrane-linked redox reactions in corn roots is suggested (Lin, 1984). Luster and Buckhout (1988) partially purified and characterized a NAD(P)H:duroquinone reductase besides NADH : ferricyanide and NADH : ascorbate-free-radical reductases from the plasma membranes of Zea mays. This work provided evidence for the presence of separate enzymatic redox components in maize. Recently, Luster and Buckhout (1989) have reported the purification and identification of a plasma membrane-associated electron transport protein from Zea mays roots. These studies provide convincing support to the concept that a transplasma-membrane electron-transporting assembly is operative in plant cells. Since in most of these studies artificial electron acceptors have been used in establishing the reactions, therefore, the questions pertaining to the true nature of electron acceptors under physiological conditions and the role of such redox system(s) in cell physiology are still to be cleared up.

Physiological Electron Acceptor

Oxygen is regarded as the natural electron acceptor for the transplasma membrane electron transport system (e.g., Crane et al., 1985; Bienfait and Lüttge, 1988). The dependence on oxygen for expression of maximum rate of transplasma membrane ferricyanide reduction by cultured carrot cells is demonstrated by Craig and Crane (1981). It is found that about 46% of the ferricyanide reduction rate is dependent on the presence of oxygen. Inhibition of oxygen uptake during transplasma membrane ferricyanide reduction in Anacystis is reported by Craig et al. (1984). This suggests that a plasma membrane respiratory system may, at least, be partially involved. These findings are further confirmed by Peschek et al. (1988) who reported that the anaerobic reduction of ferricyanide is faster than under aerobic conditions. Competition for electrons between ferricyanide and oxygen is also observed in seedlings of Zea mays (Boettger and Hilgendorf, 1988).

In addition, support in favor of oxygen as the natural electron acceptor at least in the case of the "Standard" reductase comes from observations where exogenous NAD(P)H is oxidized by cells (or protoplasts) and tissue segments. Stimulation in oxygen consumption of corn root segments and protoplasts by exogenous NADH is reported by Lin (1982) and subsequently by Kochian and Lucas (1985). Cultured carrot cells also respond to an external supply of NADH in similar fashion (Misra et al., 1984). Further support for these observations is provided by studies with oat roots (Rubinstein et al., 1984) and sugarcane protoplasts (Thom and Maretzki, 1985). Stimulated


oxygen consumption on incorporation of NADH into purified plasma membrane vesicles from wheat roots is also observed (Moller and Berczi, 1985, 1986). All these studies provide substantial support to the concept that oxygen is one of the terminal electron acceptors under physiological conditions. The role of oxygen as terminal electron acceptor and the need for intermediate electron carriers in transplasma membrane electron transport is also supported by studies using a nitroxide spin probe (cf. Crane, 1989). However, the rate of electron transport under these conditions is a matter of speculation.

On the other hand, the plasmalemma redox activity more pronounced in root cells of iron-deficient plants, referred to as the "Turbo" reductase, is involved in reducing extracellular ferric chelates (Bienfait, 1985; Roemheld and Marschner, 1986; Buckhout et al., 1989). Since such an electron transport is associated with release of H + from the cells (see following section), it is argued that this H + excretion helps in increasing the ferric ion solubility in the soll, and the electron transport from root surface cells reduces the ferric chelates before iron uptake by the plant. The resulting ferrous ions are easily absorbed by the roots (Chaney et al., 1972). The Fe 3÷ chelate splitting activity in iron-deficient roots was reported earlier (Roemheld and Marschner, 1983). As such, the proposition that ferric chelates are the natural electron acceptors under these conditions may be acceptable. Also, a role for nitrate and semidehydroascorbate as physiological electron acceptors for the system is suggested (Crane, 1989).

Proton Extrusion

Evidence for proton release associated with transplasma membrane electron transport, both in "Turbo" and "Standard" systems, has been put forward by many investigators (e.g., Crane et al., 1985; Lass et al., 1986; Belkoura et al., 1986; Luethen and Boettger, 1988; Marré et al., 1988). The proton extrusion in the presence of exogenous electron acceptors is thought to be an alternate to the better known ATP-driven proton pump (Ivankina et al., 1984; Lin, 1985; Bown and Crawford, 1988), though doubt about it contributing to the proton electrochemical gradient is expressed (Macri and Vianello, 1986; Giannini and Briskin, 1988). The stoichiometric relation between the electron transport and associated proton release in this system is still a matter of controversy. Table III represents the stoichiometry of e- /H ÷ in some of the plant cells.

