Developmental Changes in Relation to Desiccation Tolerance of Archontophoenix alexandrae (Palmae) Seeds

Germination of Archontophoenix alexandrae seeds and embryos were studied under gradient water content treatments throughout the seed development phases of maturation in 2005 to investigate seed desiccation tolerance and storage characteristics. During the maturation process, seed water content decreased gradually from55 DAF (days after flowering) to 70 DAF, and seeds reached the maximum dry-weight at 90 DAF. Seed germinability appeared after 60 DAF. Seeds germinated with a temperature range from15℃- 40℃ under alternating photoperiod (14 h light, 10 h dark, 12μmol m^{- 2}s ^{- 1} ), while the best germination percentage was obtained between 30℃- 35℃. A maximum germination capacity reached at 70 DAF. However, seed germination was greatly inhibited by light. Desiccation tolerance of seeds and embryos increasedgradually from 55 DAF to 90 DAF and reached the maximum at 90 DAF with a semilethal water content of 0.18 g/g ( seed) and 0.3 g/g ( embryo) respectively. Rapid dehydration maintained higher seed germination percentage than thatof slow dehydration when drying to the same water content. Seeds with without water content treatments failed to germinate after 1 month storage under - 18℃, whereas appropriate desiccation treatment prolonged seed longevity under 4℃, 10℃ and 15℃ storage temperatures. It revealed obviously the recalcitrant characteristics of Archontophoenix alexandrae seeds torage behaviour which are tolerant toward neither deep desiccation nor low temperatures.     

气象因子对油菜种子中油分积累的影响

选取2个甘蓝型油菜(Brassica napus)高油材料XZ37(含油量45.29%)和XZ366(含油量43.48%), 分别种植在南京、拉萨和西宁, 探讨种子发育过程中油分积累的差异, 并分析南京、拉萨和西宁3个地理生态环境下油菜花–角果期间的主要气象因子与种子油分之间的相关性及其对种子油分积累的影响。结果表明, 不同生态地区间种子中油分积累差异显著。在西宁种子油分快速积累始于开花后19天, 持续时长15天; 在南京种子油分快速积累始于开花后24天, 持续时长15天; 在拉萨种子油分快速积累始于开花后29天, 持续时间长达20天。研究显示, 日均温度、日均温差、日均降水量是影响甘蓝型油菜种子发育过程中油分积累的主要气候因子。不同地理生态地区, 影响油菜种子中油分积累的主要气候因子不同。日均温度是影响南京地区种子发育过程中油分积累的主要气候因子。该地区油菜开花后, 气温由低到高呈上升趋势, 成熟后期温度偏高, 不利于种子中油分积累。日均温差和日均降水量是影响拉萨和西宁两地种子油分积累的主要气候因子。两地种子发育过程中日均温差大, 种子中油分积累量大, 但由于拉萨日均降水量高于西宁, 日均温度偏低, 种子油分积累量低于西宁。因此, 在油菜种子发育过程中, 适宜的温度、较大的温差和较少的降水有利于种子积累油分, 并形成较高的含油量。     

Identification of differentially expressed genes in seeds of two near-isogenic Brassica napus lines with different oil content

The regulation of seed oil synthesis in rapeseed is largely unknown. In this study, we compared the gene expression during seed development between two lines of Brassica napus with a 10% difference in oil content. We isolated the immature seeds 15 and 25 days after flowering at periods preceding and including the major accumulation of storage oils and proteins. The differentially expressed gene clones between the two rape lines were isolated by subtractive suppression hybridization (SSH). All SSH clones were arrayed and screened by dot blot hybridization, followed by RT-PCR analysis for selected clones. A total of 217 cDNA clones corresponding to 30 genes were found to have a high expression in seeds with high oil content. Six genes were highly expressed in seeds with low oil content. Northern blot and enzyme activity analysis demonstrated a change in expression pattern of several genes. The results provide information on gene-encoding factors responsible for the regulation of oil synthesis. The possible role of these genes in seeds is discussed. The genes in this study may be suitable as novel targets for genetic improvement of seed oil content and may also provide molecular markers for studies of rape breeding.     

