The biosynthesis and conjugation of indole-3-acetic acid in germinating seed and seedlings ofDalbergia dolichopetala

Germinating seed ofDalbergia dolichopetala converted both [²H₅]l-tryptophan and [²H₅]indole-3-ethanol to [²H₅]indole-3-acetic acid (IAA). Metabolism of [2-¹⁴C]IAA resulted in the production of indole-3-acetylaspartic acid (IAAsp), as well as several unidentified components, referred to as metabolites I, II, IV and V. Re-application of [¹⁴C]IAAsp to the germinating seed led to the accumulation of the polar, water-soluble compound, metabolite V, as the major metabolite, together with a small amount of IAA. Metabolites I, II and IV were not detected, nor were these compounds associated with the metabolism of [2-¹⁴C]IAA by shoots and excised cotyledons and roots from 26-d-oldD. dolichopetala seedlings. Both shoots and cotyledons converted IAA to IAAsp and metabolite V, while IAAsp was the only metabolite detected in extracts from excised roots. The available evidence indicates that inDalbergia, and other species, IAAsp may not act as a storage product that can be hydrolysed to provide the plant with a ready supply of IAA.Abbreviations HPLC-RC high-performance liquid chromatography-radiocounting - IAA indole-3-acetic acid - IAAsp indole-3-acetylaspartic acid - IAlnos 2-O-indole-3-acetyl-myo-inositol - IEt indole-3-ethanol     

Post-pollination hybridization barriers in <Emphasis Type="Italic">Nicotiana</Emphasis> section <Emphasis Type="Italic">Alatae</Emphasis>

Nicotiana section Alatae contains eight species with variable flower sizes and morphologies. Section members readily hybridize in the glasshouse, but no hybrids have been observed in natural sympatric and parapatric populations. To investigate interspecific crossing relationships with respect to mechanisms preventing hybridization, all members of section Alatae were intercrossed in a complete diallel. We found positive correlation between the pistil length of the pollen donor and interspecific seed set relative to the conspecific cross. Pollen tube growth rate and pollen donor pistil length were positively correlated as well. Furthermore, pollen from short-pistil members of section Alatae could only grow a maximum distance proportional to, but greater than, their own pistil lengths. Our results show that pollen tube growth capacity (i.e., rate and distance), provides a hybridization barrier in long-pistil species × short-pistil species crosses. We also found another hybridization barrier not specifically related to pollen tube growth capacity in short-pistil species × long-pistil species. Taken together, these barriers can generally be described by a ‘pistil-length mismatch’ rule; in section Alatae, pollen has the most success fertilizing ovules from species with pistil lengths similar to their own. This rule could contribute to hybridization barriers in Section Alatae because the species display dramatically different pistil lengths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seed predation limits post-fire recruitment in the waratah (<Emphasis Type="Italic">Telopea speciosissima</Emphasis>)

Seed predation may reduce recruitment in populations that are limited by the availability of seeds rather than microsites. Fires increase the availability of both seeds and microsites, but in plants that lack a soil- or canopy-stored seed bank, post-fire recruitment is often delayed compared to the majority of species. Pyrogenic flowering species, such as Telopea speciosissima, release their non-dormant seeds more than 1 year after fire, by which time seed predation and the availability of microsites may differ from that experienced by plants recruiting soon after fire. I assessed the role of post-dispersal seed predation in limiting seedling establishment after fire in T. speciosissima, in southeastern Australia. Using a seed-planting experiment, I manipulated vertebrate access to seeds and the combined cover of litter and vegetation within experimental microsites in the 2 years of natural seed fall after a fire. Losses to vertebrate and invertebrate seed predators were rapid and substantial, with 50% of seeds consumed after 2 months in exposed locations and after 5 months when vertebrates were excluded. After 7 months, only 6% of seeds or seedlings survived, even where vertebrates were excluded. Removing litter and vegetation increased the likelihood of seed predation by vertebrates, but had little influence on losses due to invertebrates. Microsites with high-density vegetation and litter cover were more likely to have seed survival or germination than microsites with low-density cover. Recruitment in pyrogenic flowering species may depend upon the release of seeds into locations where dense cover may allow them to escape from vertebrate predators. Even here, conditions suitable for germination must occur soon after seed release for seeds to escape from invertebrate predators. Seed production will also affect recruitment after any one fire, while the ability of some juvenile and most adult plants to resprout after fire buffers populations against rapid declines when there is little successful recruitment.     

DELLA Proteins and GA Signalling in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Gibberellin (GA) is a classical plant hormone involved in many aspects of plant growth and development. A family of five homologs called the DELLA proteins, comprised of GAI, RGA, RGL1, RGL2 and RGL3, were recently found to act as critical GA signal mediators in Arabidopsis. Reports have shown that GAI and RGA are coupled together to repress stem elongation growth whereas RGL2 is a major negative regulator of seed germination. GA down-regulates DELLA proteins through protein degradation likely via the proteasome pathway. The conserved and functionally important DELLA domain is responsible for protein stability in response to GA.     

