DISTRIBUTION AND REDISTRIBUTION OF SULFUR TAKEN UP FROM NUTRIENT SOLUTION DURING VEGETATIVE GROWTH IN BARLEY

Barley plants were grown in a nutrient solution containing 25-mu-M sulphate and the roots were pulsed with [S-35]sulphate for 48-h periods at 6 different times between the emergence of leaf 5 (L5) and the emergence of leaf 8 (L8). Growth was continued in unlabelled solution until the emergence of LIO. Within the shoot system, sulphur was directed principally into the leaf undergoing expansion. A large proportion of the S-35-label delivered to young expanding leaves (< 40% of full expansion) did not occur at the time of the pulse, but subsequently during the ensuing chase indicating slow redistribution of sulphur from another site. During the later stages of leaf expansion (40-100%), most of the sulphur entered the leaf during the pulse, suggesting that sulphur was delivered more directly from the nutrient solution. Up to 75% of the sulphur delivered to L3-L6 at the time they approached or attained full expansion (70-100%) was re-exported. At least some of the sulphur exported from fully expanded leaves was redistributed to developing leaves.