Effects of aluminum and sulphate on ATP sulphurylase activity and on soluble thiol content in two sorghum cultivars

Abstract

The ATP sulphurylase enzyme catalyzes the first step of the sulphate assimilation process and its activity increase can be related to the production of soluble thiols, compounds supposedly connected with tolerance to several stress types. The aim of this experiment was to verify the possibility of this process in plants under AI toxicity and two sorghum cultivars, one Al - tolerant and the other AI - sensitive, were submitted to two S concentrations (0 and 0.6mM) and to two AI concentrations (0 and 0.185mM) for a period of tem days in a Clark nutrient solution at 4.0pH. The specific activity of ATP sulphurylase in the presence of AI increased only in the root system of both cultivars but showed no difference between them. In the absence of S, the total activity of ATP sulphurylase was extremely low, independently of AI presence. In the presence of S, its activity was highly increased but a great part of it was eliminated in the presence of AI, especially in the leaves of the sensitive cultivar where soluble thiol content was always higher than in the root system and increased in the absence of S. In the absence of S, AI increased thiol content in both cultivars, but in the presence of S it diad not affect or reduce in either sensitive or tolerant cultivar. Independent from the presence of S, the treatment with AI resulted in a thiol content increase in the root system. The tolerant cultivar showed an average thiol content respectively >76% and 81% higher than the sensitive cultivar in the presence or absence of AI.