Irrigation and Seed Quality Development in Rapid-cycling Brassica: Soluble Carbohydrates and Heat-stable Proteins

Changes in soluble carbohydrates and heat-stable proteins havebeen examined in relation to the acquisition of desiccationtolerance and/or potential seed longevity during seed developmentin rapid-cycling brassica [Brassica campestris (rapa)L.]. Ratesof seed development were moderated by different irrigation regimes.At the early stages, glucose, fructose and sucrose predominated.The raffinose series oligosaccharides accumulated during seedmaturation, and occurred earliest in seeds from plants irrigatedonly until 16 days after pollination. Stachyose content correlatedpositively, and monosaccharide content correlated negatively,with the ability of seeds to tolerate rapid desiccation andwith their potential longevity (the constantK_iof the seed viabilityequation). Similarly, the ratio of oligosaccharide[ratio]totalsugars provided strong positive correlations with ability totolerate desiccation and with potential longevity. Most of theheat-stable proteins selected for study accumulated comparativelylate, i.e. during maturation drying. The imposition of waterstress induced earlier accumulation of heat-stable proteins.The ability to tolerate desiccation was correlated with thecontent of selected heat-stable proteins, but potential longevityprovided stronger correlations. The content of a 58 kDa heat-stableprotein provided the strongest positive correlation with potentiallongevity. A simple multiple regression model of the relationsbetween potential longevity and both the oligosaccharide[ratio]totalsugar ratio and the 58 kDa heat-stable protein content was developedfor all three plant irrigation regimes to show the combinedeffect of certain sugars and proteins on seed quality. The modelsuggests that these sugars and proteins are equally likely tobe required for seed quality development, and that initiallythe sugars tend to accumulate at a greater rate than the proteins,but that during maturation drying the heat-stable proteins accumulateat the greater rate.Copyright 1998 Annals of Botany Company Brassica campestris (rapa) L., rapid-cycling brassica, potential longevity, seed development, desiccation tolerance, soluble sugars, oligosaccharides, dehydrins, heat-stable proteins.     

Quantitative trait loci analysis reveals a correlation between the ratio of sucrose/raffinose family oligosaccharides and seed vigour in Medicago truncatula

Seed vigour is important for successful establishment and high yield, especially under suboptimal environmental conditions. In legumes, raffinose oligosaccharide family (RFO) sugars have been proposed as an easily available energy reserve for seedling establishment. In this study, we investigated whether the composition or amount of soluble sugars (sucrose and RFO) is part of the genetic determinants of seed vigour of Medicago truncatula using two recombinant inbred line (RIL) populations. Quantitative trait loci (QTL) mapping for germination rate, hypocotyl and radicle growth under water deficit and nutritional stress, seed weight and soluble sugar content was performed using RIL populations LR1 and LR4. Seven of the 12 chromosomal regions containing QTL for germination rate or post-germinative radicle growth under optimal or stress conditions co-located with Suc/RFO QTL. A significant negative correlation was also found between seed vigour traits and Suc/RFO. In addition, one QTL that explained 80% of the variation in the ratio stachyose/verbascose co-located with a stachyose synthase gene whose expression profile in the parental lines could explain the variation in oligosaccharide composition. The correlation and co-location of Suc/RFO ratio with germination and radicle growth QTL suggest that an increased Suc/RFO ratio in seeds of M. truncatula might negatively affect seed vigour.     

Disappearance of desiccation tolerance of imbibed crop seeds is not associated with the decline of oligosaccharides