There exist different views on the coupling between the two processes. Some workers suggest a direct linkage of electron and proton transport via the plasma membrane redox system (Craig and Crane, 1985; Boettger et al.,

432 Misra

Table III. Ratio of Transplasmalemma Ferricyanide Reduction to Proton Release by Plants

Fe(CN)~ - Redox-induced reduction H + release

(nmolmin -~ g (nequiv • min L g Ratio Cell or tissue wet weight -1) wet weight 1) e- /H + Reference

Asparagus (mesophyll cells) Dark 1.55 a 1.54 ° 1.01 Neufeld and

Bown (1987) Light 22.9 a 26.1 « 0.88 Neufeld and

Bown (1987) Bean roots (Fe-deficient) 168 83 2.02 Sijmons et al.

(1984a) Carrot cells 48 60 0.8 Cf. Crane et al.

(1985) Corn roots 20 8.0 2.5 Federico and

Giartosio (1983)

Corn roots 18 b 30 ò 0.6 Luethen and Boettger (1988)

Cuscuta (apical stem) 455 c 59 « 7.77 Revis and Misra (1988b)

Elodea (leaves) 314 « 149 a 2.1 Marré et al. (1988)

Saceharomyces 270 230 1.17 Crane et al. (1982)

Saccharomyces 130 ~ 120 « 1.08 Yamashoji and Kajimoto (1986a)

°Rates are expressed as 10 6 cells -~. »Rates with hexachloroiridate(IV) as electron acceptor. CBased on wer weight = 10 x dry wt. «Rates are average over 90 min measurement. ~Rates promoted by vitamin K 3.

1985; Belkoura et al. , 1986; Boettger and Luethen, 1986; Neufeld and Bown,

1987; Bown and Crawford, 1988) and thus propose it to be an al ternative means for the cells to regulate t ranspor t and growth. P lant hormones , indole-

acetic acid and giberellic acid, s t imulated oxygen uptake in the presence of K C N and salicylhydroxamic acid (residual respiration) of carrot cells (Crane et al . , 1985). This pointed to the role of N A D ( P ) H oxidase in the plasma membrane , and it is interpreted that pro tons released by the t ransplasma membrane redox system may contr ibute to the total auxin- induced p ro ton release and thereby influence cell growth. In order to dist inguish the relat ion between t ransplasma membrane electron t ranspor t and associated p ro ton release in carrot cells, use of 8-hydroxyquinol ine, 4,7-dichloroquinoline, and retinoic acid as inhibi tors of plasma membrane electron t ranspor t reactions was made (Barr, 1988). It was observed that the inhibi t ion of electron

Transp|asma Membrane Electron Transport in Plants 433

transport is accompanied by a parallel inhibition in proton excretion, suggesting a direct coupling between the two processes. This view is further supported by the recent findings of Elzenga and Prins (1989) who stated that ferricyanide-induced H + extrusion in Elodea candensis is different from H ÷ transport coupled to plasma membrane ATPase.

On the other hand, studies with Zea rnays, Lemna gibba, and Elodea densa suggested no direct linkage between electron and proton transfer via the plasma membrane redox system (Rubinstein and Stern, 1986; Lass et al., 1986; Marr6 et al., 1988). These workers, like many others, observed that proton extrusion under these conditions lagged behind ferricyanide reduction. They suggested that the plasma membrane redox system transfers only electrons and this results in a rapid depolarization of the membrane potential and acidification of cytoplasm. This, in turn, causes the activation of the H÷-translocating ATPase and, in all probability, the opening of a K ÷ channel on the plasma membrane. Recently, Bienfait et al. (1989) have shown that Zn and Mn induce proton extrusion in Fe-deficient bean roots by

X H 2 -

x) in

H + ..~.. H ÷

( D e p o l a r i z a t i o n ) 4- I I ( - A p H ) 2 H ~ ,. I I I I I I I I " ' P - . I

~' ,-.- ~," ' L (act,v"~, i-on"~ H + I - - - - ~ J I H + ' - - • I P,~'I I I I i I \ . . . . - (act'vat'2". I._~ [K +

K+' L I I

Plasmalemma

Flavoprotein- cyt. complex

LH+-ATPase

channel

o u t

M

e- (-2Fo'CN':- ~db,.2Fe ( CN 146 -

Stimulation by FC

i .,inhibation by EB

. t .-H +.

