Germination dimorphism in Suaeda acuminata: A new combination of dormancy types for heteromorphic seeds

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1 Aville online t South Africn Journl of Botny 78 (212) Short communiction Germintion dimorphism in Sued cumint: A new comintion of dormncy types for heteromorphic seeds H.-L. Wng, L. Wng,, C.-Y. Tin,, Z.-Y. Hung Stte Key Lortory of Desert nd Osis Ecology, Xinjing Institute of Ecology nd Geogrphy, Chinese Acdemy of Sciences, Urumqi 8311, Chin Stte Key Lortory of Vegettion nd Environmentl Chnge, Institute of Botny, Chinese Acdemy of Sciences, Beijing 193, Chin Received 8 Ferury 211; received in revised form 13 My 211; ccepted 2 My 211 Astrct Desert nnul Sued cumint produces two morphologiclly distinct types of seeds on the sme plnt. The min ims of our study were to compre germintion chrcteristics of the dimorphic seeds, scertin their dormncy types nd give the hormonl explntion. The two seed types of S. cumint sored wter t different rtes with rown seeds imiing wter fster. Germintion percentges of rown seeds were significntly higher thn those of lck seeds in ll temperture nd light regimes tested. Eight weeks of cold strtifiction did not rek dormncy of lck seeds, wheres exogenous GA 3 promoted germintion. Excised emryos of untreted lck seeds produced norml seedlings. Contents of ZR, GA 3 nd ABA of rown seeds were significntly higher thn tht of lck seeds; while contents of IAA of lck seeds were significntly higher thn tht of rown seeds. Brown seeds of S. cumint re non-dormnt, wheres lck seeds hve intermedite physiologicl dormncy (PD). Interction mong ZR, ABA nd GA 3 my ply n importnt role in dormncy sttus of oth seed types. This is the first report of nondormncy nd intermedite PD in heteromorphic species. 211 SAAB. Pulished y Elsevier B.V. All rights reserved. Keywords: Emryo; Hormone; Physiologicl dormncy; Seed germintion; Seed heteromorphism; Sued cumint 1. Introduction Generlly speking, ech plnt species produces only one morphologicl/physiologicl type of seed. However, some plnts produce two or more distinct types of seeds on single individul (Hrper, 1977; Venle, 1985). This phenomenon is clled seed heteromorphism. Most heteromorphic species re nnuls, often in the Astercee or Chenopodicee tht grow in extreme environments such s rid, semirid nd deserts (Mndák, 1997; Imert, 22). Heteromorphic seeds re found in more thn 2 species, nd they usully differ in color, size nd shpe, s well s in dispersl cpcity nd germintion requirements (Sorensen, 1978; Khn nd Ungr, 1984; Cheplick, 1994; Bskin nd Bskin, 1998; Imert, 22; Lu et l., 21). Corresponding uthor. Tel.: ; fx: E-mil ddresses: egiwng@ms.xj.c.cn (L. Wng), hlophyte@gmil.com (Z.-Y. Hung). Desert plnts my develop vrious germintion strtegies tht re dpttions to extreme environments (Guttermn, 1993). Heteromorphic seeds from single plnt growing in desert climte my represent comintion of divergent germintion strtegies (opportunistic vs cutious strtegies) (Venle, 1985; Guttermn, 22). Previous studies hve shown tht heteromorphic seeds usully hve different germintion chrcteristics (Bskin nd Bskin, 1976; Venle nd Levin, 1985; Brändel, 27). For exmple, Mndák nd Pyšek (21) compred germintion of different fruit types of the heterocrpous Atriplex sgittt in different light nd nitrogen supply conditions in the lortory. They showed tht heteromorphic seeds, produced y different types of fruits, hve different germintion percentges tht re ffected y light qulity, nitrte concentrtion nd cold strtifiction. A field study on germintion of dimorphic seeds of A. prostrt nd Slicorni europe cross zonl communities found tht germintion ws N9% for lrge seeds of oth species plced on the soil surfce nd tht germintion of smll seeds ws N5% nd N75%, respectively (Crter nd Ungr, 23) /$ - see front mtter 211 SAAB. Pulished y Elsevier B.V. All rights reserved. doi:1.116/j.sj