Genetic variation for lettuce seed thermoinhibition is associated with temperature-sensitive expression of abscisic Acid, gibberellin, and ethylene biosynthesis, metabolism, and response genes

Lettuce (Lactuca sativa ‘Salinas’) seeds fail to germinate when imbibed at temperatures above 25°C to 30°C (termed thermoinhibition). However, seeds of an accession of Lactuca serriola (UC96US23) do not exhibit thermoinhibition up to 37°C in the light. Comparative genetics, physiology, and gene expression were analyzed in these genotypes to determine the mechanisms governing the regulation of seed germination by temperature. Germination of the two genotypes was differentially sensitive to abscisic acid (ABA) and gibberellin (GA) at elevated temperatures. Quantitative trait loci associated with these phenotypes colocated with a major quantitative trait locus (Htg6.1) from UC96US23 conferring germination thermotolerance. ABA contents were elevated in Salinas seeds that exhibited thermoinhibition, consistent with the ability of fluridone (an ABA biosynthesis inhibitor) to improve germination at high temperatures. Expression of many genes involved in ABA, GA, and ethylene biosynthesis, metabolism, and response was differentially affected by high temperature and light in the two genotypes. In general, ABA-related genes were more highly expressed when germination was inhibited, and GA- and ethylene-related genes were more highly expressed when germination was permitted. In particular, LsNCED4, a gene encoding an enzyme in the ABA biosynthetic pathway, was up-regulated by high temperature only in Salinas seeds and also colocated with Htg6.1. The temperature sensitivity of expression of LsNCED4 may determine the upper temperature limit for lettuce seed germination and may indirectly influence other regulatory pathways via interconnected effects of increased ABA biosynthesis.     

Functional disruption of the pentatricopeptide protein SLG1 affects mitochondrial RNA editing, plant development, and responses to abiotic stresses in Arabidopsis

Seed oil content is an important agronomic trait in rapeseed. However, our understanding of the regulatory processes controlling oil accumulation is still limited. Using two rapeseed lines (zy036 and 51070) with contrasting oil content, we found that maternal genotype greatly affects seed oil content. Genetic and physiological evidence indicated that difference in the local and tissue-specific photosynthetic activity in the silique wall (a maternal tissue) was responsible for the different seed oil contents. This effect was mimicked by in planta manipulation of silique wall photosynthesis. Furthermore, the starch content and expression of the important lipid synthesis regulatory gene WRINKLED1 in developing seeds were linked with silique wall photosynthetic activity. 454 pyrosequencing was performed to explore the possible molecular mechanism for the difference in silique wall photosynthesis between zy036 and 51070. Interestingly, the results suggested that photosynthesis-related genes were over-represented in both total silique wall expressed genes and genes that were differentially expressed between genotypes. A potential regulatory mechanism for elevated photosynthesis in the zy036 silique wall is proposed on the basis of knowledge from Arabidopsis. Differentially expressed ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)-related genes were used for further investigations. Oil content correlated closely with BnRBCS1A expression levels and Rubisco activities in the silique wall, but not in the leaf. Taken together, our results highlight an important role of silique wall photosynthesis in the regulation of seed oil content in terms of maternal effects.     

Studies on the physiological effects of viruses on sweet potato yield in Kenya

Much of the economic value of soybean (Glycine max) is based on the amount of protein and oil produced in the seeds. To examine the influence of temperature on seed oil and protein concentration, immature soybean seeds (cv. Williams 82) were grown in vitro at temperatures of 17°C, 21°C, 25°C, 29°C and 33°C. Dry growth rate (DGR) was calculated to be maximal at 23.7°C. Oil and protein concentration and seed growth rate did not show statistical difference (P > 0.05) within the temperature range from 21–29°C. Across all temperatures, however, a quadratic regression on oil concentration (R2 = 0.66) showed a minimum at 24.1°C and a quadratic regression on protein concentration (R2 = 0.59) showed a minimum at 24.3°C. Dilution by increased dry matter accumulation in the seed accounted for much of the variation in oil and protein concentration and the two concentrations were equally affected across temperatures. Consequently, oil and protein concentrations were positively related over the tested range of temperature. It was concluded that under these conditions the rate of dry matter accumulation by soybean seeds was critical in influencing seed oil and protein concentrations.     

