Zhu Xiao Fang, Wang Zhi Wei, Wan Jiang Xue, Sun Ying, Wu Yun Rong, Li Gui Xin, Shen Ren Fang, Zheng Shao Jian
State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences; Zhejiang University, Hangzhou 310058, China.
College of Agronomy and Biotechnology, Zhejiang University, Hangzhou 310058, China.
J Exp Bot. 2015 Feb;66(3):1017-24. doi: 10.1093/jxb/eru461. Epub 2014 Dec 20.
Plants growing in phosphorus (P)-deficient conditions can either increase their exploration of the environment (hence increasing P uptake) or can solubilize and reutilize P from established tissue sources. However, it is currently unclear if P stored in root cell wall can be reutilized. The present study shows that culture of the rice cultivars 'Nipponbare' (Nip) and 'Kasalath' (Kas) in P-deficient conditions results in progressive reductions in root soluble inorganic phosphate (Pi). However, Nip consistently maintains a higher level of soluble Pi and lower relative cell wall P content than does Kas, indicating that more cell wall P is released in Nip than in Kas. P-deficient Nip has a greater pectin and hemicellulose 1 (HC1) content than does P-deficient Kas, consistent with the significant positive relationship between pectin and root-soluble Pi levels amongst multiple rice cultivars. These observations suggest that increased soluble Pi might result from increased pectin content during P starvation. In vitro experiments showed that pectin releases Pi from insoluble FePO4. Furthermore, an Arabidopsis thaliana mutant with reduced pectin levels (qua1-2), has less root soluble Pi and is more sensitive to P deficiency than the wild type (WT) Col-0, whereas NaCl-treated WT plants exhibit both an increased root pectin content and an elevated soluble Pi content during P-starvation. These observations indicate that pectin can facilitate the remobilization of P deposited in the cell wall. This is a previously unknown mechanism for the reutilization of P in P-starved plants.
生长在缺磷条件下的植物，要么增加对环境的探索（从而增加磷的吸收），要么从已有的组织源中溶解并重新利用磷。然而，目前尚不清楚根细胞壁中储存的磷是否能够被重新利用。本研究表明，将水稻品种“日本晴”（Nip）和“卡萨拉斯”（Kas）在缺磷条件下培养，会导致根中可溶性无机磷（Pi）逐渐减少。然而，与Kas相比，Nip始终保持较高水平的可溶性Pi和较低的相对细胞壁磷含量，这表明Nip中比Kas释放了更多的细胞壁磷。缺磷的Nip比缺磷的Kas具有更高的果胶和半纤维素1（HC1）含量，这与多个水稻品种中果胶与根可溶性Pi水平之间显著的正相关关系一致。这些观察结果表明，可溶性Pi的增加可能是由于磷饥饿期间果胶含量增加所致。体外实验表明，果胶能从不溶性磷酸铁中释放Pi。此外，一个果胶水平降低的拟南芥突变体（qua1-2），其根可溶性Pi较少，并且比野生型（WT）Col-0对缺磷更敏感，而经氯化钠处理的WT植物在磷饥饿期间表现出根果胶含量增加和可溶性Pi含量升高。这些观察结果表明，果胶能够促进细胞壁中沉积的磷的再利用。这是磷饥饿植物中磷再利用的一种此前未知的机制。
