Physiological and molecular aspects of sulphate uptake in two maize hybrids in response to S-deprivation

Two maize hybrids (KW2 and KW7), chosen on the basis of their productivity with low nutritional input, showed different physiological strategies, with opposite sulphate uptake Vmax and Km values, in response to sulphate deprivation. In order to characterise the physiological differences between the two hybrids, sulphate influx rates were measured in different nutritional conditions. When grown for 7 days in S-deprived solution, significantly higher influx rates were measured in roots of KW7 than KW2. Withdrawal of sulphate, after 7 days in presence of S, induced the derepression of the sulphate transport system in both hybrids. However, maize hybrid KW2 seemed to have a more rapid activation than that of KW7, which, in turn, seemed to be more resistant to prolonged sulphur deprivation. The data obtained were not supported by the outcome of the analysis of mRNA abundance, performed with the homologue probe ZmST1 on roots of both hybrids. Root sulphate and glutathione contents were in all cases higher in KW7 than KW2. The discrepancy between the physiological and the molecular data suggests the possible existence of other root transporters involved in sulphate uptake, and/or of some post-transcriptional regulatory mechanisms.