芡实种子萌发期的生物学特性与结构解剖

本文描述了芡实种子的结构,种子的萌发和幼苗的形态特征。成熟种子必须置于水中保存,以增大胚体,并完成后熟作用。外胚乳是种子萌发和幼苗生长的主要营养来源。萌发后在子叶叶柄基部外侧形成的突起结构可能起固着作用。     

Programmed cell death in seeds of angiosperms

During the diversi fication of angiosperms, seeds have evolved structural, chemical, molecular and physiologically developing changes that specially affect the nucellus and endosperm. All through seed evolution, programmed cell death(PCD) has played a fundamental role. However,examples of PCD during seed development are limited. The present review examines PCD in integuments, nucellus,suspensor and endosperm in those representative examples of seeds studied to date.     

Morphogenetic seed types of Spermatophyta

The embryo stage of development and the nature of the reserve tissues are analyzed according to the timing of the morphogenetic factors during ontogeny. A seed characterization system and a seed formula are proposed. Several typological systems characterize seeds, based mainly on the size and position of the embryo and other external characters. This paper proposes a system based on morphogenetic factors that act on the embryo and determine the origin of reserve tissues. Seed morphogenesis results from a series of phenomena whose temporal sequence varies according to the genetic program of each species. Such peculiarities were selected for by environmental pressures, and their morphological expression reflects their adaptation. Such a system may offer insights into the ecology and evolution of particular species.     

Evolution and ecology of seed internal morphology in relation to germination characteristics in Amaranthaceae

Background and AimsInternal seed morphological traits such as embryo characteristics and nutritive tissue can vary considerably within a plant lineage. These traits play a prominent role in germination processes and the success of seedling establishment, and are therefore under high selective pressure, especially in environments hostile to seedlings, such as arid, saline or highly dynamic habitats. We investigated the relationships of seed internal morphology and germination characteristics of 84 species of Amaranthaceae s.l., a family with numerous lineages that have adapted to stressful growing conditions.MethodsWe used seed cross-sections to assess embryo type and the ratios of embryo to seed surface and radicle to cotyledon length. Furthermore, seed mass, mean time to germination, habitat preferences and further plant traits such as C₃ or C₄ photosynthesis and life form were compiled for each species. Data were analysed using phylogenetic comparative methods.Key resultsWe found embryo type (λ = 1), log seed mass (λ = 0.86) and the ratio of embryo to seed size (λ = 0.78) to be evolutionarily stable, with an annular embryo as ancestral in the family. Linked to shifts to the three derived embryos types (spiral, horseshoe-shaped and curved) is an increase in the ratio of root to cotyledon length and a reduction of nutritive tissue. We observed stabilizing selection towards seeds with relatively large embryos with longer radicles and less nutritive tissue that are able to germinate faster, especially in lineages with C₄ photosynthesis and/or salt tolerance.ConclusionsWe conclude that the evolutionary shift of nutrient storage from perisperm to embryo provides an ecological advantage in extreme environments, because it enables faster germination and seedling establishment. Furthermore, the evolutionary shift towards a higher ratio of root to cotyledon length especially in small-seeded Amaranthaceae growing in saline habitats can provide an ecological advantage for fast seedling establishment.     

Floral biology and ovule and seed ontogeny of Nymphaea thermarum,a water lily at the brink of extinction with potential as a model system for basal angiosperms

Background and Aims Nymphaea thermarum is a member of the Nymphaeales, of one of the most ancient lineages of flowering plants. This species was only recently described and then declared extinct in the wild, so little is known about its reproductive biology. In general, the complete ontogeny of ovules and seeds is not well documented among species of Nymphaea and has never been studied in the subgenus Brachyceras, the clade to which N. thermarum belongs.Methods Flowers and fruits were processed for brightfield, epifluorescence and confocal microscopy. Flower morphology, with emphasis on the timing of male and female functions, was correlated with key developmental stages of the ovule and the female gametophyte. Development of the seed tissues and dynamics of polysaccharide reserves in the endosperm, perisperm and embryo were examined.Key Results Pollen release in N. thermarum starts before the flower opens. Cell walls of the micropylar nucellus show layering of callose and cellulose in a manner reminiscent of transfer cell wall patterning. Endosperm development is ab initio cellular, with micropylar and chalazal domains that embark on distinct developmental trajectories. The surrounding maternal perisperm occupies the majority of seed volume and accumulates starch centrifugally. In mature seeds, a minute but fully developed embryo is surrounded by a single, persistent layer of endosperm.Conclusions Early male and female function indicate that N. thermarum is predisposed towards self-pollination, a phenomenon that is likely to have evolved multiple times within Nymphaea. While formation of distinct micropylar and chalazal developmental domains in the endosperm, along with a copious perisperm, characterize the seeds of most members of the Nymphaeales, seed ontogenies vary between and among the constituent families. Floral biology, life history traits and small genome size make N. thermarum uniquely promising as an early-diverging angiosperm model system for genetic and molecular studies.     

