Assimilate Flux Determines Kernel Set at Low Water Potential in Maize

Plant water deficits during flowering cause maize ( Zea mays L.) kernels to abort. Lack of current and reserve photosynthate account for much of the kernel loss, but partitioning to ovaries at low ovary water potential (ψ w ) may also be limited by lack of assimilate demand. To test this possibility, we measured the water status, carbohydrate content, and growth of ovaries on plants grown in the field in pots containing 22 kg of soil under one of three light environments Control , 75‐cm rows, 43 055 plants ha −l ; Shade, same as Control except under shade cloth (55% fight interception) from the sixth leaf stage until physiological maturity; or Isolated , 122‐cm rows, 6727 plants ha −1 and exposed to a water deficit during pollination. Water was withheld at silk emergence and plants were hand‐pollinated 4 d later when silk ψ was ≈ − 1.1 MPa, leaf ψ w was ≈ − 1.8 MPa, and photosynthesis was completely inhibited. The water deficit decreased kernel set, which was correlated with the inhibition of ovary dry matter accumulation. The concentration of sucrose and glucose increased in ovaries of water‐deficient plants, and ovary turgor remained at or above control levels. Thus, inhibition of ovary growth at low ψ w was not related to a loss of turgor, nor was it caused by a depletion of ovary sugars. Sugar accumulation at low ψ w , suggested that metabolism may have been impaired. Coupled with a low level of reserves, failure to utilize available sugars at low ψ w would severely inhibit assimilate flux to the ear and render kernel set highly vulnerable to water deficits during pollination.