The effects of cis-trans ABA on embryo germination and seed dormancy in wheat

Pre-harvest sprouting of wheat grain can cause economic losses especially in cultivars with low levels of seed dormancy. The aim of this study was to determine genotype differences in embryo sensitivity to germination in response to exogenous (+/–) cis-trans ABA treatments at different concentrations. Six white and four red seed-colored bread wheat genotypes that differed in dormancy were grown in a field near Swift Current, Saskatchewan in 2000 as a randomized complete block design with four replicates. The seed samples from this experiment were germinated in a controlled environment at 20 °C without light. The exogenous ABA treatments were 0 μM – whole seed (control), 0 μM-embryos, 25 μM – embryos and 50 μM – embryos. The ABA experiment was a factorial design with four randomized complete blocks with four ABA treatments in all combinations with the ten genotypes. A weighted (by day) germination index (WGI) was calculated for each genotype in each ABA treatment. Genotypes differed in response to ABA. The genotypes, ABA concentration and genotype by ABA concentration interaction effects were significant (p ≤ 0.05). Excised embryos showed significantly decreased dormancy in most of the experimental genotypes. The addition of exogenous ABA enhanced embryo dormancy of most genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of exogenous abscisic acid and gibberellic acid on pre-maturity α-amylase formation in wheat grains

Effects of in situ and in vitro applied abscisic acid (ABA) and gibberellic acid (GA₃) on pre-maturity ??-amylase (PMA) were investigated in glasshouse experiments under cool-temperature shock-induced and non-induced conditions using UK winter wheat varieties, Spark (low PMA susceptible) and Rialto (high PMA susceptible). In the in situ study, hormone solutions (ABA [100???M], GA₃ [50???M] and ABA?+?GA₃ [100?+?50???M]) were applied during mid-grain development to intact, developing grains of induced and non-induced plants. Alpha-amylase activity was measured in embryoless half-grains at maturity by a modified Phadebas assay. In the in situ study under non-induced conditions, applied ABA had no significant effect on ??-amylase in either variety whereas applied GA₃ significantly increased ??-amylase in Rialto, but not in Spark. In the in situ study under induced conditions, applied ABA and GA₃ produced no significant effect on ??-amylase in Spark; however in Rialto, applied ABA produced a small but significant decrease in ??-amylase whereas GA₃ significantly increased ??-amylase under induced conditions. In the in vitro study, spikes were harvested from induced/non-induced plants at 44/40?days after anthesis. Embryoless half-grains were incubated in hormone solutions at 25?°C and ??-amylase activity was measured. Results similar to the in situ study were observed in the in vitro study for both varieties and conditions, except GA₃ treatment which significantly increased ??-amylase under non-induced conditions in Spark. From these exogenous hormone studies, it appears that GA-response is a major factor during PMA induction by a cool-temperature shock whereas ABA-response seems to be of less importance.     

Drought and high temperature increases preharvest sprouting tolerance in a genotype without grain dormancy

Preharvest sprouting is common in cereals, which lack grain dormancy when maturing grain is exposed to rainfall or high moisture conditions. Environmental conditions such as drought and high temperature during grain filling have a large effect on the expression of sprouting tolerance. A dormant (DM 2001) and non-dormant (Cunderdin) hard white spring wheat were exposed to drought or irrigated conditions and either low or high temperature during grain filling. Dormancy and embryo sensitivity to ABA were analysed throughout grain filling. The conclusions from this investigation were as follows; firstly DM 2001 was more dormant than Cunderdin, with a four-fold lower germination index (GI) at maturity. Secondly during grain ripening drought increased dormancy and overrides any increase in dormancy with low temperature. Finally embryo sensitivity can be induced in a non-dormant genotype to the extent where the non-dormant genotype in a hot dry environment can have the same phenotype as a dormant genotype grown in a cool wet environment. In summary drought during grain filling increases dormancy suggesting breeders need to avoid drought when screening for sprouting tolerance in order to maximise the chances of identifying genetic differences in grain dormancy and avoid any maturity by drought interactions.     

