Changes in Nuclear DNA Content of Endosperm Cells During Grain Development in Rice (Oryza sativa)

Morphological, cytological and quantitative DNA changes associatedwith endosperm development in rice caryopsis were investigated.Following a brief free-nuclear phase, the endosperm became cellularby the 4th d after anthesis. While the mean length and breadthof grain attained maximum values at about 10, d after anthesis,f. wt of the whole grain, and of the endosperm separately, continuedto increase until about 16 d after anthesis. Cell divisionsin the endosperm continued until 10 d and following stabilizationof the cell number, the nuclei attained irregular shapes. Thesize of the nuclei and nuclei and the amount of nuclear DNAvaried considerably during endosperm development. The endospermnuclei did not retain the expected 3C–6C DNA level afterthe first few rounds of division and nuclei having more than30C DNA were frequent 8 d past anthesis. The highest C valuerecorded was 74C in a 16-d-old endosperm cell. Oryza sativa, rice, caryopsis, endosperm, cell number, nuclear area, nuclear DNA content, endoreduplication     

Changes in Cytokinin Activity during Seed Germination in Rice (Oryza sativa L.)

Cytokinin activity was determined in dry mature rice seeds,in endosperm and embryo tissues 24, 48 and 72 over imbibitionand in radicles 96 h after germination. Cytokinins with chromatographicproperties similar to zeatin, zeatin riboside, zeatin glucosideand zeatin riboside glucoside were datected in embryo and endosperm,but only the latter two were detected in mature seeds. Cytokininactivity was low during early toges of germination. Qualitativeand quantitative changes in cytokinins were observed in bothembryo and endosperm. The presence of higher cytokinin activityin the endosperm than in the embryo during the first 24 h aftergermination suggests that the endosperm may supply cytokininsuntil the embryo is able to synthaize its own cytokinins. Thepossible significance of high cytokinin glucoside activity inthe embryo early during germination and high cytokinin activityin the radicle during the later stages is discussed. Oryza sativa L., rice, cytokinin, germination, seed     

Activity and Distribution of Methane-Oxidizing Bacteria in Flooded Rice Soil Microcosms and in Rice Plants (Oryza sativa)

The activity and distribution of CH(inf4)-oxidizing bacteria (MOB) in flooded rice (Oryza sativa) soil microcosms was investigated. CH(inf4) oxidation was shown to occur in undisturbed microcosms by using (sup14)CH(inf4), and model calculations indicated that almost 90% of the oxidation measured had taken place at a depth where only roots could provide the O(inf2) necessary. Slurry from soil planted with rice had an apparent K(infm) for CH(inf4) of 4 (mu)M and a V(infmax) of 0.1 (mu)mol g (dry weight)(sup-1) h(sup-1). At a depth of 1 to 2 cm, there was no significant difference (P > 0.05) in numbers of MOB between soil from planted and nonplanted microcosms (mean, 7.7 x 10(sup5) g [fresh weight](sup-1)). Thus, the densely rooted soil at 1 to 2 cm deep did not represent rhizospheric soil with respect to the number of MOB. A significantly increased number of MOB was found only in soil immediately around the roots (1.2 x 10(sup6) g [fresh weight](sup-1)), corresponding to a layer of 0.1 to 0.2 mm. Plant-associated CH(inf4) oxidation was shown in a double chamber with carefully washed intact rice plants. Up to 90% of the CH(inf4) supplied to the root compartment was oxidized in the plants. CH(inf4) oxidation on isolated roots was higher and had a larger variability than that in soil slurries. Roots had an apparent K(infm) for CH(inf4) of 6 (mu)M and a V(infmax) of 5 (mu)mol g (dry weight)(sup-1) h(sup-1). The average number of MOB in homogenized roots was larger than on the rhizoplane and increased with plant age. MOB also were found in surface-sterilized roots and basal culms, indicating the ability of these bacteria to colonize the interior of roots and culms.     

Comparison of Rice (Oryza sativa L.) Seed Proteins from Several Varieties

Enzymatically modified proteins (EMP) with different methionine levels were produced from soy protein isolate using an improved plastein reaction. The products having methionine at approximate levels of 4%, 7%, and 14%, designated as EMP₄, EMP₇, and EMP₁₄, respectively, were investigated to characterize their chemical properties particularly in terms of the state and location of the methionine residues. Leucine aminopeptidase treatment of the EMP products did not find any significant amount of methionine residues at the N-terminals, but carboxypeptidase A treatment liberated methionine efficiently in accordance with the methionine levels in the EMP products. Treatment with LiBH₄ reduced the methionine content of EMP₁₄ by approximately 64%. A significant amount of homoserine was produced when EMP₁₄ was treated with BrCN. All these data indicate that the covalently attached methionine molecules are localized at or near the C-terminals of the EMP molecules, probably as oligomers.     