4 -

Fe (CN) e

-AIH+4 - K*)

. K ~- 4-

=1

Fig. 1. Possible relationship between ferricyanide-induced transplasmalemma electron transport and associated H ÷ release implicating the role of ATPase (cf. Marr6 et al., 1988, with the permission of the publishers).

434 Misra

activating the synthesis of a highly unstable polypeptide which influences the proton-pumping ATPase in the plasma membrane. Also, a 22% increase in Mg2+-ATPase activity in plasma membrane from roots of iron-deficient plants is reported by Buckhout et al. (1989). Partial support of the redox- induced excretion of protons in cultured carrot cells by plasma membrane ATPase is also shown (Barr et al., 1987). Figure 1 shows the model for the proposed relationship between the transplasma membrane electron transport system and an ATP-driven H + -extrusion according to Marré et al. (1988). An implication of such a mechanism is the efflux of substrate and inhibition of growth. Such observations are reported for some plants (see following section).

Physiological Role

The significance of redox activities associated with membranes of mito- chondria and chloroplasts in energy-transducing processes in plants is well established. By analogy, relating transplasma membrane electron transport and associated H +-extrusion to some important cellular processes in plants appeared very exciting. The important aspects of cell physiology are growth and transport. Regulation of transport across the plasma membrane is a prerequisite to understanding the mechanism of cell growth and metabolism. The electrochemical proton gradient as the energy source for transport in cells is well recognized (Poole, 1978; Leonard, 1984). This proton gradient is generated on hydrolysis of intracellular ATP by plasmalemma ATPase(s) acting as proton pumps (Sze, 1985; Briskin, 1986; Anton and Spanswick, 1987). The proton extrusion associated with transplasma membrane electron transport suggests its role in energy-transducing processes, e.g., active transport. A relation between respiration and ion transport was postulated long ago (Robertson, 1960). The studies with L e m n a by Löppert (1981, 1983) provided evidence against the need for participation of a proton pump in hyperpolarization of plasma membrane. This indirectly supported a relationship between plasma membrane redox system and membrane potential. But this view was questioned recently by Ullrich-Eberius et al. (1989). Ivankina and Novak (1988), while studying the role of transplasmalemma electron transfer activity on K + transport in photosynthetic and heterotrophic plant cells, reported inhibition of uptake and excessive efflux of the ion that paralleled depolarization of membrane potential. It was proposed that such a redox system might play a regulatory role for H + -ATPase activity. Similar observations for K + influx/efflux associated with transplasmalemma ferricyanide reduction in plants have been made earlier (Sijmons et al., 1984a; Beilby, 1985; Kochian and Lucas, 1985; Rubinstein and Stern, 1986).


Table IV. Rate of Oxygen Consumption and L-Arabinose Uptake by the Yeast Rhodolorula glutinis Treated With Ferricyanide a

435

Rate of oxygen uptake Amount of sugar accumulated Sample ~molmin i mg dry weight -1) (#g mg dry weight -t • 10min -t)

Cells cultivated with ferricyanide

Control 3.73 15.8 Experimental 2.00 ( - 46.4) d 3.8 ( - 76)

Gells treated with ferricyanide for short time »

Control 3.94 14.2 Experimental 5.81 (+47.4) 34.3 (+ i41.5)

Cells treated with ferricyanide for lónger time «

Control 2.95 13.6 Experimental 2.39 (-18.9) 5.8 (-57.4)

~The concentration of ferricyanide was 1.0 mM and there was no cell death (Srivastava, R., and Misra, P. C., unpublished results). Yeast growth and measurements based on Srivastava and Misra (1981).

»Cells were treated with ferricyanide for 15 min before reaction initiated. «Cells were first treated for 14 h with ferricyanide. «Values in parentheses represent percent change from control runs.