Chromosomes responsible for sensitivity of embryo to abscisic acid and dormancy in wheat

The sensitivity of the embryo to abscisic acid (ABA) has been reported toplay an important role in seed dormancy. Using ditelocentric lines of wheatcv. Chinese Spring (CS, nondormant and ABA insensitive), F₂ seedsbetween monosomic lines of CS and a wheat line Kitakei-1354 (dormant,ABA sensitive) and deletion lines of CS chromosome 4A, germinability ofseeds and embryo-half seeds incubated in water and ABA were examined. The results indicated that the long arm of chromosome 4A carried majorgene(s) for the embryo sensitivity to ABA and dormancy. Chromosome2D might be also involved in the sensitivity to ABA.     

Regulation of high pI α-amylase synthesis in wheat aleurone by a gene(s) located on chromosome 6B

Synthesis of high and low pI α-amylase in germinating wheat grains and GA₃-treated de-embryonated grains of Chinese Spring (CS) and its ditelosomic derivative (CS dit 6BS) were compared and related to high pI α-amylase production in grains affected by late maturity α-amylase (LMA). In de-embryonated grains of CS dit 6BS (lacking the long arm of chromosome 6B) treated with GA₃, synthesis of high pI α-amylase isozymes controlled by Amy-1 genes on chromosomes 6A and 6D was dramatically reduced compared to Chinese Spring. The results suggest the presence of a gene(s) on the long arm of chromosome 6B, which is (are) required for GA-induced α-amylase synthesis in the aleurone. Similarly, in wheat grains affected by LMA, high pI α- Amy genes on the group 6 chromosomes are activated apparently by a single gene, tentatively located on chromosome 6B. Both genes may be part of the GA-induced amylase synthesis pathway in the aleurone. By contrast, synthesis of the high pI α-amylase isozymes in the early stages of germination of CS dit 6BS grains was very similar to CS. This contrast between GA₃-treated de-embryonated grains and germinating grains could be explained by control of α-amylase synthesis in scutellum in the early stages of germination being different to that in GA₃-treated aleurone. This revised version was published online in August 2006 with corrections to the Cover Date.     

外源一氧化氮供体硝普钠对小麦种子萌发早期β-淀粉酶及其亚细胞分布的影响

采用药理学和生物化学实验技术, 研究了外源一氧化氮(nitric oxide, NO)供体硝普钠(sodium nitroprusside, SNP)处理对小麦种子萌发早期β-淀粉酶及其亚细胞分布的影响。β-淀粉酶的专一性抑制剂α-环糊精可以明显抑制0.5 mmol L^-1 SNP诱导的小麦种子萌发, SNP还能诱导自由型β-淀粉酶酶活性, 上调β-淀粉酶基因转录本的水平。Western blotting结果发现, SNP处理可以增加β-淀粉酶蛋白的表达; 运用NO专一性清除剂cPTIO及转录抑制剂放线菌素D可以逆转上述转录本和蛋白水平的变化。免疫电镜亚细胞定位证实小麦胚内的β-淀粉酶主要定位于蛋白储藏体内, 并可能附着在淀粉粒上, SNP处理增加了β-淀粉酶蛋白的分布。推测外源NO供体SNP在小麦种子萌发早期不仅提高了自由型β-淀粉酶的活性, 还可能诱导了β-淀粉酶的重新合成。     

Characterization of preharvest sprouting resistance in Clark's Cream white winter wheat

Summary Resistance to preharvest sprouting has been observed in several white wheat (Triticum aestivum L.) genotypes, but the mode of resistance has not been determined. Studies were conducted to characterize the strong preharvest sprouting resistance in Clark's Cream genotype to facilitate breeding for the trait. Clark's Cream and five other hard red and white wheat genotypes were grown in the glasshouse and field and effects of simulated rain, embryo maturity, inhibitors in floral parts and GA, endogenous inhibitors, and ABA and GA combinations on sprouting were measured. The six genotypes differed significantly in sprouting after simulated rain, -amylase activity, and response to GA and ABA. Embryo maturity and inhibition levels in floral parts and caryopses were nearly similar for all genotypes. Clark's Cream appeared to differ most in high embryo sensitivity, which was fairly nonspecific for ABA, GA, and endogenous inhibitor, and in low -amylase production during sprouting. Breeding procedures that lead to the preharvest sprouting resistance of Clark's Cream are discussed.     

