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O R IG IN A L PA PE R

Butenolide from plant-derived smoke enhances

germination and seedling growth of arable weed speciesMatthew I. Daws Jennifer DaviesHugh W. Pritchard Neville A. C. Brown Johannes Van Staden

Received: 14 September 2006 / Accepted: 6 November 2006 / Published online: 23 December 2006 Springer Science+Business Media B.V. 2006

Abstract We tested the applicability of therecently identified major germination cue from

smoke (a butenolide 3-methyl-2Hfuro[2,3-c]pyr-

an-2-one) on 18 weed species from non-fire proneenvironments. For the study species we compared

the relative effectiveness of alternating tempera-

tures, KNO3, GA3, smoke water and the buteno-lide on germination percentage, germination rate

and seedling mass. We found that while smoke

stimulated germination in a number of species it

also had negative impacts on other species. Inaddition, the butenolide was effective on the

widest range of species in terms of enhancinggermination percentage, rate and seedling mass.

However, none of the treatments, including but-enolide were effective on all species. Our data

demonstrate that butenolide may have wideapplicability as a germination and seedling

growth stimulant irrespective of whether the

species come from fire-prone habitats.

Keywords Arable weed ButenolideGermination Seed Smoke

Introduction

Smoke and smoke solutions from the combustionof plant material stimulate germination in a wide

range of species from fire-prone environments

differing in plant growth form, reproductivestrategy and seed size (Brown et al. 2003; Brown

and Botha2004). Smoke also markedly improves

post-germinative growth (seedling vigour) inseeds of the Amaryllidaceae, even though in

these species there was no effect on germination(Brown et al.2003; Sparg et al.2005). Smoke can

also stimulate the germination of species fromnon-fire prone environments such as a number oftemperate arable weeds (Adkins and Peters

2001), lettuce (Lactuca sativa L., Drewes et al.

1995), celery (Apium graveolens L., Thomas andVan Staden 1995) and red rice (Oryza sativa,

Doherty and Cohn2000). However, even among

functionally similar species, e.g. arable weeds,smoke can have positive, neutral or negative

impacts on germination (e.g. see Adkins and

M. I. Daws (&) J. Davies H. W. PritchardSeed Conservation Department, Royal BotanicGardens Kew, Wakehurst Place, Ardingly, West

Sussex RH17 6TN, UKe-mail: [email protected]

N. A. C. BrownHorticultural Research, Kirstenbosch ResearchCentre, South African National Biodiversity Institute,Cape Town, Western Cape 7735, South Africa

J. Van StadenResearch Centre for Plant Growth and Development,School of Biological and Conservation Sciences,University of Kwazulu-Natal, Private Bag X01,Scottsville 3209, South Africa

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Plant Growth Regul (2007) 51:7382

DOI 10.1007/s10725-006-9149-8


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Peters2001). These contrasting effects of smokeon germination and its inhibitory impact at high

concentrations suggest that in addition to the

main germination stimulant there are a range ofgermination inhibitors for which there are spe-

cies-specific responses (Drewes et al.1995).

More recently the main germination stimulat-ing component in smoke has been identified as 3-

methyl-2Hfuro[2,3-c]pyran-2-one (Flematti et al.

2004; Van Staden et al. 2004). This compound isactive at very low concentrations (c. 109 M) and

unlike smoke solutions is not inhibitory at high

concentration (Van Staden et al.2004). Similar tosmoke, butenolide has been shown to improve

seedling vigour in the crop species Lycopersiconesculentum, Abelmoschus esculentus, Phaseolus

vulgaris and Zea mays (Van Staden et al. 2006)

and widen the temperature range for germinationin L. esculentum (Jain and Van Staden in press).Consequently it has been proposed that buteno-

lide may have broad applicability as an ecological

and restoration tool (Flematti et al. 2004; Lightand Van Staden 2004). However, to date the

compound only appears to have been tested on

less than 30 species (Flematti et al. 2004; VanStaden et al. 2004, 2006; Merritt et al. 2006). In