2 H.-L. Wng et l. / South Africn Journl of Botny 78 (212) Mny ppers reported differentil germintion of heteromorphic seeds, ut few studies defined the dormncy clss, level nd type in the seeds (Philipupilli nd Ungr, 1984; Bskin nd Bskin, 1998; Crter nd Ungr, 23; Brändel, 27). Dormncy chrcteristics of seeds of heteromorphic species cn e sorted into two ctegories. Prtil types re nondormnt nd the others re dormnt; ll types of seeds re dormnt. Lrge rown seeds of A. sgittt re non-dormnt, medium lck seeds re dormnt nd smll lck seeds re deeply dormnt (Mndák nd Pyšek, 21). All three types of chenes of the nnul ephemerl species Grhdiolus ppposus re dormnt (Sun et l., 29). Wng et l. (28) reported tht freshly-mtured rown seeds of Sued rlocspic re nondormnt nd lck seeds hve non-deep type 2 physiologicl dormncy (PD). This ws the first report of the comintion of non-dormnt nd non-deep type 2 PD for heteromorphic seeds. We surmised tht there re other comintions of dormncy types for heteromorphic species. Former studies hve ttempted to correlte dormncy levels with interctions of hormones (Kucer et l., 25). Chnges in the contents of ABA, GA nd cytokinins hve een exmined in mny seeds nd no consistent correltion etween dormncy levels nd hormone contents hve een estlished (Khn nd Smimy, 1982). In most studies, ABA is positive regultor of dormncy induction nd mintennce, while GA releses dormncy nd countercts ABA effects (Kucer et l., 25). Heteromorphic seeds re unique iologicl models to test hormone regultion hypothesis ecuse different seed types in the sme plnt hve differentil dormncy levels nd germintion chrcters. We recently discovered tht the desert nnul hlophyte Sued cumint (Chenopodicee) produces dimorphic seeds (Ding et l., 21). This species, ntive to centrl Asi, ws reported to produce smll lck seeds (Delectis Flore Reipulice Populris Sinice Agende Acdemie Sinice Edit, 1979; Commissione Redctorum Flore Xinjingensis, 1994). However, in ddition to smll lck seeds, we oserved lrge rown seeds on single plnt of S. cumint in northern Xinjing, Chin. Seed heteromorphism provides us with n optiml opportunity to study different dormncy types nd dormncy-reking mechnisms of the sme plnt species. The gols of this study re to determine whether there is difference in germintion of dimorphic seeds, nd to scertin the dormncy type (if ny) of these seeds. Menwhile, we use oth seed types to test the theoreticl prediction tht hormone regulte seed dormncy. Specificlly, we ddressed three questions. (1) How do temperture nd light ffect germintion of dimorphic seeds of S. cumint? (2) Does seed type determine if seeds re dormnt or non-dormnt? If so, wht type of dormncy does ech type of seeds hve? (3) Wht is the difference in contents of hormone etween different seed types? 2. Mterils nd methods 2.1. Study species nd sites Sued cumint L. (Chenopodicee) is desert her restricted to centrl Asi (Delectis Flore Reipulice Populris Sinice Agende Acdemie Sinice Edit, 1979). In Chin, S. cumint is found only in the inlnd sline-lkline deserts in Xinjing province (Commissione Redctorum Flore Xinjingensis, 1994). Field oservtions hve shown tht S. cumint ehves s summer nnul in northern Xinjing province, Chin. Germintion occurs only in spring. Newlygerminted seedlings hve een seen in lte Mrch, ut most of the germintion occurs in April. By lte April, thousnds of seedlings with only cotyledons re present. Plnts egin to flower in mid-june, ut the pek of flowering is from lte June to mid-july. Seed dispersl egins in mid-july. In