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.