Grain size,sucrose level and starch accumulation in developing rice grain

Five rices (Oryza sativa L.) differing in final grain size were studied at the midmilky stage to determine if any factor could be identified which might limit rate of starch accumulation. Only UDP glucose pyrophosphorylase activity increased with increasing grain size. Detached rice panicles incubated in liquid medium containing 1% sucrose and 0.1% glutamine, in addition to minerals and vitamins, produced grains similar to those on intact plants. Sucrose level (0–1.5%) in the medium determined the extent of dry matter and starch accumulation and influenced physiological development of the ripening grains. Chemical and enzymic composition of the grain were similar to previously reported levels in grains of intact panicles analysed at regular intervals after anthesis. Addition of 3-P glycerate or K⁺ to the medium did not improve dry matter accumulation in the developing grain.     

水稻OsPR10A的表达特征及其在干旱胁迫应答过程中的功能

利用免疫印迹(WB)分析了水稻(Oryza sativa) OsPR10A在其不同生长时期、不同组织部位及多种非生物逆境胁迫下的表达特征, 发现OsPR10A在干旱、盐胁迫以及茉莉酸甲酯(MeJA)和脱落酸(ABA)诱导下表达量明显升高, 表明该蛋白可能在干旱和盐胁迫应答过程中发挥作用。为证明这一推测, 我们构建了OsPR10A超表达载体, 经农杆菌介导转化水稻, 获得超表达OsPR10A的纯合株系。田间表型观察表明, 转基因株系株高变矮、穗长变短、结实率降低。用20% PEG6000在水稻种子萌发过程中进行干旱处理, 结果显示, OsPR10A超表达株系的根长和芽长均显著高于野生型, 证明超表达OsPR10A可增强水稻萌发期耐旱性。该研究有助于增进人们对水稻OsPR10A功能的了解。     

籼、粳杂种的“随体丢失”

1985—1986,观察籼、粳及籼,粳F_1杂种终变期核仁染色体数,籼为2个二价核仁染色体,粳为1个二价核仁染色体,籼、粳F_1杂种核仁染色体数与父本水稻的核仁染色体数相同。由此,讨论了“随体丢失”在水稻育种,粳稻起源及遗传学方面的意义。     

Comparison of Reproduction by Meloidogyne graminicola and M. incognita on Trifolium Species

The reproductive potential of Meloidogyne graminicola was compared with that of M. incognita on Trifolium species in greenhouse studies. Twenty-five Trifolium plant introductions, cultivars, or populations representing 23 species were evaluated for nematode reproduction and root galling 45 days after inoculation with 3,000 eggs of M. graminicola or M. incognita. Root galling and egg production by the two root-knot nematode species was similar on most of the Trifolium species. In a separate study, the effect of initial population densities (Pi) of M. graminicola and M. incognita on the growth of white clover (T. repens) was determined. Reproductive and pathogenic capabilities of M. graminicola and M. incognita on Trifolium spp. were similar. Pi levels of both root-knot nematode species as low as 125 eggs per 10-cm-d pots severely galled white clover plants after 90 days. Meloidogyne graminicola has the potential to be a major pest of Trifolium species in the southeastern United States.     

Biological N2 Fixation in wetland rice fields: Estimation and contribution to nitrogen balance