However, these findings go against the role assigned to the proton electrochemical gradient generated by an H ÷ -pumping ATPase. On the other hand, transport of L-arabinose and 02 consumption in the yeast Rhodotorula glutinis is stimulated by ferricyanide. However, cells either cultivated with ferricyanide or exposed to it for long periods (14h) showed inhibition (Table IV). These findings are interpreted on the basis that the initial transport of electrons to ferricyanide marginally increases the NAD(P)+/ NAD(P)H ratio and this stimulates cell metabolism (Berger et al., 1982), but longer exposure to ferricyanide lowers the intracellular concentration of NAD(P)H to a level that is insufläcient to supply necessary metabolic energy for transport and/or reducing power to support growth (Table V). Ferri- cyanide induced an increase in 02 uptake in Elodea densa, as reported earlier (Trockner and Marré, 1988). Increased transmembrane electron transport activity in the roots of iron-deficient plants (Sijmons et al., 1984a, b) is correlated with the reduction of Fe 3÷ as a precondition for iron uptake (Chaney et aI., 1972). Though the experiments of Roemheld and Marschner (1983) with iron-deficient peanut plants using »9Fe[14C]EDDHA demonstrated that increased transmembrane reduction of iron chelates correlated well with their increased dissociation and accumulation of »9Fe by the plants, the observations of Sijmons et al. (1984a) and others (e.g., Ivankina and Novak,

436 Misra

Table V. Effect of Ferricyanide on Growth of the Yeast Rhodotorula glutiniß

Concentration of potassium ferricyanide in growth

medium (M)

Dry weight of cell mass after 24 h

(mg ml of growth medium ')

0.0 2.17 _+ 0.37 (10) b 5.0 x 10 7 2.11 ± 0.01 (4) 5.0 x 10 -5 0.97 _+ 0.28 (4) 1.0 x 10 -3 0.56 __+ 0.04 (4)

aSrivastava, R., and Misra, P. C., unpublished results. bValues in parentheses are number of runs.

1988) on depolarization of plasma membrane potential and K + eIttux are not in support of the concept of active iron uptake by plants. Nevertheless, involvement of such an electron transport for the reduction, prior to uptake, of cupric and nitrate ions is proposed (Crane, 1989). At present it is not known whether the induction of the so-called "Turbo" reductase in plants is peculiar to iron deficiency or whether it is a general response to any stressed condition. If it is a general response to stress, then the proposal of Bienfait and Luettge (1988), that the "Standard" plasma membrane reductase [NAD(P)H dehydrogenase] may have a functional role in providing reducing equivalents to counter the oxidative attack on plasma membrane proteins, may have wider implications. Iron deficiency is found to induce the appear- ance of new proteins in plasma membranes (Guikema and Sherman, 1984; Bienfait, 1988). Also a model proposing control of iron-sensing proteins on the transcription of genes involved in Fe-efficiency reactions is forwarded (Bienfait, 1988), but experimental support of such a role of these proteins in iron-efficiency reactions is still lacking.

Though a direct evidence relating oxidation of NAD(P)H at the cyto- plasmic face by so-called "Standard" reductase involved in transporting electrons across the plasmalemma to the uptake of mineral ions is desirable, observations are reported where exogenous NADH caused stimulation in 02 consumption and K + uptake by cells and protoplasts (Lin, 1982, 1984; Misra et al., 1984). On the contrary, in some other studies NADH oxidation was linked with inhibition and/or ef[tux of K + (Kochian and Lucas, 1985; Thom and Maretzki, 1985). At present the reason for this difference in observations is not known and, at the same time, the relation between transplasma membrane electron transport and exogenous NADH oxidation is a marter of speculation.

Support of the concept of involvement of transplasma membrane electron transport in plant growth comes mainly from the two types of observations. First, the protonophoric nature of such an electron transport system is thought to play a similar role as the long-recognized transmembrane H +

