SENSITIVITY OF ROOT AND LEAF WATER STATUS IN MAIZE (ZEA-MAYS) SUBJECTED TO MILD SOIL DRYNESS

The aim of this work was to test the sensitivity of the water potentia l (Psi(w)), osmotic potential (Psi(s)) and turgor (Psi(p)) Of roots an d leaves of maize seedlings (Zea mays L, cv. Carla) subjected to a mil d stress in drying soil in a growth chamber. To the best of our knowle dge there are no experimental data which describes diurnal courses of Psi(w) in soil, roots, and leaves and the parallel changes in the osmo tic potential (Psi(s)) and turgor (Psi(p)) of roots and leaves from pl ants grown in moist and drying soil. Root and leaf Psi(w) varied diurn ally, the amplitude being much more marked in leaves than in roots. Ro ot and leaf Psi(w) did not achieve equilibrium at predawn with the bul k soil matric potential (Psi(m)) but became higher. Our results are at variance with data indicating root Psi(w) is a sensitive indicator of soil dryness. Root Psi(w) in the well-watered and drought-stressed tr eatments did not differ, whereas daytime leaf Psi(w) in the droughted treatment was lower 6 days after water was withheld. Diurnal changes i n Psi(s) and Psi(p) were more marked in leaves than in roots. Withhold ing water lowered leaf Psi(p), whereas root Psi(p) substantially incre ased after only 3 days of withholding water. Early mild stress can be more easily and or the divergence in root and leaf more quickly identi fied by changes in root Psi(s), increases in root Psi(p), or the diver gence in root and leaf Psi(p) than by a lower Psi(w) of root or leaf. Relative water contents of roots and leaves measured in the light peri od indicated also sensitively falling Psi(m).