A study is underway in our laboratory to determine the effect of loss of a particular chromosome on the maize heat shock response at the level of protein synthesis. In the summer of 1984, ten groups of plants were produced, each monosomic for one of the ten chromosomes of Zea mays L. The r-X1 deficiency was used to generate monosomics. We are grateful to Jerry Kermicle and John and Susan Laughnan for the provision of r-X1 stocks several years ago. The seed used in this study was produced in our nurseries during the period 1975-1980. Seed produced by crossing females carrying the r-X1 deficiency with males homozygous recessive for a visible seedling marker was germinated and grown to the 2-4 leaf stage (14 days). Plants expressing the recessive phenotype, suggesting loss of the chromosome carrying the marker gene, were selected. Disomic plants from the same cob were retained as controls. Table 1 lists the markers used for each chromosome and indicates the frequency of plants expressing the recessive phenotype. Cytogenetic confirmation of chromosome constitution was obtained from primary root tips.

Presently, the patterns of polypeptide synthesis (generated by SDS-PAGE and fluorography) in secondary roots of plants at the 6 leaf stage (50 days) are being compared before and following heat shock of intact plants. Preliminary results suggest that loss of chromosomes 1, 2, 3, 4, 7, 8, 9 and 10 does not affect the response to heat shock at the level examined. Plants monosomic for chromosomes 5 and 6 have not been examined. The change in the pattern of polypeptide synthesis following heat shock appears the same for specific monosomic plants and their disomic controls. The group of polypeptides (HSPs) characteristic of the heat shock response is evident in both disomic and monosomic plants. The level of synthesis of these polypeptides also appears similar. Fluorograms are being scanned spectrophotometrically and the distribution of ³⁵S-Methionine among polypeptides is being compared in monosomic and disomic plants. Antiserum raised to the 18,000 dalton polypeptide will be used to immunoprecipitate and quantify this polypeptide.

Table 1.

C. A. Rees and D. B. Walden

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