Exposure to red light, temperature and exogenous gibberellins influenced germination of some winter weeds

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1 Africn Journl of Biotechnology Vol. 11(2), pp , 5 Jnury, 2012 Avilble online t DOI: /AJB ISSN Acdemic Journls Full Length Reserch Pper Exposure to red light, temperture nd exogenous gibberellins influenced germintion of some winter weeds Dong-Sheng Tng 1#, Muhmmd Hmyun 2#, Abdul Ltif Khn 3, Smin Jn 4, Ysmin Nwz 5, Muhmmd Irshd 2, Young-Eun N 6 nd In-Jung Lee 3 * 1 Key Lbortory of Agri-biodiversity nd Pest Mngement, Yunnn Agriculturl University, Chin. 2 Deprtment of Botny, Abdul Wli Khn University, Mrdn, Pkistn. 3 Flower Reserch Institute, Yunnn Acdemy of Agriculturl Sciences, Chin. 4 Deprtment of Botny, Islmi College University, Peshwr, KPK, Pkistn. 5 Deprtment of Zoology, Abdul Wli Khn University, Mrdn, KPK, Pkistn. 6 Climte Chnge nd Agroecology Division, Ntionl Acdemy of Agriculturl Sciences, RDA, Suwon, Kore. Accepted 7 December, 2011 Red light, temperture nd gibberellins re well known for their cpcity to induce higher germintion in dormnt seeds of severl plnt species. In the current study, we investigted the effect of vrious temperture (10, 13, 16, 19, 22 nd 25 C) nd gibberellic cid (GA 3 ) nd GA 4+7 concentrtions (0.1, 1, 10, nd 100 um) on germintion of Po nnu, Alopecurus equlis nd Stellri qutic seeds incubted under continuous drk or treted with red light pulse of 80 mol m -2 s -1 red light (660 nm) for 10 min fter 12 h of drk period. We found tht incubtion temperture nd gibberellins (GAs) significntly enhnced seed germintion in red light treted seeds, s mximum germintion ws observed for A. equlis (67.3% t 13 C), P. nnu (61.3% t 13 C), nd S. qutic (42% t 19 C) in such tretments. Exogenous GA 4+7 significntly promoted germintion of P. nnu nd A. equlis seeds, while GA 3 induced higher germintion in S. qutic seeds. It ws observed tht GAs were more effective in the presence of red light s lest germintion stimultion ws recorded for GAs under drk condition nd no germintion ws found in weed seeds t control nd 0.1 mm GA 3 nd GA 4+7 tretments. It cn be concluded tht lower temperture (13 C) nd GA 4+7 in conjunctions with red light pulse, induced mximum germintion in dormnt weed seeds. Key words: Germintion, temperture, nitrogen-contining compounds, red light, gibberellins. INTRODUCTION Seed dormncy could be considered simply s block to the completion of germintion of n intct vible seed under fvorble conditions, lthough to some reserchers, it is one of the lest understood phenomen in the field of seed biology (Hilhorst, 1995; Bewley, 1997). In *Corresponding uthor. E- mil: ijlee@knu.c.kr. Tel: Fx: #These uthors contributed eqully to the pper Abbrevition: GA 3, Gibberellic cid. the lst yers, significnt progress hs been mde in understnding seed dormncy; however, there hve lso been some potentil sources of confusion tht hve been reported in the literture (Finch-Svge nd Leubner- Metzger, 2006). In ecologicl studies, there hs been confusion reported between seed dormncy nd persistence in soil (Thompson et l., 2003; Fenner nd Thompson, 2005; Wlck et l., 2005). This hs resulted in prt from different views on dormncy, such s whether light termintes dormncy or induces germintion. Environmentl fctors re believed to regulte seed dormncy nd germintion. Temperture substntilly ffects the dormncy level of weed seeds (Forcell,

