Water Deficits and Reproduction in Maize

Reproductive development in maize (Zea mays L.) is vulnerable to plant water deficits during anthesis but becomes less sensitive as reproduction progresses. To determine whether changes in tissue water status correlated with the change in sensitivity, we examined the water potential (Psi(w)), osmotic potential (Psi(s)), and turgor of reproductive tissues during a short-term water deficit imposed at anthesis or mid-grain fill. Plants were grown in controlled environments in soil. At anthesis, leaf, husk, silk, and ovary Psi(w) of control plants was similar (-0.5 to -0.65 megapascal) at midday. When water was withheld, Psi(w) decreased to -1.75, -1.3, -1.2, and -1.0 megapascal in these tissues. Net water uptake by the ovaries was inhibited, but final dry weight, solute content, and total extractable carbohydrates were similar to the controls. At mid-grain fill, leaf, husk, grain, and embryo Psi(w) of control plants were -0.55, -0.35, -0.75, and -0.80 megapascal at midday. When water was withheld, leaf and husk Psi(w) decreased to -2.4 and -1.4 megapascal within 6 days. However, grain and embryo Psi(w) remained within 0.15 megapascal of control values. The grain continued to accumulate dry matter despite a net loss of water and a reduction in total solute content. These results indicate that the response of the reproductive tissues to plant water deficits varies with stage of grain development. The maintenance of a favorable water status only after grain filling is under way may explain, at least in part, the high sensitivity to plant water deficits early in reproductive development and the decrease in sensitivity as reproduction progresses.