The relationship between sugar content and loss of desiccation tolerance of hydrated crop seeds (tomato, okra, snow pea, mung bean, and cucumber) was evaluated by imbibing seeds with or without ABA, followed by dehydration and germination. During the process of hydration, but before the seeds lost desiccation tolerance, monosaccharide content increased only slightly, sucrose increased in snow peas, mung bean and cucumber, but maintained its original level in other species and the oligosaccharides declined dramatically. At the time of losing desiccation tolerance, the sucrose content of imbibed seeds was 2-3 times higher than the original level in most species. Positive significant correlation coefficients (r) were found in many, but not all crop seeds between desiccation tolerance and the oligosaccharide mass, or oligo/sucrose ratio. The ratio of oligo/sucrose in intact seeds at the time of losing desiccation tolerance, however, was not a fixed value and varied among species. Oligosaccharides declined significantly in different seed parts of imbibed cucumber seeds while sucrose increased to a higher level in the radicle than in the hypocotyl. Radicles were far more sensitive to desiccation than hypocotyls. The same observation was found for cucumber seeds imbibed in 100 M ABA, yet desiccation tolerance was largely maintained in hypocotyls and cotyledons. It is concluded that sucrose and oligosaccharides are not the determinants of the loss of desiccation tolerance in hydrated seeds.Imbibed seeds did not show any differences between seed parts in their ability to resynthesize sugars during the process of slow dehydration. Differences in sensitivity to desiccation among seed parts were not due to differences in the initial water content or to the rate of water content increase among seed parts. Physiological regulation of the loss of desiccation tolerance in crop seeds during hydration is discussed.     

Changes in oligosaccharide content and antioxidant enzyme activities in developing bean seeds as related to acquisition of drying tolerance and seed quality.

Seeds of bean (Phaseolus vulgaris cv. Vernel) were collected throughout their development on the plant and dried at 15 degrees C and 75% relative humidity to a final moisture content of about 16% (fresh weight basis) to determine whether the onset of tolerance to this drying condition was related to changes in soluble sugars or the activities of the main antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR). Measurements of soluble sugars and enzyme activities were made after drying the seeds, and drying tolerance was evaluated by the ability of dried seeds to germinate and to produce normal seedlings. Seeds became tolerant to drying at 45 d after anthesis, a time marking physiological maturity. At physiological maturity, the moisture content of seeds was about 50-55% (fresh weight basis) and seed dry matter reached about 190 mg per seed. Seed vigour, evaluated by controlled deterioration and conductivity measurements, continued to increase after seed mass maturity, but decreased when seeds remained thereafter for more than 7 d on the plant. Acquisition of drying tolerance was coincident with an accumulation of raffinose and stachyose. Dried-tolerant seeds were also characterized by a high amount of sucrose, the most abundant sugar, and by a low content of monosaccharides. The (raffinose+stachyose)/sucrose ratio increased during seed filling, reaching a value close to 1 when all the seeds became tolerant to drying, and maintaining this proportion during the final stages of maturation. Acquisition of drying tolerance was also related to a reorientation of the enzymatic antioxidant defence system. Drying-tolerant dried seeds displayed high CAT and GR activities and low SOD and APX activities, while the opposite condition was observed in immature dried seeds. The shift in antioxidant enzymes corresponded to the beginning of the maturation-drying phase. These results suggest that oligosaccharide metabolism and enzymatic antioxidant defences may be involved in acquisition of drying tolerance during bean seed development, but are not related to seed vigour.     

Is there a role for oligosaccharides in seed longevity? An assessment of intracellular glass stability

We examined whether oligosaccharides extend seed longevity by increasing the intracellular glass stability. For that purpose, we used a spin probe technique to measure the molecular mobility and glass transition temperature of the cytoplasm of impatiens (Impatiens walleriana) and bell pepper (Capsicum annuum) seeds that were osmo-primed to change oligosaccharide content and longevity. Using saturation transfer electron paramagnetic resonance spectroscopy, we found that the rotational correlation time of the polar spin probe 3-carboxy-proxyl in the cytoplasm decreased, together with longevity, as a function of increasing seed water content, suggesting that longevity may indeed be regulated by cytoplasmic mobility. Osmo-priming of the seeds resulted in considerable decreases in longevity and oligosaccharide content, while the sucrose content increased. No difference in the glass transition temperature was found between control and primed impatiens seeds at the same temperature and water content. Similarly, there was no difference in the rotational motion of the spin probe in the cytoplasm between control and primed impatiens and bell pepper seeds. We therefore conclude that oligosaccharides in seeds do not affect the stability of the intracellular glassy state, and that the reduced longevity after priming is not the result of increased molecular mobility in the cytoplasm.     

