Changes in Polyamine Titer in Rice Seedlings Following NaCl Salinity Stress

J. Agronomy & Crop Science 165, 19—27 (1990)© 1990 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Department of Biochemistry, Faculty of Science, BanarasHindu University, Varanasi — 221005, India

Changes in Polyamine Titer in Rice SeedlingsFollowing NaCl Salinity Stress

SADHANA KATIVAR and R. S. DUBEY

Authors' address: Dr. R. S. DUBEY (corresponding author) and SADHANA KATIYAR, Department ofBiochemistry, Faculty of Science, Banaras Hindu University, Varanasi — 221005, India.

With 4 figures and one table

Received November 8, 1989; accepted March I, 1990

Abstract

Seedlings of four rice cultivars differing in salt tolerance were raised in sand cultures under increasing levels ofNaCl salinity and metabolic levels of total polyamines, spermidinc, spermine, agmatine and the diamineputrescine were determined in roots and shoots during 5—20 days growth period. Salinity caused aremarkable increase in total polyamines level in rice seedlings. At similar level of salinity roots as well asshoots of salt sensitive cvs. Ratna zn6.]aya showed higher level of total polyamines than tolerants. Salinity of14 dSm"' NaCl caused more than 2 times polyamine level in shoots of sensitive cultivars compared totolerants. Accumulation of polyamines was greater in salt stressed shoots than roots. In nonsalinizedseedlings there appeared a gradual increase in putrescine level during 5 to 20 days growth period. Salttreatment caused sharp increase in putrescine level in all cultivars, however under similar level of salmizationsalt stressed seedlings of sensitive cultivars had higher putrescine level than tolerants. In nonsalinizedseedlings of sensitive cultivars spermidine level increased gradually during 5 to 20 days growth period whereasa decline in the level was observed in seedlings of tolerant cultivars during this period. Higher level of salinitycaused marked increase in spermidine level in sensitive cultivars. Specially during 5 to 10 days of growthsalinity caused increase in spermine level in seedlings of sensitive cultivars. In all cultivars salt stressedseedlings had higher agmatine level compared to non-stressed. Salinity led to greater accumulation of certainunidentified polyamines in seedlings of sensitive cultivars. Increased levels of total polyamines, putrescine,spermidine and unknown polyamines in rice seedlings under salinization suggest their possible role incombating the adverse effects of salinity stress.

Key words: Salinity, polyamines, putrescine, spermidine, spermine, agmatine, Or)>za sativa.

Introduction

Polyamines spermidine and spermine and thediamine putrescine are widely distributed tnplants and are intimately related with plantgrowth and development (ALTMAN and BACI-I-

RACH 1981). They retard senescence, regulatecell proliferation and differentiation and pro-mote macromolecular synthesis (SMITH 1981,WEINSTEIN et al. 1986). Various types of envi-ronmental stresses i.e. osmotic stress (FI.ORES

and GALSTON 1984), heat stress (SOUMITRA et al.1987), acid stress (SMITH and SINCLAIR 1967,FLORES et al. 1985) influence polyamine metab-olism and cause accumulation of the diamineputrescine at high concentration in plant tis-sues. Only recently we described accumulationof putrescine and an increase in the level oftotal polyamines in embryoaxcs of germinatingrice seeds under NaCl salinity (KATIYAR andDuBtY 1990).

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20 KATIYAR and DUBEY

Salinity in the soil adversely affects germina-tion of seeds, plant growth and metabolism(DuBCY I9S2, GRATTAN and GRIEVE 1985,DuBE^ and RANI 1987). Germinating seeds aswell as different parts of the plants growingunder saline stress accumulate various types ofsoluble nitrogenous compounds such as aminoacids proline, alanine (DL'BEY and RANI 1989),quaternary ammonium compounds like gly-cine betaine, /^-alanine betaine (STOKI;Y andWYN JONES 1978, STEWART and LARHER 1980)

etc. These compounds act as components ofsalt tolerance mechanism and build up a fa-vourable osmotic potential inside the cell in

order to combat the effects of salt stress(GREENWAY and MUNNS 1980). Seedling stage isone of the critical stages for salt damage duringlife cycle of rice plant as proper seedling de-velopment is prerequisite for flowering andgrain development.

