WATER STATUS AND DEVELOPMENT OF THE MAIZE ENDOSPERM AND EMBRYO DURING DROUGHT

Drought during grain filling decreases final kernel mass in maize (Zea mays L.). Lack of assimilates or an unfavorable water status within the embryo or endosperm could limit kernel development. To test these possibilities, remobilization of reduced C and N as well as kernel and embryo water status were measured in plants exposed to a water deficit during grain fill. Irrigation was withheld from field-grown plants after final kernel number was established. This treatment resulted in a soil moisture deficit of 224 mm and decreased endosperm and embryo mass by 16%, compared with controls. The water deficit shortened the effective filling period, but did not alter the rate of dry matter accumulation in either the endosperm or embryo. Carbohydrate reserves in leaf and stalk tissues as well as N stored in the leaves were remobilized to support kernel growth. However, grain filling ceased before these reserves were depleted completely. Grain filling continued in both well-watered and water-deficient plants until the moisture content of the endosperm and embryo decreased to 280 and 430 g kg(-1) fresh wt., respectively. Water-deficient plants reached these values 10 d earlier because water loss from the endosperm began sooner after anthesis and maximum water content of the embryo was lower, compared with the controls. Kernel and embryo osmotic potentials (psi(s)) decreased rapidly late in grain filling and were - 2.2 to - 2.6 MPa when growth ceased. The results indicate that kernel water status is affected directly by drought and may be an important determinant of kernel development. They suggest that a water deficit after anthesis shortens the duration of grain filling by causing premature desiccation of the endosperm and by limiting embryo volume.