Determinism of carbon and nitrogen reserve accumulation in legume seeds

In legume plants, the determination of individual seed weight is a complex phenomenon that depends on two main factors. The first one corresponds to the number of cotyledon cells, which determines the potential seed weight as the cotyledon cell number is related to seed growth rate during seed filling. Since cell divisions take place between flowering and the beginning of seed filling, any stress occurring before the beginning of seed filling can affect individual seed growth rate (C and N reserve accumulation in seeds), and thus individual seed weights. The second factor concerns carbon and nitrogen supply to the growing seed to support reserve accumulation. Grain legume species produce protein-rich seeds involving high requirement of nitrogen. Since seed growth rate as determined by cotyledon cell number is hardly affected by photoassimilate availability during the filling period, a reduction of photosynthetic activity caused by nitrogen remobilization in leaves (e.g., remobilization of essential proteins involved in photosynthesis) can lead to shorten the duration of the filling period, and by that can provoke a limitation of individual seed weights. Accordingly, any biotic or abiotic stress during seed filling causing a decrease in photosynthetic activity should lead to a reduction of the duration of seed filling.     

Seed growth rate in grain legumes II. Seed growth rate depends on cotyledon cell number

Individual seed weight and seed growth rate are variable within the plant and among environmental conditions. Seed growth rate remains constant during the filling period even if assimilate availability is modified. This paper describes the relationship between the cotyledon cell number fixed at the beginning of seed filling and the seed growth rate. Two genotypes of pea were grown in various environmental conditions: field, glasshouse and growth chamber. One genotype of soybean was sown in field. Seed growth rate and cotyledon cell number were measured. Variations in seed growth rate (0.24 to 1.07 mg per degree-day for pea, 0.23 to 0.42 mg per degree-day for soybean) largely account for differences in individual seed weight. For each species, cotyledon cell number (from 3.4 x 10⁵ to 10.2 x 10⁵ per seed for pea, from 6.7 x 10⁶ to 9 x 10⁶ per seed for soybean) and seed growth rate are strongly correlated regardless of environmental conditions and intraplant position. Consequently, seed growth rate observed during the seed filling period is determined before this period during the cell division in the embryo: variations in seed growth rate depend on the growing conditions during the period between flowering and the beginning of seed filling.     

Relationship of endogenous abscisic Acid to sucrose level and seed growth rate of soybeans

It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. The levels of ABA and sucrose in seed tissues were compared in nine diverse Plant Introduction lines having seed growth rates ranging from 2.5 to 10.0 milligrams dry weight per seed per day. At 14 days after anthesis (DAA), seeds of all genotypes contained less than 2 micrograms of ABA per gram fresh weight. Levels of ABA increased rapidly, however, reaching maxima at 20 to 30 DAA, depending upon tissue type and genotype. ABA accumulated first in seed coats and then in embryos, and ABA maxima were higher in seed coats (8 to 20 micrograms per gram fresh weight) than in embryos (4 to 9 micrograms per gram fresh weight. From 30 to 50 DAA, ABA levels in both tissues decreased to less than 2 micrograms per gram fresh weight. Levels of sucrose were also low early in development, less than 10 milligrams per gram fresh weight at 14 DAA. However, by 30 DAA, sucrose levels in seed coats had increased to 20 milligrams per gram fresh weight and remained fairly constant for the remainder of the filling period. In contrast, sucrose accumulated in embryos throughout the filling period, reaching levels greater than 40 milligrams per gram fresh weight by 50 DAA. Correlation analyses indicated that the level of ABA in seed coats and embryos was not directly correlated to the level of sucrose measured in those tissues or to the rate of seed dry matter accumulation during the linear filling period. Rather, the ubiquitous pattern of ABA accumulation early in development appeared to coincide with water uptake and the rapid expansion of cotyledons occurring at that time. Whole tissue sucrose levels in embryos and seed coats, as well as sucrose levels in the embryo apoplast, were generally not correlated with the rate of dry matter accumulation. Thus, it appears that, in this set of diverse soybean genotypes, seed growth rate was not limited by endogenous concentrations of ABA or sucrose in reproductive tissues.     

