Tissue specificity of the heat-shock response in maize

The tissue specificity of the heat-shock response in maize was investigated. The ability to synthesize heat shock proteins (hsp) at 40°C, as well as the intensity and duration of that synthesis, was analyzed in coleoptiles, scutella, green and etiolated leaves, suspension-cultured cells, germinating pollen grains, and primary root sections at different stages of development. One-dimensional sodium dodecyl sulfate gel electrophoresis of extracted proteins revealed that most of the tissues synthesized the typical set of 10 hsp, but that the exact characteristics of the response depended upon the tissue type. While elongating portions of the primary root exhibited a strong heat shock response, the more mature portions showed a reduced ability to synthesize hsp. Leaves, whether green or etiolated, excised or intact, constitutively synthesized a low level of hsp at 25°C, and high levels could be induced at 40°C. Suspension-cultures of Black Mexican sweet corn synthesized, besides the typical set of hsp, two additional polypeptides. In contrast to all the other tissues, germinating pollen grains could not be induced to synthesize the typical set of hsp but did synthesize two new polypeptides of 92 and 56 kD molecular weight.

The heat shock response was transient for most of the tissues which synthesized the standard set of hsp. Hsp synthesis was detected up to 2 to 3 hours, but not at 10 hours of continuous 40°C treatment. The exception was suspension cultured cells, in which hsp synthesis showed only a slight reduction after 10 hours at 40°C. Tissue-specific differences in the heat-shock response suggest that there are differences in the way a given tissue is able to adapt to high temperature.

We have confirmed the previous suggestion that maize hsp do not accumulate in substantial quantities. Using two-dimensional gel analysis, hsp could be detected by autoradiography but not by sensitive silver staining techniques.