Distribution of sulfur within oilseed rape leaves in response to sulfur deficiency during vegetative growth

The distribution of S to sulfate, glucosinolates, glutathione, and the inso luble fraction within oilseed rape (Brassica napus L.) leaves of different ages was investigated during vegetative growth. The concentrations of gluta thione and glucosinolates increased from the oldest to the youngest leaves, whereas the opposite was observed for SO42-. The concentration of insolubl e S was similar among all of the leaves. At sufficient S supply and in the youngest leaves, 2% of total S was allocated to glutathione, 6% to glucosin olates, 50% to the insoluble fraction, and the remainder accumulated as SO4 2-. In the middle and oldest leaves, 70% to 90% of total S accumulated as S O42-, whereas glutathione and glucosinolates together accounted for less th an 1% of S. When the S supply was withdrawn (minus S), the concentrations o f all S-containing compounds, particularly SO42-, decreased in the youngest and middle leaves. Neither glucosinolates nor glutathione were major sourc es of S during S deficiency. Plants grown on nutrient solution containing m inus S and low N were less deficient than plants grown on solution containi ng minus S and high N. The effect of N was explained by differences in grow th rate. The different responses of leaves of different ages to S deficienc y have to be taken into account for the development of field diagnostic tes ts to determine whether plants are S deficient.