The heat shock response of pollen and other tissues of maize.

While a heat shock treatment of 40 degrees C or 45 degrees C induced the vegetative tissues of maize to produce the typical heat shock proteins (HSPs), germinating maize pollen exposed to the same temperatures did not synthesize these characteristic HSPs. Comparison of RNA accumulation in shoot and tassel tissue showed that mRNAs for HSP70 and HSP18 increased several-fold, reaching high levels within 1 or 2 hours. At the higher temperature of 45 degrees C these vegetative tissues were blocked in removal of an intron from the HSP70 mRNA precursor, which accumulated to a high level in tassel tissue. In germinating pollen exposed to heat shock, mRNAs for these HSPs were induced but accumulated only to low levels. The stressed pollen maintained high levels of RNA for alpha-tubulin, a representative normal transcript. It is likely that the defective heat shock response of maize pollen is due to inefficient induction of heat shock gene transcription.