磷胁迫下蔗糖对水稻苗期根适应性和磷酸转运蛋白基因表达的影响

磷是植物生长和发育中最重要的必须元素之一。尽管土壤中磷资源很丰富,但大部分磷是以植物不能吸收利用的固定态和有机态存在,特别是以酸性土壤为主的南方稻田,水稻缺磷现象非常严重。理解和掌握水稻对低磷的适应机制有助于利用分子手段培育磷高效利用水稻品种。为阐明蔗糖提高水稻耐低磷的机制,本研究对水稻幼苗进行不同磷、糖处理,分析水稻幼苗在不同磷糖配比培养基中的根系结构、无机磷、酸性磷酸酶活性的变化,并利用定量RT-PCR技术分析水稻磷酸转运蛋白基因(OsPT)和酸性磷酸酶基因(OsSAP1)的表达。试验设2个磷浓度:无磷和85 mg·L?1KH2PO4,2个蔗糖浓度:无糖和3%蔗糖,正交设计。结果表明,在低磷胁迫时添加蔗糖,能使水稻幼苗的根总长度、总根数、根冠比显著增加,根分泌的酸性磷酸酶活性降低,但水稻体内的磷酸转运酶活性提高。11个与磷具有高度亲和力的磷酸转运酶的表达发生了改变,其中根优势表达的4个基因OsPT2、OsPT3、OsPT4、OsPT6对磷、糖的影响最为敏感,暗示了蔗糖是通过调节磷转运蛋白维持磷的吸收和平衡。增加根系的蔗糖分配能够提高水稻幼苗对磷胁迫的耐受性。

Effects of sucrose on rice root adaptability and phosphate transporter gene expression under phosphorus stress

Phosphate is one of the most important essential elements for plant growth and development. Although soils are normally rich in phosphorus, most phosphorus compounds exist as either insoluble inorganic phosphate (Pi) or organic phosphate and rice Pi availability is extremely low particularly in acidic paddy fields. Breeding low phosphorus tolerance plants has been the most fundamental method for meeting phosphours deficiency and improving fertilizer use efficiency. It is important to highlight the adaptation mechanism of plants to low soil phosphorus availability. Thus the aim of this work was to understand the role of sucrose in regulating rice seedling response to phosphorus stress. Rice (Oryza sativa L.) cultivar ('Minhui86') was grown for 35 days under normal phosphate (85 mg·L ^-1 KH₂PO₄) without sucrose (PS-), normal phosphate with 3% sucrose (PS+), no phosphate without sucrose (P-S-) and no phosphate with 3% sucrose (P-S+). The morphological and physiological responses of rice to phosphorus deficiency and the expression of acid phosphatase 1 gene (OsSAP1) and 11 of phosphate transporter genes (OsPTs) under low phosphorus stress were analyzed. The results showed that rice seedling root growth in sucrose conditions had striking changes in morphology and architecture under low phosphorus stress. The root changes included increases in both total and lateral root numbers, length of root and root/shoot ratio. Analysis of acid phosphatase activity indicated that root-secreted acid phosphatase was depressed under PS condition, while activity of acid phosphatase in plant cell improved. Among 11 high affinities phosphate transporter genes (OsPTs), 4 of them, OsPT2, OsPT3, OsPT4, OsPT6, were expressed predominantly in root and displayed sensitivity to exogenous sucrose under low phosphorus stress. This suggested that sucrose likely played a role in maintaining phosphorus absorption and homeostasis by regulating phosphate transporter.