Last year we reported preliminary results obtained in a study characterizing shifts in the pattern of protein synthesis occurring as a function of development in some maize inbreds and hybrids (MNL 57:163-164, 1983). The technique employed involved the dissection of embryos from kernels at successive stages following pollination and labelling them with 35S-methionine in Murashige and Skoog medium. When the work was continued this past summer, a different technique was adopted which, it is believed, more closely approximates conditions found in vivo. This procedure was previously described by Kriz (MNL 56:14-15, 1982) and entails the labelling of intact kernels while attached to an ear which has been removed from the plant. 35S-methionine is introduced into the kernel through injection with a Hamilton syringe. For our purpose, optimal incorporation was achieved with 3 ul of undiluted 35S-methionine injected into the embryo side of the kernel, followed by a 2 hr incubation period. Embryos were subsequently dissected from labelled kernels, homogenized in plant extraction buffer (MNL 55:117, 1981) and protein samples subjected to one and two dimensional electrophoresis.
The cultivars employed in this study included Oh43, M14 and W23, as well as some of the reciprocal hybrids produced from crosses of the latter two with Oh43. Results obtained from the previous summer indicated that a minimum of 3-5 days between sampling times is required to observe significant changes in the patterns of protein synthesis. The earliest at which individual embryos could be manipulated was found to be 17 days post-pollination. For these reasons, we selected embryos at 17, 20, 25, 30, 35 and 40 days post-pollination. Samples were arranged on one-dimensional gels to allow analysis of the effects of genotype, developmental stage and period during the growing season over which saturation occurred, on the pattern of protein synthesis. Results indicate that both qualitative and quantitative changes in the synthetic pattern occur during the course of development in all genotypes. Variation between genotypes is also observed, this being mainly quantitative in nature. Hybrids appear to exhibit patterns intermediate to the parental inbreds, but more closely resembling the female parent. In some instances the stage during the growing season at which pollinations were made appeared to affect the rate at which development occurred, as determined by the protein synthetic pattern.
J. Boothe, D. B. Walden and B. G. Atkinson
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