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Communication mechanisms between root and shoot in the reduction of photosynthesis during senescence in crop plants under water stress

水分胁迫下作物衰老过程中光合作用减少的根冠通讯机制

基本信息

批准号：
11460007
负责人：
HIRASAWA Tadashi
金额：
$ 9.02万
依托单位：
Tokyo University of Agriculture and Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

In order to clarify the mechanism of the reduction in photosynthesis during senescence under water stress with reference to root-shoot relations, we investigated photosynthetic rate, content of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), which is, a key enzyme of the rate of photosynthesis, and the expression of Rubisco genes during senescence under various conditions.1. There were close correlations among Rubisco content and the abundances of rbcL and rbcS (genes encoding the large subunit and small subunit of Rubisco, respectively) mRNA of a leaf during the reduction of photosynthetic rate due to senescence.2. Partitioning of nitrogen decreased to leaves and increased to roots under deficient soil moisture conditions, causing the reduction of leaf nitrogen content and, therefore, photosynthetic rate.3. There were close correlations among nitrogen content and the abundances of rbcL and rbcS mRNA of a leaf during senescence and the nitrogen topdressing increased their abundances.4. When plants were treated with exogenous cytokinin, nitrogen content and the abundances of rbcL and rbcS mRNA of a leaf increased without the increase in total nitrogen content of a plant, suggesting that cytokinin might increase the partitioning of nitrogen to leaves.5. The activity of cytokinin transported from root to shoot decreased in plants grown under deficient soil moisture conditions.From these results, it was suggested that one of the causal factors in the significant reduction of photosynthetic rate under deficient soil moisture conditions might be the reduction of leaf nitrogen content due to smaller partitioning of leaf nitrogen to leaves and that the levels of cytokinin transported from root to shoot might affect the leaf nitrogen content by changing the nitrogen partitioning.

为了从根冠关系的角度阐明水分胁迫下衰老过程中光合作用降低的机理，本研究对不同条件下衰老过程中光合速率、光合速率关键酶1，5-二磷酸核酮糖羧化酶/加氧酶（Rubisco）的含量以及Rubisco基因的表达进行了研究.在衰老导致光合速率下降的过程中，Rubisco含量与Rubisco大亚基和小亚基基因rbcL和rbcS mRNA的丰度密切相关.土壤水分亏缺条件下，氮素向叶片的分配减少，向根系的分配增加，导致叶片含氮量降低，光合速率降低.叶片衰老过程中rbcL和rbcS mRNA的丰度与氮素含量密切相关，追氮提高了其丰度.外源细胞分裂素处理植株后，叶片氮含量和rbcL、rbcS mRNA丰度增加，但植株总氮含量不增加，表明细胞分裂素可能增加氮素向叶片的分配.在土壤水分不足的条件下，植物从根向地上部运输的细胞分裂素活性降低。结果表明，在土壤水分亏缺条件下，叶片氮素分配减少，导致叶片氮含量降低，同时根向地上部运输的细胞分裂素水平降低，可能是光合速率显著降低的原因之一。通过改变氮素分配来影响叶片氮素含量。