Arabidopsis sucrose synthase 2 and 3 modulate metabolic homeostasis and direct carbon towards starch synthesis in developing seeds

Two genes encoding sucrose synthase (SUS), namely SUS2 (At5g49190) and SUS3 (At4g02280), are strongly and differentially expressed in Arabidopsis seed. Detailed biochemical analysis was carried out in developing seeds 9–21 days after flowering (DAF) of wild type and two knockouts. SUS2 and SUS3 are not redundant genes since single knockouts show a phenotype in developing seeds. The mutants had 30–50% less SUS activity and therefore accumulated 40% more sucrose and 50% less fructose at 15 DAF. This did not affect the hexose-P pool, but led to 30–70% less starch in embryo and seed coat. Lipids were 55% higher in both mutants at 9–15 DAF. It seems that sucrolysis via SUS is not required for oil or protein synthesis but rather for channeling carbon toward ADP-glucose and starch in seeds. Metabolite profiling with GC–TOF revealed specific downstream changes in primary metabolism as a consequence of signaling or regulatory fine-tuning. While sucrose increased, hexoses and specific amino acids decreased reciprocally. There was a developmental shift regarding an earlier timing of dry weight accumulation, germinative maturity, oil deposition, sugar levels, transient starch buildup, and protein storage. Nevertheless, final seed size and composition were unaltered due to an earlier cessation of growth, thus giving rise to an apparent silent phenotype of mature mutant seeds. We conclude that SUS is important for metabolite homeostasis and timing of seed development, and propose that an altered sucrose/hexose ratio can modify carbon partitioning and the pattern of storage compounds in Arabidopsis.     

High-Oleate Oilseeds Fail to Develop at Low Temperature

The fad2 mutants of Arabidopsis thaliana are deficient in activity of the endoplasmic reticulum oleate desaturase that is the main enzyme responsible for polyunsaturated lipid synthesis in developing seeds of oil crops. A comparison of wild-type and fad2 seeds developing on heterozygous (FAD2/-) plants was used as a model for genetically engineered high-oleate oilseeds of species such as soybean and canola. When fad2 seeds developed at normal temperatures (22[deg]C), they showed high viability compared to wild-type seeds. When a portion of seed development took place at 6[deg]C, germination of the wild-type siblings remained high but germination of fad2 segregants declined considerably. This was true even when exposure to low temperature was limited to the final stages of seed filling and maturation. Compared to wild-type seeds, fully viable fad2 seeds produced at 22[deg]C had reduced lipid contents and were slower to germinate at 10 and 6[deg]C. Taken together, these results indicate that for some oilseed species at least, molecular genetic manipulation of oleate levels in the oil may result in plant lines with unacceptable performance in the field.     

Ecological genetics of seed germination regulation in Bromus tectorum L.

The probability that a seed will germinate depends on factors associated with genotype, maturation environment, post-maturation history, and germination environment. In this study, we examined the interaction among these sets of factors for 18 inbred lines from six populations of Bromus tectorum L., a winter annual grass that is an important weed in the semi-arid western United States. Seeds of this species are at least conditionally dormant at dispersal and become germinable through dry-afterripening under summer conditions. Populations and inbred lines of B. tectorum possess contrasting dormancy patterns. Seeds of each inbred line were produced in a greenhouse under one of three levels of maturation water stress, then subjected to immediate incubation under five incubation regimes or to dry storage at 20°C for 4 weeks, 12 weeks, or 1 year. Dry-stored seeds were subsequently placed in incubation at 20/30°C. Narrow-sense heritability estimates based on parent-offspring regressions for germination percentage of recently harvested seeds at each incubation temperature were high (0.518–0.993). Germination percentage increased with increasing water stress overall, but there were strong interactions with inbred line and incubation temperature. Inbred lines whose seeds were non-dormant over the full range of incubation temperatures when produced at low maturation water stress showed reaction norms characterized by little or no change as a function of increasing stress. For inbred lines whose dormancy status varied with incubation temperature, incubation treatments where seeds exhibited either very low or very high levels of dormancy showed the least change in response to maturation water stress. Inbred lines also varied in their pattern of dormancy loss during storage at 20°C, but maturation water stress had only a minor effect on this pattern. For fully afterripened seeds (1 year in storage at 20°C), inbred line and maturation water stress effects were no longer evident, indicating that differences in genotype and maturation environment function mainly to regulate dormancy and dormancy loss in B. tectorum, rather than to mediate response patterns of non-dormant seeds.     