2 274 Afr. J. Biotechnol. 1998), s diurnl nd sesonl temperture fluctution nd men temperture ffect the breking of dormncy nd thus the germintion rte. Some weeds require periods in which the temperture either increses or decreses slowly, wheres other species require dily temperture fluctutions or chilling to brek dormncy (Bskin nd Bskin, 2004). Likewise temperture, light is nother environmentl fctor regulting seed dormncy nd germintion. Such regultion is medited by photoreceptors clled phytochromes, which initite or stop physiologicl processes in the seed depending on the chrcteristics of the light to which it is exposed. The phytochromes chnge their form depending on the wvelength of the light to which they re exposed. The phytochrome Pr bsorbs red light (R) nd is biologiclly inctive, while Pfr bsorbs fr-red light (FR) nd is considered the ctive form tht promotes germintion (Benech-Arnold et l., 2000). The wvelength, flux density, nd exposure durtion of light determine the extent of germintion induction nd breking dormncy (Bllre nd Csl, 2000). Plnt-hormones re nturlly occurring orgnic substnces, which influence physiologicl processes t very low concentrtions either in distnt tissues to which they re trnsported or in the tissue where synthesis occurred (Dvies, 1995). Due to their structurl simplicity, plnt hormones re not specific enough to mtch the vriety of controlled rections (Cnny, 1985). Contrry to this, it hs been suggested tht hormones only provide "turn on" or "turn off' signls nd tht the ctul informtion s re provided by the cell. Gibberellins re considered importnt in the regultion of seed dormncy. Gibberellins re tetrcyclic diterpenes, which re reported s necessry for seed germintion in mny plnt species (Swd et l., 2008; Clvo et l., 2004). Gibberellic cid (GA 3 ) is lso reported to reprogrm plnts to higher growth nd significntly meliorte the dverse effects of slt stress nd rescue the productivity nd qulity of soyben (Hmyun et l., 2010). The first objective of the current study ws to investigte the effect of red light nd temperture on seed germintion rte nd dormncy relese of Po nnu, Alopecurus equlis nd Stellri qutic. These re common weeds of griculture fields during winter seson. The second objective ws to observe the stimulting effect of bioctive GAs on seed germintion, nd compre the effectiveness of GA 3 nd GA 4+7 in the regultion of seed germintion of these three weeds. MATERIALS AND METHODS Generl procedure Seeds of P. nnu, A. equlis vriety murensis, nd S. qutic were collected from griculture fields in Suwen, South Kore. Seeds were then properly dried for two weeks t green house nd kept in ir-tight polyethylene continers t cold room t 4 C. The seeds were surfce sterilized by immersion in 0.5% (w/v) NClO for 5 min nd wshed with sterile distilled wter. Fifty seeds of ech weed species were plced in 9 cm Petri pltes with two lyers of Whtmn No. 1 filter pper nd moistened with 4 ml of distilled wter. The Petri pltes were wrpped in luminum foil, covered with drk cloth nd trnsferred to incubtor set t 25 C. Seeds germintion ws observed fter one week of red light tretment nd emergence of rdicl (2 mm) ws the criterion for germintion (Andersson et l., 2002). Ech tretment comprised 3 replictes nd ws repeted twice. Appliction of red light, temperture nd gibberellins For red light tretment, seeds were irrdited with red light for 10 min fter 12 h of imbibition. Light emitting diode (LED) lmp (Mil- R18: Snyo Biomedicl) with irrdition of 660 nm, with irrdition of 660 nm (80 mol.m -2 s -1 ) ws used s light source for seed germintion throughout the experiment (Tng et l., 2008). Treted seeds were trnsferred bck to incubtor. The temperture tretment comprised tempertures rnging from 10 to 30 C t 3 C intervls. For investigting GAs effect, seeds were incubted in the drk t 25 C nd treted with 0.1, 1, 10 nd 100 um of GA 3 nd GA 4+7. GA 3 nd GA 4+7 re commercilly vilble bioctive gibberellins. GAs (GA 3 nd GA 4+7) were dissolved in 1 N NOH nd then solutions were mde with distilled H 2O. Sttisticl nlysis The mens nd stndrd errors for ll tretments were compred using nlysis of vrince (ANOVA SAS relese 9.1; SAS, Cry, NC, USA) in order to define whether the differences were significnt. Men percentge germintion ws grphiclly compred through Sigm Plot softwre (Sigmplot 9.0, Systt Softwre Inc., 2004). Vlues included in the sme group indicte tht the differences mong the vlues re not significnt. But, vlues divided into the different groups mens tht the differences re significnt otherwise. RESULTS AND DISCUSSION Influence of vrying tempertures on germintion of winter weeds Vible seeds re dormnt when their germintion is prevented by block within the seed, so tht they cnnot germinte in n otherwise fvorble environment (Bewley nd Blck, 1982). Temperture hs double effect on seed germintion. Both the finl germintion percentge nd the rte t which this percentge is reched re ffected by temperture. Generlly, the mximum finl germintion percentge is reched in brod temperture rnge, wheres the germintion rte hs shrp optimum temperture (Grci-Huidobro et l., 1982). We observed tht the seeds of P. nnu nd A. equlis vriety murensi germinted t 10 C nd the germintion rte incresed with temperture nd mximum seed were germinted t 13 C in both red light nd control tretments. However, with further increse in temperture, the germintion grdully declined nd lest germintion ws observed in seeds kept t 25 C. Current results showed tht P. nnu seeds filed to germinte below 10 C nd bove 25 C (Figures 1 nd 2). Addition

3 Lee et l. 275 Figure 1. Germintion of P. nnu seeds t different tempertures. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout. Figure 2. Germintion of A. equlis vr. murensi seeds t different tempertures. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout.

