Diversity in seed germination behavior in relation to heterocarpy inSalsola komarovii Iljin

Seed germination behavior in two types of dimorphic fruits inSalsola komarovii Iljin (Chenopodiaceae) was studied. The germination percentage was much higher in the long-winged type than in the short-winged type when the fruits were tested for germinability. If lignified perianths were removed from the fruits, seeds of both types germinated at higher percentages and the difference in the germination percentage between two types decreased. The extract of the perianths inhibited the seed germination. Abscisic acid was detected in the extract of the perianths by enzyme-linked immunosorbent assay and its level was higher in the short-winged type than in the long-winged type. Germinability in both types was lost one year after harvest when the fruits were stored at room temperature and the germination was tested with fruits. When the seeds were tested, however, the short-winged type germinated even two years after the harvest; the germinability of the short-winged type lasted one year longer than that of the long-winged type. Light irradiation was not required for the seed germination in either type regardless of presence or absence of the perianths. No clear difference between the two types was observed either in optimal temperature for the germination or in strength of the resistance to salinity.     

散枝猪毛菜的种子多型性及其萌发行为

散枝猪毛菜(Salsola bracchita)主要分布于新疆准噶尔荒漠,具有很强的抗干旱和抗盐碱能力。该文对散枝猪毛菜的果实进行了观察,表明散枝猪毛菜具有4种类型的散布单位和果实,这4种果实在形状、大小、颜色和着生方式上均有显著差异。A型果实绿色、球形、大,着生方式为横生,宿存花被革质,背部有紫红色翅状附属物,直径为(2.161±0.138) mm,单粒重为(3.810±0.113) mg;B型果实绿色、大、扁平、长圆形,着生方式为直立,宿存花被革质,背部有翅状附属物,长为(2.062±0.188) mm,宽为(1.720±0.148) mm,单粒重为(2.665±0.113) mg;C型果实绿色、大、扁平、长圆形,着生方式为直立,宿存花被膜质,背部无翅状附属物,长为(2.239±0.277) mm,宽为(1.844±0.150) mm,单粒重为(2.723±0.559) mg;D型果实黄色、小、扁平、长卵形,着生方式为直立,宿存花被膜质,背部无翅状附属物,长为(1.678±0.163) mm,宽为(1.390±0.110) mm,单粒重为(0.928±0.025) mg。A型、B型和C型种子(果实)在5 ℃/15 ℃、5 ℃/25 ℃、15 ℃/25 ℃(暗12 h/光12 h)变温条件下萌发率>68%,且B型和C型种子比A型种子有较高的萌发率和萌发速率。D型种子在3种变温条件下萌发缓慢,最终萌发率始终维持在较低水平(<20%),划破果皮和种皮能够显著提高D型种子的萌发率和萌发指数,表明D型种子处于生理休眠状态。散枝猪毛菜的种子多型性是对荒漠异质环境的一种适应。     

紫翅猪毛菜的种子多型性及其结实格局

紫翅猪毛菜(Salsola affinis)主要分布于新疆准噶尔荒漠, 具有很强的抗干旱和耐盐碱能力, 其种子具有多型现象。我们对紫翅猪毛菜的种子形态、萌发特性及结实格局进行了观测研究。结果表明: (1) 紫翅猪毛菜3种类型的种子在形状、大小、颜色、着生方式及包被其花被片背部是否具翅方面均有明显不同; (2) 3种类型的种子具有不同的散布特性和萌发行为: A型种子容易从母体脱落, 发达的果翅能够借助风进行远距离传播; B、C型种子成熟时紧连母体, 不易脱落。在变温下A型种子和B型种子能够快速萌发, 且B型种子比A型种子的萌发速度快; 而C型种子萌发缓慢, 最终萌发率小于10%, 表明其处于休眠状态; (3)随植株个体的增大, A型种子所占比例逐渐增多, 由0.43%增加到51.07%; B型种子所占比例逐渐减少, 由65.80%减少到18.06%; C型种子所占比例没有显著变化, 约为30–35%。紫翅猪毛菜的种子多型性以及种子输出的灵活性有利于其在荒漠异质环境中成功定居。对种子多型性及其结实格局的研究将为探讨其生态适应机制及生活史进化研究提供科学依据。     

Quantification of ABA and its metabolites in sweet cherries usingdeuterium-labeled internal standards