南北样带温带区栎属树种种子化学组成与气候因子的关系

选取南北样带温带区8个核心分布区的7种优势栎属树种作为对象,通过检测种子的化学组成,包括淀粉、蛋白质、油脂、可溶性总糖、单宁和脯氨酸,分析其化学组成与气候因子之间的关系,结果发现:在气候因子中,温度是影响种子化学组成的主要因素,日照时数次之,而降水没有明显影响.在南北样带温带区,随纬度的增加,温度降低,年日照时数增加,生长积温减少,生长季缩短,淀粉含量积累下降,并趋向于水解为可溶性糖类;同时,从南到北,为适应低温的环境条件,栎属树种通过增加种子蛋白质、可溶性总糖和脯氨酸的含量,以提高种子的抗寒性.栎属树种种子的化学组成之间存在一定的相互关系,可溶性总糖、蛋白质和脯氨酸之间呈正相关关系,它们三者与淀粉均为负相关,种子化学组成之间的这种相互关系是植物对环境适应的生态策略.     

The regulatory gamma subunit SNF4b of the sucrose non-fermenting-related kinase complex is involved in longevity and stachyose accumulation during maturation of Medicago truncatula seeds

The sucrose non-fermenting-related kinase complex (SnRK1) is a heterotrimeric complex that plays a central role in metabolic adaptation to nutritional or environmental stresses. Here we investigate the role of a regulatory gamma-subunit of the complex, MtSNF4b, in Medicago truncatula seeds. Western blot indicated that MtSNF4b accumulated during seed filling, whereas it disappeared during imbibition of mature seeds. Gel filtration chromatography suggested that MtSNF4b assembled into a complex (450-600 kDa) at the onset of maturation drying, and dissociated during subsequent imbibition. Drying of desiccation-tolerant radicles led to a reassembly of the complex, in contrast to sensitive tissues. Silencing of MtSNF4b using a RNA interference (RNAi) approach resulted in a phenotype with reduced seed longevity, evident from the reduction in both germination percentage and seedling vigour in aged RNAi MtSNF4b seeds compared with the wild-type seeds. In parallel to the assembly of the complex, seeds of the RNAi MtSNF4b lines showed impaired accumulation of raffinose family oligosaccharides compared with control seeds. In mature seeds, the amount of stachyose was reduced by 50-80%, whereas the sucrose content was 60% higher. During imbibition, the differences in non-reducing sugar compared with the control disappeared in parallel to the disassembly of the complex. No difference was observed in dry weight or reserve accumulation such as proteins, lipids and starch. These data suggest that the regulatory gamma-subunit MtSNF4b confers a specific and temporal function to SnRK1 complexes in seeds, improving seed longevity and affecting the non-reducing sugar content at later stages of seed maturation.     

Changes in soluble sugars in relation to desiccation tolerance and effects of dehydration on freezing characteristics of Acer platanoides and Acer pseudoplatanus seeds

The role of soluble sugars in desiccation tolerance was investigated in seeds of two species from the genus Acer: Norway maple (Acer platanoides L.) — tolerant and sycamore (Acer pseudoplatanus L.) — intolerant to dehydration. During two years of observations it was found that seeds of Norway maple acquire desiccation tolerance at the end of August i.e. about 125 days after flowering (DAF). During seed development, the transition from intolerant to tolerant state in Norway maple seeds was accompanied by the accumulation in seed tissues of raffinose, stachyose and sucrose. The sucrose/raffinose ratio in Norway maple seeds was lower than in sycamore. In mature Norway maple seeds sucrose and raffinose contents were higher than in sycamore. It was concluded, that soluble sugars such as sucrose, raffinose and stachyose may play an important role in desiccation tolerance and/or intolerance of Norway maple and sycamore seeds. Differential thermal analysis (DTA) was used to study the relationship between desiccation sensitivity and the state of water in seed tissues. The level of non-freezable water was the same in both analysed seed species, but the temperature of water crystallization during desiccation was lower in sycamore seeds.     

Cytological and physiological changes related to cryotolerance in recalcitrant <Emphasis Type="Italic">Livistona chinensis</Emphasis> embryos during seed development