Characterization of a green non‐dormant sunflower (Helianthus annuus) mutant NDG

A sunflower (Helianthus annuus L.) mutant was observed in the progeny of a cross between the sunflower cultivar ‘HA 89’ and an amphiploid of a Helianthus divaricatus L. × P21 cross that exhibited loss of dormancy induction in the developing embryo. Seeds of this mutant frequently germinate on the head about 40 days after pollination. The cotyledons of this mutant remain green, whereas some other non‐dormant mutants exhibit loss of pigmentation. The objectives of this investigation were to compare levels and activities of abscisic acid (ABA), a plant hormone that induces dormancy in developing embryos, in the non‐dormant green mutant (NDG) and ‘HA 89’ from which NDG was derived. Immunoassays showed that abscisic acid was present in NDG and the levels were not significantly different from those in ‘HA 89’. Exposure of excised NDG mutant embryos to 40 μm abscisic acid failed to prevent germination, suggesting that non‐dormancy could result from impairment in ABA receptors or from a defect in other proteins participating in the subsequent signalling pathway that normally induces dormancy.     

Abscisic acid response to water status in Dactylis glomerata differs with expression of summer dormancy

Summer dormancy confers superior drought survival in cool-season perennial grasses and is likely to be of increasing importance as climate change proceeds although relatively little is known about this trait. This paper explores the relationship between the level of abscisic acid (ABA), the expression of summer dormancy and the onset and relief of water deficit in cool-season perennial grasses. Three cultivars of Dactylis glomerata L. (cocksfoot) known to differ in expression of summer dormancy were grown in the field over summer and in the glasshouse over winter under water deficit or full irrigation. Hydration and osmotic potentials of basal tissues were measured to assess the level of water deficit, and endogenous ABA was determined in the tissues by monoclonal immunoassay analysis. In a winter trial, higher contents of ABA were present when plant water deficits became greater so that there were no differences between the cultivars in the concentrations of ABA observed. In a summer trial a short period of waterlogging caused water status to increase in all cultivars, although in the maritime cultivar Oasis this was also associated with a rise in ABA contents. In contrast, in the summer-dormant cultivar Kasbah, only low ABA concentrations were observed throughout the entire period whether waterlogged or in drying soil. Heightened ABA levels are not induced by water deficit when summer dormancy is expressed in Dactylis glomerata. This contrasted with those cultivars unable to express summer dormancy where particularly in early summer severe water deficit was associated with heightened ABA levels.     

假色槭种子透水性及内源抑制物质的初步研究

为研究假色槭种子透水性及种子不同部位甲醇浸提液生物活性,初步探讨假色槭种子休眠原因,比较了假色槭完整种子和剪裂种皮种子的吸水率,测定了种子各部位浸提液对小麦种子萌发及幼苗生长的抑制强度。结果表明,种皮透水性良好,对假色槭种子休眠影响较小。假色槭种子的果皮、种皮、胚浸提液处理后,对小麦种子发芽率影响较小,但却严重影响了小麦苗高、苗鲜重、根长、根鲜重的生长,降低了叶绿素含量、淀粉酶活性,抑制了小麦种子对自身淀粉和可溶性糖的吸收利用,而且随着各部位浸提液浓度比例的不断提升,其抑制活性也表现得愈加强烈。在各部位浸提液浓度比例相同的情况下,胚浸提液对小麦种子发芽率、苗高、苗鲜重、根长、根鲜重的生长以及各项生理指标的抑制影响强于种皮和果皮。说明假色槭种子果皮透水性不是其休眠的主要原因,种子各部位存在发芽抑制成分,尤其是胚的抑制活性最强可能是其休眠期较长、不易发芽的主要原因。     