Abscisic acid (ABA), phaseic acid (PA), dihydrophaseic acid (DPA), and epi-dihydrophaseic acid (epi-DPA) were quantified in developing fruit and seeds of sweet cherry using each deuterium-labeled internal standard. ABA concentrations in the pulp were low at the early stage of fruit development, reached to the maximum before maturation, and subsequently declined during maturation. The significant increase of ABA after 29 days after full bloom (DAFB) coincides with the softening suggests that ABA may play a role to induce fruit maturation in sweet cherries. ABA metabolite levels were high at the immature stage and decreased with fruit maturation. This fact suggests that fruit may not need ABA in the early stage of fruit development. It was considered that DPA may be the major metabolite of ABA since the concentrations were higher than PA and epi-DPA at all stages of fruit development. ABA concentrations increased at the beginning of seed maturation and then decreased toward harvest. This decrease may be necessary to end seed dormancy. DPA in seeds changed similarly with ABA but its concentrations were always higher than those of ABA.     

野生玫瑰果实发育过程中种子的细胞组织结构和内源激素变化对其休眠性的影响

以吉林珲春自然群落的野生玫瑰(Rosa rugosa Thunb.)为试验材料,探究野生玫瑰在果实形成过程中种子的发育及休眠性的形成和变化。选取青果期(1~35 d)、转色期(35~60 d)、红果期(60~75 d)的果实及种子,结合形态学、组织细胞学观察法及高效液相色谱技术,对果实各发育时期的种子形态、种胚及内果皮的发育进行研究,并分析种子内源激素含量变化与果实发育、种子休眠之间的关系。结果表明:果实和种子在青果期(1~35 d)时发育速度最快,种胚在花后24 d发育完全,种子不存在形态休眠。花后24 d内果皮开始沉积木质素并逐渐木质化,种子开始产生机械休眠。种子激素含量的变化与果实的发育、转色及内果皮的木质化密切相关,种子内源GA3和ABA含量在青果期(1~35 d)达到峰值,内源IAA含量在果实转色期(35~60 d)达到最大值,高浓度的ABA含量是种子尚未脱离果实时便已进入生理休眠的主要原因。     

Reproductive ecology of Thymelaea velutina (Thymelaeaceae)- Factors contributing to the maintenance of heterocarpy

Thymelaea velutina (Thymelaeaceae) is a dioecious shrub that presents a unique type of heterocarpy which consists of the simultaneous production of dry and fleshy fruits. It is endemic to the Balearic Islands (Western Mediterranean) and is found both in dunes and mountain areas. The goal of this study was to identify which factors influence the production of both fruit types, examining the variation of their effects at a spatio-temporal scale (comparing two localities in different years). Specifically, we investigated (1) whether pollen limitation influences the type of fruit produced, and (2) the possible differences in seed size, mass, dispersal capacity, seed predation, germination patterns and seedling survival between fruit types. We also examined if the production of fleshy fruits was modified with the application of gibberellins to reproductive branches. Although fleshy fruits were consistently more abundant than dry ones at both populations, their proportion was significantly higher at the site with greater precipitation. The addition of either pollen or gibberellins did not affect the proportion of each fruit type. Seeds in fleshy fruits are consistently larger, heavier and more likely to be dispersed than seeds in dry fruits, but germinability, germination rate and seedling survival was similar among fruit types. Heterocarpy in this species is currently maintained as there is no apparent factor that exerts any strong selective pressure on either fruit type. The two fruit types might even have different `functions', one serving especially for dispersal and population expansion and the other for producing a seed bank that ensures an eventual germination.     

Seasonal wing length dimorphism in a tropical seed bug: ecological significance of the short-winged form

Summary Short-winged forms of the bug, Jadera aeola, were discovered during the late dry season at a study site on Barro Colorado Island, Panama. They were smaller than long-winged adults not only in elytron and hindwing sizes but also in head, thorax, rostrum and hind femur dimentions. When newly emerged adults were kept under natural photothermal conditions, short-winged females started ovipositing earlier, produced more eggs, and died earlier than did long-winged females. This was partly due to the fact that long-winged adults usually enter diapause after adult energence (Tanaka et al. 1987b). Egg size was another factor contributing to the high egg production in the short-winged form; it was significantly smaller in the short-winged form than that in the long-winged form. Wing form was apparently environmentally induced because all off-spring of short-winged adults became long-winged. No short-winged form was obtained in the laboratory when nymphs were reared on different species of seeds at different photoperiods. Although the factor(s) responsible for determination of the wing form remains unknown, the ecological significance of this short-winged form seems clear, i.e. exploitation of the food resource left in the late dry season. Wing length dimorphism in J. aeola could be a response to unpredictable availability of the food resource determined by seed production of the host plants (Sapindaceae) and by the timing of the onset of a wet season.     

