Roles Of Organic Acid Metabolism In Plant Tolerance To Phosphorus-Deficiency

On 30-40% of the world's arable land, crop yield is limited by phosphorus (P) availability. Phosphorus fertilizer use increased fourfold to fivefold between 1960 and 2000 and the demand for P was predicted to increase by 50-100% by 2050 with increased global demand for food and diets. Continually increasing demand for P will deplete existing phosphate (Pi) rock reserves by the end of the century. Improvement of soil P-acquisition and utilization by plants is one approach to alleviate the scarcity of P resources and to reduce environmental pollution. Many plants have evolved different strategies of enhancing P-acquisition from low-P soils, and one of these strategies involves the secretion of organic acid (OA) anions. Although the causes are not fully understood, the P-deficiency-induced secretion of OA anions may be related to several factors, including (a) internal concentrations of OAs in plant tissues; (b) proteoid or cluster root formation; (c) permeability of root membranes; (d) root plasma membrane H+-ATPase; and (e) anion channels. Besides increased acquisition of soil P, plants respond adaptively to P-deficiency through the induction of alternative glycolytic pathways and tonoplast pumping bypassing Pi- and/or adenylate-dependent reactions. Apart from pyrophosphate (PPi)-dependent tonoplast pyrophosphatase (V-PPiase), several Pi-and adenylate-independent glycolytic bypass enzymes [i.e., UDP-glucose pyrophosphorylase (UGPase), PPi-dependent phosphofructokinase (PPi-PFK), NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD-G3PDH), phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvate phosphatase (PEPP), pyruvate phosphate dikinase (PPDK), NAD-malic enzyme (NAD-ME)] in plant tissues have been reported to be upregulated by P-deficiency. Genetically modified plants and cells with higher P-deficiency-tolerance by overexpressing genes for the transporter and biosynthesis of OAs, as well as V-PPiase have been obtained. In addition, some aspects needed to be further studied are also discussed.