不同Wx蛋白缺失类型小麦穗发芽特性的初步研究

以11份Wx蛋白全部缺失类型（糯性），11份Wx蛋白部分缺失类型（非糯性）和大面积推广品种扬麦158、扬麦12（非糯性）为试验材料，以白皮品种豫麦47为穗发芽对照，研究了它们的穗发芽特性、α-淀粉酶活性和籽粒可溶性糖含量。结果表明，糯小麦的穗发芽率和籽粒可溶性糖含量均极显著高于非糯小麦，而α-淀粉酶活性与非糯小麦差异不显著。α-淀粉酶活性高是非糯小麦穗发芽的原因之一，两者呈指数关系，y=0.4145e^0.4864x(R²=0.3513*)；对于糯小麦，籽粒可溶性糖含量高可能是其穗发芽严重的诱导因素，两者亦呈指数关系，y=0.0001e^2.5599x(R²=0.5338**)。     

Screening methods and identification of QTLs associated with late maturity α-amylase in wheat

The synthesis of high levels of germination-type (high pI isozymes) α-amylase was induced in wheat genotypes prone to late maturityα-amylase (LMA) following the exposure of detached tillers to cool temperature during grain development. The detached tiller method was successfully applied to a range of genotypes and to a doubled haploid (DH) population derived from the cross Cranbrook (LMA genotype) × Halberd (low amylase). The number of grains in ripe, treated tillers that contained high pI α-amylase isozymes was measured using an ELISA antibody kit highly specific for high pI isozymes. Quantitative trait loci (QTL) controlling the expression of LMA in wheat were detected in DH population Cranbrook × Halberd. The DH population and parents were sown in 2 replicated sowings at the same location with sowing times differing by 2 weeks. QTL analyses were conducted separately for each sowing, but results from both sowings were consistent and indicated a highly significant (it p > 0.01) QTL on the long arm of chromosome7B, with Cranbrook contributing the higher value allele. A second QTL with less significant effect was found on the long arm of chromosome 3B, on the basis of data from the first sowing. This revised version was published online in August 2006 with corrections to the Cover Date.     

水稻穗上发芽生理生化及颖壳扫描电镜观察

对易萌和不易萌水稻（Oryza sativa ssp.japonica）品种进行扫描电镜观察、穗上发芽1~4d水稻的α-淀粉酶活性和内源激素含量测定。结果表明：易萌品种穗上发芽过程中α-淀粉酶活性较高;IAA、GA1+3、ZR含量也高于不易萌的品种;而ABA含量低于不易萌品种。GA1+3/ABA比值含量的变化与GA1+3含量变化基本一致。扫描电镜观察显示：易萌品种水稻颖壳外表面细胞排列疏松,茸毛较多且孔洞大,萌发孔也大,体现其机械阻力小,易吸水。说明水稻穗上发芽与α-淀粉酶活性,内源激素含量及颖壳结构有关。     

Wheat ABA-insensitive mutants result in reduced grain dormancy

This paper describes the isolation of wheat mutants in the hard red spring Scarlet resulting in reduced sensitivity to the plant hormone abscisic acid (ABA) during seed germination. ABA induces seed dormancy during embryo maturation and inhibits the germination of mature seeds. Wheat sensitivity to ABA gradually decreases with dry after-ripening. Scarlet grain normally fails to germinate when fully dormant, shows ABA sensitive germination when partially after-ripened, and becomes ABA insensitive when after-ripened for 8?C12?months. Scarlet ABA-insensitive (ScABI) mutants were isolated based on the ability to germinate on 5???M ABA after only 3?weeks of after-ripening, a condition under which Scarlet would fail to germinate. Six independent seed-specific mutants were recovered. ScABI1, ScABI2, ScABI3 and ScABI4 are able to germinate more efficiently than Scarlet at up to 25???M ABA. The two strongest ABA insensitive lines, ScABI3 and ScABI4, both proved to be partly dominant suggesting that they result from gain-of-function mutations. The ScABI1, ScABI2, ScABI3, ScABI4, and ScABI5 mutants after-ripen more rapidly than Scarlet. Thus, ABA insensitivity is associated with decreased grain dormancy in Scarlet wheat. This suggests that ABA sensitivity is an important factor controlling grain dormancy in wheat, a trait that impacts seedling emergence and pre-harvest sprouting resistance.     

