Light-enhanced Chloride Uptake by Wheat Laminae: A Comparison of Chopped and Vacuum-infiltrated Tissue.

The time course of (36)Cl(-) uptake from 5 mm KCl by 1.5-mm leaf segments of Triticum aestivum L. seedlings has been determined over 24 hours both in the light and in the dark. A light-enhanced uptake of Cl(-) develops after a few hours. Using whole laminae which have been water-injected by vacuum infiltration, a light-enhanced uptake is apparent from zero time. Uptake values achieved in the light by the two types of tissue are similar but in the dark there is a restricted uptake by the whole infiltrated laminae. It is considered that the slower uptake by whole laminae relative to chopped tissue in the dark is due to cuticular resistance to solute penetration, whereas in the light the impediment is overcome by stomatal opening. A light-enhanced uptake unrelated to stomatal opening is discernible in both tissues. Its energetic basis has not been defined but may be related to substrate exhaustion. The absorption mechanism is not impaired by vacuum infiltration.