灰飞虱长、短翅型品系对高、低温的适应能力差异

【目的】灰飞虱Laodelphax striatellus种群存在长翅和短翅个体,其翅型分化受遗传和环境条件的影响。本研究旨在明确经连续定向选育的灰飞虱长、短翅型品系对高、低温的适应能力差异。【方法】在室内分别长期定向筛选63和65代建立灰飞虱长、短翅型品系,并在南京田间采集灰飞虱自然种群;分别在25℃, 30℃和35℃恒温条件下测定上述灰飞虱长、短翅型品系和自然种群的繁殖力、存活率和发育历期,测定若虫在5℃和-20℃下的存活率以及若虫和成虫的过冷却点,通过品系间存活率、发育历期、生殖力和过冷却点的比较分析,确定灰飞虱长、短翅型品系对高温和低温的耐受能力。【结果】在25℃, 30℃和35℃下,灰飞虱自然种群雌成虫的繁殖力均显著高于室内筛选后的长、短翅型品系,而长、短翅型品系雌成虫之间的繁殖力均无显著差异;长、短翅型品系的繁殖力在25℃和30℃之间均无显著差异,但自然种群在25℃下的繁殖力显著高于30℃条件下的繁殖力;35℃下长、短翅型品系基本无若虫产生。25℃下长翅型品系、短翅型品系和自然种群若虫的存活率无显著差异,但在30℃下,短翅型品系若虫的存活率显著低于自然种群,而与长翅型品系差异不显著;35℃下长、短翅型品系的若虫最长只能存活到3龄,且两品系间无显著差异,而自然种群可存活到5龄。25℃下,短翅型品系若虫的发育历期显著短于自然种群,而与长翅型品系无差异;但是在30℃下,短翅型品系若虫历期显著长于长翅型品系和自然种群。长翅型品系、短翅型品系和自然种群灰飞虱3-4龄若虫在5℃低温下的存活天数无显著差异,并且长翅和短翅型品系在-20℃极端低温下暴露10 min后其死亡率也无显著差异且均显著高于自然种群。3个品系(种群)成虫的过冷却点无显著差异,但5龄若虫的过冷却点表现为短翅型品系显著高于自然种群,而与长翅型品系无显著差异。【结论】经连续定向选育的灰飞虱长、短翅型品系对低温和高温的适应力基本相当,且低于自然种群。在高温条件下灰飞虱短翅型品系的发育速率低于长翅型品系。     

Seed Dormancy in Acer: The Role of Testa-imposed and Embryo Dormancy in Acer velutinum

The embryo dormancy shown in freshly harvested samples of Acervelutinum seeds is weakly established and very short-lived.Loss of this embryo dormancy occurred during post-harvest fruitstorage at either 5 or 17 C. In contrast, the dormancy of intactfruits and seeds was overcome only during storage at the lowertemperature. Removal of the cotyledons from embryos of freshlyharvested fruits allowed more rapid germination of the embryonicaxes, indicating that the cotyledons exert an inhibitory effect,although the axes still retained a measure of innate dormancy.The inhibitory effect of the cotyledons became less marked withincreasing duration of fruit storage, this loss of inhibitoryeffect occurring at both storage temperatures. Applied ABA stronglysuppressed germinative capacity in intact embryos and isolatedembryonic axes from freshly harvested fruits, but when ABA wasapplied to embryos of fruits that had been stored for variousperiods at 5 or 17 C, the inhibitory effect was first weakenedand then lost with increased storage. Although dormancy in the seeds of A. velutinum may be describedas intermediate between testa-imposed dormancy and true dormancy,it is perhaps more properly included in the former category. Acer velutinum Boiss. var. vanvolxemii, abscisic acid, embryo dormancy, germination, seed storage, testa-imposed dormancy, tissue sensitivity     

AtPER1 enhances primary seed dormancy and reduces seed germination by suppressing the ABA catabolism and GA biosynthesis in Arabidopsis seeds