Flor of Chin nd Flor Xinjingensis, only one type of seed (redrown to lck,.8 1 mm nd smooth) ws descried. However, we found two types of seeds on ech plnt of S. cumint: rown with soft corse seed cot nd lck with rigid smooth seed cot. The reserch re is n inlnd cold desert ( E; N; 5 m.s.l) with typicl temperte desert climte. Assocites of S. cumint include Klidium cspicum, S. microphyll, S. physophor, Petrosimoni siiric (Chenopodicee) nd Pegnum hrml (Zygophyllcee). Men nnul temperture is 6.8 C, men temperture of wrmest month (July) is 25.6 C, nd men temperture of coldest month (Jnury) is 16.9 C. Annul precipittion (rin nd snow) is out 2 mm Seeds Plnts of S. cumint grew under low competitive environment in slt desert ner the Fukng Desert Ecologicl Sttion of the Xinjing Institute of Ecology nd Geogrphy, Chinese Acdemy of Sciences. Mture fruits were collected from c. 2 plnts tht were not shded on 1 Octoer 29. Fruits were collected rndomly from the entire plnt in popultion. The fruits were llowed to dry for 1 dys, nd then the seeds were clened nd seprted y their colour. Germintion experiments nd cold strtifiction tretment were strted on 28 Octoer 29. Other seeds were stored dry (reltive humidity: 25 28%) t 4 C until used in experiments. Dimeter nd thickness of 2 seeds of ech of the two seed types were mesured, nd four groups of 1 seeds of ech type were weighed to determine seed mss Imiition tests Imiition tests were conducted t room temperture (19 23 C, 3% reltive humidity) using four replictes of 25 dry seeds of ech morph. Seeds were plced in 9-mm-dimeter Petri dishes with distilled wter-moistened filter pper. Then, seed mss ws mesured t time nd fter 1, 3, 6, 9, 12, 22 h. The imiition test of rown seeds ws terminted fter 6 h ecuse the seeds hd egun to germinte. The reltive increse in fresh weight (W r ) of seeds ws clculted s W r =[(W f W i )/W i ] 1, where W i is the initil seed weight nd W f the weight fter certin time (Bskin et l., 24).

3 272 H.-L. Wng et l. / South Africn Journl of Botny 78 (212) Effect of light nd temperture on germintion of dimorphic seeds Three replictes of 5 freshly-mtured seeds of ech morph were incuted on two lyers of Whtmn No.1 filter pper moistened with 2.5 ml of distilled wter in 5-cm-dimeter Petri dishes. Petri dishes were seled with prfilm nd incuted t dily (12/12-h) temperture regimes of 5:15, 5:25, 1:25, 15:3, nd 2:35 C in light (12-h dily photoperiod) for 2 d. Menwhile, seprte set of petri dishes were plced in continuous drkness. These thermoperiods represent the men dily mximum nd minimum monthly tempertures t the Fukng Field Reserch Sttion of CAS during the growing seson: 5:15 (erly April nd Octoer), 5:25 (lte April), 1:25 (My nd Septemer), 15:3 (June nd August) nd 2:35 C (July). A seed ws regrded s germinted when it grew rdicle 5 mm long. Germintion in light ws exmined every 2 d for 2 d; germinted seeds were removed from the dishes t ech counting. Seeds incuted in drkness were checked only fter 2 d Breking dormncy of lck seeds Cold strtifiction Wshed qurtz snd moistened with distilled wter (snd moisture content 9 12%) ws plced eneth two lyers of filter pper in 15-cm-deep 2-cm-dimeter metl oxes. Freshly-mtured lck seeds were plced on the filter pper, nd the metl oxes were closed nd plced in refrigertor in drkness for 2, 4 or 8 weeks t constnt 5 C. After tretments, lck seeds were trnsferred to Petri dishes under green light (the sfe light for checking sttus of drk-incuted seeds). Petri dishes were incuted t 1:25 C in light. Blck seeds collected t the sme time were stored t 4 C dry nd used s control. Germintion ws checked s descried ove GA 3 tretments Blck seeds were incuted in (distilled wter control), 1 nd 1 mmol