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The role of phosphorus in aluminium‐induced citrate and malate exudation from rape ( Brassica napus )
Author(s) -
Ligaba Ayalew,
Shen Hong,
Shibata Koichi,
Yamamoto Yoko,
Tanakamaru Shigemi,
Matsumoto Hideaki
Publication year - 2004
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.0031-9317.2004.0290.x
Subject(s) - brassica , phosphorus , chemistry , malate dehydrogenase , aluminium , botany , biochemistry , biology , enzyme , organic chemistry
Exudation of organic anions is believed to be a common tolerance mechanism for both aluminium toxicity and phosphorus deficiency. Nevertheless, which of these stresses that actually elicit the exudation of organic anions from rape ( Brassica napus L) remains unknown, and the combined effects of Al toxicity and P deficiency on rape have not been reported before. Therefore, in the current study, Brassica napus var. Natane nourin plants grown with or without 0.25 m M P were exposed to 0 or 50 µ M AlCl 3 and several parameters related to the exudation of organic anions from the roots were investigated. Eight days of P deficiency resulted in a significant growth reduction, but P deficiency alone did not induce exudation of organic anions. In contrast, Al strongly induced organic acid exudation, while simultaneously inhibiting root growth. Increased in‐vitro activity of citrate synthase (CS, EC 4.1.3.7), malate dehydrogenase (MDH, EC 1.1.1.37) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), together with reduced root respiration, indicated that the Al‐induced accumulation and subsequent exudation of citrate and malate were associated with both increased biosynthesis and reduced metabolism of citric and malic acid. Phosphorus‐sufficient plants showed more pronounced aluminium‐induced accumulation and exudation of organic anions than P‐deficient plants. A divided root chamber experiment showed the necessity of direct contact between Al and roots to elicit exudation of organic anions. Prolonged exposure (10 days) to Al resulted in a decrease in the net exudation of citrate and malate, and the rate of decrease was much more rapid in P‐deficient plants than in P‐sufficient plants. It is concluded that P nutrition affects the level of Al‐induced synthesis and exudation of organic anions. However, the mechanism needs further investigation.