Transplasma Membrane Eiectron Transport in Plants 437

efflux on growth of plant cells termed the acid growth hypothesis (e.g., Cleland, 1976). Second, the hormone responsiveness of plasma membrane redox systems of plant cells (Crane et al., 1983; Morré et al., 1986, 1988a; Brightman et al., 1988; Revis and Misra, 1988b) provides another basis for assigning it a role in growth control. Morré et al. (1988b) proposed a role of the plasma membrane redox reactions in elongation growth in soybean hypocotyls, using selective inhibitors for transplasma membrane electron transport activity. In addition, the inhibition of transplasma membrane ferricyanide reduction by Ca2+-calmodulin antagonists in carrot cells (Barr et al., 1985b) lends further support to this concept. The relation between growth and transplasma membrane electron transport is also supported by observations where this activity is highest in cells that are in a rapid growth phase (Crane et al., 1988; Barr et al., 1985b; Qiu et al., 1985; Revis and Misra, 1986). However, so far there has not emerged any well-defined relationship between the hormone effect on plasma membrane redox reactions and growth in plants. The picture becomes more confusing where inhibition of growth (Crane et al., 1984; Morré et al., 1988a; Table V) and depolarization of plasma membrane potential (Sijmons et al., 1984a; Ivankina and Novak, 1988) by external oxidants are observed. These findings are in sharp contrast to the observations with mammalian systems where growth stimulation by transplasma membrane electron transport is reported (Ellem and Kay, 1983; Sun et al., 1984; Crane et al., 1985). Nevertheless, the interpretations of Bienfait and Lüttge (1988) and Crane and Barr (1989) on the possible reduction of oxygen at lower rates by the "Standard" reductase under natural conditions and the data on the time-dependent effect of ferricyanide on oxygen consumption and sugar uptake by the yeast R. glutinis (Table IV) point to the role of this system in energy metabolism and growth. Crane et al. (1988) have tried to distinguish the role of "Standard" and "Turbo" redox systems in growth and iron reduction on the basis of high- and low-potential external redox sites. A role for plasma membrane transport systems in second messenger function is also postulated (Crane, 1989). Involvement of this system in cell wall lignification is proposed (DeLuca et al., 1984). Some recent studies on plasma membrane-bound nitrate reductase (NR) point to its relation with transplasma membrane electron transport. Balch et al. (1987) indicated the presence of plasmalemma-bound NR in diatoms and dinoflagellates by immunochemical studies. Subsequently, a plasma membrane-bound NR isolated from barley roots was found to have an antigenic relationship to nitrate transport (Ward et al., 1988). At the same time, Jones and Morrel (1988) proposed a model which shows that the role of transplasma-membrane electron transport is fulfilled by a plasma membrane-bound form of NR in the diatom Thalassiosira. Recently, nitrate uptake in barley seedlings was found to be independent of NR (Warner and

438 Misra

Huffaker, 1989). Further investigation on the intimate relationship between NR and transplasma membrane electron transport is desirable. The ferric citrate reductase activity of NR and its role in iron assimilation was already pointed out by Campbell and Redinbaugh (1984).

Since the true nature of a transplasma-membrane electron transport system in terms of its constitution and physiological role is still in the early stages of emergence, the discrepancies in the reported findings area natural corollary. However, the studies on resolution of components and reconsti- tution of the system with purer plasma membrane preparations are being given due attention (see, e.g., Giannini and Briskin, 1988; Askerlund et al., 1988; Boettger, 1989) and it is hoped that a clearer picture will soon emerge.

Note Added in Proof

When this article was in press, Barr et al. (1990) reported that membrane-permeable electron donors, duroquinol, diphenylcarbazide, pyro- catechol and ter t -oc ty lcatechol , influenced the ratio of H+/e - transport across the plasma membrane in cultured carrot cells. It was postulated that a forced opening of proton channels occurred. The membrane depolarization observed in the roots of Z e a m a y s with exogenous electron acceptors led Döring et al. (1990) to suggest a model of the redox-dependent proton secretion. A critical review of redox processes in the plant plasma membrane has appeared (Moller and Crane, 1990).

Acknowledgment

The facilities provided by the University Grants Commission, New Delhi, under Special Assistance and COSIST Programmes are thankfully acknowledged.

References

Anton, G. E., and Spanswick, R. M. (1987). Plant Physiol. 81, 1080-1085. Askerlund, P., Larsson, C., and Widell, S. (1988). FEBS Lett. 239, 23-28. Balch, W. M., Yentsch, C. M., Reguera, B., and Campbell, W. H. (1987). In Immunochemical

Approach to Oceanography (Yentsch, C. M., Mague, F. C., and Horan, P. K., eds.), Springer-Verlag, New York.

Barr, R. (1988). Physiol. Plant. 73, 194-199. Barr, R., Böttger, M., Crane, F. L., and Morré, D. J. (1990). Biochirn. Biophys. Acta 1017, 91-95. Barr, R., Crane, F. L., and Craig, T. A. (1984). J. Plant Growth Regul. 2, 243-249. Barr, R., Craig, T. A., and Crane, F. L. (1985a). Biochim. Biophys. Acta 812, 49-54. Barr, R., Stone, B., Craig, T. A., and Crane, F. L. (1985b). Biochem. Biophys. Res. Commun. 126~

262-268.