The Effect of Source-Sink Alterations on Soybean Seed Growth

Soybeans (Glycine max L. Merrill) were grown in the greenhouseand in the field to investigate the effect of variations inthe assimilate supply during the linear phase of seed developmenton the rate and duration of growth of individual seeds. Increasedassimilate supplies, created by partial fruit removal, increasedrates of dry matter accumulation, duration of seed growth, andfinal seed size (weight per seed). Reductions in the supplyof assimilate to the developing seed, created by shading (60per cent) the plants during the linear phase of seed development,lowered seed growth rate but did not affect final seed sizebecause of a longer duration of seed growth. Nitrogen stressduring seed development, created by removing N from the nutrientmedium, did not affect seed growth rate but shortened the durationof seed growth and reduced final seed size. The data indicatethat the growth characteristics of soybean seed are influencedby the supply of assimilate to the seed during the linear phaseof seed development. Glycine max L., soybean, seed growth rate, duration of seed growth, effective filling period     

Demand and supply of N in seed production of soybean (<Emphasis Type="Italic">Glycine max</Emphasis>) at different N fertilization levels after flowering

Nitrogen (N) has been suggested as a determinant of seed production especially in species with high seed N content. Assuming that seed yield was determined as the balance between N demand and supply for seed production, we studied the effect of N fertilization after flowering on soybean (Glycine max L. Merr.) yield. Seed N concentration was nearly constant irrespective of N fertilization, indicating that seed production was proportional to the amount of N available for seed growth. N demand for seed production was analyzed as the product of seed number, the rate of N filling in individual seeds, and the length of the reproductive period. N fertilization increased seed number and the reproductive period, but did not influence the N filling rate. Seed number was positively correlated with dry mass productivity after flowering. Three N sources were distinguished: mineral N uptake, symbiotic N₂ fixation and N remobilization from vegetative body. N fertilization increased N uptake and N remobilization, but lowered N₂ fixation. We concluded that N availability in the reproductive period determined seed yield directly through increasing N supply for seed growth and indirectly through increasing seed N demand with enhanced plant dry mass productivity.     

Seed growth rate and carbohydrate pool sizes of the soybean fruit

The relationships between various carbohydrate pools of the soybean (Glycine max [L.] Merrill) fruit and growth rate of seeds were evaluated. Plants during midpod-fill were subjected to various CO₂ concentrations or light intensities for 7 days to generate different rates of seed growth. Dry matter accumulation rates of seeds and pod wall, along with glucose, sucrose, and starch concentrations in the pod wall, seed coat, and embryo were measured in three-seeded fruits located from nodes six through ten. Seed growth rates ranged from 4 to 37 milligrams·day⁻¹·fruit⁻¹. When seed growth rates were greater than 12 milligrams·day⁻¹·fruit⁻¹, sucrose concentration remained relatively constant in the pod wall (1.5 milligrams·100 milligrams dry weight⁻¹), seed coat (8.5 milligrams·100 milligrams dry weight⁻¹), and embryo (5.0 milligrams·100 milligrams dry weight⁻¹). However, sucrose concentrations decreased in all three parts of the fruit as growth rate of the seeds fell below 12 milligrams·day⁻¹·fruit⁻¹. This relationship suggests that at high seed growth rates, flux of sucrose through the sucrose pools of the fruit was more important than pool size for growth. Starch concentration in the pod wall remained relatively constant (2 milligrams·100 milligrams dry weight⁻¹) at higher rates of seed growth but decreased as seed growth rates fell below 12 milligrams·day⁻¹·fruit⁻¹. This suggests that pod wall starch may buffer seed growth under conditions of limiting assimilate availability. There was no indication that carbohydrate pools of the fruit were a limitation to transport or growth processes of the soybean fruit.     