Cytological and biochemical changes in recalcitrant Livistona chinensis embryos following the acquisition and loss of cryotolerance to liquid nitrogen during seed development were studied. The embryonic cells were always hydrated and contained fully functional organelles throughout seed development. However, the central cells in the root-epicotyl end of the embryo exhibited partial dedifferentiation during the middle developmental stages, although extensive reduction of mitochondria and vacuolation and intensive accumulation of starch grains, lipid, and protein bodies were not observed. Total soluble sugar content rose then decreased on a fresh weight and water weight basis, while soluble and heat-stable proteins increased in number and content then decreased, as seeds matured. These cytological and biochemical features differ from those of orthodox seeds, providing a physiological basis for the recalcitrant behavior of L. chinensis seeds. The changes were closely correlated with acquisition and loss of cryotolerance in L. chinensis embryos and are presumed to contribute to cryotolerance, which would account for the cryotolerance variation in L. chinensis embryos. Cryotolerance is suggested to be a complex, multifaceted process, and accumulation of soluble sugars and soluble and heat-stable proteins alone is not enough to increase cryotolerance per se without acting in combination with a decrease of cellular metabolic activity.     

Sugar metabolism and developmental stages of rubber tree (Hevea brasiliensis L.) seeds

Changes in the concentration of sugars and sucrose metabolism enzymes can characterize the developmental stages of a seed. In recalcitrant species such as Hevea brasiliensis L., little is known about these changes. We aimed to evaluate the three main stages of development of rubber tree seeds – histodifferentiation, cell elongation and accumulation of reserves. The activities of acid and neutral invertases (E.C. 3.2.1.26) and sucrose synthase (EC 2.4.1.13), and the concentrations of reducing sugars (RS), total soluble sugars (TSS) and sucrose (Suc) were determined concomitantly with the histochemical and anatomical evaluation of seed structure. Histodifferentiation in rubber tree seeds occurs up to 75 days after anthesis (DAA). The concentration of RS is high and of Suc is low during seed histodifferentiation, which occurs along with a visible increase in the number of cell divisions. After that period, there is an increase in the concentration of Suc (mg g^?1) and in the number and size of starch granules, and a decrease in the concentration of RS (mg g^?1). At that point, cell elongation occurs. At 135 DAA, there is an inversion in the concentration of these two sugars and an increase in reserve accumulation. Thus, in seeds of the evaluated clone, the period up to 75 DAA is characterized as the histodifferentiation stage, while from that time up to 120 DAA the cell elongation stage takes place. The final stage of seed maturation and reserve accumulation begins at 135 DAA, and the seed, including the embryo, is completely formed at 175 DAA.     

Temporal release of fatty acids and sugars in the spermosphere: impacts on Enterobacter cloacae-induced biological control

The aim of this study was to determine the temporal release of fatty acids and sugars from corn and cucumber seeds during the early stages of seed germination in order to establish whether sugars found in exudate can prevent exudate fatty acid degradation by Enterobacter cloacae. Both saturated (long-chain saturated fatty acids [LCSFA]) and unsaturated (long-chain unsaturated fatty acids [LCUFA]) fatty acids were detected in corn and cucumber seed exudates within 15 min after seed sowing. LCSFA and LCUFA were released at a rate of 26.1 and 6.44 ng/min/seed by corn and cucumber seeds, respectively. The unsaturated portion of the total fatty acid pool from both plant species contained primarily oleic and linoleic acids, and these fatty acids were released at a combined rate of 6.6 and 0.67 ng/min/seed from corn and cucumber, respectively. In the absence of seed exudate sugars, E. cloacae degraded linoleic acid at rates of 29 to 39 ng/min, exceeding the rate of total fatty acid release from seeds. Sugars constituted a significant percentage of corn seed exudate, accounting for 41% of the total dry seed weight. Only 5% of cucumber seed exudate was comprised of sugars. Glucose, fructose, and sucrose were the most abundant sugars present in seed exudate from both plant species. Corn seeds released a total of 137 microg/seed of these three sugars within 30 min of sowing, whereas cucumber seeds released 0.83 microg/seed within the same time frame. Levels of glucose, fructose, and sucrose found in corn seed exudate (90 to 342 microg) reduced the rate of linoleic acid degradation by E. cloacae to 7.5 to 8.8 ng/min in the presence of either sugar, leaving sufficient concentrations of linoleic acid to activate Pythium ultimum sporangia Our results demonstrate that elevated levels of sugars in the corn spermosphere can prevent the degradation of LCUFA by E. cloacae, leading to its failure to suppress P. ultimum sporangial activation, germination, and subsequent disease development.     

Does pre-dispersal seed predation limit reproduction and population growth in the alpine clonal plant Geum reptans?

