硝酸还原酶（Nitrate reductase, NR）是植物体内同化硝态氮的关键酶，其活性受翻译后磷酸化修饰调控。通过分析硝酸还原酶NIA1磷酸化位点定向突变株系（S532D和S532A）、OsNia1过表达株系（OE）及野生型（WT）的表型、氮代谢和活性氧代谢的差异，探究不同形态氮素营养下NIA1蛋白的去磷酸化对水稻生长和生理生化的影响。研究表明，与WT和OE相比，S532D和S532A具有更强的氮素同化能力。以硝酸铵作为氮源时，S532D和S532A的株高、地上部干重和叶绿素含量均低于WT和OE，H₂O₂、MDA和亚硝酸盐含量则较高；以硝酸钾作为氮源时，S532D和S532A的株高、地上部干重和叶绿素含量高于WT和OE，所有株系叶片中的H₂O₂和MDA含量无明显差异，各株系间亚硝酸盐含量差异减小；以硫酸铵作为氮源，除NR活性外，各株系间的其它生理指标均无显著差异。相较于硝酸铵和硫酸铵，以硝酸钾作为氮源时各株系叶片中NH₄⁺-N的含量较低。q-PCR分析表明OsGS和OsNGS1基因表达受下游代谢产物的负调控，OsNrt2.2受硝酸盐诱导表达。综上，硝酸铵作为氮源时NIA1磷酸化位点定向突变株系长势较弱是由于过量积累的亚硝酸盐对自身的毒害；硝酸钾作为氮源时NIA1磷酸化位点定向突变株系对硝酸盐、亚硝酸盐和铵盐的同化速率加快，能够提供较多的氮素营养，提高了水稻对铵态氮缺乏的耐受性。

硝酸还原酶（Nitrate reductase, NR）是植物体内同化硝态氮的关键酶，其活性受翻译后磷酸化修饰调控。通过分析磷酸化位点定向突变株系（S532D 和S532A）、OsNia1过表达株系（OE）及野生型（WT）的表型、NR蛋白I（NIA1）及其磷酸化水平、NR活性、硝态氮代谢和活性氧代谢的差异，探究NIA1蛋白的去磷酸化对NR活性、氮代谢和水稻生长的影响。研究表明，S532D和S532A株系中的外源NIA1蛋白不能被磷酸化，其NR活性、NR活性状态和NO₃^--N的同化效率均高于WT和OE。OE中以上生理生化指标均小于S532D和S532A。表明解除转录水平控制对N代谢没有太大影响，而翻译后修饰的解除对N代谢水平有深刻的影响。随着NIA1蛋白磷酸化的解除和硝酸盐同化能力的增强，S532D 和 S532A的株高和叶绿素含量均降低，过氧化氢（H₂O₂）和丙二醛（MDA）的含量升高，这可能与硝酸盐代谢的中间产物亚硝酸盐的过度积累有关。以上结果表明NR的磷酸化可能是水稻的一种自我保护机制，NIA1磷酸化水平的降低能够促进硝酸盐的同化，而磷酸化水平的提高则会降低亚硝酸盐的积累，降低活性氧积累对水稻的毒害作用。

由于劳动力投入少、经济效益高，水稻直播已成为中国南方地区主要的种植方式。旱直播方式在单季水稻栽培技术方面运用广泛。然而，对早籼稻机械旱直播试验的研究还少有报导。通过两年大田间试验，以2个籼稻品种（中嘉早17和株两优819）为材料，研究旱直播、淹水直播和湿直播模式下的水稻倒伏特性和产量形成。结果表明，在旱直播方式下，株两优819和中嘉早17的年均产量分别比湿直播和淹水直播高14.42-26.34%和6.64-24.58%，这主要是由于穗数的提高。旱直播方式显著提高了早籼稻品种的出苗率，增加总干重和作物生长速率。同时，与淹水直播和湿直播相比，旱直播基部节间较短，茎粗和茎壁较厚，倒伏指数较低。尤其是旱直播提高了茎秆的抗倒伏能力。本研究结果表明，适宜的直播方式有利于提高早籼稻的产量和抗倒伏能力。