4 276 Afr. J. Biotechnol. 50 Drk Red-light pulse 40 Germintion (%) b c b b c 10 d Incubtion temperture ( o C) Figure 3. Germintion of S. qutic seeds t different incubtion tempertures. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout. of red light significntly stimulted seed germintion t tempertures rnging from 10 to 22 C s compred to drk tretments, but it filed to induce germintion below 10 C nd bove 25 C. The overll germintion cpcity of A. equlis vriety murensi ws found higher thn P. nnu under similr environmentl condition. It ws previously reported tht t tempertures below the optimum, germintion rte increses linerly with temperture (Hegrty, 1973; Grci-Huidobro et l., 1982); however, the current study showed tht in weeds, t tempertures bove the optimum, germintion rte decreses linerly n increse in temperture. Seeds of S. qutic germinted t low temperture (10 C), nd further increse in temperture regime stimulted germintion till mximum germintion ws ttined t 16 C. However, grdul further increse in temperture cused mrked reduction in germintion of S. qutic seeds (Figure 3). Similr to the other two weed studied, red light provided n dditive stimultion for seed germintion, lthough t extreme lower nd higher tempertures, the red light filed to induce ny germintion. Current results proved tht tretment of weed seeds with red light for brief period significntly enhnce germintion percentges of treted seeds. It is becuse the red light promotes phytochrome biosynthesis which induces seed germintion. Our current findings confirm previous report on fvorble role of red light in seed germintion (Tng et l., 2008). Influence of GA 3 nd GA 4+7 on germintion of winter weeds Physiologiclly ctive GAs is known for inducing seed germintion in wide rnge of plnt species, s they induce hydrolytic enzymes. The hydrolytic enzymes weken the brrier tissues such s the endosperm or seed cot, inducing mobiliztion of seed storge reserves, nd stimulting expnsion of embryo (Bewley nd Blck, 1994). In the current study, exogenous GA 3 nd GA 4+7 pplictions induced higher germintion in P. nnu, A. equlis vr. murensi, nd S. qutic, while higher temperture fvored seed dormncy (Figure 4). Moreover, red light exposure showed n dditive effect to seed germintion of weed species in-conjunction with these GAs. However, the effect of GA 3 nd GA 4+7 vried for different weed species s GA 3 seems to show lesser effect on P. nnu seeds s compred to GA 4+7 tretments (Figure 4). The stimultory effect of GAs ws enhnced when there ws n increse in GAs concentrtion from 0.1 to 100 M (Figures 4, 5 nd 6). In cse of A. equlis vr. murensi, either of GA 3 nd GA 4+7 significntly prompted seed germintion (Figure 5), which ws similr to tht of P. nnu. On the contrry, lower

5 Lee et l. 277 Figure 4. Germintion (%) of P. nnu seeds treted with elevted GA 3 nd GA 4+7. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout. D stnds for drk, while R stnds for red light. Figure 5. Germintion (%) of A. equlis vr. murensis treted with elevted GA 3 nd GA 4+7. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout. D stnds for drk, while R stnds for red light.

6 278 Afr. J. Biotechnol. Figure 6. Germintion (%) of S. qutic treted with elevted GA 3 nd GA 4+7. Seeds were treted with red light for 10 min fter 12 h of drk, while the control seeds were kept under drk throughout. D stnds for drk, while R stnds for red light. concentrtions of GA 3 nd GA 4+7 induced seed germintion of S. qutic, s mximum germintion ws chieved t 0.1 M GA 3 nd 10 M GA 4+7 (Figure 6). Conclusion Weed erdiction is difficult tsk s weed seeds possess differentil dormncy levels nd cn survive under the soil for mny yers. An efficient erdiction of these undesired plnts cn be chieved by dopting two pronged strtegy, tht is, either to induce permnent dormncy in these seeds or to brek the existing vrying degrees of seed dormncy, so tht ll seeds germinte t the sme seson nd cn be effectively erdicted by pplying chemicls or through trditionl weeding prctices. Our study is linked to the ltter prt nd nrrtes bout the fvorble role of red light nd N-compounds in germintion induction or breking of seed dormncy. The current study explins how interctions between environmentl fctors hve gret impct on the germintion of weeds. The vrible responses of weeds to environmentl fctors nd their interction could ccount for differences in seed germintion nd seedling emergence timing, which represent differences in dpttion nd survivl strtegies. This study would help in understnding the fvorble role of red light, temperture nd exogenous GA 3 nd GA 4+7 in germintion induction of weed seeds, s weed erdiction from crop fields is highly desirble, which will increse crop production nd reduce the use of herbicides. However, further reserch is needed on the topic in order to understnd nd elborte the germintion induction mechnism of weed seeds. ACKNOWLEDGEMENTS This reserch work ws supported by the Agend Progrm (Project No.PJ007522), Rurl Development Administrtion, Republic of Kore. REFERENCES Andersson L, Miberg P, Schutz W, Steinmetz O (2002). Germintion chrcteristics nd emergence time of nnul Bromus species of differing weediness in Sweden. Weed Res. 42: Bllré CL, Csl JJ (2000). Light signls perceived by crop nd weed plnts. Field Crops Res. 67:

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