SEQUENCE OF DROUGHT RESPONSE OF MAIZE SEEDLINGS IN DRYING SOIL

Leaf elongation in monocotyledonous plants is sensitive to drought. To better understand the sequence of events in plants subjected to soil drying, leaf elongation and transpiration of maize seedlings (Zea mays L.) of 4 cultivars were monitored continuously and the diurnal course s of the root and leaf water relations were determined. Results from t his study indicate the following sequence of drought response: Leaf el ongation decreased before changes in the leaf water relations of non-g rowing zones of leaf blades were detected and before transpiration dec reased. Reductions in leaf elongation preceded changes in the root wat er potential (Psi(w)). Root Psi(w) was not a very sensitive indicator of soil dryness, whereas the root osmotic potential (Psi(s)) and root turgor (Psi(p)) were more sensitive indicators. The earliest events ob served in drying soil were a significant increase in the largest root diameter class (1720 to 1960 mu m) and a decrease in leaf elongation ( P = 0.08) 2 days after withholding water. Significant increases in roo t length were observed 2 days later. Soil drying increased the number of frne roots with diameters of <240 mu m. Slight increases in soil st rength did not affect leaf elongation in the drying soil.