种子散布位置对格氏栲幼苗根系形态及生长特征的影响

种子从母株掉落于地面萌发后,其根系在不同散布位置(凋落物上层、土壤表层和凋落物下层)的生长形态影响幼苗定居及建成,而目前对其根系形态及生长特征的了解并不充分,限制了对幼苗根系在不同散布下适应策略的理解。为此,以格氏栲(Castanopsis kawakamii)为研究对象,通过模拟种子在凋落物中位置,设置凋落物上层(种子下层铺垫2 cm和4 cm凋落物,U2和U4处理)、土壤表层与凋落物下层(种子上层覆盖0、2、4、6 cm和8 cm凋落物,CK、D2、D4、D6和D8处理)等3种散布,探讨不同散布位置对格氏栲幼苗根系9个生长指标的影响。结果表明：(1)种子散布位置对幼苗根干物质质量具有显著影响,D2处理达最大值。(2)D2处理的幼苗根长、根表面积、根尖数、分枝数和比根长高于其它处理;根系平均直径在D6处理达最大值。(3)相关分析表明根长、根表面积、根尖数、分枝数和比根长与根系平均直径呈显著负相关关系。(4)对根系9个生长指标提取主成分后聚类为4个类群,D2与D4处理各划分一类;U2与U4处理划分一类,其余三个处理划分一类。综上所述,凋落物浅层覆盖(D2处理)适宜格氏栲根系生长;凋落物...     

外源水杨酸对盐胁迫下大黄种子萌发及幼苗生长的影响

该研究以掌叶大黄、唐古特大黄和药用大黄种子为材料,采用双层滤纸培养法,设置系列浓度NaCl (0、100、150、200、250 mmol/L) 胁迫试验,以及系列浓度水杨酸(SA)溶液(0、50、100、150、200、250 mg/L)拌种和浸种后盐胁迫实验,测定3种大黄种子萌发及幼苗生长指标,揭示外源水杨酸对盐胁迫下大黄种子萌发及幼苗生长的影响。结果显示：(1)随NaCl浓度增大3种大黄种子的发芽率均呈直线下降趋势,且子叶、胚轴、根和苗等生长均受到强烈抑制。(2)在拌种条件下, 200 mmol/L NaCl胁迫下掌叶大黄苗长在200 mg/L SA处理下受到显著促进; 200 mmol/L NaCl浓度盐胁迫下唐古特大黄种子发芽率在250 mg/L SA处理下受到显著抑制;100 mmol/L NaCl胁迫下药用大黄种子发芽势在200 mg/L SA处理下受到显著抑制,其发芽率在150 mg/L SA处理下得到显著抑制,其苗长在250 mg/L SA处理下受到显著抑制。(3)在浸种条件下, 200 mmol/L NaCl胁迫下掌叶大黄种子发芽率在50 mg/L SA处理下显著提高,其幼苗根长和苗长的生长在250 mg/L SA处理受到显著促进;200 mmol/L NaCl胁迫下唐古特大黄种子的发芽势在200 mg/L SA处理下得到显著促进,其幼苗根和苗的生长在50 mg/L SA处理下得到显著促进;100 mmol/L NaCl 胁迫下药用大黄根和苗的生长在100 mg/L SA处理下均得到显著促进。研究表明,3种大黄种子和幼苗对盐胁迫的响应趋势一致,但对不同浓度SA拌种和浸种的响应有较大差异。     

Effect ofLupinus seed diffusates onBradyrhizobium sp. growth and nodulation of lupine

