穇属颖果微形态及其系统学意义

在电子扫描显微镜下观察了穆属(Eleusine Gaertn.)9种植物颖果的微形态特征.结果表明,穆属颖果有卵形、披针形和矩圆形3种腹面形状,压扁方式有背腹压扁及两侧压扁,腹面形态有平腹面和凹腹面两种,胚比为0.29～0.58,种脐比为0.10～0.24,颖果纹饰有2种,包括疣突状一级纹饰和疣突规则排列构成的复合网状...     

Rice caryopsis structure in relation to distribution of micronutrients (iron, zinc, β-carotene) of rice cultivars including transgenic indica rice

The transgenic indica rice lines of IR68144 and BR29, developed using endosperm-specific promoters were analyzed for their iron, zinc and β-carotene content in the endosperm. Biochemical analysis clearly revealed the presence of higher accumulation of iron, zinc and β-carotene in transgenic rice grains in comparison with control. Prussian blue staining reaction evidenced the presence of iron in the endosperm cells of transgenic rice grains in comparison with control where iron is restricted only to aleurone and embryo. The rice grain structure of IR64, IR72, IR68144, Swarna, BRRI Dhan 29 (BR29), BR28, Taipai 309 (T309) and New Plant Type-3 (NPT3) indicated that the number of aleurone layers, size of the embryo and size of the caryopsis determines the quantity of important micronutrients (iron, zinc) in the grains. Biochemical analysis revealed that iron and zinc content drastically varies in polished and unpolished rice and among the varieties examined. During the polishing process almost entire aleurone and most part of the embryo is removed which are the main storehouse for major micronutrients. It is estimated that more than 70% of micronutrients are lost during polishing process.     

燕麦属颖果微形态特征及其分类学意义

为探讨燕麦属颖果微形态特征的分类学意义,采用体视显微镜和扫描电子显微镜观察燕麦属27种颖果的微形态特征,结合分子系统发育证据分析其分类学意义。燕麦属颖果有纺锤形、倒披针形、椭圆形3种形状,条纹、棱纹、网纹3种纹饰。燕麦属颖果形状、纹饰和花柱基宿存模式具有有限的属下分类学意义,颖果大小和表面大毛密度具有种间鉴定价值,而颖果腹面形态、压扁方式、胚比不具有种间鉴定价值。大穗燕麦(Avena macrostachya Balansa ex Coss.Durieu)颖果纺锤形,条纹纹饰,隶属于燕麦属颖果微形态特征的变异范围。大粒裸燕麦(A.nuda L.)与普通栽培燕麦(A.sativa L.)颖果大小、形状及纹饰特征的差异支持将大粒裸燕麦作为独立种处理。燕麦属颖果大小、表面大毛密度、胚比变异幅度大,推测与分布区广幅的气候变异相适应,凹腹面颖果体积相对缩减,有利于颖果快速发育、成熟,推测与燕麦属植物在温带、寒带分布区适生期较短相适应。     

Spatial and temporal profiles of cytokinin biosynthesis and accumulation in developing caryopses of maize

Background and Aims

Cytokinins are a major group of plant hormones and are associated with various developmental processes. Developing caryopses of maize have high levels of cytokinins, but little is known about their spatial and temporal distribution. The localization and quantification of cytokinins was investigated in maize (Zea mays) caryopsis from 0 to 28 d after pollination together with the expression and localization of isopentenyltransferase ZmIPT1 involved in cytokinin biosynthesis and ZmCNGT, the gene putatively involved in N9-glucosylation.

Methods

Biochemical, cellular and molecular approaches resolved the overall cytokinin profiles, and several gene expression assays were used for two critical genes to assess cytokinin cell-specific biosynthesis and conversion to the biologically inactive form. Cytokinins were immunolocalized for the first time in maize caryopses.

Key Results

During the period 0–28 d after pollination (DAP): (1) large quantities of cytokinins were detected in the maternal pedicel region relative to the filial tissues during the early stages after fertilization; (2) unpollinated ovules did not accumulate cytokinins; (3) the maternal nucellar region showed little or no cytokinin signal; (4) the highest cytokinin concentrations in filial endosperm and embryo were detected at 12 DAP, predominantly zeatin riboside and zeatin-9-glucoside, respectively; and (5) a strong cytokinin immuno-signal was detected in specific cell types in the pedicel, endosperm and embryo.

