HSP synthesis in the male gametophyte

Most plant tissues respond to heat shock by synthesizing a specific set of polypeptides (HSPs). Pollen seems to be the only exception. Analysis of germinating pollen showed no HSP synthesis in Tradescantia (J.P. Mascarenhas and M.V. Altschuler, 1983, in "Pollen: Biology and Implications for Plant Breeding" pp. 3-8, D.L. Mulcahy and E. Ottaviano eds.) and only two, non-typical polypeptides in maize (P. Cooper et al., 1984, Plant Physiol. 75:431-441). However, there are no data concerning HSPs during pollen maturation, a time during which corn plants are very likely to suffer high temperature stresses.

In this report we analyze heat-shock response of immature pollen. Whole anthers, taken 12 days after meiosis or at anthesis, were heat-shocked (37 C) for 3 hours. Pollen was then collected, extracted, subjected to 1D SDS PAGE and the gels exposed at -80 C.

At anthesis no incorporation of 35S-methionine into proteins could be detected. Twelve days after meiosis both heat-shock and heat-stroke proteins were found, although they differed both in the size and in the number from the typical HSPs induced in sporophytic tissues. Also, unlike most of the sporophytic ones, they appeared to be genotype dependent. Inbred N172 showed 2 HSPs, approx. 81 and 72 kD, while inbred Mo17 showed 4 HSPs, approx. 72, 69, 63 and 53 kD. These data indicate that: i) HSPs are inducible in pollen, during its maturation within the anthers. ii) gametophytic genetic variability in response to high temperature stress exists also at the molecular level, although no correlations can be established between specific HSPs and the degree of tolerance to heat shock expressed by different genotypes in terms of germination and tube growth.

We also explored the existence of such variability in the sporophyte. In a preliminary screening of 22 inbred lines, using root tips as sporophytic tissue, several differences between genotypes were found.

Further analysis of gametophytic HSPs induced at different stages of pollen maturation is in progress.

C. Frova, G. Binelli and E. Ottaviano

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