Seeds of three species of lupine (Lupinus termis, L. triticale andL. albus) were tested to determine if the seed contains diffusable substances toxic to bradyrhizobia.L. albus seeds were less toxic to bradyrhizobia, followed byL. triticale. Six strains ofBradyrhizobium were evaluated for their resistance to the toxic substances in lupine seeds. Zones of growth inhibition were determined on yeast-mannitol-agar medium surrounding surface-sterilized seed. The effect of surface sterilization of seeds by different chemical treatments on seed toxicity was assessed. Seeds soaked in water for 1 h before placing on agar surface significantly decreased the inhibition zone. Also, the effect of soaking seeds in water for 4 h before planting and inoculation on nodulation, nitrogen fixation and plant growth were investigated. Addition of seed diffusate to soaked seeds significantly decreased nodulation and plant growth. Autoclaving the seed diffusate had no effect on the toxicity of the seed diffusate. Addition of the absorbent polyvinylpolypyrrolidone (PVPP) to seed diffusates significantly decreased the inhibitory effect of seed diffusate on nodulation and plant growth. Seed diffusate substances were water-soluble, heat-stable and partially bound to PVPP.     

Drought affects the rate and duration of organ growth but not inter-organ growth coordination

Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs—though an extension of growth duration partially compensated for this—culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops.

When affected by drought, the plant responds by adjusting the growth of individual organs but not the coordination between the organs.     

Pathogenic response of seed mycoflora associated with cowpea,Vigna unguiculata

Cowpea, Vigna unguiculata (L.) Walp. (Fabaceae), has always been an important grain legume in tropical countries and a veritable source of dietary protein for the teeming population of human and livestock. The crop is often attacked and deteriorated by a number of pathogens; many of these are seed-borne fungi, which produce an adverse effect on the growth and development of plants. In this study, the effects of fungi on germinability and seedling health were determined, and the pathogenicity was established. Eleven fungal species were isolated from cowpea seeds which were used as inocula on cowpea. All the tested fungi show a reduction in the germination rate of the cowpea plants, and different types of disease symptoms including reduction in shoot and root lengths were noted for different pathogenic fungi. The symptoms included seed rot, seedling rot, yellowing of leaves, deformation of leaves, etc. Many phytopathogenic fungi penetrate deep into the seeds. These fungi produce enzymes, toxins and metabolites which adversely affect the plant growth and produce characteristic symptoms and cause deterioration of this important protein-rich crop.     

Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.)

The relative importance of growth rate and calcium concentration in sweet pepper fruits (Capsicum annuum L.) for the induction of blossom-end rot (BER) was investigated in (1) four pollination treatments in one cultivar, (2) four cultivars with the same fruit load and (3) three fruit load treatments in four cultivars. For fruits with the same pollination treatment those eventually developing BER had a higher initial fruit growth rate than those not developing BER. Within the same experiment both the growth rate of the young fruit and BER increased with the number of seeds. The Ca concentration of the pericarp in mature fruits was negatively related to both fruit size and BER incidence. Differences in levels of BER between different pollination experiments could not be explained solely by differences in growth rate of the young fruit, but related to different Ca concentrations in the mature fruits. In the spring, but not in the summer, cultivars more susceptible to BER had a larger final size but lower Ca concentration in the young fruit than the resistant ones. By lowering the fruit load in the summer both the final fruit size and the BER incidence increased, but the Ca concentrations of both proximal and distal pericarp in the young fruit of all cultivars were not consistently affected. Despite a correlation between growth rate and low Ca concentration in the fruit, the incidence of BER may only be predicted from separate effects of fruit growth and of Ca concentration of fruit. The data indicated that at a higher growth rate a higher Ca concentration is required to prevent the induction of BER. The usefulness of the total Ca concentration of the fruit for determining the critical Ca concentration in the induction of BER is discussed.Key words: Capiscum annuum L., sweet pepper, blossom-end rot, calcium, growth rate, pollination, fruit load.      