Barr, R., Sandelius, A. S., Crane, F. L., and Morré, D. J. (1986). Biochim. Biophys. Acta 852, 254-261.

Barr, R., Martin, O., Jr., and Crane, F. L. (1987). Proc. lndiana Acad. Sci. 96, 139-144. Beilby, M. J. (1985). J. Exp. Bot. 36, 228-239. Belkoura, M., Ranjeva, R., and Merigo, G. (1986). Plant Cell Environ. 9, 653-656. Berger, W. A., Berger, S. J., Sikorski, G. W., and Catino, D. M. (1982). Exp. Cell Res. 137,

79-88. Bienfait, H. F. (1985). J. Bioenerg. Biomembr. 17, 73-83. Bienfait, H. F. (1988). Plant PhysioL 88, 785-787. Beinfait, H. F., Lubberding, H. J., Heutink, P., Linder, L., Visser, J., Kaptein, R., and Dijkstra,

K. (1989). Plant. Physiol. 90, 359-364. Beinfait, F., and Lüettge, U. (1988). Plant Physiol. Biochem. 26, 665-671. Blein, J. P., Canivenc, M.-C., De Cherade, X., Bergon, M., Calmon, J.-P., and Scalla, R. (1986).

Plant Sci. 46, 77-85. Boettger, M. (1989). In Plant Membrane Transport (Dainty, J., ed.), Elsevier, New York,

pp. 55-60. Boettger, M., and Hilgendorf, F. (1988). Plant Physiol. 86, 1038-1043. Boettger, M., and Luethen, H. (1986). J. Exp. Bot. 37, 666-675. Boettger, M., Bigdon, M., and Sell, H.-J. (1985). Planta 163, 376-380. Bown, A. W., and Crawford, L. A. (1988). Physiol. Plant. 73, 170-174. Brightman, A. O., Barr, R., Crane, F. L., and Morré, D. J. (1988). Plant Physiol. 86, 1264-1269. Briskin, D. P. (1986). Physiol. Plant. 68, 159-163. Buckhout, T. J., and Hrubec, T. C. (1986). Protoplasma 135, 144-154. Buckhout, T. J., Bell, P. F., Luster, D. G., and Chaney, R. L. (1989). Plant Physiol. 90, 151-156. Campbell, W. H., and Redinbaugh, M. G. (1984). J. Plant Nutr. 7, 799-806. Chalmers, J. C. D., and Coleman, J. O. D. (1983). Biochem. Int. 7, 785-791. Chaney, R. L., Brown, J. C., and Tiffin, L. O. (1972). Plant Physiol. 50, 208-213. Cteland, R. E. (1976). Plant Physiol. 58, 210-213. Craig, T. A., and Crane, F. L. (1981). Proc. lndiana Acad. Sei. 90, 150-155. Craig; T. A., and Crane, F. L. (1985). In Current Topics in Plant Biochemistry and Physiology

(Randall, D., Blevins, D. G., and Larson, R. L., eds.), Vol. 4, Univ. Missouri, Columbia, p. 247.

Craig, T. A., Crane, F. L., Misra, P. C., and Bart, R. (1984). Plant Sci. Lett. 35, 11-17. Crane, F. L. (1989). In Second Messengers in Plant Growth and Development (Boss, W., and

Morré, D. J., eds.), Alan R. Liss, New York, pp. 115-143. Crane, F. L., and Barr, R. (1989). Critical Reviews in Plant Sciences, Vol. 8, CRC Press, Boca

Raton, Florida, pp. 273-307. Crane, F. L., Roberts, H., Linnane, A. W., and Loew, H. (1982). J. Bioenerg. Biomembr. 14,

191-205. Crane, F. L., Craig, T. A., Misra, P. C., and Barr, R. (1983). Proe. Plant Growth Regul. Soe. Am.

10, 70-75. Crane, F. L., Barr, R., Craig, T. A., and Misra, P. C. (1984). Proc. Plant Growth Regul. Soc. Am.