Effects of desiccation and a change in temperature on germination of immature grains of wheat (Triticum aestivum L.)

A study was made of the effects of desiccation and a change in temperature on the germination of wheat grains harvested 20 days after anthesis. When the germination test was performed immediately after harvesting, germination percentages ranged from 5.2% to 10.7%. Germination percentages increased to 48.2% to 90.3% after grain had been desiccated at 20 °C and then hydrated at 10 °C. This increase occurred even if grains had been desiccated in an atmosphere of high relative humidity. The germination percentage of non-desiccated grains depended on the germination temperature. When the pericarp and testa were removed from embryos, the germination percentage of grains incubated at 20 °C and then at 10 °C was higher than that of grains incubated at 10 °C. In general, a low germination temperature is believed to be effective in breaking dormancy of wheat grains. However, a change in temperature stimulated germination to a greater extent than a constant low temperature. The germination percentage of 5-day cycle alternating temperature was greater than that with 1-day, 2-day and 10-day cycles. Although the germination of immature wheat grains was stimulated by both high and low germination temperatures, it is likely that cycles shorter and, also, longer than a critical period induce limited germination. Loss of dormancy commonly occurs when development of wheat grains proceeds at a high temperature, with imbibition at a low temperature. However, germination ability of non-desiccated immature wheat grain was enhanced by a change in temperature during germination. This revised version was published online in August 2006 with corrections to the Cover Date.     

滇重楼种子休眠机理研究

探讨滇重楼种子休眠机理,为打破种子休眠促进滇重楼实生育苗提供理论基础。采用重量法、胚率测定、ELISA等方法对种子吸水特性、萌发抑制物及种胚休眠与发育的内源机理进行了研究。结果表明,滇重楼种子休眠属于形态学-生理学休眠类型。滇重楼种胚发育不完全、种子中存在萌发抑制物质是种子休眠的主要原因。种子不存在吸水障碍,与休眠无关。内源激素ABA和GA3在滇重楼种子休眠与萌发过程中起着重要作用,ABA是引起休眠的关键因素,ABA含量的降低是滇重楼种胚发育的始动因子,GA3有助于种子的生理后熟。萌发抑制物的存在可能抑制了种胚发育,而与生理学后熟过程无关。在自然条件下,滇重楼生境中较长的低温时期可能是滇重楼种子具有较长时间休眠的外界原因。     

Mapping a diploid wheat abscisic acid 8′-hydroxylase homologue in the seed dormancy QTL region on chromosome 5A<Superscript>m</Superscript>

In Arabidopsis, two genes of abscisic acid (ABA) 8′-hydroxylase (cytochrome P450 (CYP) 707A1 and A2) have been found to play important roles in seed dormancy through the regulation of ABA content in seeds. In order to examine the role of wheat ABA 8′-hydroxylase gene in seed dormancy, a diploid wheat ABA 8′-hydroxylase gene was cloned that showed high similarity to a barley ABA8′-hydroxylase gene (HvABA8′OH-2), and the cloned gene was designated as TmABA8′OH-2. Using recombinant inbred lines derived from a cross between diploid wheat Triticum boeoticum L. (Tb) and Triticum monococcum L. (Tm), TmABA8′OH-2 has been mapped to near the centromeric region of the long arm of chromosome 5A^m, where the major seed dormancy QTL has been previously found. Comparison of the deduced amino acid sequences of TmABA8′OH-2 between Tb and Tm revealed five amino acid residue substitutions. These amino acid residues have distinctly different characteristics, and one of the substitutions occurs in the highly conserved amino acid residues in CYP707A family, indicating that these substitutions may have effects on the enzyme activities. Moreover, hexaploid wheat TmABA8′OH-2 homologue revealed that the level of its expression during seed development peaks at mid-maturation stage. This resembles the expression pattern of the Arabidopsis CYP707A1, which was shown to control seed dormancy. These results imply a possibility that TmABA8′OH-2 might be involved in seed dormancy, and associated with the QTL on chromosome 5A^m.     