We studied the impact of the seed damaging gall midge larva Geomyia alpina on its perennial alpine host plant Geum reptans. We analysed the effect of seed predation on reproduction by seeds, i.e. seed number, seed mass, and seed viability and on growth and clonal propagation of non-protected plants in comparison to plants protected from predation by an insecticide. Additionally, we assessed the consequences of seed predation for population growth using matrix projection modelling. Seed predation resulted in a decrease in total seed mass per flower head by 23.8% in non-protected plants (P < 0.05). Individual seed mass decreased with increasing infestation intensity (P < 0.05). Seed number remained unaffected because the sucking feeding behaviour by gall midge larvae does not evoke seed abortion. Percent germination of seeds from non-protected plants was reduced by 97.9% compared to seeds from protected plants. According to reduced seed viability, modelling revealed a decrease in population growth rate from λ = 1.055 to λ = 1.041. Predation did neither influence total plant biomass nor biomass fractions. But stolon dry-weight of non-protected plants increased by 24.1% (P < 0.05), which may indicate a trade-off between sexual reproduction and clonal propagation. Our results demonstrate that despite substantial reduction of viable seeds, predation by gall midge larvae only slightly affected population growth of G. reptans suggesting that in this alpine species, persistence by longevity and clonal propagation can balance potential seed losses by predation, at least for local population growth.     

From Avicennia to Zizania: seed recalcitrance in perspective

BACKGROUND: Considered only in terms of tolerance of, or sensitivity to, desiccation (which is an oversimplification), orthodox seeds are those which tolerate dehydration and are storable in this condition, while highly recalcitrant seeds are damaged by loss of only a small proportion of water and are unstorable for practical purposes. Between these extremes, however, there may be a gradation of the responses to dehydration--and also to other factors--suggesting perhaps that seed behaviour might be best considered as constituting a continuum subtended by extreme orthodoxy and the highest degree of recalcitrance. As the characteristics of seeds of an increasing number of species are elucidated, non-orthodox seed behaviour is emerging as considerably more commonplace--and its basis far more complex--than previously suspected. SCOPE: Whatever the post-harvest responses of seeds of individual species may be, they are the outcome of the properties of pre-shedding development, and a full understanding of the subtleties of various degrees of non-orthodox behaviour must await the identification of, and interaction among, all the factors conferring extreme orthodoxy. Appreciation of the phenomenon of recalcitrance is confounded by intra- and interseasonal variability across species, as well as within individual species. However, recent evidence suggests that provenance is a pivotal factor in determining the degree of recalcitrant behaviour exhibited by seeds of individual species. Non-orthodox--and, in particular, recalcitrant--seed behaviour is not merely a matter of desiccation sensitivity: the primary basis is that the seeds are actively metabolic when they are shed, in contrast to orthodox types which are quiescent. This affects all aspects of the handling and storage of recalcitrant seeds. In the short to medium term, recalcitrant seeds should be stored in as hydrated a condition as when they are shed, and at the lowest temperature not diminishing vigour or viability. Such hydrated storage has attendant problems of fungal proliferation which, unless minimized, will inevitably and significantly affect seed quality. The life span of seeds in hydrated storage even under the best conditions is variable among species, but is curtailed (days to months), and various approaches attempting to extend non-orthodox seed longevity are discussed. Conservation of the genetic resources by means other than seed storage is then briefly considered, with detail on the potential for, and difficulties with, cryostorage highlighted. CONCLUSIONS: There appears to be little taxonomic relationship among species exhibiting the phenomenon of seed recalcitrance, suggesting that it is a derived trait, with tolerance having been lost a number of times. Although recalcitrant seededness is best represented in the mesic tropics, particularly among rainforest climax species, it does occur in cooler, drier and markedly seasonal habitats. The selective advantages of the trait are considered.     