Seed is vital to the conservation of germplasm and plant biodiversity. Seed dormancy is an adaptive trait in numerous seed‐plant species, enabling plants to survive under stressful conditions. Seed dormancy is mainly controlled by abscisic acid (ABA) and gibberellin (GA) and can be classified as primary and secondary seed dormancy. The primary seed dormancy is induced by maternal ABA. Here we found that AtPER1, a seed‐specific peroxiredoxin, is involved in enhancing primary seed dormancy. Two loss‐of‐function atper1 mutants, atper1‐1 and atper1‐2, displayed suppressed primary seed dormancy accompanied with reduced ABA and increased GA contents in seeds. Furthermore, atper1 mutant seeds were insensitive to abiotic stresses during seed germination. The expression of several ABA catabolism genes (CYP707A1, CYP707A2, and CYP707A3) and GA biosynthesis genes (GA20ox1, GA20ox3, and KAO3) in atper1 mutant seeds was increased compared to wild‐type seeds. The suppressed primary seed dormancy of atper1‐1 was completely reduced by deletion of CYP707A genes. Furthermore, loss‐of‐function of AtPER1 cannot enhance the seed germination ratio of aba2‐1 or ga1‐t, suggesting that AtPER1‐enhanced primary seed dormancy is dependent on ABA and GA. Additionally, the level of reactive oxygen species (ROS) in atper1 mutant seeds was significantly higher than that in wild‐type seeds. Taken together, our results demonstrate that AtPER1 eliminates ROS to suppress ABA catabolism and GA biosynthesis, and thus improves the primary seed dormancy and make the seeds less sensitive to adverse environmental conditions.     

Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds

Abscisic acid (ABA) is derived from epoxycarotenoid cleavage and regulates seed development and maturation. A detailed carotenoid analysis was undertaken to study the contribution of epoxycarotenoid synthesis to the regulation of ABA accumulation in Nicotiana plumbaginifolia developing seeds. Maximal accumulation of xanthophylls occurred at mid-development in wild type seeds, when total ABA levels also peaked. In contrast, in ABA-deficient mutants xanthophyll synthesis was delayed, in agreement with the retardation in seed maturation. Seed dormancy was restored in mutants impaired in the conversion of zeaxanthin into violaxanthin by zeaxanthin epoxidase (ZEP), by the introduction of the Arabidopsis AtZEP gene under the control of promoters inducing expression during later stages of seed development compared to wild type NpZEP, and in dry and imbibed seeds. Alterations in the timing and level of ZEP expression did not highly affect the temporal regulation of ABA accumulation in transgenic seeds, despite notable perturbations in xanthophyll accumulation. Therefore, major regulatory control of ABA accumulation might occur downstream of epoxycarotenoid synthesis.     

药用植物黄精种子休眠特性研究

从黄精(Polygonatum sibiricum Red.)种子的形态、解剖结构、果实及种子部分抑制物质的生物测定和种子成熟过程中内源激素ABA含量的变化等方面研究种子的休眠特性。结果表明:黄精种子休眠属于综合休眠,首先黄精种子秋季采收后其种胚存在生理后熟,是导致黄精种子深休眠的主要原因;其次黄精种子的胚乳细胞小、细胞质浓厚、排列致密,胞间隙小,影响物质的共质体运输;果实及种子中含有不同程度的发芽抑制物质;种子成熟时ABA含量升高是导致种子休眠的又一原因。     

Cryptic female choice predicated on wing dimorphism in decorated crickets

Male decorated crickets, Gryttodes sigllatus, normally lackbind wings and are incapable of flight (short-winged males),but occasionally exhibit fully developed hind wings that makerudimentary flight possible (long-winged males). Long-wingedmales bear a cost of flight in the form of decreased inseminationsuccess, which arises as a consequence of two interrelated factors:(1) long-winged males exhibit a lower reproductive investmentrelative to short-winged males, as measured by the mass of amale's spermatophore and reproductive organs and (2) the postcopulatorybehavior of females favors males that maximize their reproductiveinvestment. Of particular importance to male mating successis the spermatophylax, a large gelatinous mass forming partof the spermatophore and consumed by the female after mating.Consumption of the spermatophylax keeps the female preoccupiedwhile sperm are discharged from the remaining portion of thespermatophore (sperm ampulla) into her repro ductive tract.The spermatophylax of long-winged males is significantly smallerthan that of short-winged males and consequently requires lesstime to consume. As a result, the sperm ampulla of long-wingedmales is frequently removed before its complete evacuation andsignificantly sooner than that of short-winged males. Becausethe spermatophore-removal behavior of females mediates the relativeinsemination success of short-winged and long-winged males,it can be considered a form of cryptic female choice     

Dormancy and Germination of Abscisic Acid-Deficient Tomato Seeds : Studies with the sitiens Mutant