Response of maize inbred lines to a defoliation treatment inducing tolerance to cold at germination

Defoliation during maize (Zea mays L.) kernel development has been observed to induce tolerance to cold of germinating seeds in responsive genotypes. The objectives of this study were to evaluate the response to defoliation of immature embryo and mature seed germinability at cold and to verify if the response was influenced by the developmental stage at which the treatment was applied. In three environments, six inbred lines (B73, IABO78, Lo1016, Lo964, Mo17, Os420) were defoliated (D) approximately 20 days after pollination (DAP) or not defoliated (ND). Immature embryos were excised three days after defoliation and germinated in vitro at 9 or 25 ^∘C. At maturation, kernel germination was tested at the same temperatures. Defoliation improved cold tolerance and mean time to germination (MTG) at 9 ^∘C of both embryos and kernels of Lo1016. To study the effect of kernel developmental stage on response to defoliation, plants of B73, Lo1016 and Lo964 were defoliated at 15, 18, 21, 24, 27, 30, 33, 36, and 39 DAP, or not defoliated. At the same DAP, immature grains were analyzed for dry weight, water and abscisic acid (ABA) content. In Lo1016, low amounts of kernel ABA were detected at all stages, while in Lo964 and B73 ABA increased during development. Lo1016 mature kernels showed an improvement of cold tolerance due to defoliation at all times, while the other genotypes did not. In conclusion inbred lines showed variability for mature seed and immature embryo tolerance to cold at germination and for the ability to acquire tolerance after defoliation.     

Profiles of Trinexapac-ethyl- and ABA-induced heat-stable proteins in embryonic axes of wheat seeds

Treatment of plants with abscisic acid (ABA) can enhance resistance to environmental stresses in general and to preharvest sprouting in particular. Inhibitors of gibberellin (GA) synthesis have been reported to enhance the metabolic activity or effectiveness of ABA. Wheat seeds(Triticum aestivum L., cv. Bet Hashita) were soaked for 2 h in100 μm ABA, in 1250 ppm trinexapac-ethyl (TE, anacylcyclohexanedione-based GA synthesis inhibitor), or in a combination of the two. After drying, seeds were imbibed 24 h in water and the protein in heat-stable extracts from embryos was examined. Treatment with ABA alone increased expression of dehydrin and of a 37 kDa protein. Treatment with TE more than doubled protein concentration in the embryo and enhanced expression of dehydrin and of proteins weighing 37, 20, and15 kDa. Combined treatments of TE and ABA led to enhanced expression of dehydrin and of a 15 kDa protein. This revised version was published online in August 2006 with corrections to the Cover Date.     

脱落酸(ABA)生物学作用研究进展

脱落酸(ABA)是目前公认的五大植物激素之一,本文主要综述了ABA在植物生长发育、非生物胁迫和生物胁迫中的多重作用,如在植物生长发育中ABA促进器官脱落、种子成熟和休眠,调节气孔,抑制种子萌发、生长和加速衰老,调节种子胚的发育及开花;在非生物胁迫中ABA可以促进植物对非生物胁迫的耐性,因此,ABA也称为应激激素或胁迫激素;在生物胁迫中ABA随着病原菌种类和入侵方式的不同起正调控或者负调控的作用。最后笔者对ABA在生物胁迫中的作用进行了展望,如其参与植物防御的动力学研究、作用方式及与其它激素信号的互作等有待进一步研究。