模拟四季温度层积对南方红豆杉种子生理性状的影响

为了解濒危物种南方红豆杉(Taxus chinensis var. mairei)种子内含物含量受温度和湿度层积的影响,设置4个季节、2种湿度(16%和24%)基质层积处理,对种子的可溶性糖、淀粉、可溶性蛋白和脂肪等内含物质的变化进行研究。结果表明,不同层积处理下种子贮藏物质的含量有显著变化,春季层积9个月后,可溶性蛋白含量达到最高值;可溶性糖含量呈现降低-升高-降低的变化趋势;淀粉和脂肪含量均随层积逐渐减少。秋季层积9个月后,淀粉含量降至最低。相比于24%湿度,16%湿度的春季、秋季、冬季层积9个月后,脂肪含量均减少较多,说明16%湿度下种子代谢活动更强。春季和秋季的暖温更能促进种子代谢,促进种子形态后熟。夏季温度过高,导致种子生活力下降,夏季层积处理3个月后,种子已经发霉和腐烂。层积过程中,种子内含物在相关酶的作用下,降解为可溶性蛋白、可溶性糖等,为种子萌发提供物质与能量。种子层积时间、温度和湿度及交互作用可作为种子内含物的调控因子。     

The effects of desiccation on seeds of Acer saccharinum and Aesculus pavia: recalcitrance in temperate tree seeds

This study was undertaken to determine how the results from lipid, moisture, and differential scanning calorimetry analyses conducted on silver maple (Aceraceae: Acer saccharinum L.) and red buckeye (Hippocastanaceae: Aesculus pavia L.) compared with those obtained from previous studies on white and water oaks (Fagaceae: Quercus alba and Q. nigra), and the tropical zone species American muskwood (Meliaceae: Guarea guidonia) and carapa (Meliaceae: Carapa guianensis). Seeds were air-dried at room temperature for 9-11 days. At intervals, germination was tested, moisture determined, and lipids extracted. It was found that, like the other recalcitrant seeds, (1) viability was greatly reduced or lost after 11 days of drying, (2) percentage changes in individual fatty acids were not related to seed viability, and (3) results from the differential scanning calorimetry studies revealed a strong relationship between enthalpy/onset data from the embryo and cotyledon tissues and loss of viability. Also, silver maple seeds experienced a 50% reduction in viability by day 5 of drying and retained an axis moisture content over 25% throughout the experiment. However, unlike the other recalcitrant seeds surveyed, both silver maple and red buckeye had a significant reduction in the total amount (mg/g) of cotyledon lipids as the experiment progressed. However, no decrease in the unsaturated/saturated fatty acid ratio was found, so we conclude that in these species lipid peroxidation is not a marker of declining seed viability. Also, red buckeye seeds did not lose 50% viability until after day 8 of the experiment, and axis moisture content fell well below 20% as the seeds dried.     

异子蓬二型性种子的种皮结构及离子含量差异

异子蓬(Borszczowia aralocaspica)是中亚荒漠区系特有的一年生盐生植物,其种子具有二型性。通过检测异子蓬二型性种子中的生理生化物质以及观察种皮的结构,比较异子蓬二型性种子中营养物质、养分全量以及种皮结构的差异,结果表明:(1)异子蓬的棕色种子只有一层薄种皮,而黑色种子不但具有一层薄的内种皮还有一层坚硬致密的外种皮;(2)棕色种子的质量大、质量频数分布较为集中,并且吸水迅速,在吸水率较低时就能够大量萌发;(3)棕色种子的可溶性糖、可溶性蛋白质、全氮、全磷以及K+、Na+、K+/Na+和Mg2+/Na+都显著高于黑色种子。说明在繁殖子代、产生二型性种子时,异子蓬对棕色种子和黑色种子之间的繁殖投入存在着巨大的差异,这可能是导致异子蓬二型性种子产生差异性萌发机制的重要原因。     

Effects of Moisture Content on Germination of Seeds of Hancornia speciosa Gom. (Apocynaceae)

Seeds of Hancornia speciosa germinated best at a temperatureof 20–30 °C. The viability of the seeds during storagewas short and the best storage conditions for viability entailedkeeping the seeds in polyethylene bags. Seed viability was maintainedonly when the seeds were stored at a moisture content above30%; storage conditions which allowed dehydration resulted ina rapid loss of viability (the seeds showed recalcitrant behaviour). Low temperature during storage did not improve longevity. Arelationship between germination and moisture content was established,but when the moisture content fell below 25% there was a drasticreduction of germination. After 9 weeks of storage, even athigh moisture content, seeds lost viability. Loss of seed viability during seed dehydration was associatedwith increased leakage of electrolytes and organic solutes,and reduced tetrazolium staining during subsequent imbibition. Hancornia speciosa, germination, recalcitrant seeds, storage, moisture     

