Carbohydrate Reserves and Reproductive Development at Low Leaf Water Potentials in Maize1

Abstract

Low water potentials (ψw) during anthesis and early grain fill can decrease yields in grain crops. If photosynthesis is inhibited under these conditions, carbohydrate reserves may become limiting for grain growth. We measured the mobilization of stored nonstructural carbohydrates in the maize plant (Zea mays L.) during low ψw, imposed at silk emergence (T1), early grain fill (T2), and mid‐grain fill (T3) and maintained to maturity. low leaf ψw, completely inhibited photosynthesis, and reproductive development depended entirely on reserves. The control yield was equivalent to 9910 kg ha−1. Mean yields on a per‐plant basis were 139, 89, 25, and 0 g for the control, T3, T2, and T1 treatments, respectively. Yield losses resulted from decreased seed size in T3, decreased seed size and number in T2, and a cessation of silk and ear development in T1. After anthesis, dry matter accumulated in the stems and leaves and was mobilized to the ear at low ψw in T3 and T2 but not in T1. All the mobilized dry matter from the stems and a sizable fraction from the leaves was carbohydrate. By maturity, the mobilized carbohydrates had been depleted to the level at anthesis. In T1, there was no mobilization and the carbohydrates remained at the low anthesis levels until maturity. The low carbohydrate at T1 indicates that reserves were not sufficient to support reproductive development when photosynthesis was inhibited at low ψw. The lack of reserves may explain the high sensitivity of anthesis and early grain fill to low ψw, as well as previous reports of the inability of silks to maintain turgor by osmotic adjustment. The decreasing sensitivity of grain development to low ψw as reproduction progresses may result from an increasing availability of reserves.