Sugar and Starch Redistribution in Maize in Response to Shade and Ear Temperature Treatment1

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Abstract
Based on previous studies, it has been suggested that sugars stored in the maize (Zea mays L.) stem can be exported to growing kernels, and thus contribute to kernel dry matter. The objective of the current study was to determine to what extent sugar and starch depletion from maize (cv. Cornell 175) stem responds to shade and ear temperature treatments. Stem sugar concentrations in pith and vascular bundle tissues of stem remained at stable levels throughout a diurnal time course and after 3 days of canopy shading. In contrast, free space sugar concentrations were lower at 0600 h than at 1800 h (EST). When ear temperatures were controlled at 6, 16, 25, and 32°C from 18 to 27 days after pollination (DAP), plants had similar glucose, sucrose, and starch cooncentrations in leaf blades and sheaths at all ear temperatures; however, sucrose concentrations in a composite sample of cobs, shanks, and husks (CSHs), and in stems were higher in plants with the 6°C ear temperature than in plants with the 25°C ear temperature treatment. When plants were shaded to exclude 85% of light flux and ear temperatures were controlled during the period from 34 to 44 DAP, sugar and starch concentrations in leaf blades and sheaths were not affected. Glucose, sucrose, and starch concentrations in certain stem fractions were higher in plants with 6°C treatments than in corresponding stem fractions of plants with higher ear temperature. The differences between total sugar content in stems of the 6°C treatment and the contents in stems of the 16, 25, and 32°C treatments were 3.6, 4.1, and 4.1 g/plant, respectively. These differences were not attributed to respiratory loss because, at the end of the treatment period, stem and ear respiration rates among plants with various ear temperatures were not discernibly different. It appears that temperature‐induced increases in kernel sink strength at the middle and late kernel‐fill stages increase the extent of carbohydrate redistribution from vegetative plant parts to kernels.