模拟酸雨对农作物种子萌发和幼苗生长的影响

研究模拟酸雨对3种农作物种子萌发年和幼苗生长的影响。结果表明：不同pH值(2．5,4．5,5．6)的模拟酸雨对水稻和小麦的种子萌发没有影响,但明显抑制了玉米种子萌发。模拟酸雨条件下,3种农作物幼苗的生长受到抑制,生物量减少,叶绿素和类胡萝卜素含量下降,而叶绿素a/b的变化却不明显。pH4．5和5．6的模拟酸雨对玉米Fv／Fm、光化学猝灭(qP)的影响较小,非光化学猝灭(NPQ)却明显下降,表明酸雨伤害了植物PSⅡ天线对激发能的非辐射耗散能力。     

Vertical stratification of figs and fig-eaters in a Bornean lowland rain forest: how is the canopy different?

Fig trees (Ficus spp; Moraceae) are a common constituent of many tropical forests, where they produce figs that are eaten by a wide range of bird and mammal species. In our Bornean field site six Ficus seed dispersal guilds can be recognised, differentially attracting subsets of the frugivore community. Guild membership appears to be determined by figs' size, colour, crop size and height above ground, and frugivores' size, sensory and locomotory physiology and foraging height. Vertical stratification therefore appears to be an important determinant of fig and frugivore partitioning. The guild structure observed is discussed with respect to implications for seed dispersal and the differences between the canopy and understorey. Regarding figs eaten primarily by birds, larger fruit and crops can be found in the canopy where they are exposed to larger assemblages of potential frugivores than those presented in the understorey.     

广东东部不同生活型植物热带植物区系属性的比较研究

通过对粤东种子植物生活型的调查和统计分析,将粤东2226种种子植物划分为6类生活型。各种木本生活型共有1198种,占53.8%;各种草本类型共有1028种植物,占46.2%。从各生活型的种的区系成分分析来看,该地各生活型热带性成分比例强弱的顺序是：乔木种〉木质藤本种〉灌木种〉陆生草本〉草质藤本〉水生草本。     

Seed Dispersal in Páramo Plants: Epizoochorous and Hydrochorous Taxa

Abstract: On the basis of a recent checklist of plant diversity in páramos, diaspores collected from herbaria were studied for adaptations to dispersal on animals and by water. This study shows that the páramo flora has a relatively high percentage of genera with morphological adaptations to epizoochorous and to hydrochorous diaspore dispersal. Genera with hooked and straight appendages are present throughout the páramo belt, while their number decreases in the higher páramo zones. About half of the hydrochorous genera and one-third of the epizoochorous ones can be found throughout all páramo zones. The contribution of holarctic epizoochorous genera to the páramo flora seems to be greater than that of austral-antarctic genera, whereas in hydrochorous genera it is the reverse.     

Characterising spatial and temporal variation in the finite rate of population increase across the northern range boundary of the annual grass <Emphasis Type="Italic">Vulpia fasciculata</Emphasis>

Understanding the factors that influence plant distributions is a considerable challenge for ecologists in the face of environmental change. Here, we quantify spatial and temporal variation in the finite rate of population increase of the annual grass Vulpia fasciculata. Specifically, we test the hypothesis that the northern range boundary is associated with finite rates of population increase of less than one. Seeds of three ecotypes of the annual grass V. fasciculata were introduced annually across a range of sites in Great Britain both within (11) and to the north (4) of its current range boundary in each of 4 years. Populations failed to establish at 17% of target sites due to disturbance. At the remaining target sites, the finite rate of population increase, λ, varied from 0.06 to 33.3 with a geometric mean of 1.88. Of the total variance in the rate of population growth, site and year effects accounted independently for 40% of the variation and in interaction for 50%; ecotype accounted for less than 5% of the variation. Variation in the weather between sites and years had little impact on plant performance, and there was no indication that the rate of population growth was lower to the north of the current range boundary. We conclude that current climatic conditions on the coast of Great Britain are not limiting the distribution of V. fasciculata and that seeds from across its current range have roughly equivalent colonising potential.     

种子大小及其命运对植被更新贡献研究进展

种子是种子植物的繁殖体.种子对后代的资源投入将会直接影响后代的适合度进而影响到植被群落的更新.一般较大种子物种在种子萌发和幼苗生长阶段是具有较大优势的;但较小种子物种在逃避被动物采食和形成持久的土壤种子库成为植被更新的后备动力方面具有较大的优势.在不同的选择压力下,不同大小种子在以后的生活史中具有不同的命运,对植被的更新也具有不同的贡献.本文主要从种子大小和种子的传播散布、种子萌发、种子存活以及种子土壤库等方面综述了国外关于种子大小及其以后命运对植被更新贡献的研究结果,并对国内的相关研究提出了一些建议：种子生态学研究需要结合群落特点以及微环境等,开展从种子生产到幼苗更新全过程的系统性研究,为植物物种多样性保育和退化植被恢复方面提出有科学依据的管理措施.