Photothermal Responses of Flowering in Rice (Oryza sativa)

Durations from sowing to panicle emergence in 16 diverse genotypesof rice (Oryza sativa L.) were recorded in 13 different photothermalregimes, comprising constant and diurnally alternating temperaturesbetween 16 and 32 °C and photoperiods between 10.5 and 15.0h d^–1—all provided by controlled-environment growthcabinets. In 11.5 h days and at sub-optimal temperatures, relationsbetween the rate of progress towards panicle emergence and meantemperature were linear in all genotypes, and amongst thesethe base temperature at that photoperiod varied between 6.6and 11.9 °C. In most cases progress was most rapid at 24–26°C, i.e. the optimum temperature was much cooler than expectedfrom previously published values of times to panicle emergencein a less extensive range of photothermal regimes. Only in threecultivars was it warmer than 28 °C, and in these there weresufficient data to establish that relations between rates ofprogress to panicle emergence and photoperiod in the diurnallyalternating temperature regime of 28–20 °C are alsolinear. Also, the responses of these three cultivars provideno evidence of any interaction between the effects of photoperiodand temperature. We conclude, then, that the model in whichrate of development is a linear function of both temperatureand photoperiod with no interaction, which has been shown tobe common to many other species, also applies to rice. Differencesamong genotypes in relative sensitivity of rate of progresstowards panicle emergence to both temperature and to photoperiodwere considerable; japonica cultivars tended to be more sensitiveto temperature and less sensitive to photoperiod than indicacultivars. Four indica cultivars bred and selected at The InternationalRice Research Institute (IRRI) in the Philippines did not differ(P > 0.10) in their relations between rate of progress towardspanicle emergence and sub-optimal temperatures in a daylengthof 11.5 h, but the optimum temperature for cv. IR 36 was appreciablywarmer than that for the cvs IR 5, IR 8 and IR 42. Oryza sativa, rice, flowering, temperature, photoperiod, photothermal responses     

水稻染色体G—带的研究

用改良的ASG法首次在籼稻(O.sativa subsp.indica)品种珍汕97和粳稻(O.subsp.iaponica)品种秀岭的有丝分裂染色体上显示了G-带,并作了相应的G-带核型分析。就同一材料来说,随着有丝分裂时期的推进,染色体上带纹数目逐渐减少。籼、粳亚种间相对应的同源染色体上G-带带纹特征彼此相似。讨论了水稻G-带带型与染色体不同区域分化的关系;G-带带型与籼、粳稻分歧的关系;以及G-显带的方法。     

高温胁迫下水稻基因组DNA表观遗传变化MSAP分析

目的:研究高温胁迫对水稻基因组DNA甲基化变化的影响,筛选出一批与高温胁迫的相关基因,研究DNA基因化与基因转录水平之间的关系。方法:在人工气候箱子中,对四叶期的水稻幼苗进行38度高温处理,分别取0 h、2 h、4 h、8 h、12 h、16 h和24 h七个不同时间点的幼叶提取DNA与RNA,利用MSAP技术检测总甲基化水平变化,RT-PCR检测相关基因的转录本的表达量变化。结果:与对照组0 h幼叶相比,高温处理下的2 h、4 h、8 h、12 h、16 h和24 h幼叶的总体甲基化水平依次是37.14%、36.79%、36.00%、35.50%、35.43%、34.64%和34.57%,可知幼叶DNA甲基化水平在高温处理后不断降低。此外,RT-PCR结果显示筛选的两个与甲基化相关的基因(PP2C和RAFP)的转录水平与甲基化水平呈负相关。结论:基因组甲基化作为一种重要的表观遗传调控方式,可以通过调控相关的基因的表达量水平来防御高温胁迫。     

超高产杂交稻剑叶衰老过程中PSII功能的变化

对田间自然条件下培矮64S/E32和对照汕优63的剑叶衰老过程中PSII光化学效率、光能耗散和叶黄素循环组分的动态变化进行了研究.结果表明,水稻剑叶衰老过程中PSⅡ光化学效率(F/Fm)、PSII量子产量(φPSII)、光化学猝灭系数(qP)和光合速率(Pn)均降低,但非辐射热耗散(NPQ)、叶黄素循环库和中午时的脱环氧化状态则升高.移栽后55-75 d两品种剑叶的φPSII和qP变化相近,此后培矮64S/E32比汕优63下降缓慢.在生育后期的衰老过程中培矮64S/E32剑叶的PSII功能比汕优63下降慢,并具有更高的光能利用效率.     

