Download or read book Mechanisms by which Heat Stress Affects Protein Accumulation in Maize Kernels written by Paulo Ferreira Mendes Monjardino and published by . This book was released on 1997 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: Heat stress imposed during maize kernel cell division stage affects protein accumulation, but the extent of the effect and the mechanisms by which this disruption occur are not known. Growth chamber- and field- and field-grown kernels were exposed to continuous 35oC for 2 and 4 days, starting at 5 days after pollination (DAP). Kernel growth, namely the fertilized tissues (i.e., the embryo and the endosperm), was affected by both periods of heat stress. However, the endosperm protein accumulation was only repressed by 4 days of heat stress (DHS). Within the protein solubility fractions, the zeins were the most affected by 4 DHS, thus changing endosperm protein composition (the albumins plus globulins and glutelins were less affected), but not to the point of significantly altering its total amino acid composition. Zeins were most affected by 4 DHS at early development stages, probably at the synthesis level, as suggested by a short-term (3h) experiment where incorporation of L-[35S] methionine between protein fractions was measured, and by the developmental accumulation pattern of the 27 KD zein. Tha analysis of the mRNA steady-state levels and transcription rates of the 27 KD zein and the cluster 1 zeins of the subfamily 4 (ZSF4CI) also showed that zeins are repressed at the transcriptional level by 4 DHS treatments. Endoreduplication was also measured at the transcriptional level by 4 DHS treatments. Endoreduplication was also measured in endosperm tissue and in the nuclei used for the transcription run-ons. Two DHS significantly delayed endoreduplication, whereas 4 DHS significantly repressed it. During the preparation of nuclei for the transcription run-ons, the high C class nuclei were unintentionally excluded, resulting in much smaller differences in the average C values of the control and 4 DHS nuclei. However, the developmental pattern of the 27 kD and ZSF4CI zeins transcription rates of the control and 4 DHS samples was similar to their protein and mRNA steady-state levels. This seems to indicate that the differences in endoreduplication between the control and 4 DHS endosperms are not related to the differences in zein genes transcription rates, but that both must be affected by the disruption of endosperm development caused by heat stress.