This paper 1) reviews improvements and new approaches in methodologies for estimating biological N₂ fixation (BNF) in wetland soils, 2) summarizes earlier quantitative estimates and recent data, and 3) discusses the contribution of BNF to N balance in wetland-rice culture.Measuring acetylene reducing activity (ARA) is still the most popular method for assessing BNF in rice fields. Recent studies confirm that ARA measurements present a number of problems that may render quantitative extrapolations questionable. On the other hand, few comparative measures show ARA's potential as a quantitative estimate. Methods for measuring photodependent and associative ARA in field studies have been standardized, and major progress has been made in sampling procedures. Standardized ARA measurements have shown significant differences in associative N₂ fixation among rice varieties.The ¹⁵N dilution method is suitable for measuring the percentage of N derived from the atmosphere (% Ndfa) in legumes and rice. In particular, the ¹⁵N dilution technique, using available soil N as control, appears to be a promising method for screening rice varieties for ability to utilize biologically fixed N. Attempts to adapt the ¹⁵N dilution method to aquatic N₂ fixers (Azolla and blue-green algae [BGA]) encountered difficulties due to the rapid change in ¹⁵N enrichment of the water.Differences in natural ¹⁵N abundance have been used to show differences among plant organs and species or varieties in rice and Azolla, and to estimate Ndfa by Azolla, but the method appears to be semi-quantitative.Recent pot experiments using stabilized ¹⁵N-labelled soil or balances in pots covered with black cloth indicate a contribution of 10–30 kg N ha^-1 crop^-1 by heterotrophic BNF in flooded planted soil with no or little N fertilizer used.Associative BNF extrapolated from ARA and ¹⁵N incorporation range from 1 to 7 kg N ha^-1 crop^-1. Straw application increases heterotrophic and photodependent BNF. Pot experiments show N gains of 2–4 mg N g^-1 straw added at 10 tons ha^-1.N₂ fixation by BGA has been almost exclusively estimated by ARA and biomass measurements. Estimates by ARA range from a few to 80 kg N ha^-1 crop^-1 (average 27 kg). Recent extensive measurements show extrapolated values of about 20 kg N ha^-1 crop^-1 in no-N plots, 8 kg in plots with broadcast urea, and 12 kg in plots with deep-placed urea.Most information on N₂ fixed by Azolla and legume green manure comes from N accumulation measurements and determination of % Ndfa. Recent trials in an international network show standing crops of Azolla averaging 30–40 kg N ha^-1 and the accumulation of 50–90 kg N ha^-1 for two crops of Azolla grown before and after transplanting rice. Estimates of % Ndfa in Azolla by ¹⁵N dilution and delta ¹⁵N methods range from 51 to 99%. Assuming 50–80% Ndfa in legume green manures, one crop can provide 50–100 kg N ha^-1 in 50 days. Few balance studies in microplots or pots report extrapolated N gains of 150–250 kg N ha^-1 crop^-1.N balances in long-term fertility experiments range from 19 to 98 kg N ha^-1 crop^-1 (average 50 kg N) in fields with no N fertilizer applied. The problems encountered with ARA and ¹⁵N methods have revived interest in N balance studies in pots. Balances are usually highest in flooded planted pots exposed to light and receiving no N fertilizer; extrapolated values range from 16 to 70 kg N ha^-1 crop^-1 (average 38 kg N). A compilation of balance experiments with rice soil shows an average balance of about 30 kg N ha^-1 crop^-1 in soils where no inorganic fertilizer N was applied.Biological N₂ fixation by individual systems can be estimated more or less accurately, but total BNF in a rice field has not yet been estimated by measuring simultaneously the activities of the various components in situ. As a result, it is not clear if the activities of the different N₂-fixing systems are independent or related. A method to estimate in situ the contribution of N₂ fixed to rice nutrition is still not available. Dynamics of BNF during the crop cycle is known for indigenous agents but the pattern of fixed N availability to rice is known only for a few green manure crops.     

Plant-induced changes in the redox potentials of rice rhizospheres

Redox potentials in microsites of the rhizosphere of flooded rice were continuously measured for several days. Close to the root tips redox potential markedly increased. The highest increase was measured in the rhizosphere of the tips of short lateral roots. Aerobic redox conditions were reached there, except in a very strongly reduced soil. Both the extension of the oxidation zone around the root tips and the maximum redox potential reached were influenced by the reducing capacity of the soil. The radius of the redox rhizosphere varied from less than 1 mm in a strongly reduced soil up to 4 mm in a weakly reduced one. The root-induced oxidation processes in the rhizosphere depended on the atmospheric oxygen supply to the roots.     

