Maize Kernel Set at Low Water Potential: II. Sensitivity to Reduced Assimilates at Pollination

Abstract

Plant water deficits at pollination decrease kernel set in maize. An important component of this kernel loss is developmental failure after fertilization. This study was undertaken to determine if zygotic abortion in water‐deficient plants results primarily from a decrease in assimilate supply daring the critical period around pollination. Plants were grown in soil/sand media in a controlled environment, and photosynthesis was inhibited by water‐deficit or low‐light treatments. Plants were hand‐pollinated when silk water potential of control, low‐light, and water‐deficient plants was −0.4, −0.4, and −1.0 MPa, respectively. Corresponding leaf water potentials were −0.3, −0.3, and −1.7 MPa. The water deficit decreased ovary water potential, osmotic potential, and turgor by 0.6, 0.3, and 0.3 MPa, respectively, compared with values in well‐watered plants. Treatments were terminated 2 d after pollination, and leaf photosynthesis recovered to control values within 24 h. Kernel numbers per ear were 598 ± 17 for control, 222 ± 72 for low light, and 15 ± 6 for water‐deficit treatments. The brief inhibition of photosynthesis had little impact on C and N accumulation in vegetative sinks, but severely reduced assimilate movement to reproductive sinks. At pollination, concentrations (mg g−1 dry wt.) of fructose, glucose, and sucrose in ovaries were similar for all treatments. The high levels of these soluble sugars in both setting and aborting ovaries suggests that kernel set depends on the rate of movement of assimilates into the ovaries, rather than the concentration of soluble sugars per se. Sucrose uptake by isolated ovaries was inhibited at low water potential, suggesting a direct effect of ovary water status on kernel development. The nearly complete kernel loss observed in the water‐deficit plants indicates that low ovary water potential at pollination decreased kernel set beyond that which can be attributed to reduced assimilate supplies alone.