addition, tests on the effectiveness of butenolide

for 13 of the species have only involved compar-

ing butenolide with a water control (Flemattiet al. 2004) and for a further seven species just

smoke, butenolide and a water control werecompared (Merritt et al. 2006). Thus, there is a

need to test both the efficacy of this compound on

germination and seedling growth for a widerrange of species and assess its effectiveness

relative to other potential germination stimulat-

ing compounds and environmental cues.In this paper, we compare across 18 weed

species the relative impacts of butenolide and

smoke solution on seed germination and seedlingvigour. We also widen the comparison of treat-

ments to include the use of GA3, KNO3 andalternating temperatures. Both KNO3 and alter-

nating temperatures have previously been shown

to be ecologically relevant germination triggersfor a wide range of weedy species (Hilton 1984;

Pons 1989; Daws et al. 2002). In the natural

environment these signals indicate that a seed iseither close to the soil surface or in a disturbed

site (Pons1989; Daws et al. 2002; Pearson et al.2002). In addition, the plant growth regulator

GA3 is a widely used germination stimulant that

is effective across a broad range of species(Bewley and Black1994).

Materials and methods

Seedlot details

Commercially available seedlots of a range of

temperate and sub-tropical weed species (seeTable1) were obtained from Herbiseed (Twy-

ford, United Kingdom) and stored at 15C and

15% relative humidity until used in the germina-tion experiments.

Germination tests

For each species, four replicates of 25 seeds eachwere sown on the surface of two layers of

Table 1 Species used in the comparisons of the variousgermination treatments

Species Family Seedmass

(mg)

Speciescodea

Alopecurusmyosuroides

Poaceae 1.82 Am

Avena fatua Poaceae 15.26 Af Bromus sterilis Poaceae 7.10 BsBromus tectorum Poaceae 2.79 BtCapsella bursa-

pastorisBrassicaceae 0.10 Cbp

Chenopodium album Amaranthaceae 0.59 CaChrysanthemum

segetumAsteraceae 0.55 Cs

Galium aparine Rubiaceae 9.80 GaMalva neglecta Malvaceae 1.76 Mn

Matricariamatricoides

Asteraceae 0.28 Mm

Papaver rhoeas Papaveraceae 0.20 PrPhalaris paradoxa Poaceae 1.89 PpPolygonum

arvicularePolygonaceae 2.79 Pa

Rumex obtusifolius Polygonaceae 1.94 RoSenecio jacobinae Asteraceae 0.23 SjSinapis alba Brassicaceae 5.62 SaSorghum halepense Poaceae 5.63 ShStellaria media Caryophyllaceae 0.48 Sm

a Used in Figs.13

74 Plant Growth Regul (2007) 51:7382

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Whatman No. 42 filter paper in either 50 or90 mm Petri dishes (dependent on seed size). The

filter papers were moistened with either 1.5 or

4.5 ml of 107 M butenolide solution, 103 MKNO3, 10

4 M GA3or distilled water (alternating

temperature, smoke treatment and control) for

the 50 and 90 mm Petri dishes, respectively. Forthe smoke treatment, seeds were soaked in smoke

solution for 24 h at 20C before sowing. Smoke

solutions were prepared, according to manufac-turers instructions using smoked filter paper

provided by Capeseed (Cape Town, South Afri-

ca). The butenolide used in the experiments wasisolated, purified and identified from smoke-

saturated water derived from burned Passerinavulgaris Thoday and Themeda triandra L. asdescribed by Van Staden et al. (2004). The

concentrations of butenolide, KNO3 and GA3were chosen because they have been shown to beeffective in stimulating germination in other

studies (Daws et al. 2002; Van Staden et al.

2004; Kepczynski et al. 2006). All treatmentsexcept the alternating temperature were germi-

nated at a constant 15C with an 8/16 h photope-

riod. Seeds in the alternating temperaturetreatments were sown at 25/10C with the high

temperature experienced for 8 h coinciding with

the light period. Consequently the mean temper-

ature in this treatment is 15C as in the constanttemperature treatment.