Salt tolerance and sensitivity depend on anumber of physiological and biochemical char-acteristics (LEVITT 1972). Various workers haveattempted to study the behaviours of differentkey enzymes of germination and later growthstages, metabolic levels of various mac-romolecules and nitrogenous compounds inorder to achieve a possible correlation

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Fig. 1. Total polyamines level in roots (—) and shoots (—) of sail sensitive rice cvs. Ratna ^ndi Jay a andtolerant cvs, CSR-1 and CSR-3 at different days after germination under increasing coductivities of NaClsalinity (0 Control, • 7 dSm"' NaCl, A 14 dSm"' NaCl)

Changes in Polyamine Titer in Rice Seedlings Following NaCl Salinity Stress 21

behaviours of enzymes, levels of metabolitesand degree of salt tolerance (DUBEY 1983, 1985;GRATTAN and GRIEVP^ 1985, DUBEY and RANI

1987). Since metabolism of polyamines undersaline situations is not properly understood,the role of polyamines in relation to salt toler-ance still remains obscure (KATIYAR and DUBEY

1990).In order to understand salmity induced

changes in the titre of polyamines and toachieve a possible correlation between thelevels of polyamines and degree of salt toler-ance in rice, the present study using two saltsensitive and two salt tolerant rice cultivars wasundertaken with the objectives to evaluate the

metabolic levels of polyamines spermine, sper-midine, agmatine and the diamine putrescine indifferent parts of seedlings growmg under in-creasing levels of NaCl salinity.

Materials and Methods

Plant material

Four rice cultivars differing in salt tolerance wereused, CVS. CSR-I and CSR-3 were salt tolerant andCVS. Ratna and ]aya as salt sensitives. Seeds werethoroughly washed with water and then surfacesterilized with 1 percent sodium hypochlorite solu-tion. After soaking in water for 24 h in an incubatorat 28 ± 1 °C, seedlings were raised in sand culturesas described earher (DUBEY and RANI 1989). Soaked

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Fig. 2. Putrescine level in roots (—) and shoots (—) or rice cvs. Ratna, Jaya, CSR-I and CSR-3 at differentdays after germination under increasing conductivity of NaCl salinity (0 Control, • 7 dSm ' NaCl,• 14 dSm-' NaCl)


seeds were sown in plastic pots containing purifiedquartz sea sand saturated with either Hoagland nu-trient solution (HOAGLAND and ARNON 1938) whichserved as control or nutrient solutions supplementedwith NaCl to achieve electrical conductivities of 7.ind 14 dSm"'. Pots were kept for growth of seedlingsin a B.O.D. cum humidity cabmet (York ScientificIndustries, New Delhi) at 28 ± 1 °C under 80 per-cent relative humidity and 12 h cycle of light anddark period. At five days of periodic intervals thepots received control and respective salt solutions tosaturate the sand.

Seedlings were uprooted at five days intervals aftersowing up to 20 days and polyamines were deter-mined in roots and shoots.

Determination of polyamines

It was done by the method of FLORES and GALSTON

(19S2) with some modifications. About 200 mgfreshly weighed roots and shoots were homogenizedm 2 ml 5 percent HClOj in a perchilled mortar. Thehomogenates were placed in ice for about 1 hour andthen centrifuged at 4 °C at 22,000 g for 15min.From the resulting supernatant fractions, for dansy-laiion 0.2 ml of the supernatant was added to amixture of 0.4 ml dansyl chloride (5 mg/ml inacetone) and 0.2 ml of a saturated solution of sodiumcarbonate and contents were allowed to react over-night in the dark at room temperature. To the mix-ture was added 0,1 ml proline (100 mg/ml in water)and vortexed for 10 seconds and kept in the dark for

10 15 20 5 10

DAYS AFTER GERMINATION

15 20

Fig. 3. Spermidine level in roots (—) and shoots (---) of rice cvs. Ratna,Jaya, CSR-1 and CSR~J at differentdays after germmation under increasing conductivities of NaCl salinity (0 Control, # 7 dSm"̂ ' NaCl,• 14 dSm-' NaCl)

Changes in Polyamine Titcr in Rice Seedlings Following NaCl Salinity Stress 23

30 min. The dansylated products were then ex-tracted with 0.5 ml benzene and separated on silicagel thin layer plates.