The role of abscisic acid (ABA) in the dormancy induction of tomato (Lycopersicon esculentum) seeds was studied by comparison of the germination behavior of the ABA-deficient sitiens mutant with that of the isogenic wild-type genotype. Freshly harvested mutant seeds, in contrast to wild-type seeds, always readily germinate and even exhibit viviparous germination in overripe fruits. Crosses between mutant and wild-type and self-pollination of heterozygous plants show that in particular the ABA fraction of embryo and endosperm is decisive for the induction of dormancy. After-ripened wild-type seeds fully germinate in water but are more sensitive toward osmotic inhibition than mutant seeds. Germination of both wild-type and mutant seeds is equally sensitive toward inhibition by exogenous ABA. ABA content of mature wild-type seeds is about 10-fold the level found in mutant seeds. Nevertheless, it is argued that the differences in dormancy between the seeds of both genotypes are not a result of actual ABA levels in the mature seeds or fruits but a result of differences in ABA levels during seed development. It is hypothesized that the high levels of ABA that occur during seed development in wild-type seeds induce an inhibition of cell elongation of the radicle that can still be observed after long periods of dry storage.     

Engineering seed dormancy by the modification of zeaxanthin epoxidase gene expression

Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding zeaxanthin epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.     

Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L.) Heynh.

Mutant lines of Arabidopsis thaliana (L.) Heynh., which are characterized by symptoms of withering and the absence of seed dormancy, showed much lower levels of endogenous abscisic acid (ABA) in developing seeds and fruits (siliquae) than the wild type. Reciprocal crosses of wild type and ABA-deficient mutants showed a dual origin of ABA in developing seeds. The genotype of the mother plant regulated a sharp rise in ABA content half-way seed development (maternal ABA). The genotype of the embryo and endosperm was responsible for a second ABA fraction (embryonic ABA), which reached much lower levels, but persisted for some time after the maximum in maternal ABA. The onset of dormancy correlated well with the presence of the embryonic ABA fraction and not with the maternal ABA. Dormancy developed in both the absence and presence of maternal ABA in the seeds. In this respect maternal ABA resembled exogenously applied ABA which did not induce dormancy in ABA-deficient seeds. However, both maternal and applied ABA stimulated the formation of a mucilage layer around the testa, which could be observed during imbibition of the mature seeds. In the mature state, ABA-deficient seeds germinated in the siliquae on the plant, but only when the atmosphere surrounding the plant was kept at high relative humidity. In younger stages germination in siliquae occurred after isolation from the plants and incubation on wet filter paper. Therefore, it seems that limited access to water is the primary trigger for the developmental arrest in these seeds.     

Genetic variation in developmental times among four pure lines exhibiting specific wing form and body color in the brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis> (Hemiptera: Auchenorrhyncha)

Developmental times were compared among four pure lines of wing-dimorphic Nilaparvata lugens generated by successive selections for the following designated characteristics: blackish short-winged (BS), blackish long-winged (BL), yellowish brown short-winged (YS) and yellowish brown long-winged (YL). When the nymphs were reared on rice seedlings at low density, the developmental time was in the order of BS = BL < YS = YL, while with an increase in rearing density, the time lengthened markedly in long-winged lines but only slightly in short-winged lines, rearranging the order to BS < BL = YS < YL. Among F₁ progeny of BS × YL, the developmental time in short-winged phenotypes was the same as those of BS lines at any of the densities tested, but the long-winged phenotypes emerged as adults at intermediate time between BS and YL lines at high density. This method of inheritance of developmental time and the differences in the duration observed among the four pure lines suggest that the genes regulating wing form and body color expression are also involved in the regulation of developmental time.     

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

Desert annual Suaeda acuminata produces two morphologically distinct types of seeds on the same plant. The main aims of our study were to compare germination characteristics of the dimorphic seeds, ascertain their dormancy types and give the hormonal explanation. The two seed types of S. acuminata absorbed water at different rates with brown seeds imbibing water faster. Germination percentages of brown seeds were significantly higher than those of black seeds in all temperature and light regimes tested. Eight weeks of cold stratification did not break dormancy of black seeds, whereas exogenous GA₃ promoted germination. Excised embryos of untreated black seeds produced normal seedlings. Contents of ZR, GA₃ and ABA of brown seeds were significantly higher than that of black seeds; while contents of IAA of black seeds were significantly higher than that of brown seeds. Brown seeds of S. acuminata are non-dormant, whereas black seeds have intermediate physiological dormancy (PD). Interaction among ZR, ABA and GA₃ may play an important role in dormancy status of both seed types. This is the first report of non-dormancy and intermediate PD in a heteromorphic species.     

Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA₃) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA₃ in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA₃ inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy maintenance in imbibed seeds. Received: 31 December 1998 / Accepted: 9 July 1999