Conclusions

The cytokinins of developing maize caryopsis may originate from both local syntheses as well as by transport. High levels of fertilization-dependent cytokinins in the pedicel suggest filial control on metabolism in the maternal tissue; they may also trigger developmental programmed cell death in the pedicel.     

Water uptake and splitting of wild oat caryopsis

Imbibition and germination experiments were conducted on the caryopses of wild oats (Avena fatua L.). The embryo envelopes, pericarp and aleurone layer, which completely cover the embryo-endosperm, do not form barriers against water uptake. The initial uptake of water is passive and the water moves across the pericarp with ease as it contains cracks; it is, however, transported across the aleurone layer through its cell walls into the endosperm and embryo of the caryopsis. The starchy endosperm enlarges due to water uptake causing the pericarp to rupture, thus exposing the aleuronelayer-covered seed. The aleurone layer is structurally heterogenous consistings of radially compressed irregular cells and cuboidal or radiallys tretched cells; the latter contains thicker walls. The former type is present along the abaxial side of the embryo and in the crease on the adaxial side of the caryopsis; the latter type covers the endosperm. The physical distention of the endosperm due to water uptake causes the rupture of the pericarp and the aleurone layer, and facilitates the emergence of the radicle and coleorhiza of the embryo during caryopsis germination.     

Characterization of the caryopsis of common wheat varieties and F2 generation hybrids by means of multivariate analysis

Summary Nineteen parameters of common wheat kernels were investigated by the multivariate procedure. A relationship between the DBC parameter and both specific gravity and kernel filling was found. In some populations an interdependence of the DBC parameter and the subaleurone endosperm thickness was found. In the analysis of principal components the DBC parameter was represented mostly by particular component. Significant dependences were found between the dimensions as well as the weight of the caryopsis and some dimensions of the crease and endosperm cavity. The dendrite constructed on the basis of the calculated Mahalanobis's generalized distances matrix represents the near affinity of reciprocal hybrids or pure lines originating from a single cultivar as well as hybrids and their parental forms.     

Cultivar differences in soluble sugar content of mature rice grain

Mature grain from 31 rice ( Oryza sativa L.) cultivars grown in the same location was analyzed for soluble sugar content to determine quantitative differences in this parameter. Cultivar variation in caryopsis sucrose content was 4-fold ranging from 15 to 59 μmol sucrose (g fresh weight)⁻¹. Soluble reducing sugar ranged from 7 to 15 μmol hexose (g fresh weight)⁻¹. Soluble sugar content was much greater in the outer part of the grain than in the endosperm. Caryopsis enzyme activities were measured in 8 cultivars having a range of grain sucrose content. No relationship between grain sucrose content of these cultivars and the level of enzymes of sucrose metabolism, glycolysis, and oxidative pentose pathway was established. Caryopsis respiration after 1 h of imbibition also was not related to the amount of soluble sugars available in the grain among these 8 cultivars. The results show that there are significant differences in the sugar-accumulating capacity of the caryopsis of different rice cultivars. The detection of a fructose 2,6-bisphosphate-sensitive, PP_i: fructose 6-phosphate phosphototransferase (EC 2.7.1.90) in the endosperm suggests the presence of a regulatory mechanism for sucrose/starch partitioning established in other plant tissues.     

Genotypic effects of the maternal tissues of wheat on its grain weight

Summary Reciprocal crosses were made between semi dwarf spring wheat cultivars (Triticum aestivum L.) differing in grain weight. The weights of the F₁ grains (on maternal spikes), from intact as well as from defoliated plants, and those of the F₂ grains (on f₁ spikes), were examined. Grain weight was controlled primarily by the genotype of the maternal tissues (pericarp, testa or other floret or spikelet organs, including the vascular system), with complete dominance of heaviness. No indications suggesting maternal inheritance were obtained. The frequency distribution of the weights of the F₂ grains indicated the presence of genotypic effects exerted by the endosperm or embryo. The embryo or endosperm factors for heaviness also seemed to be dominant.This study is based on data obtained by the senior author in his Ph. D. research at The Hebrew University of Jerusalem. The research was financed in part by The Fund for the Encouragement of Research — Histadrut — The General Federation of Labor in Israel. Contribution from the Agricultural Research Organization, Bet Dagan, Israel. No. 173-E, 1980 series