Kernel Abortion in Maize : II. Distribution of C among Kernel Carbohydrates

Abstract

This study was designed to compare the uptake and distribution of (14)C among fructose, glucose, sucrose, and starch in the cob, pedicel, and endosperm tissues of maize (Zea mays L.) kernels induced to abort by high temperature with those that develop normally. Kernels cultured in vitro at 30 and 35 degrees C were transferred to [(14)C]sucrose media 10 days after pollination. Kernels cultured at 35 degrees C aborted prior to the onset of linear dry matter accumulation. Significant uptake into the cob, pedicel, and endosperm of radioactivity associated with the soluble and starch fractions of the tissues was detected after 24 hours in culture on labeled media. After 8 days in culture on [(14)C]sucrose media, 48 and 40% of the radioactivity associated with the cob carbohydrates was found in the reducing sugars at 30 and 35 degrees C, respectively. This indicates that some of the sucrose taken up by the cob tissue was cleaved to fructose and glucose in the cob. Of the total carbohydrates, a higher percentage of label was associated with sucrose and a lower percentage with fructose and glucose in pedicel tissue of kernels cultured at 35 degrees C compared to kernels cultured at 30 degrees C. These results indicate that sucrose was not cleaved to fructose and glucose as rapidly during the unloading process in the pedicel of kernels induced to abort by high temperature. Kernels cultured at 35 degrees C had a much lower proportion of label associated with endosperm starch (29%) than did kernels cultured at 30 degrees C (89%). Kernels cultured at 35 degrees C had a correspondingly higher proportion of (14)C in endosperm fructose, glucose, and sucrose. These results indicate that starch synthesis in the endosperm is strongly inhibited in kernels induced to abort by high temperature even though there is an adequate supply of sugar.