Effect of N source during soybean pod filling on nitrogen and sulfur assimilation and remobilization

During pod filling, a grain legume remobilizes vegetative nitrogen and sulfur to its developing fruit. This study was conducted to determine whether different nitrogen sources affected N and S assimilation and remobilization during pod filling. Well-nodulated plants fed 1.0 mM KNO₃, 0.5 mM urea, or 2.5 mM urea assimilated 0%, 37%, or 114% more N, respectively, and 25%, 46%, or 56% more S, respectively, than did the average non-nodulated control plant fed 5.0 mM KNO₃. Thus, N source during pod filling greatly affected both N and S assimilation. Depending upon N source, plant N concentration during pod filling decreased from 2.96% to between 1.36% and 1.82%. Non-nodulated control plants fed 5.0 mM KNO₃ had the highest residual N at harvest. During the same treatments, plant S concentration decreased from 0.246% to a relatively uniform 0.215%. Thus, during pod filling, vegetative N was seemingly remobilized more efficiently (38–54%) than was S (13%). N source also affected seed yield and seed quality. Non-nodulated control plants fed 5.0 mM KNO₃ produced the lowest yield (21.1 g seeds plant^-1), whereas well nodulated plants fed 1.0 mM KNO₃, 0.5 mM urea, or 2.5 mM urea produced yields of 26.2 g, 31.8 g, and 36.7 g seeds plant^-1, respectively. Non-nodulated plants fed 2.5 mM urea yielded 28.6 g of seeds plant^-1. Seed N concentrations of non-nodulated plants and nodulated plants fed 2.5 mM urea were high, 6.30% and 6.11% N, respectively, whereas their seed S concentrations were low, 0.348% and 0.330% S, respectively. N sources that produced both a relatively high seed yield and seed N concentration (i.e., a relatively high total seed N plant^-1) produced a proportionately smaller increase in total seed sulfur. Consequently, seed quality, as judged solely by seed S concentration, was lowered.     

Sexual reproduction of Lolium perenne L. and Trifolium repens L. under free air CO2 enrichment (FACE) at two levels of nitrogen application

Field experiments in managed grassland have shown that the response of vegetative growth to elevated CO₂ is nitrogen‐dependent in grasses, but independent in N₂‐fixing legumes. In the present study, we tested whether this is also true for reproduction. We evaluated reproductive growth, flowering phenology, seed development, reproductive success and seed germination in the grass Lolium perenne L. and the legume Trifolium repens L., growing in monocultures in a free air carbon dioxide enrichment (FACE) system at ambient (35 Pa) and elevated (60 Pa) partial pressure of CO₂ and two levels of nitrogen fertilization (14 and 56 g N m^?2 a^?1). In both species, elevated CO₂ had no significant effect on sexual reproduction. In L. perenne, reproduction was mainly nitrogen‐dependent. The weak interactions between CO₂ and mineral N supply (13% more flowers and 8% more grains per spike at high N, 7% less flowers and 8% less grains at low N) were not significant. Under elevated CO₂, grain maturation was slightly enhanced and grain weight tended to decrease. No influence could be ascertained in the date of anthesis, the temporal pattern of grain growth, the rate of grain abortion and germination. Trifolium repens, grown under CO₂ enrichment at both levels of N fertilization, flowered 10 d earlier, tended to form more inflorescences per ground area and more flowers (8–12%) and seeds (>18%) per inflorescence than at ambient CO₂. The temporal pattern of seed growth was about the same in all treatments; embryo development, however, was accelerated in fumigated plants. The number of aborted seeds per pod, seed size, thousand‐seed weight and germinability did not show any influence of CO₂. Fumigated plants at high N were attacked slightly more frequently by seed‐eating weevils, which lowered the seed output per pod. In summary, the reproductive response of L. perenne and T. repens to CO₂ enrichment on the flower and inflorescence level was far weaker than expected from the results on vegetative growth.     

Abscisic Acid and its relationship to seed filling in soybeans

The effect of exogenous abscisic acid (ABA) on the rate of sucrose uptake by soybean (Glycine max L. Merr.) embryos was evaluated in an in vitro system. In addition, the concentrations of endogenous ABA in seeds of three soybean Plant Introduction (PI) lines, differing in seed size, were commpared to their seed growth rates. ABA (10⁻⁷ molar) stimulated in vitro sucrose uptake in soybean (cv `Clay') embryos removed from plants grown in a controlled environment chamber, but not in embryos removed from field-grown plants of the three PI lines. However, the concentration of ABA in seeds of the three field-grown PI lines correlated well with their in situ seed growth rates and in vitro [¹⁴C] sucrose uptake rates.

