STEM INFUSION OF LIQUID CULTURE-MEDIUM PREVENTS REPRODUCTIVE FAILURE OF MAIZE AT LOW WATER POTENTIAL

Maize (Zea mays L.) plants exposed to low water potentials (psi-w) at anthesis frequently experience failure of reproduction despite high plant psi-w before and after anthesis. Since the supply of reserve carbohydrates in maize stems may be low at anthesis and low psi-w can inhibit photosynthesis, it is possible that a water deficit at anthesis causes a deficit of photosynthetic products or their derivatives, which could lead to premature cessation of reproductive development. To test this hypothesis, a high-sucrose (150 g L-1 liquid tissue culture medium was supplied to the stems of dehydrating maize plants from an external reservoir using a new stem infusion technique. Plants were grown in controlled environment chambers in large pots containing soil. At midday, the rates of net photosynthesis of upper leaves of well-watered plants were almost-equal-to 20-mu-mol m-2 s-1 and the psi-w of these leaves was - 0.6 MPa. Approximately 5 d after water was withheld from pots, upper leaf psi-w dropped to -1.6 to -1.8 MPa and photosynthetic rates of the same leaves were almost-equal-to 0.0-mu-mol m-2 s-1. Stem infusion of liquid tissue culture medium during 5- or 7.5-d water-deficit periods initiated 1 d after silking prevented reproductive failure without rehydrating the plant. Final grain yields of some of the medium-infused plants approached control yields. Dehydrated plants which received infusion of a similar volume of water or which were not infused experienced nearly complete reproductive failure. Following rehydration, photosynthesis of all plants exposed to low psi-w during anthesis recovered, but only those infused with the medium during low psi-w continued kernel development to maturity. Additional experiments indicated that plant growth regulators were not required for an effective medium. These experiments identify assimilate supply and not low plant psi-w per se as a limiting factor in maize reproductive failure near anthesis and suggest that improvement in drought tolerance may be achieved by changes in the assimilate storage patterns and/or the phenology of maize plants. Additionally, this whole plant system provides an agriculturally relevant model system for studying the cellular and subcellular mechanisms associated with failure of reproductive growth at low psi-w.