Seed Germination Traits of Loquat (<i>Eriobotrya japonica</i> Lindl.) as Affected by Various Pre-Sowing Treatments (Cutting of Cotyledons,Removal of Perisperm,Moist Chilling and/or Exogenous Application of Gibberellin)

The purpose of this study was to investigate the effects of various presowing treatments on the germinability (final germination percentage) and germination rate of loquat seeds in order to increase seedling production in nurseries (applied research) as well as provide answers for important physiological issues related to loquat seeds and their seed coat (basic research). Three experiments were carried out with various pre-sowing treatments. These treatments included full or partial removal of seed coat (perisperm), partial cutting of cotyledons as well as moist chilling at 5°C for 13 days and/or soaking the seeds in water or 250 ppm gibberellic acid (GA3) solution for 24 h. According to the results, cotyledons excision resulted in delayed germination, regardless of the presence or absence of the seed coat in comparison with the decoated seeds that demonstrated the highest germination rate amongst them. In addition, even the partial excision of seed coats affected positively both the germinability and the germination rate, compared to the control-intact seeds. Furthermore, control-intact seeds had a higher germination percentage when exposed to moist chilling independently of the application or not of gibberellin; while the combination of gibberellin application and moist chilling improved both the percentage and the rate of germination of decoated seeds. In conclusion, the role of perisperm (seed coat) in the germination procedure of loquat seeds seems to be important, indicating the existence of seed coat-imposed dormancy on loquat seeds. Finally, the existence of a mild endogenous embryo-dormancy on loquat is also discussed.     

中国睡莲科植物种子胚及其营养组织的研究

研究了中国睡莲科的3属3种即芡（Euryale ferox Salisb.）、睡莲（Nymphaea tetragona Georgi）和萍蓬草（Nuphar pumilum (Hoffm.) DC.）的胚、胚乳及外胚乳。它们的胚的共同特点是苗端发育良好,特别是胚芽具2～4枚胚芽叶,而根端滞育。三个种皆既有胚乳,又有外胚乳,但在成熟种子中作为胚的营养组织则胚乳弱育而外胚乳发达。最后对上述特点在系统发生中的意义进行了讨论。     

Antimutagenic properties of a polyphenol-enriched extract derived from sesame-seed perisperm

A polyphenolic mixture derived from sesame-seed perisperm (SSP) strongly reduced the mutagenicity of hydrogen peroxide (H₂O₂), sodium azide (NaN₃), and benzo[a]pyrene (BaP) in strains TA100 and/or TA98 of Salmonella typhimurium. It exhibited desmutagenic activity against H₂O₂, BaP in TA98 and/or TA100 and biomutagenic activity (apparently by affecting the DNA-repair system) against NaN₃ in strain TA100. According to in vitro experiments the polyphenolic mixture inhibited the activity of the CYP1A1 (EROD) enzyme responsible for the activation of BaP in the Ames’ test, as well as that of the cytosolic enzyme GST.A cytosolic fraction from liver of male Wistar rats treated with either 20% SSP in the food, or 3 mg or 6 mg of polyphenolic mixture/20 g food/day for a time period of 8 weeks reduced the mutagenic potential of BaP in strains TA100 and TA98, with the cytosolic fraction from rats treated with SSP causing the strongest reduction. Furthermore, a microsomal fraction from the 20% SSP-treated rats inhibited the mutagenicity of BaP in strains TA100 (26.3%) and TA98 (23%). In contrast, a microsomal fraction from rats treated with 3 mg of polyphenolic mixture stimulated the mutagenicity of BaP in TA100 but reduced it in TA98, while for the microsomal fraction from rats treated with 6 mg of polyphenolic mixture, these effects on TA100 and TA98 were reversed.     

Ovular development and perisperm formation of Phytolacca americana (Phytolaccaceae) and their systematic significance in Caryophyllales

Phytolacca is the most original and biggest genus in Phytolaccaceae and one special genus in plant systematic studies as well. The light microscopy observation results show that Ph. americana L. ovule arises from caulis (floral receptacle). The perisperm and hypostase are initiated from the top several layers cells of chalaza simultaneously after fertilizing, and the perisperm is located between nucellus and hypostase. The hypostase cells are thin-walled with dense cytoplasm, clear nuclear, and some reserve granules in earlier stage, and change to thick-walled and dead cells at heart-shaped embryo stage. Its main function may maintain the cellular division and perisperm growth without delivering nutrient materials to perisperm. Furthermore, an evolutionary picture of placentation in Caryophyllales is presented by authors in the paper.