水稻早衰突变体esl6的鉴定与基因定位

自然衰老提高了植物对环境的适应性，是其生长发育的重要生命历程，但在农业生产中，叶片一旦早衰，将极大影响作物的产量和品质。为探索水稻叶片衰老的分子机理，我们对EMS诱变获得的一个早衰突变体esl6进行了研究。田间种植情况下，四叶期之前，esl6与野生型无明显差异，之后心叶发育成完整叶后叶尖黄化，叶基部保持正常绿色，一直持续到开花期；在灌浆期，esl6的所有叶片均不同程度地黄化早衰，且叶片上部的衰老程度明显严重于叶片基部。衰老部位细胞结构异常，主要表现为细胞膜破裂、液泡变大和细胞器不完整等，叶绿体中基质类囊体破裂，含有较多的淀粉粒。与野生型相比，esl6叶尖衰老部位的SOD、CAT和POD活性以及超氧阴离子O₂^?、H₂O₂和羟自由基·OH含量均极显著升高。早衰不仅导致esl6叶片光合色素含量和净光合速率极显著降低，还引起esl6的植株变矮和叶片变短，倒一和倒二节间极显著变短是导致esl6植株矮化的主要原因。遗传分析表明该性状受一对隐性核基因调控，利用西大1A/esl6的F₂分离群体，最终将调控基因定位在第9染色体203 kb的物理范围内，为下一步基因的克隆和功能研究奠定了基础，有利于水稻叶片衰老分子机理的阐释。

Identification and Gene Mapping of an Early Senescent Leaf Mutant esl6 in Oryza sativa L.

As an essential process in life, natural senescenceis necessary to adapt plant to environment diversity, while earlier senescence could reduce yield per unit and cause inferior quality in crop production. Therefore, it is significant to elucidate senescence molecular mechanism in plant. Here, we reported a novel rice mutant esl6 derived from the progeny of EMS-induced restorer line Jinhui10, which senescent peculiarity was observed at the early stage of life. In detail, cultivated under the paddy field, the esl6 had no obvious difference with the wild type before the 4-leaf stage, while after that the whole leaf blade of esl6 displayed chlorosis in the tip and kept normal green in the base until the flowering stage. Subsequently, all leaf blades in the esl6 demonstrated chlorosis and senescence, still more severe at the upper position. Observation by scanning electron microscope showed that cell structures in the senescent location of esl6 leaf blade were abnormal and filled with ruptured cell membranes, enlarged vacuoles and broken organelles such as the chloroplasts containing incomplete stroma thylakoids and excessive starch grains. Meanwhile, early senescence significantly lessened photosynthetic pigment contents and photosynthetic rate. The activities of SOD, CAT, and POD raised and the contents of O₂^?, H₂O₂, and ·OH increased in the esl6 leaf tip, and all of the differences led to the extremely significant level compared with those of the wild type. Additionally, the mutational plant showed semi-dwarfism and shorter leaf blades, the first and second internodes decreased to the extremely significant level in statistics. Genetic analysis suggested that the mutational traitswere controlled by a recessive nuclear gene. The gene was finally mapped on chromosome 9 with 203 kb physical distances between Indel markers Sind09-3 and Sind09-4 on the basis of F₂ generation of Xida1A/esl6. All of these provide a foundation for ESL6 cloning and function analysis and then are beneficial to ascertaining the molecular mechanism of senescence in Oryza sativa L.