Influence of iron nutrition on sulphur uptake and metabolism in maize (Zea mays L.) roots

Recent research has evidenced a relationship between Fe nutrition and S nutrition. Aim of the present work was to investigate the effect of Fe deficiency on the capacity of maize roots to take up and metabolize S. Maize (Zea mays L. cv. Cecilia) plants were grown for 10 d in nutrient solution (NS) with (+S) or without (-S) sulphate and Fe was added as Fe-III-EDTA at 80 mum. After removing the extraplasmatic Fe pool, half of the plants of each treatment (+S and -S) were transferred to a new Fe-free NS. Roots were collected 4 and 24 h from the beginning of Fe deprivation. Fe deprivation slightly increased root thiols content in both nutritive conditions (+S and -S). ATP sulphurylase activity was enhanced by sulphur deprivation, but greatly depressed when Fe and S were both omitted from the nutrient solution. O-Acetylserine sulphydrylase activity was also enhanced by S deprivation; this activity was increased by Fe starvation in +S plants, while it was unaffected by Fe nutrition in -S plants. S deprivation greatly increased uptake rates of (SO42-)-S-35 (1.9 +/- 0.1 vs. 5.2 +/- 0.2 mumol g(-1) root d.w. h(-1)); furthermore, Fe deficiency increased (SO42-)-S-35 uptake rates by 11 and 55% in +S and -S plants, respectively. Data show that Fe-deficiency in maize results in a higher ability to take up sulphate, while limiting the first step of S assimilation in S deprived plants.