L 1 GA 3 solutions t 1:25 C in light or drkness for 2 d. Germintion ws checked s descried ove Incution of emryos isolted from lck seeds Seed cots of 1 lck seeds were crefully removed nd emryos were incuted t dily (12:12 h) temperture regime of 15:3 C Anlyses of hormone contents The endogenous contents of free zetin rioside (ZR), scisic cid (ABA), gierellic cid (GA 3 ) nd indole-3-cetic cid (IAA) in mture seeds were nlyzed with n enzyme linked immunosorent ssy (ELISA) technique. The hormone ELISA kits were developed t the College of Crop Sciences, Chin Agriculturl University. These ELISA kits hve een widely ville commercilly. Extrction, purifiction nd determintion of endogenous hormones were performed s descried y Li nd Zhou (1996). Ech seed types hve three independent smples Dt nlysis All dt were expressed s men ± s.e. Germintion dt were trnsformed (rcsine) efore sttisticl nlysis to ensure homogeneity of vrince (non-trnsformed dt pper in ll figures). One- or two-wy ANOVA ws used to compre tretment effects. Tukey's test ws used to test for differences mong tretments when ANOVA showed significnt effects (P.5). When dt were not normlly distriuted nd heterogeneity ws oserved fter trnsformtion, nonprmetric tests were used. 3. Results 3.1. Seeds Sued cumint produces two types of seeds on single plnt. Brown seeds hve soft seed cots nd lck seeds hve rigid seed cots. The rown nd lck seeds lso differ in dimeter, thickness nd weight. Brown seeds hve men dimeter of 1.91±.4 mm, men thickness of.55±.3 mm nd men dry mss of 1.28±.7 mg. Blck seeds hve men dimeter of.96±.2 mm, men thickness of.62 ±.4 mm nd men dry mss of.22±.1 mg. Emryos of dimorphic seeds re fully developed Imiition tests The dimorphic seeds hve different wter uptke chrcteristics. Brown seeds imied wter redily nd followed typicl pttern of rpid initil wter uptke with seed mss incresing y 79.6±6.1% fter 1 h, 131.2±2.4% fter 3 h nd 139.±2.6% fter 6 h (Fig. 1). On the other hnd, lck seeds imied wter slowly, with seed mss incresing y 2.9 ±.5% fter 1 h, 8.1±1.2% fter 6 h nd only 14±1.4% fter 22 h (Fig. 1). Increse in mss (%) G Brown seeds Blck seeds Time (h) Fig. 1. Imiition curves for rown nd lck seeds of Sued cumint in distilled wter. G, initition of germintion.

4 H.-L. Wng et l. / South Africn Journl of Botny 78 (212) Effect of light nd temperture on germintion of dimorphic seeds Germintion ws significntly ffected y temperture. Both seed types reched highest germintion percentges t 15:3 C except lck seeds in light (Tle 1). Brown seeds germinted to high percentges in oth light nd drkness over wide rnge of tempertures. In light, rown seeds germinted to 66.7% t ll tempertures, nd in drkness they germinted to 5.% t ll tempertures. In light, 6.7% ws the highest germintion percentge otined y lck seeds, nd in drkness 2.7% ws the highest (Tle 1) Breking dormncy of lck seeds Cold strtifiction Germintion of lck seeds ws not ffected y length of cold strtifiction period in our experiment (P =.287). The highest germintion percentge ws.7% for control, nd 4% fter 8 weeks cold strtifiction GA 3 tretments Germintion percentges of lck seeds were significntly ffected y GA 3 (P=.2). No significnt difference (P=.395) ws oserved in germintion percentge etween incution in light nd incution in drkness (Fig. 2). Germintion percentge ws the highest t 1 mmol L 1 GA 3 in drkness nd reched 16% (Fig. 2) Incution of emryos isolted from lck seeds Isolted emryos produced norml seedlings. The resulting seedlings were the sme s those from intct lck seeds Anlyses of hormone contents ZR nd ABA contents of rown seeds were significntly higher thn tht of lck seeds (P.1) (Fig. 3). ZR in rown seeds ws 1.5 times higher thn tht of lck seeds (Fig. 3A), while ABA in rown seeds ws 7.4 times s high s tht of lck seeds (Fig. 3B). GA 3 content of rown seeds ws significntly higher thn tht of lck seeds (P.1). GA 3 in rown seeds Tle 1 Germintion percentges (men±s.e) of fresh dimorphic seeds of Sued cumint t five thermoperiods in light nd drkness fter 2 dys. Brown seeds Blck seeds Temperture ( C) Light Drkness Light Drkness 5: ±4.4 5.