Il , 87-95. Crane, F. L., Sun, I. L., Clark, M. G., Grebing, C., and Loew, H. (1985). Biochim. Biophys. Acta

811,233-264. Crane, F. L., Barr, R., Craig, T. A., and Morré, D. J. (t988). J. Plant Nutr. 11, 1117-1126. De Luca, L., Bader, U., Hertel, R., and Pupillo, P. (1984). Plant Sei. Lett. 36, 93-98. Dharmawardhane, S., Stern, A. I., and Rubinstein, B. (1987). Plant Sei. 51, 193-197. Döring, O., Lüthje, S., Hilgendorf, F., and Böttger, M. (1990). J. Exptl. Botany 41, 1055-106l. Ellem, K. A. O., and Kay, G. F. (1983). Bioehem. Biophys. Res. Commun. 112, 183-190." Elzenga, J. T. M., and Prins, H. B. A. (1989). Plant Physiol. 91, 68-72. Federico, R., and Giartosio, C. E. (1983). Plant Physiol. 73, 182-184. Giannini, J. L., and Briskin, D. P. (1988). Arch. Biochem. Biophys. 260, 653-660. Guikema, J. A., and Sherman, L. A. (1984). Plant Physiol. 74, 90-95. Hassidim, M., Rubinstein, B., Lerner, H., and Reinhold, R. (1987). Plant Physiol. 85, 872-875. Ivankina, N. G., and Novak, V. A. (1981). Stud. Biophys. 83, 197-206.

440 Misra

Ivankina, N. G., and Novak, V. A. (1988). Physiol. Plant. 73, 16t-164. lvankina, N. G., Novak, V. A., and Miclashevich, A. I. (1984). In Membrane Transport in Plants

(Cram, M. J., Janacek, K., Rybova, R., and Sigler, S., eds.), Wiley, Chichester, Sussex, England, pp. 404-405.

Jones, G. J., and Morel, F. M. M. (1988). Plant Physiol. 87, 143-147. Kjellbom, P., Larsson, C., Askerlund, P., Schelin, C., and Widell, S. (1985). Photoehem.

Photobiol. 42, 779-783. Kochian, L. V., and Lucas, W. J. (1985). Plant Physiol. 77, 429-436. Lass, B., Thiel, G., and Ullrich-Eberius, C. I. (1986). Planta 169, 251-259. Leonard, R. T. (1984). In Advances in Plant Nutrition (Tinker, P. B., and Laeuchli, A., eds.),

Praeger Scientific, New York, pp. 209-240. Leong, T.-Y., and Briggs, W. T. R. (1981). Plant Physiol. 67, 1042-1046. Lin, W. (1982). Proc. Natl. Acad. Sci. USA 79, 3773-3776. Lin, W. (1984). Plant Physiol. 74, 219-222. Lin, W. (1985). Physiol. Plant. 65, 102-108. Löppert, H. (1981). Planta 151, 293-297. Löppert, H. (1983). Planta 159, 322-335. Lubberding, H. J., De Graaf, F. H. J. M., and Bienfait, H. F. (1988). Biochem. Physiol. Pflanzen

183, 271-276. Luethen, H., and Boettger, M. (1988). Plant Physiol. 86, 1044-1047. Lundborg, T., Widell, S., and Larsson, C. (1981). Physiol. Plant. 52, 89-95. Luster, D. G., and Buckhout, T. J. (1988). Physiol. Plant. 73, 339-347. Luster, D. G., and Buckhout, T. J. (1989). Plant Physiol. 91, 1014-1019. Macri, F., and Vianello, A. (1986). Plant Sci. 43, 25-30. Marré, M. T., Moroni, A. M., Albergoni, F. G., and Marré, E. (1988). Plant Physiol. 87,

25-29. Misra, P. C., Craig, T. A., and Crane, F. L. (1984). J. Bioenerg. Biomembr. 16, 143-152. Moller, I. M., and Berczi, A. (1985). FEBS Lett. 103, 180-181. Moller, I. M., and Berczi, A. (1986). Physiol. Plant. 68, 67-74. Moller, I. M., and Lin, W. (1986). Annu. Rer. Plant Physiol. 37, 309-334. Moller, I. M., and Crane, F. L. (1990). In The Plant Plasma Membrane (Larsson, C., and Moller,

I. M., eds.), Springer-Verlag, Berlin-Heidelberg, pp. 93-126. Morré, D. J., Novas, P., Penel, C., and Castillo, F. J. (1986). Protoplasma 133, 195-197. Morré, D. J., Brightrnan, A. O., Wu, L.-Y., Barr, R., Leak, B., and Crane, F. L. (1988a). Physiol.