Analysis of QTLs for erucic acid and oil content in seeds on A8 chromosome and the linkage drag between the alleles for the two traits in Brassica napus

The history of canola breeding began with the discovery of germplasm with low erucic acid content in seeds of spring forage cultivar in tbe 1950's.FAEI,mutations led to a dramatic decrease of the seed erucic acid content in Arabidopsis thaliana.The products of the two FAEI loci.BnA8.FAEI and BnC3.FAEI,showed additive effects to the level of erucic acid content in oilseed rape.Previous research believed that the pleiotropy of FAEI was responsible for the decrease in seed oil content along with the reduction of seed erucic acid content in the modern cultivars.TN DH population was developed from a canola cultivar Tapidor and a Chinese traditional cultivar Ningyou7.The population had been tested in 10 and 11 environments to map QTLs for the erucic acid content and oil content in seeds.As the map resolution increased,a novel QTL for seed erucic acid content was revealed,after Meta-analysis,7 cM away from the most significant seed erucic acid content QTL where BnA8.FAEI is located.Seven independent QTLs for seed oil content(qOC) were detected around the two seed erucic acid content QTLs(qEA)across 39.20 cM on linkage group A8.Two of the qOCs co-localized with the two qEAs,respectively,and were detected in a single environment.The otherfive qOCs were detected in 10 of ll environments independent of qEAs.Alleles from Tapidor in all the QTLs at the 0-39.20 cM region contributed negative effects to either erucic acid content or oil content in seeds.Parallel,genocontent source.Through rounds of crossbreeding with oil-cropped cultivars and intensive selection for multi generations,Tapidor still had the controlled by the five qEA-independent qOCs,with low seed erucic acid content.Ninety cultivars of B.napus from 8 countries were used to analyze the genetic drag with 9 molecular markers located in the QTL confidence intervals (24.04cM) on linkage group A8.It was noticed that more than 46% of the cultivars with low seed erucic acid content trait remained the genotype of low seed oil content at least in one locus.Backcross and marker-assisted selection could break the genetic drag between the low oil content and erucic acid in seeds in the process for breeding modern high seed oil content canola cultivars.     

Acyl-acyl carrier protein thioesterase activity from sunflower (Helianthus annuus L.) seeds

During sunflower (Helianthus annuus L.) seed formation there was an active period of lipid biosynthesis between 12 and 28 days after flowering (DAF). The maximum in-vitro acyl-acyl carrier protein (ACP) thioesterase activities (EC 3.1.2.14) were found at 15 DAF, preceding the largest accumulation of lipid in the seed. Data from the apparent kinetic parameters, V _max and K _m, from seeds of 15 and 30 DAF, showed that changes in acyl-ACP thioesterase activity are not only quantitative, but also qualitative, since, although the preferred substrate was always oleoyl-ACP, the affinity for palmitoyl-ACP decreased, whereas that for stearoyl-ACP increased with seed maturation. Bisubstrate assays carried out at 30 DAF seemed to indicate that the total activity found in mature seeds is due to a single enzyme with 100/75/15 affinity for oleoyl-ACP/stearoyl-ACP/palmitoyl-ACP. In contrast, at 15 DAF, enzymatic data together with partial sequences from cDNAs indicated the presence of at least two enzymes with different properties, a FatA-like thioesterase, with a high affinity for oleoyl-ACP, plus a FatB-like enzyme, with preference for long-chain saturated fatty acids, both being expressed during the active lipid biosynthesis period. Competition assays carried out with CAS-5, a mutant with a higher content of palmitic acid in the seed oil, indicated that a modified FatA-type thioesterase is involved in the mutant phenotype. Received: 17 December 1999 / Accepted: 25 February 2000     

粳稻孕穗期耐冷性NILs的形态评价和分子验证

2004年在海拔1916m昆明两种冷害（水温19.5±0.7℃,低田温冷泉水温17.8±1.1℃)、阿子营冷害(海拔2150m,水温18.2±0.22℃)条件下对5个亲本及其25个近等基因系进行耐冷性鉴定,用Statistica对17个农艺性状进行形态聚类和SSR分子标记聚类分析。结果表明：(1)已培育的穗期耐冷性NILs与轮回亲本十和田的形态极为相似,但与耐冷性相关的性状(穗颈长、实粒数、结实率、花药长和花药体积)有明显的差异;(2)从78个SSR标记筛选出了7个标记在十和田和NILs间存在多态性, 其中RM7452标记与耐冷基因连锁,各个近等基因系间遗传背景相似,但与十和田耐冷性差异大,证明了这些NILs是水稻穗期耐冷基因精细定位和克隆的理想材料。