Herbicide-resistant Indica rice plants from IRRI breeding line IR72 after PEG-mediated transformation of protoplasts

The commercially important Indica rice cultivar Oryza sativa cv. IR72 has been transformed using direct gene transfer to protoplasts. PEG-mediated transformation was done with two plasmid constructs containing either a CaMV 35S promoter/HPH chimaeric gene conferring resistance to hygromycin (Hg) or a CaMV 35S promoter/BAR chimaeric gene conferring resistance to a commercial herbicide (Basta) containing phosphinothricin (PPT). We have obtained so far 92 Hg^r and 170 PPT^r IR72 plants from protoplasts through selection. 31 Hg^r and 70 PPT^r plants are being grown in the greenhouse to maturity. Data from Southern analysis and enzyme assays proved that the transgene was stably integrated into the host genome and expressed. Transgenic plants showed complete resistance to high doses of the commercial formulations of PPT.     

Vertical profiles of CH4 concentrations,dissolved substrates and processes involved in CH4 production in a flooded Italian rice field

Vertical profiles were measured in soil cores taken from flooded rice fields in the Po valley during July and August 1990. Methane concentrations generally increased with depth and reached maximum values of 150–500 μM in 5–13 cm depth. However, the shape of the profiles was very different when studying different soil cores. The CH₄ content of gas bubbles showed a similar variability which apparently was due to spatial rather than temporal inhomogeneities. Similar inhomogeneities were observed in the vertical profiles of acetate, propionate, lactate, and formate which showed maximum values of 1500, 66, 135, and 153, μM, respectively. However, maxima and minima of the vertical profiles of the different substates usually coincided in one particular soil core. Large inhomogeneities in the vertical profiles were also observed for the rates of total CH₄ production, however, the percentage contribution of H₂/CO₂ to CH₄ production was relatively homogeneous at 24 ± 7% (SD). Similarly, the H₂ content of gas bubbles was relatively constant at 93.3 ± 9.6 ppmv when randomly sampled in the rice field at different times of the day. A small contribution (6%) of H₂/CO₂ to acetate production was also observed. Vertical profiles of the respiratory index (RI) for [2-¹⁴C] acetate showed that acetate was predominantly degraded by methanogenesis in 5–11 cm depth, but by respiration in the surface soil (3 cm depth) and in soil layers below 13–16 cm depth which coincided with a transition of the colour (grey to reddish) and the physical characteristics (porosity, density) of the soil. The observations indicate that the microbial community which degrades organic matter to CH₄ is in itself relatively homogenous, but operates at highly variable rates within the soil structure. Author for correspondence     

水稻食叶类害虫等量损害系统与复合防治指标

稻纵卷叶螟Cnaphalocrocis.medinalis Guenèe中华稻蝗Oxya chinensis(Thunberg)稻苞虫Parnara guttatus (Bremer et Grey)是江苏地区水稻的主要食叶类害虫,取食水稻叶片,导致光合叶面积减少.剪叶模拟试验表明,水稻不同生育阶段叶面积损失率与产量损失率呈线性相关.其回归方程分蘖期、孕穗期、腊熟期分别为 D(I_t)=72.50759I_t^1.15906、D(I_t)=141.61737I_t^1.08002、D(I_t)=25.12434I_t^1.00569.在叶面积损失率相同的情况下,产量损失率孕穗期>分蘖期>腊熟期.试验通过三种害虫的各龄取食量,不同生育阶段水稻叶面积及为害与损失率之间的关系,建立了不同生育阶段的经济允许损害水平(EIL_t).并根据各种害虫的相对潜在取食量,计算了校正等量损害系数,为制订复合防治指标提供了依据.实践证明:以等量损害为单位的复合防治指标有较大的实用价值,生态效益、经济效益、社会效益明显.