Across genotypes, the concentration of ABA in seeds peaked at 8.5 micrograms per gram fresh weight, corresponding to the time of most rapid seed growth rate, and declined to 1.2 micrograms per gram at physiological maturity. Seeds of the large-seeded genotype maintained an ABA concentration at least 50% greater than that of the small-seeded genotype throughout the latter half of seed filling. A higher concentration of ABA was found in seed coats and cotyledons than in embryonic axes. Seed coats of the large-seeded genotype always had a higher concentration of ABA than seed coats of the small-seeded line. It is suggested that this higher concentration of ABA in seed coats of the large-seeded genotype stimulates sucrose unloading into the seed coat apoplast and that ABA in cotyledons may enhance sucrose uptake by the cotyledons.

     

Influence of plant growth regulators on growth, morpho-physiological characters and yield of summer sesame (Sesamum indicum L. cv. Rama) under moisture stress

Field experiments were conducted with sesame (Sesamum indicum L. cv. Rama) for two years (1997 and 1998) to study the effect of three level of irrigation (F+C, B+C, B+F+C) and two growth regulators (CCC, 200 ppm CCC; 100 ppm and BX-112, 100 ppm; BX-112, 50 ppm) on growth (root and shoot length, average number of primary branches/plant), morpho-physiological growth parameters(LAI, LAD, CGR and NAR), yield attributing parameters(average number of capsule/plant, average number of seeds/capsule) and seed yield. Irrigation at B+F+C stage showed significant effect on these parameters. Among the growth regulators, CCC, 200 ppm showed remarkable results on these parameters and seed yield. Seed yield in CCC, 200 ppm treatment was more than 53% in comparison to water soaked seeds. The interaction between irrigation and PGR showed better seed yield and it was concluded that the growth regulator CCC might be utilized for enhancement of seed yield of summer sesame under field condition.     

Stability of the Nitrogen Concentration of Inoculated White Lupins during Pod Development

The general pattern of decrease of the 'critical' plant N concentration(i.e. minimum concentration required for maximum growth rate)during growth has been described for several C₃ non grain-legumespecies, and this can be used as a reference curve for diagnosisof N nutrition in these species. The present study was undertakento investigate changes of N concentration during growth of agrain legume, in different conditions of N nutrition. Whitelupin (Lupinus albus L.) was grown for six crop seasons in fieldtrials in which inoculation with Rhizobium lupini, nitrogenfertilizer rate, cultivar and plant density were density weremanipulated. The yield and dry matter production of noninoculatedplants were lower than, or at the best similar to, those ofinoculated plants, whatever the level of N supply. From anthesisto the beginning of seed filling, the N concentration of shootsof inoculated plants was found to be remarkably stable betweenyears, N fertilization regimes, cultivars, and for individualplants within a plot. Nitrogen concentration only varied withplant density. By contrast, the N concentration of noninoculatedplants was highly variable and generally lower than that ofinoculated plants, whatever the level of N supply. The highand stable N concentration of inoculated plants did not appearto be necessary for maximum growth rate but seemed to be requiredfor maximum production of seed dry matter and N. The potentialuse of these results to diagnose, in any white lupin crop, aninefficiency of the lupin-R. lupini interaction is evaluated.Copyright1993, 1999 Academic Press Lupinus albus L., white lupin, N₂ concentration, inoculated plants, non-inoculated plants, N₂ fixation efficiency, diagnosis     