Plant. 73, 187-193. Morré, D. J., Crane, F. L., Barr, R., Penel, C., and Wu, L.-Y. (1988b). Physiol. Plant. 72,

236-240. Neufeld, E., and Bown, A. W. (1987). Plant Physiol. 83, 895-899. Peschek, G. A., Kurz, M. A., and Erber, W. A. (1988). Physiol. Plant. 73, 175-181. Poole, R. J. (1978). Annu. Rev. Plant Physiol. 29, 473-480. Pupillo, P., and DeLuca, L. (1982). In Plasmalemma and Tonoplast: Their Function in Plant Cell

(Marmé, E., Marré, E., and Hertel, R., eds.), Elsevier, Amsterdam, pp. 321-326. Qiu, Z.-S., Rubinstein, B., and Stern, A. I. (1985). Planta 165, 383-391. Ramirez, J. M., Gallego, G. G., and Serrano, R. (1984). Plant Sci. Lett. 34, 103-110. Rensch, C., and Boettger, M. (1988). Milt. Inst. Allg. Bot. Hambg. 22, 5 18 (cf. Biol. Abstr.,

Vol. 87 (1989), Abstr. No. 130551). Revis, S., and Misra, P. C. (1986). J. Plant Physiol. 122, 337-345. Revis, S., and Misra, P. C. (1988a). Biochem. Biophys. Res. Commun. 156, 940-946. Revis, S., and Misra, P. C. (1988b). Biochem. Physiol. Pflanzen. 183, 487-494. Robertson, R. N. (1960). Biol. Rer. 35, 231-264. Roemheld, V., and Marschner, H. (1983). Plant Physiol. 71,949-954. Roemheld, V., and Marschner, H. (1986). Adv. Plant Nutr. 2, 155-204. Rubinstein, B., and Stern, A. I. (1986). Plant Physiol. 80, 805-811. Rubinstein, B., Stern, A. I., and Stout, R. G. (1984). Plant Physiol. 76, 386-391. Sandelius, A. S., Bart, R., Crane, F. L., and Morré, D. J. (1986). Plant Sci. 48, 1-10. Sijmons, P. C., and Bienfait, H. F. (1983). Physiol. Plant. 59, 409415.


Sijmons, P. C., Lanfermeijer, F. C.+ deBoer, A. H., Prins, H. B. A., and Bienfait, H. F. (1984a). Plant Physio]. 76, 943-946.

Sijmons+ P. C., Van Den Briel, W., and Bienfait, H. F. (1984b). Plant Physiol. 75, 219-221. Srivastava, V., and Misra, P. C. (I9813. Toxi«ol. Lett. 7. 475-480. Sun, I. L., Crane, F. L., Grebing, C.+ and Loew, H. (1984). J. Bioenerg. Biomemhr. 16+ 583-595. Sze, H. (1985). Annu. Rev. Plant Physio[. 36, 175 208. Thom, M., and Maretzki, A. (1985). Plant Physiol. 77, 873-876. Trockner, V., and Marré, E. (1988). Plant Physiol. 87, 30 35. Ullrich-Eberius, C. I., Sanz, A.+ and Novacky, A. J. (19893. J. Exp. Bot. 40, 119-128. Vani, T., and Raghavendra, A. S. (19893. Plant Physiol. 90, 59-62. Ward, M. R., Tischner, R., and Huffaker, R. C. (1988). Plant Physiol. 88, 1141 1145. Warner, R. L., and Huffaker, R. C. (1989). Plant Physiol. 91,947-953. Widell, S., and Sundqvist, C. (1987). Physiol+ Plant. 70, 27-34. Widell, S., Britz, J. S., and Briggs, W. R. (1980). Photochem. Photobiol. 32+ 669-677. Wide]l, S., Lundborg, T., and Larsson, C. (1982). Plant Phvsiol. 70, 142%1435. Yarnamoto, Y., Niki, E., Eguchi+ J., Kamiya, Y., and Shinasaki, H. (19853. Bio«him. Biophys.

A«ta 819, 29-36. Yamashoji+ S., and Kajimoto, G. (1986a). Biochim. Biophys. A«•a 849. 223-228. Yamashoji, S., and Kajimoto, G. (1986b). Bio«him. Biophys. A«ta 852, 25-29.

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Transplasma membrane electron transport in plants