Seeds were scored for germination daily, withgermination defined as radicle emergence greater

than 1 mm.

Seedling dry mass determinations

Upon visible germination, ten seedlings wererandomly selected from each species/treatment

combination and removed 7-day post-germina-

tion for dry mass determination, i.e. each seedlinghad had 7 days of growth post-germination.

Seedling dry mass was determined by drying

individual seedlings at 103C for 17 h.

Statistical analyses

For each species/treatment combination the mean

time to germinate (MTG) was calculated using

the equation:

MTGX

nd =N 1

where n is the number of seeds germinated

between scoring intervals,dthe incubation period

in days at that time point, and N is the total

number of seeds germinated in the treatment(Tompsett and Pritchard1998).

To provide an assessment of the relativeeffectiveness of the six treatments (including the

control) in promoting germination and impacting

on seedling growth, within each species thetreatments were ranked for their effectiveness.

Subsequently the ranks for each treatment were

summed across species, which provides an indexfor comparing treatments across species, i.e.

which treatment stimulates germination to the

greatest extent and in the highest number ofspecies. In addition, the percentage change in

each of the three parameters that were measured

(germination percentage, MTG and seedlingmass) from the value in the control treatment

was calculated. To ascertain whether the response

to butenolide was similar to that for the othertreatments, the Pearsons correlation coefficients

were determined for the percentage change data

for butenolide with each of the other fourtreatments in turn. In addition, the relationship

between seed size and change in percentagegermination, across species, was tested using aPearsons correlation.

For each species, one-way ANOVA, imple-

mented in Minitab 11 (Minitab Inc., State Col-lage, PA, USA), followed by Tukeys pair-wise

comparisons was conducted to test for significant

differences between treatments with respect toeach of the three measured parameters; germina-

tion percentage, MTG and seedling mass.

Results

Seed germination

All five of the germination treatments had signif-

icant positive effects on germination percentage,

relative to the control, for at least some of the 18species (Fig.1). However, smoke also had signif-

icant negative impacts on germination for two

Plant Growth Regul (2007) 51:7382 75

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species (Avena fatua and Bromus sterilis) and

KNO3 had a significant negative effect on Pha-

laris paradoxa(P< 0.05; Fig. 1b, d). In addition,

there was no significant correlation (P> 0.05)

between change in percentage germination withthe smoke treatment (relative to the control) and

seed mass. Ranking the effectiveness of the

six treatments (including the control) for each

individual species in turn and then summing the

ranks revealed that the order of effectiveness ofthe treatments was: butenolide > GA3> alternat-

ing temperatures > KNO3> control > smoke.

Pearson correlations of the percentage change(relative to the control) germination data for

butenolide with the additional four treatments

revealed a significant positive correlation

Butenolide

-20

0

20

40

Smoke

-20

0

20

40

GA3

Percen

tagedifferenceingerminationp

ercentagefromt

hecontrol

-20

0

20

40

KNO3

-20

0

20

40

Alternating temperatures

Species

-20

0

20

40

60

**

*

*

*

*

* *

*

*

*

*

*

*

*

*

*

**

* *

*

*

*

*

*

*

**

*

**

Am Af Bs Bt Cbp Ca Cs Ga Mn Mm Pr Pp Pa Ro Sj Sa Sh Sm

Am Af Bs Bt Cbp Ca Cs Ga Mn Mm Pr Pp Pa Ro Sj Sa Sh SmFig. 1 The percentagedifference in germinationlevel between the fivegermination treatmentsand the controlgermination levelassessed at a constant

15

C (except for thealternating temperaturetreatment which was at25/10C) for the 18 weedspecies. Positive bars referto higher germinationpercentages relative tothe control.Error barsare+1 SE of the mean. Anasteriskabove a columnindicates a significantdifference from thecontrol (P< 0.05). Labelson the x-axis refer to

species codes in Table 1


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(P < 0.05) between the responses to butenolideand GA3 (Table2).

