Lipid histochemistry and fine structure of microspores and tapetal cells in the male sterility phenotype of the hybrid Oenothera (h) hookeri. velans

In Oenothera, mutations in two loci,fr and ster, cause male sterility (mst) related to alterations in lipid metabolism. The distribution of lipids in sterile anthers of the genotype Oenothera (h) hookeri. velans srer/ster and in anthers of sister plants with normal fertile pollen, which contain the allele +ster is analyzed by histochemical methods during mat development an d compared with the distribution of osmiophylic material observed by electr on microscopy. Changes in lipid histochemistry relative to wild type are se en in the tapetum of mst anthers from the late tetrad stage onwards and lat er in the pollenkit and microspore/pollen cytoplasm. Electron microscopy re veals osmiophylic material in the same locations than the Sudan BE test and also shows that exine material disintegrates. Microspores undergo mitosis and reach the vacuolated pollen grain stage with highly abnormal sporoderms but do not accumulate lipid bodies nor starch grains. Later an intense acc umulation of lipid material occurs in the contracted tapetum cells, while p ollen remnants are reabsorbed. With the exception of the tapetum, developme nt of the sporophytic tissues of the anther is normal throughout ontogeny i n ster/ster plants. In the second mst mutant, fr/fr, the earliest abnormali ties also concern lipid production, but were first seen in the cell layers of the anther wall, while the tapetum is essentially normal. In both mutant s, a dysfunction in lipid metabolism in sporophytic tissues is the first de tectable aberration in anther development followed in the ster/ster genotyp e by the failure of pollenkit deposition on the sporoderm and the absence o f gametophytic lipid land starch) production. After that, disintegration of the whole microspore/pollen occurs. Male sterility can be seen as a conseq uence of a mutation which concerns the expression of sporophyte and gametop hyte lipid metabolism in both studied genotypes.