长期秸秆还田是提高农田土壤有机碳储量的重要碳源，秸秆焚烧还田在我国南方也屡见不鲜。然而，长期稻草管理对土壤有机碳组分、酶活性及其相互关系的影响，以及其影响是否存在季节差异却尚未明确。我们基于2009年开始建立的长期定位试验平台，通过设置3个N、P、K等养分输入(包括秸秆/灰分和化学养分)的处理：秸秆不还田(CK)、秸秆还田(SR)和秸秆焚烧还田(SBR)，探讨长期秸秆还田条件对南方双季稻田土壤有机碳组分及土壤酶活性的影响。结果表明，与CK相比，长期秸秆还田有利于提高早稻产量(P=0.057)，并显著增加早晚稻田土壤的总有机碳（TOC）和微生物量碳(MBC)含量。而稻草焚烧还田对TOC无显著影响，但降低了早稻轻组有机碳（LFOC）和晚稻易氧化有机碳(EOC)含量，而显著增加了可溶性有机碳（DOC），且显著降低了土壤pH。我们研究还表明，长期秸秆还田条件下，MBC是评估双季稻系统土壤有机碳变化最敏感的指标；此外，SBR和SR对土壤酶活性的影响早晚稻稻田土壤呈现相反趋势，进而导致土壤有机碳组分含量存在季节差异，尤其是改变了土壤DOC含量，而早晚稻DOC与β-木糖苷酶均呈正相关。可见，秸秆还田较秸秆焚烧还田更有利于土壤有机碳组分的固持与提高，但其对晚稻土壤酶活性的负作用有待进一步研究。

Received  29 September, 2017    Accepted  11 February, 2018

Dwarf mutants are the crucial resources for molecular biology research and rice breeding.  Here, a rice mutant, dwarf and deformed flower3 (ddf3), was identified in tissue culture of Oryza sativa cv. Dongjin.  Compared with wild type, the ddf3mutant exhibited severe dwarfism, a greater number of tillers and significantly decreased fertility.  In addition, leaf length, panicle length, and grain length, were significantly shorter.  All internodes of ddf3were shorter than those of wild type, and histological analysis revealed that internode cell elongation was significantly inhibited in ddf3.  In the ddf3mutant, pollen activity was significantly decreased, and the development of most stigmas was abnormal.  Genetic analysis indicated that the ddf3mutant phenotypes are controlled by a single or tightly linked nuclear genes.  Using an F₂ mapping population generated from a cross between ddf3and Yangdao 6 (9311), the DDF3 gene was mapped to a 45.21-kb region between insertion-deletion (InDel) markers M15 and M16 on the long arm of chromosome 7.  Sequencing revealed a 13.98-kb-deletion in this region in the ddf3 mutant genome that resulted in the complete or partial deletion of ZF (DHHC type zinc finger protein), EP (expressed protein), and FH2 (actin-binding FH2 domain-containing protein) genes.  Quantitative RT-PCR analyses revealed that in wild type, the transcript levels of FH2 were almost the same in all organs, while ZF was mainly expressed in the panicle, and no expression of EP was detected in any organ.  Based on these results, ZF and FH2 could be potential DDF3 candidate genes involved in the regulation of rice morphology and flower organ development.  Our work has laid the foundation for future functional analysis of these candidate genes and has provided a profitable gene resource for rice breeding for increased fertility in the future. 

A hydroponic study was conducted to determine the effects of selenium (Se: 0, 3, 6 μmol L−1) on senescence-related oxidative stress in garlic plants grown under two sulfur (S) levels. We evaluated the yields of plants harvested at 160 and 200 days after sowing. Plants grown under a low Se dose (0.3 μmol L−1) at low S level showed higher yields (12.0% increase in fresh weight yield, 13.7% increase in dry weight yield) than the controls, despite a decrease in chlorophyll concentration. Compared with control plants, the Se-treated plants showed lower levels of lipid peroxidation. The Se-treated plants also showed higher activities of glutathione peroxidase and catalase, but lower superoxide dismutase activities. Changes in Fv/Fm values and proline contents were affected more strongly by S than by Se. On the basis of our results, we can conclude that Se plays a key role in the antioxidant systems in garlic seedlings. It delays senescence by alleviating the peroxide stress, but it can be toxic at high levels. A high S level may increase tolerance to high Se concentrations through reducing Se accumulation in plants.