Individual polyamines were separated using0.2 ml benzene extracts. Extracts were spotted onthin layer plates and developed in solvent systemchloroform : triethylamine (25 : 2 v/v). The dansy-lated polyamines separated well permitting scrapingof U.V. fluorescent spots, which were eluted with2 ml ethylacetate and quantified with an Aminco-Bowman Spectrophotofluorimeter, with excitationat 350 nm and emission at 500 nm. Polyamine stand-ards spermine, spermidine, agmatine, and thediamine putrescine (obtained from Sigma ChemicalCompany, U.S.A.) were similarly dansylated andchromatographed.

Results

Effect of salinity on total polyamines level

Figure I shows the pattern of total polyaminesin roots as well as shoots of control as well assalt stressed seedlings during 5 to 20 daysgrowth period. As it is evident from the figurein both sets of rice cultivars increased level ofNaCl salinity caused a remarkable mcrease intotal polyamine level in seedlings. In roots aswell as shoots of salt sensitive cvs. Ratna andJaya level of polyamines under salinization wasgreater than tolerant cvs. CSR-1 and CSR-3under similar levels of salinity. Higher level ofsalinization i.e. 14 dSm*' NaCI caused sharp

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Fig. 4. Spermine level in roots (—) and shoots (—) or rice cvs. Raina.Jaya, CSR-1 and CSR-3 at differentdays after gertnination under increasing conductivities of NaCl salinity (0 Control. # 7 dSm"' NaCl,A 14


increase m total polyamine level in sensitivecultivars over tolerants. During 5—20 daysgrowth period highly salt stressed shoots ofsensitive cultivars had more than 2 times poly-amines level than that of tolerants. In all cul-tivars shoots maintained higher polyaminelevel than roots in both controls as well as salttreatments.

Effect of salinity on putrescine level

In nonsalinized roots as well as shoots of allrice cultivars the level of diamine putrescineincreased gradually during 5 to 20 days growthperiod (Fig. 2). Salt treatment caused sharpincrease in putrescine level in both roots andshoots of all cultivars. Under similar levels ofsalinization salt stressed seedlings of sensitivecultivars had higher putrescine level than toler-ants. Accumulation of putrescine was alwaysmore in shoots than roots under salinization.

Effect of salmity on spermidine level

As it IS evident from Figure 3 in nonsalinizedroots and shoots of salt sensitive cv. Jaya andin the roots of another sensitive cv. Ratnathere was a gradual increase in spermidine levelduring 5 to 20 days of growth period understudy whereas in salt tolerant cvs. CSR-1 andCSR-3 a regular decline in spermidine level

was observed in shoots of nonsalinized seed-lings during 5 to 20 days growth period. In-creased level of salinity caused pronouncedincrease in spermidine level in roots and shootsof sensitive cultivars. In tolerant cvs. CSR-1and CSR-3 low level of salinity decreased sper-midme level in roots and shoots whereas high-er salinity level caused pronounced increase inthe level. At 14 dSm"' NaCl salinity levelsensitive cultivars showed greater spermidinelevel compared to tolerants.

Effect of salinity on spermine level

In both salt sensitive cvs. Ratna and Jaya inroots of nonsalinized seedlings there appeareda regular increase in spermine level during5—20 days growth period whereas in shoots ofthese cultivars during this period a sharp in-crease in spermine level was observed (Fig. 4).In tolerant cultivars no such regular trend ofchange in spermine level could be observed.Increased level of salmity caused increase inspermine level in roots as well as shoots ofsensitive cultivars specially during 5—10 daysgrowth period whereas thereafter no definitetrend in spermine pattern was observed undersalinization. In salt tolerant cws. CSR-1 andCSR-3 too increased level of salinity caused anincrease in spermine level in shoots and to a

Table 1. Level of agmatine and unknown polyamines [n moles/g fresh wt.) in 10 and 20 days old seedlingsgrowing under increasing levels ot NaCl salinity'"'

Cultivars

Jaya

Ratna

CSR-1

CSR-3

Conductivit\'of NaCl '(dSm-')