±5..7±.7.±. 5:25 8.7± ±1.8.±..7±.7 1:25 84.±2.3A 88.7±1.8A.±..7±.7 15:3 94.7±.7A 98.±1.2A 4.±2.Ac 2.7±.7A 2: ±1.3A 96.7±1.8A 6.7±.7Ac 1.3±1.3B Note: Different upper-cse letters indicte significnt differences in germintion percentges etween light nd drkness t the sme temperture for ech seed type. Different lower-cse letters in ech column indicte significnt differences in germintion percentges of seeds mong different tempertures (P.5). Germintion (%) ws 3.9 times s high s tht of lck seeds (Fig. 3C). IAA content of rown seeds ws significntly lower thn tht of lck seeds (P=.1). IAA in rown seeds ws 87% s high s tht of lck seeds (Fig. 3D). 4. Discussion GA 3 concentrtions (mmol L -1 ) Light Drkness Light condition Fig. 2. Effect of GA 3 on germintion of lck seeds of Sued cumint in light nd drkness. Different upper-cse letters indicte significnt difference in germintion percentges etween light nd drkness t the sme GA 3 concentrtion. Different lower-cse letters indicte significnt difference in germintion percentges of seeds mong different GA 3 concentrtions in the sme light condition t P.5. This study demonstrted tht there re differences in seed morphology, dormncy, germintion nd hormonl contents of dimorphic seeds of inlnd desert nnul hlophyte S. cumint. These differences represent the comintion of different dptive strtegies in one plnt nd my hve ecologicl significnce for its successful survivl in inlnd slt deserts. Freshly-mtured rown seeds of S. cumint re highly permele to wter, hve fully developed emryo nd germinte rpidly to high percentges in wter over wide rnge of lternting temperture regimes in light or in drkness. These results indicted tht freshly-mtured rown seeds of S. cumint re non-dormnt. Though mount nd rte of wter sorption y freshlymtured lck seeds of S. cumint re lower thn tht of rown seeds, lck seeds indeed re wter-permele. In the dormncy clssifiction system of Bskin nd Bskin (1998, 24), seeds with PD, MD nd MPD hve wter-permele seed cot. According to our oservtion, lck seeds of S. cumint hve fully developed emryos. So we infer tht lck seeds hve PD. PD is divided into three levels (non-deep, intermedite, deep) y Bskin nd Bskin (1998, 24). We found tht 8 weeks of cold strtifiction did not rek dormncy of lck seeds of S. cumint, GA 3 promoted germintion in drkness nd excised emryos produce norml seedlings. Bsed on these chrcteristics, we conclude tht lck seeds of S. cumint hve intermedite PD. The evolution of different seed types in heteromorphic seeds, which my vry in their type of dormncy, cn extend the 1 1 A

5 274 H.-L. Wng et l. / South Africn Journl of Botny 78 (212) ZR content (ng.g -1.fw) A B ABA content (ng.g -1.fw) GA content (ng.g -1.fw) C D IAA content (ng.g -1.fw). Brown Blck Brown Blck Seed type Seed type Fig. 3. Contents of endogenous free ZR, ABA, GA nd IAA in oth seed morphs of Sued cumint. Different lower-cse letters indicte significnt difference t P.5. germintion period nd lso produce persistent seed nk tht provides for the long-term recruitment of seedlings (Mndák nd Pyšek, 21; Imert, 22). Freshly-mtured rown seeds of S. cumint re non-dormnt nd will germinte in light nd drkness over wide rnge of tempertures tht simulte those in the hitt. Therefore, rown seeds re expected to hve n opportunistic germintion strtegy (Guttermn, 1993, 22). Freshly-mtured