Development of pepper (Capsicum annuum) seed quality

Changes in seed quality in pepper (Capsicum annuum L.) were monitored during seed development and maturation in two seasons. Seed quality was assessed by a number of different tests, but principally by determining seed storage longevity in laboratory tests and seedling growth in glasshouse tests. Mass maturity (defined as the end of the seed-filling phase) occurred 49–53 days after anthesis (DAA) in 1989 (varying among fruit layers) and 53 DAA in 1990 when seed moisture contents were 51–53%. The onset of both germinability and desiccation tolerance occurred either just before or at mass maturity. Maximum potential longevity (assessed by the value of the seed lot constant K_i) was achieved 63–65 DAA, i.e. not until 10–12 days after mass maturity (DAMM), in both years. Seedling dry weights in the glasshouse growth tests were maximal later still - for seeds harvested 17–21 DAMM in 1989 and 17 DAMM in 1990; the effects on seedling weight arose from differences in times from sowing to emergence (P < 0.005) among different seed harvests, with no significant differences in subsequent relative growth rates (P > 0.25). Seed priming reduced mean germination times for seeds harvested at all stages of development, but had little effect on germination capacity and potential longevity, and did not affect the pattern of changes in potential longevity during seed development and maturation. The results contradict the hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline immediately thereafter.     

Protein and free amino acids in field-grown cowpea seeds as affected by water stress at various growth stages

Summary This study was undertaken to evaluate water stress effects during vegetative, flowering, and podfilling stages of cowpea plants (Vigna unguiculata L.) grown under natural field conditions in southern California on seed yield and protein and free amino acid content of the cowpea seeds. The lowest concentration of N was found in the seeds of the control treatment plants while the seed yield from these treatments was the highest as compared with the N concentration and yield of seeds from plants subjected to water stress during flowering and podfilling stages. The concentration of N in the seeds was inversely related to the seed dry weight yield. Protein arginine,-threonine,-serine,-cystine,-valine,-methionine, and-isoleucine were significantly affected by water stress at the three growth stages. There was no consistent pattern in the effect of water stress on the individual amino acids. The sum of protein amino acids in the cowpea seeds was not significantly influenced by the various treatments since some of the protein amino acids increased and others decreased producing an averaging effect on the figures comprising the sums of the amino acids. Water stress during the flowering and pod-filling stages increased the free amino acid pool, and at the same time, inhibited incorporation of the amino acids into the protein chain-thus lowering the protein amino acid fraction simultaneously. With the exception of methionine plus cystine, the essential amino acids in the seeds were present at concentrations equal to or greater than recommended by the World Health Organization and FAO. It is of particular importance to note that the concentration of lysine in the cowpeas was substantially higher than that found in wheat grain. It is also important to note that the amount of essential amino acids per gram of protein was not measurably affected by the water stress treatments during any of the growth stages.     

盐磷胁迫对木麻黄和台湾相思种子萌发及幼苗生长的影响

恶劣环境下,人工海防林因面临养分胁迫而经营困难。为探讨盐、磷胁迫对主要海防林树种木麻黄和台湾相思种子萌发及生长的影响,该研究分别用不同浓度的NaCl(盐)和KH₂PO₄(磷)溶液处理种子和浇灌幼苗,测定种子萌发和幼苗生长指标。结果表明：(1)高盐胁迫显著抑制种子萌发,对幼苗生长有一定影响,但两种植物影响程度不同;台湾相思种子萌发耐盐性高于木麻黄,前者相对盐害率最大值为23.03%,后者为89.15%;随着盐浓度增加,木麻黄和台湾相思种子的发芽率、发芽势、发芽指数和活力指数均降低,对应最大值分别为38.70%、34.67%、18.70、0.055和76.67%、62.22%、48.46、6.11。(2)两种植物的株高和根长随盐浓度增加而降低,木麻黄和台湾相思株高分别为12.29～6.01 mm和48.27～17.33 mm,根长分别为8.57～1.45 mm和33.41～5.88 mm;台湾相思根、茎、叶生物量及根冠比均随盐浓度的增加逐渐减小,木麻黄各处理差异较小。(3)台湾相思的种子和幼苗较木麻黄更耐低磷环境,二者最适磷浓度存在差异;木麻黄种...