Changes in phosphate content and phosphatase activities in rice seedlings exposed to arsenite

Abstract

The effect of arsenite (As 2 O 3 ) in situ on the level of the phosphate pool and activities of phosphohydrolytic enzymes was examined in rice (Oryza sativa L.) seedlings grown for 5-20 d in sand cultures. The effects were manifested via a decline in phosphate content and inhibition of the activities of key phosphatases. Application of 50 µM As 2 O 3 in situ resulted in 34 to 77% inhibition of acid phosphatase activity in roots and about 38 to 50% inhibition of activity in shoots of 15-20-d-old seedlings. Similarly, alkaline phosphatase activity was inhibited in shoots under in situ As (III) toxicity. Varietal as well as organ specific differences were observed in the response of inorganic pyrophosphatase activity to in situ As (III) treatment. A moderately toxic in situ As 2 O 3 level of 25 µM as well as a highly toxic level of 50 µM inhibited mitochondrial-ATPase activity whereas 25 µM As (III) stimulated the chloroplastic isoform of ATPase but at a higher level (50 µM) As (III) was inhibitory. The results suggest that exposure of rice plants to arsenite leads to lowering of the phosphate pool and alteration in the activities of key phosphohydrolytic enzymes which might contribute to metabolic perturbations and decreased growth of rice plants in an As (III) polluted environment. Key words: arsenite, chloroplast, mitochondria, Oryza sativa, phosphate, phosphatases Variações no conteúdo de fosfato e atividades de fosfatases em plântulas de arroz expostas a arsenito: Examinou-se, in situ, o efeito do arsenito (As 2 O 3 ) sobre o estoque de fosfato e atividades de enzimas fosfoidrolíticas em plântulas de arroz (Oryza sativa L.) cultivadas por 5-20 d em areia. Os efeitos foram manifestados via decréscimos no conteúdo de fosfato e inibição das atividades de fosfatases-chave. A aplicação de 50 µM de As 2 O 3 in situ resultou em inibição de 34 a 77% na atividade de fosfatases nas raízes, e uma inibição na atividade de cerca de 38 a 50% na parte aérea de plântulas com 15 a 20 d. Similarmente, a atividade da fosfatase alcalina foi inibida na parte aérea sob toxidez de As(III). Observaram-se diferenças específicas entre variedades e órgãos na resposta da atividade da fosfatase inorgânica ao tratamento in situ com As(III). Toxidez moderada de As 2 O 3 (25 µM) assim como um nível altamente tóxico de 50 µM inibiram a atividade de ATPase mitocondrial enquanto 25 µM As(III) estimulou a isoforma cloroplastídica da ATPase, porém a dose mais elevada (50 µM) foi inibitória. Os resultados sugerem que a exposição de plantas de arroz ao arsenito leva a um decréscimo do estoque de fosfato e alteração nas atividades de enzimas fosfoidrolíticas, o que poderia contribuir para causar distúrbios metabólicos e redução do crescimento de plantas de arroz em ambientes contaminados com As(III).

Formation and Functioning of Chaetomium Cochliodes / Fagopyrum Еsculentum Endophytic Association

“…Functioning of acid phosphatase activity (AP) allowed maintaining the mobility of a large part of inorganic phosphorus during maturation of the crop (Turner, Plaxton, 2001). ALP and AP widespread in cells and played an important role in the metabolism of inorganic phosphates and cellular metabolism (Tabaldi et al, 2007;Mishra, Dubey, 2008). The evaluation of alkaline phosphatase activity in plant tissues colonized by mycorrhizal fungi is now widely used as a parameter of the physiological efficiency of mycorrhization.…”

Biochemical Investigation on the activities of Acid and Alkaline Phosphatases in two varieties of <i>Carica papaya</i> L. (Pawpaw) during ripening

“…Acid phosphatase (EC 3.1.3.2) and alkaline phosphatase (EC 3.1.3.1) are non -specific phosphatases that are grouped as acid or alkaline, based on their optimum pH below or above pH 7. They are enzymes that catalyse the hydrolysis of phosphate esters to produce inorganic phosphate and their main function in plants is to supply the inorganic phosphate that is required for the * 1 AGOREYO, BO; NWEKE, MA maintenance of cellular metabolism (Tabaldi et al, 2007;Mishra et al, 2008). Alkaline phosphatase is also employed in molecular biology for the construction of recombinant plasmids because of their ability to cleave 5΄ terminal phosphate from DNA fragments (Vemuri et al, 2010).…”