lck seeds hve intermedite PD nd they need very long period of time to rek dormncy efore they cn germinte. Blck seeds re expected to hve cutious germintion strtegy, in which not ll of the seeds germinte in one seson (Guttermn, 1993, 22). From the differentil dormncy comintion etween S. rlocspic nd S. cumint we cn infer tht diversity in dormncy comintion of dormncy exist in heteromorphic seeds. Bskin nd Bskin (1998, 24) developed comprehensive clssifiction system for seed dormncy y modifying the dormncy system of the Russin seed physiologist Mrinn G. Nikolev. Theoreticlly, ny comintion of non-dormncy nd/or dormncy clsses (level or type) is possile. However, few studies hve demonstrly shown tht heteromorphic seeds re non-dormnt or hve PD (Bskin nd Bskin, 1976; Wng et l., 28). The inlnd slt desert nnul Slsol ffinis produces three types of seeds. Type A nd B seeds re nondormnt, wheres type C seeds need 4-week cold strtifiction period to rek non-deep PD (Wei et l., 27). In support of this, recent work (L Wng nd CY Tin, EGI, CAS, Urumchi, Chin, unpul. res.) hs shown tht heteromorphic seeds of 1 species in Chin re non-dormnt or hve PD nd new comintions of dormncy types re recognized. More reserch is clerly needed to fully understnd the ecologicl function of vrious comintions of different dormncy types in single plnt. A model ws proposed to explin the interctions of different hormones in the control of seed dormncy (Khn nd Smimy, 1982). According to this model, GA is the originl stimulus for germintion, nd germintion my occur even when the content of n inhiitor is reltively high. Our results indicted tht high level of ABA does not inhiit germintion in rown seeds. Becuse the role of cytokinins nd inhiitors is secondry, mye the negtive effect of ABA is countercted y high concentrtion of ZR. Brown seeds re non-dormnt, though IAA (the growth promoter) of rown seeds is lower thn tht of lck seeds. We my infer tht IAA does not ffect seed dormncy nd germintion. GA reks dormncy, ccelertes germintion nd countercts inhiitory effects of ABA in direct or indirect wy (Kucer et l., 25). GA in dimorphic seeds of S. cumint lso plys the sme role. In conclusion, dormncy nd germintion chrcteristics etween rown nd lck seeds of S. cumint differed. Brown seeds re non-dormnt nd cn rech high germintion percentges cross wide rnge of tempertures in light nd in drkness. In contrst, lck seeds hve intermedite PD nd reched low germintion percentges under ll germintion test conditions. Our study on desert nnul provides evidence in support of the hypothesis tht dormncy comintion of heteromorphic seeds is diverse nd new comintion type exists. Menwhile, our results support theoreticl model tht dormncy regultion through interction of cytokinin, ABA nd GA. As fr s is known, ours is the first report of comintion of non-dormnt nd intermedite PD for heteromorphic seeds. Acknowledgements We thnk Prof. Crol Bskin nd Jerry Bskin (University of Kentucky) for providing writing ssistnce nd useful comments

6 H.-L. Wng et l. / South Africn Journl of Botny 78 (212) on n erly version of the mnuscript. This work ws supported y the Specil Fund for Agro-scientific Reserch in the Pulic Interest [2931 4], the Opening Project of Key Lortory of Osis Ecology nd Desert Environment [291 4] nd the Opening Project of Key Lortory of Biogeogrphy nd Bioresource in Arid Lnd, Xinjing Institute of Ecology nd Geogrphy, Chinese Acdemy of Sciences [LBB-21-1]. References Bskin, J.M., Bskin, C.C., Germintion dimorphism in Heterothec suxillris vr. suxillris. Bulletin of the Torrey Botnicl Clu 13, Bskin, C.C., Bskin, J.M., Seeds: ecology, iogeogrphy, nd evolution of dormncy nd germintion. Acdemic Press, Sn