Developmental Changes in the Structure of Endosperm Starch of Rice (Oryza sativa L.)

The developmental changes in the structure and properties of endosperm starches were investigated using the near-isogenic lines for wx alleles of rice. The amylose content in nonwaxy starch was increased during the development of rice grains. Because the accumulation of amylose in endosperm stopped earlier than that of amylopectin during development, the percentages of amylose reached a maximum at the 17th day after flowering in nonwaxy endosperm. Since the distributions of the unit-chain length of amylopectin in waxy and nonwaxy starches were unchanged with the development of the grains, these amylopectins would be synthesized in a similar manner through development. The structure and properties of endosperm starches were reconfirmed to be conspicuously affected by the temperature at the early developmental stages of the grain-filling period, namely, they appeared to be characterized by the temperature at which the starch was accumulated in the endosperm.     

Physiological Processes Contributing to the Difference in Grain Amino Acid Content between Two Hybrid Rice (Oryza sativa L.) Cultivars

Improving grain amino acid content of rice (Oryza sativa L.) is essential for the health of consumers. This study was conducted to identify the physiological processes that contribute to the higher grain amino acid content in hybrid rice cultivar Lingliangyou 268 compared to Luliangyou 996. The results showed that total amino acid content in grains was 9% higher in Lingliangyou 268 than in Luliangyou 996. There was no significant difference in grain nitrogen (N) content between Lingliangyou 268 and Luliangyou 996, while ratio of amino acid to N was 6% higher in Lingliangyou 268 compared to Luliangyou 996. A total of 16 differentially expressed proteins related to amino acid metabolism (e.g., erythronate-4-phosphate dehydrogenase domain containing protein) were identified in grains between Lingliangyou 268 and Luliangyou 996. The identified proteins were involved in 10 molecular functions. Six of the 10 defined functions were related to binding (heterocyclic compound binding, nucleoside phosphate binding, nucleotide binding, organic cyclic compound binding, protein binding, and small molecule binding) and the other 4 defined functions were catalytic activity, enzyme regulator activity, hydrolase activity, and transferase activity. These results indicate that the higher grain amino acid content in Lingliangyou 268 compared to Luliangyou 996 is attributed to increased efficiency of converting N to amino acid that results from altered expression of proteins related to amino acid metabolism.     

Comparative Analysis of the Endosperm Proteins Separated by 2-D Electrophoresis for Two Cultivars of Hybrid Rice （Oryza sativa L,）

Liangyoupeijiu is a two-parental-line, and Shanyou63 is a three-parental-line hybrid rice （Oryza sativa L.）. Although both belong to the indica subspecies, they have obvious differences with respect to morphology, physiology and grain quality. Variations in endosperm protein compositions were studied by comparing the 2-D electrophoresis （2-DE） maps for these two cultivars of hybrid rice. After matrix-assisted laser desorption/ionization time of flight mass spectrometry （MALDI-TOF/MS） analysis, a 21-kDa precursor of 19- kDa globulin was identified as the major storage protein for both cultivars. Some isoforms of peroxiredoxin and seed maturation protein were found to only exist in Shanyou63, whereas aldose reductase and starch granule-bound starch synthase were only detected in Liangyoupeijiu. These data might provide a foundation for further comparative studies of these two cultivars of hybrid rice.     

NaCl-and Gibberellic Acid-induced Changes in the Content of Auxin and the Activities of Cellulase and Pectin Lyase During Leaf Growth in Rice (Oryza sativa)

The interactive effect of NaCl salinity and gibberellic acidin the activities of cellulase and pectin lyase, and on thecontent of auxin and chlorophyll, has been determined duringleaf growth (fifth from base) in rice. The linear growth, chlorophyllcontent, activity of cellulase, and the auxin level of leaveswere markedly decreased when plants were exposed to salt stress(12 dS m^–1). However pectin lyase activity did not registerany significant alteration in the leaves of salt-stressed plantscompared with the control. Treatment of plants with gibberellicacid (GA₃) (10 ppm) increased the leaf growth and chlorophyllcontent with a concomitant rise in the activity of cellulaseunder stressed as well as non-stressed conditions. A markedincrease in the content of auxin was discernible in the leavesof salt-stressed plants treated with GA₃ compared with non-treatedsalinized ones. An appreciable increment in the activity ofpectin lyase in response to GA₃ administration was detectedonly in the leaves of non-stressed plants. These results indicatethat enhancement of cellulase activity and the augmentationof endogenous auxin content may be involved in the stimulationof rice leaf growth by GA₃ under saline conditions. Oryza sativa, rice, leaf growth, NaCl salinity, gibberellic acid, cellulase, pectin lyase, auxin