Control7

14

Control7

14

Control7

14

Control7

14

10

0.0980.1560.220

0.1040.1770.216

0.1480.1570.1 S6

0.1160.1450.167

AgmatineRoot

20

0.1950.3120.422

0.2040.3650.412

0.1300.1410.186

0.1400.1650.190

Shoot10

0.1150.1960.215

0.1260.2070.289

0.1650.1700.180

0.0960.1480.185

20

0.1850.2480.295

0.2070.2150.285

0.1230.1410.162

O.120

0.182

0.220

10

0.075

0.286

0.582

0.082

0.42S

0.625

0.062

0.115

0.16S

0.075

0.1 OS

0.156

UnknownRoot

20

0.0900.6500.950

0.0950.6280.865

0.0700.1460.156

0.0960.1350.160

PolyaminesShoot

10

0.1080.9561.586

0.1350.8651.965

0.0850.2560.565

0.0950.1900.465

20

0.2401.7622.150

0.1702.021.95

0.1080.3050.536

0.1050.4250.615

^' Each value represents the mean of three independent observations.


lesser extent in roots. Fiighly salt stressedshoots of tolerant cultivars showed higher levelof spermine during early days of growth i.e.5—10 days and a decrease thereafter.

Effect of salinity on agmatine and unknownpolyamines

Table 1 describes the levels of agmatine andunknown polyamines in roots as well as shootsof rice seedlings at 10 and 20 days of growthunder increasing levels of NaCl salinity. As itIS evident from the table the level of agmatinewas higher in roots and shoots of salt stressedseedlings m all cultivars compared to controlsbut there was no significant variation in theextent of agmatine increase in the seedlings ofthe two sets of cultivars under salinization.

When dansylated products from roots andshoots of all cultivars were spotted on TLCplates and the plates were developed in solventsystem certain fluorescent spots appearedranging in nos. 2 to 3 in each sample whichwere not identified as any of the polyaminesspermine, spermidine agmatine or the diamineputrescine. Such spots were eluted together asunknown polyamines. When 10 and 20 daysold seedlings were quantified for unknownpolyamines it was observed that increased levelof salinity caused significant increase in un-known polyamines level in roots as well asshoots of all cultivars. Salt stressed shoots hadhigher level than roots. Salinity induced in-crease in unknown polyamine level was greaterin sensitive cultivars than tolerants. At 14dSm" NaCi salinity level shoots of sensitivecultivars showed about 3 times more unknownpolyamine level than tolerants.

Discussion

Our results indicate marked increase in thelevels of total polyamines, putrescine, sper-midine and certain unknown polyamines inrice seedlings growing under NaCl salinity andthat in seedlings of salt sensitive cultivars ac-cumulation of these polyamines is greater thansalt tolerant cultivars under salinization. Thissuggests a possible correlation between extentof accumulation of polyamines putrescine,spermidine under salinization and degree ofsalt tolerance in rice. Magnitude of accumula-tion of putrescine and spermidine is much

higher compared to spermme and agmatine.The study thus reflects possible role of poly-amines in rice seedlings under salt stress.

Polyamines spermidine, spermine, ca-daverine and the diamine putrescine due totheir universal distribution in plants and theirability to interact with nucleic acids, are con-sidered as regulators of growth in plants (SMITH

1981). Conditions which affect growth anddevelopment of plant tissues cause significantchange in intracellular concentration of poly-amines (SMITH 1977).

Though it has been shown that differentforms of environmental stresses like Mg"^ defi-ciency, low external pH, high levels of NH4"^,SOT fumigation and osmotic shock induce ac-cumulation of diamine putrescine in plant parts(YOUNG and GALSTON 1983), studies pertainingto overall physiology of polyamines in re-sponse to various stresses remain more ne-glected (FLORES et al. 1985). Recently we re-ported sharp accumulation of the diamine pu-trescine and the polyamine spermidine in em-bryoaxes of germinating rice seeds under NaClsalinity stress (KATIYAR and DUBEY 1990). Inthe present study we observed about 5—6times increase in putrescine and spermidinetitre in seedlings of salt sensitive rice cultivarsraised under 14 dSm"' NaCl salinity. SOjfumigation induced accumulation of putrescineas well as spermidine has been shown in peaseedlings (PRIEBE et al. 1978). FLORES and GAL-

STON (1984) observed sharp increase in putres-cine and spermidine level in oat and corn leavessubjected to saline stress.

The increased titre of total polyamines, pu-trescine, spermidine and certain unknownpolyamines in rice seedlings noted in the pres-ent study suggests a possible common underly-ing mechanism of fast increase in polyaminestitre under various types of environmentalstresses. Stress induced accumulation of poly-amines might be possibly helpful to the cells inmaintaining a more favourable ionic environ-ment and in regulating cellular pH. More ac-cumulation of polyamines in seedlings of saltsensitive cultivars under salinization appears tobe due to increased demand of polyamines bythe cells of sensitive rice cultivars to combatthe effect of salt stress compared to tolerants.