濒危植物多毛坡垒种子萌发的生理生态特性

研究了多毛坡垒（Hopea mollissima）种子在自然条件下的寿命及成熟度、温度、光照、土壤水分条件对多毛坡垒种子萌发的影响,结果表明：多毛坡垒种子适宜萌发的温度范围是20～30℃,最适宜温度为25℃;光照对多毛坡垒种子的萌发没有显著性影响,但在周期性光照条件下以25～30℃萌发结果最好,全黑暗条件下以20～25℃萌发结果最好;种子适宜萌发的土壤含水量为20％～60％,最适含水量为50％～60％;种子成熟后在树上长时间宿存明显降低了种子的发芽率和活力;在室内自然摊放条件下,10天后发芽率减半,16天后完全丧失发芽能力。研究认为,该物种对热带湿性季节性雨林原生境有很强的依赖性,目前多毛坡牟的濒危状态主要是由于滥砍乱伐和森林破坏造成的,由于其种子具有顽拗性种子的一些特点,日前该物种宜采取活体保仔的方法,以就地保护为主,活植物迁地保护为辅。     

A continental-scale study of seed lifespan in experimental storage examining seed,plant, and environmental traits associated with longevity

Management of seed banks conserving the biodiversity of phylogenetically diverse species requires insight into seed longevity. This study determined the seed longevity of 172 species sourced from across the mega-diverse flora of the Australia continent. Seeds were aged via a controlled ageing experiment through storage at 45 °C and 60 % RH, or 60 °C and 60 % RH, and regularly tested for germination. Relative seed longevity between species was determined by comparing the time to 50 % viability loss (p ₅₀), calculated via probit analysis of seed survival curves. Seed, plant, and environmental traits were examined for associations with longevity. The p ₅₀ values varied between species from 3.0 to 588.6 days. Serotinous species, and woody trees and shrubs, had significantly longer-lived seeds than geosporous species, and species of herbaceous habit. Seeds that possess physical dormancy, and seeds with large embryos with little endosperm, were also long-lived. There was a weak, but significant, positive correlation between seed mass and longevity. Seeds sourced from regions of higher mean annual temperature and rainfall were significantly longer-lived than seeds from cooler and drier regions, although both environmental factors were weakly associated with longevity. Compared with species from other regions of the world, prolonged longevity is a feature of many Australian species. Nevertheless, seed life-spans vary substantially between species and close consideration of seed traits along with biotic and abiotic components of the plants and their environment can assist to differentiate between potentially long- and short-lived seeds.     

Nectar to improve parasitoid fitness in biological control: Does the sucrose:hexose ratio matter?

The consumption of saccharide-rich foods such as floral nectar is crucial for the survival of many adult parasitoid wasps. The importance to parasitoids of nectar quality, with regards to its sucrose:hexose ratio, was investigated. Nectar, an aqueous solution of sugars, amino acids and other compounds, differs between plant species. Nectar composition is dominated by sucrose, glucose and fructose. Previous studies have shown that the ratio of sucrose to hexose (glucose+fructose) sugars can explain nectar associations in a range of flower visiting arthropods. It has been suggested that this ratio may be important in terms of parasitoid fitness. Analysis of floral nectar from fourteen plant species confirmed that the sucrose/hexose ratio significantly differed between species. An opportunity to select floral resources based on this measure of nectar quality arose and highlighted the potential to utilize native flowering plant species in place of the seven most commonly deployed, which are usually not native to the countries in which they are used.Results presented in this paper indicate, however, that the sucrose/hexose ratio is not a significant factor explaining parasitoid longevity. The hymenopteran parasitoids Diadegma semiclausum (Ichneumonidae) and Dolichogenidea tasmanica (Braconidae) were fed 40% w/w sugar solutions, differing in their sugar ratios. Solutions were classified as either sucrose-dominant (ratio >0.99), sucrose-rich (ratio 0.5–0.99), hexose-rich (ratio 0.1–0.499) or hexose-dominant (ratio <0.1). No significant differences in parasitoid longevity were found between the different treatments for either species. This suggests there is not an optimal sucrose/hexose ratio for parasitoid wasps, although a greater number of parasitoid species should ideally be tested to confirm if this is true for the wider parasitoid taxonomic groups.