Diego, CA. Bskin, J.M., Bskin, C.C., 24. A clssifiction system for seed dormncy. Seed Science Reserch 14, Bskin, J.M., Dvis, B.H., Bskin, C.C., Gleson, S.M., Cordell, S., 24. Physicl dormncy in seeds of Dodone viscos (Spindles, Spindcee) from Hwii. Seed Science Reserch 14, Brändel, M., 27. Ecology of chene dimorphism in Leontodon sxtilis. Annls of Botny 1, Crter, C.T., Ungr, I.A., 23. Germintion response of dimorphic seeds of two hlophyte species to environmentlly controlled nd nturl conditions. Cndin Journl of Botny 81, Cheplick, G.P., Life history evolution in Amphicrpic plnts. Plnt Species Biology 9, Commissione Redctorum Flore Xinjingensis, Flor Xinjingensis. Xinjing Science & Technology & Hygiene Pulishing House, Urumchi. Delectis Flore Reipulice Populris Sinice Agende Acdemie Sinice Edit, Flor Reipulice Populris Sinice. Science Press, Beijing. Ding, X.D., Zhng, S.R., Li, Y., Tin, C.Y., Feng, G., 21. Seed polymorphism of n euhlophyte, Sued cumint nd its dpttion strtegy to extremely sline soil. Act Botnic Boreli Occidentli Sinic 3, (in chinese). Guttermn, Y., Seed germintion of desert plnts. Springer-Verlg, Berlin. Guttermn, Y., 22. Survivl strtegies of nnul desert plnts. Springer- Verlg, Berlin. Hrper, J.L., Popultion iology of plnts. Acdemic Press, London. Imert, E., 22. Ecologicl consequences nd ontogeny of seed heteromorphism. Perspectives in Plnt Ecology, Evolution nd Systemtics 5, Khn, A.A., Smimy, C., Hormones in reltion to primry nd secondry seed dormncy. In: Khn, A.A. (Ed.), The physiology nd iochemistry of seed development, dormncy nd germintion. Elsevier Biomedicl Press, Amsterdm, pp Khn, M.A., Ungr, I.A., The effect of slinity nd temperture on the germintion of polymorphic seeds nd growth of Atriplex tringulris WILLD. Americn Journl of Botny 71, Kucer, B., Cohn, M.A., Leuner-Metzger, G., 25. Plnt hormone interctions during seed dormncy relese nd germintion. Seed Science Reserch 15, Li, Z.T., Zhou, X., Plnt hormone nd its immunossy technique. Jingsu Science & Technology Press, Nnjing. Lu, J.J., Tn, D.Y., Bskin, J.M., Bskin, C.C., 21. Fruit nd seed heteromorphism in the cold desert nnul ephemerl Diptychocrpus strictus (Brssiccee) nd possile dptive significnce. Annls of Botny 15, Mndák, B., Seed heteromorphism nd the life cycle of plnts: literture review. Presli 69, Mndák, B., Pyšek, P., 21. The effects of light qulity, nitrte concentrtion nd presence of rcteoles on germintion of different fruit types in the heterocrpous Atriplex sgittt. Journl of Ecology 89, Mndák, B., Pyšek, P., 21. Fruit dispersl nd seed nks in Atriplex sgittt: the role of heterocrpy. Journl of Ecology 89, Philipupilli, J., Ungr, I.A., The effect of seed dimorphism on the germintion nd survivl of Slicorni europe L. popultions. Americn Journl of Botny 71, Sorensen, A.E., Somtic polymorphism nd seed dispersl. Nture 276, Sun, H.Z., Lu, J.J., Tn, D.Y., Bskin, J.M., Bskin, C.C., 29. Dormncy nd germintion chrcteristics of the trimorphic chenes of Grhdiolus ppposus (Astercee), n nnul ephemerl from the Junggr Desert, Chin. South Africn Journl of Botny 75, Venle, D.L., The evolutionry ecology of seed heteromorphism. Americn Nturlist 126, Venle, D.L., Levin, D.A., Ecology of chene dimorphism in Heterothec ltifoli:i. Achene structure, germintion nd dispersl. Journl of Ecology 73, Wng, L., Hung, Z.Y., Bskin, C.C., Bskin, J.M., Dong, M., 28. Germintion of dimorphic seeds of the desert nnul hlophyte Sued rlocspic (Chenopodicee), C 4 plnt without Krnz ntomy. Annls of Botny 12, Wei, Y., Dong, M., Hung, Z.Y., 27. Seed polymorphism, dormncy, nd germintion of Slsol ffinis (Chenopodicee), dominnt desert nnul inhiting the Junggr Bsin of Xinjing, Chin. Austrlin Journl of Botny 55, 1 7. Edited y TR Mrks