Salt tolerance and susceptibility do not re-side in a single factor but results from thepossession of a number of in built biochemical


characteristics (STEWART and LARHER 1980).Our observations showing different levels ofaccumulation of total polyamines, putrescine,spermidine, spermine, agmatine and unknownpolyamines under salinization in the two setsof cultivars differing in salt tolerance strength-en the view that the two sets of cultivars havedifferent biochemical make ups with respect tothe metabolism of polyamines and that moreaccumulation of polyamines under salinizationis correlated with salt sensitivity of the cul-tivars. Accumulation of the major polyamineslike putrescine, spermidine, spermine, ag-matine under saline stress possibly suggeststheir potential role in combating the effect ofsalt stress. Fiowever, the detailed studies relat-ing to the underlying mechanism of polyamineaccumulation and their function in higherplants are essential in order to define the exactrole of polyamines in environmental stresses.

Zusammenfassung

Anderungen im Polyamintiter bei Reissam-lingen nach NaCl-Salzstrefi

Samlinge von vier Reiskultivaren mit unter-schiedlicher Salztoleranz wurden in Sandkul-turen mit zunehmenden Konzentrationen vonNaCl behandelt und die metabolischen Kon-zentrationen der Gesamtgehalte an Polyami-nen, Spermidin, Spermin, Agmatin und Dia-min-Putrescin in Wurzeln und Sprossen wah-rend einer 5—^20tagigen Wachstumsperiodeuntersucht. Salz verursachte eine bemerkens-werte Zunahme im Gesamtgehalt der Polya-min-Konzentrationen bei Reissamlingen. Aufgleichen Versalzungshohen zeigten die Wur-zeln und die Sprosse der salzempfindlichenKultivare Ratna und Jaya hohere Konzentra-tionen von Polyaminen als die toleranten Kul-tivare. Eine Versalzung von 14 dSm"' NaClverursachte mehr als zweimal so hohe Polya-min-Konzentrationen in den Sprossen emp-findlicher Kultivare im Vergleich zu den tole-ranten. Die Akkumulation von Polyaminenwar in salzgestrelken Sprossen und Wurzelnhoher. In nicht-salzgestrelken Samlingen zeig-te sich eine graduelle Zunahme in der Putres-cin-Konzentration wahrend der 5—20tagigenWachstumsperiode. Die Salzbehandlung ver-ursachte eine scharfe Zunahme im Purrescin-

Gehalt bei alien Kultivaren; unter vergleichba-rer Versalzungskonzentration zeigten die salz-gestrel^ten Samlinge der sensitiven Kultivarehohere Putrescin-Konzentrationen als die tole-ranten Kultivare. In nicht-salzgestrefiten Sam-lingen der empfindlichen Kultivare nahm dieSpermidin-Konzentration graduell wahrendder 5—20tagigen Wachstumsperiode zu, wah-rend eine Abnahme in der Konzentration fiirSamlinge toleranter Kultivare wahrend dieserPeriode beobachtet wurde. Fiohere Versal-zungskonzentrationen verursachten eine deut-hche Zunahme in dem Spermidin-Gehalt emp-findlichcr Kultivare. Insbesondere wahrend ei-ner Periode von 5—10 Tagen Wachstum verur-sachte die Versalzung eine Zunahme im Sper-min-Gehalt in Samlingen der empfindlichenKultivare. In alien Kultivaren zeigten die salz-gestreEten Samlinge eine hohere Agmatin-Konzentration im Vergleich zu den nicht ge-streEten Samlingen. Versalzung fuhrte zu einergroi^eren Akkumulation von anderen nichtidentifizierten Polyaminen in den Samlingensensitiver Kultivare. Eine erhohte Konzentra-tion des Gesamtgehaltes von Polyaminen,.Pu-trescin, Spermidin und unbekannten Polyami-nen in Samlingen von Reis unter Versalzunglassen vermuten, daft diese Verbindungen eineRolle in der Abwehr unglinstiger Einfllisse desSalzstresses spielen. ,̂

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Documents

Changes in Polyamine Titer in Rice Seedlings Following NaCl Salinity Stress