Control of Leaf Expansion in Wheat Seedlings Growing in Drying Soil

Abstract

The relative leaf expansion rate (RLER) of plants in drying soil eventually falls behind that of well watered plants. There is increasing evidence that the roots sense the drying of the soil and send signals to the leaves that control their behaviour independently of any effects of the soil's drying on the water status of the leaves. The roots could be sensing the falling availability of phosphorus, the falling water status, or the hardening of the soil. This paper explores these possibilities and concludes that, in the soil used, the roots were sensing both the water status and the strength of the soil but not the availability of phosphorus. Some of the experiments were done with a high evaporative demand on the leaves to see if the RLER would then be sensitive to the leaves' water status; it was not.