Similarly all five of the germination treatments

had either significant positive or negative effectson MTG of the study species (Fig.2). Smoke and

alternating temperatures had significant negative

effects on MTG for the greatest number ofspecies (four and five species, respectively),

although these treatments also had significant

positive effects for other species (P< 0.05;Fig.2b, e). Ranking the six treatments revealed

that the order of effectiveness at decreasing MTG

was: butenolide > GA3> KNO3> smoke > alter-nating temperatures > control. For MTG there

were no significant relationships between the

response to butenolide (percentage change data)and the additional four treatments (P> 0.05;

Table2).

Seedling mass

The majority of the species/treatment combina-tions resulted in an increase in seedling dry

mass relative to the control (Fig.3). However,

for three species smoke had a significantnegative effect on seedling mass (Fig.3b).

Again ranking the six treatments indicated

that the effectiveness decreased in the order:

butenolide > GA3> alternating temperatures >KNO3> smoke > control. Pearson correlations

of the percentage change (relative to the control)

seedling mass data for butenolide with the addi-tionalfourtreatmentsrevealedasignificantpositive

correlation (P< 0.05) between the responses to

butenolide and GA3(Table2); none of the otherrelationships were significant.

However, although GA3 was ranked as the

second most effective treatment in terms ofincreasing seedling mass, it also had a negative

effect on seedling morphology, typically resulting

in etiolated seedlings; this effect was not observedwith butenolide (Fig.4).

Discussion

We have found that across six germination

treatments butenolide was, on average, the mosteffective at enhancing germination percentage

and rate and seedling growth (mass) across a

diverse range of weed species spanning ninefamilies and seed masses from 0.1 to 15 mg

including both 16 temperate and two sub-tropical

species (Phalaris paradoxa and Sorghum hale-pense). Consequently we propose that butenolide

may have wide applicability as a germination and

growth stimulant with potential implications forboth weed management and improving seedling

growth.

The effectiveness of butenolide versus smoke

Among the germination treatments, smoke had

significant negative effects on a number of species

in terms of germination percentage, rate andseedling growth whilst across the 18 species

butenolide was the most effective in terms of

enhancing these parameters. These differences inthe response to smoke and butenolide were

reflected in the absence of significant correlations

between the effect of butenolide and smoke onthe three measured parameters (Table2). The

greater effectiveness of butenolide than smoke

may be related to toxic or germination inhibitingcompounds in smoke, which potentially act in a

species-specific manner. Similarly, prolonged

smoke treatment or high concentrations have

Table 2 Pearsons correlation coefficients describing therelationships among the 18 species in their percentagechange values (relative to the control) for the five treat-ments

GERMINATION (%)Smoke GA3 KNO3 Alt temp

a

Butenolide 0.031 0.503* 0.314 0.408

MTGSmoke GA3 KNO3 Alt temp

a

Butenolide 0.168 0.103 0.225 0.039

SEEDLING MASSSmoke GA3 KNO3 Alt temp

a

Butenolide 0.127 0.486* 0.293 0.426

Correlation coefficients are presented separately forgermination percentage, mean time to germinate (MTG)and seedling mass

*P< 0.05a alternating temperatures


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been shown to inhibit germination in other

species (Drewes et al. 1995). Smoke is a highly

complex mix of several thousand compounds(Maga1988) with no two batches being either at

the same concentration or containing the

same balance of compounds. Consequently, theuse of smoke in germination testing is further

complicated by the need to calibrate individual

batches to identify optimum concentrations

(Boucher and Meets2004).Across our study species, butenolide posi-

tively affected germination percentage and rate

in 12 (eight significantly) of 18 cases. For fourof the species where there was either no effect

Butenolide

-80

-60

-40

-20

0

20

40

60

Smoke

-80

-60

-40

-20

0

20

40

60

GA3

PercentagedifferenceinMTG

fromt

hecontrol

-80

-60

-40

-20

0

2040

60

KNO3

-80

-60-40

-20

0

20

40

60

Species

-80

-60

-40

-20

0

20

40

60

*

**

*

*

*

*

*

*

*

*

* *

*

*

*

*

*

*

*

* *

*



**

*

Am Af Bs Bt Cbp Ca Cs Ga Mn Mm Pr Pp Pa Ro Sj Sa Sh SmFig. 2 The percentagedifference in mean time togerminate (MTG)between the fivegermination treatmentsand the controlgermination level

assessed at a constant15C (except for thealternating treatmentwhich was at 25/10C) forthe 18 weed species.Positive barsrefer tofaster germination, i.e. alower MTG, than in thecontrol. Anasteriskabovea column indicates asignificant difference fromthe control (P< 0.05).Error bars are +1 SE ofthe mean. Labelson the

x-axis refer to speciescodes in Table 1


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of butenolide on germination percentage, orthe effect was negative, seedling mass in-

creased significantly (Alopecurus myosuroides,Bromus sterilis, Capsella bursa-pastoris andGalium aparine). The absence of an effect on

germination for some species (e.g. B. sterilis)

may indicate that these seedlots were non-dormant. Similarly for non-dormant seeds of

tomato, butenolide had no effect on germina-tion percentage although it did significantly

increase seedling growth (Jain and Van Staden

in press). Consequently although butenolidemay be highly effective in stimulating germi-

nation across a wide range of species it may

also have broad applicability for promotingseedling growth.

Smoke

-100

-50

0

50

100

150

GA3

Perc

entagedifferenceinseedlingm

assfromt

hecontrol

-100

-50

0

50

100

150

KNO3

-100

-50

0

50

100

150


Species

-100

-50

0

50

100

150

Butenolide

-100

-50

0

50

100

150

*

**

*

*

* *

*

* **

*

*

* **

*

**

*

***

*

*

**

**


Am Af Bs Bt Cbp Ca Cs Ga Mn Mm Pr Pp Pa Ro Sj Sa Sh SmFig. 3 The percentagedifference in seedlingmass, after 7 days,between the fivegermination treatmentsand the controlgermination level

assessed at a constant15C (except for thealternating treatmentwhich was at 25/10C) forthe 18 weed species.Positive barsrefer to ahigher seedling massrelative to the control. Anasterisk above a columnindicates a significantdifference from thecontrol (P< 0.05). Errorbarsare +1 SE of themean.Labelson the x-

axis refer to species codesin Table 1


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The effectiveness of butenolide versus

remaining treatments

Butenolide was not only more effective than the

smoke treatment, but also in many cases KNO3,

GA3and alternating temperatures, at stimulating

germination and seedling growth. However, forsome species, e.g. Chenopodium album, both

alternating temperatures and KNO3 were moreeffective than butenolide and for others GA3was

the most effective, e.g. Capsella bursa-pastoralis.

KNO3and alternating temperatures are knowngermination cues for a range of species in

particular weedy, early successional species. Re-duced vegetation results in greater irradiance

reaching the soil surface, which causes greater soil

temperature fluctuations. In addition, the distur-

bance associated with the formation of vegetationgaps can result in soil nitrate levels increasing

(Pons1989; Daws et al. 2002). Consequently forweedy species, these cues provide an environ-

mental signal that seeds are in an open, high-light

micro-site which is potentially suitable for onwardseedling growth (Baskin and Baskin1998; Daws

et al. 2002) explaining the effectiveness of these

treatments, for at least some of the species.GA3 was more widely applicable for stimulat-

ing germination percentage and seed growth than

either KNO3 or alternating temperatures. BothKNO3 and alternating temperatures are environ-

mentally relevant germination cues for which a

positive germination response is likely to reflectspecies-specific germination strategies. In com-

parison, gibberellins (including GA3) are endog-

enous plant growth regulators with broadeffectiveness in stimulating cell elongation (and

hence germination; Lange and Lange 2006).

Nonetheless butenolide was more effective thanGA3. This raises the question of why a fire

associated chemical is so effective at stimulatinggermination and growth of species that are nottypical of fire associated environments. A partial

explanation for this apparent paradox may be that

some arable environments are subjected to fire(e.g. stubble burning). However, such practices

are not universally applied and stubble burn-

ing has been banned in Western Europe for atleast the last decade. For such species the

role of butenolide (and smoke) in the natural

environment would be clarified by determiningwhether such changes in land use practice have

impacted on the recruitment and diversity of

arable weed species. However, an alternativeexplanation for the effectiveness of butenolide is

that structurally, butenolide is analogous to

endogenous plant growth regulators (e.g. gibber-ellins or auxins). Thus, our hypothesis is that the

apparent broad-scale efficacy of butenolide may

be related to it functioning, in the natural envi-ronment, as an exogenous plant growth regulator

analogue.

How does butenolide work?

The mode of action of smoke and butenolide hasbeen ascribed to an interaction with the gibber-

ellin pathway in seeds. Thus, butenolide has beenreported to have similar effects on germination asGA3 on Australian Asteraceae (Merritt et al.

2006) and smoke affects endogenous GA synthe-

sis and ABA content (Van Staden et al. 2000). Inaddition, smoke has a similar effect to GA3 in

substituting for red light (640 nm) in the stimu-

lation of lettuce cv. Grand Rapids germination(Drewes et al.1995; Van Staden et al.1995). Our

data partially support this hypothesis; for germi-

nation percentage and seedling mass there were

significant relationships between the response ofspecies to butenolide and GA3. However, bute-

nolide was more effective than GA3and buteno-lide had the advantage of not resulting in the

elongated internodes that are typically associated

with GA3 (Fig.4). Consequently butenolide islikely to be of greater value than GA3 for

germination testing on diverse species since the

resulting seedlings are more likely to be morpho-logically normal.

While based on this study and earlier literature

there are clear similarities in the responses ofseeds to butenolide/smoke and GA3, there are

few obvious similarities between the chemical

structures of the two compounds. However, thereare structural similarities between butenolide and

the strigolactones, which stimulate germination in

the parasitic plants Orobanche sp. and Striga sp.(Flematti et al.2004). On a functional level, this is

supported by the finding that synthetic strigol

analogues can stimulate germination in Avena


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fatua(Bradow et al.1990). However, the effect of

butenolide on seed germination of parasitic plantshas not been tested.

Interestingly, related butenolides are alsoproduced by a range of micro-organisms. For

example, Fusarium sp. produces a butenolide

that functions as a mycotoxin; the mode of actionof this compound results from an impact on the

intracellular redox environment (Wang et al.

2006). Since oxidative stress has been proposedto have a signalling role in germination (Kranner

et al.2006), this area may also be worth pursuing

in relation to the role of butenolide in germina-tion.

In conclusion, we have found that a butenolidefrom plant derived smoke is a highly effective

germination and seedling growth stimulant for a

range of arable weeds. In addition, this compoundappears to have no negative impact on seedling

morphology, as observed with GA3, and may

have wide-scale applicability as a germination andearly growth stimulant.

Fig. 4 A comparison ofseedling size and form for(A)Bromus sterilis (B)Chenopodium album and(C) Sorghum halepense,subjected to the sixgermination conditions

(1 = butenolide,2 = smoke, 3 = GA3,4 = KNO3,5 = alternatingtemperatures and 6 = thecontrol)


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Acknowledgements Financial support to M.I. Daws andJ. Davies was provided by the Millennium Commission,The Wellcome Trust and Orange plc. The Royal BotanicGardens, Kew receives grant-aided support from Defra,UK. J. Van Staden was supported by the NationalResearch Foundation, South Africa.

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