ESTERASES IN POLLEN AND STIGMA OF BRASSICA

The dry type stigma of Brassica is covered with a continuous layer of cuticle. Cutinase and non-specific esterases may be involved in breakd own of this cuticle barrier during pollen-stigma interaction, but only a little is known about their nature and characteristics. We report h ere the presence of two distinct esterases from stigma and pollen of B rassica. A 33 kD esterase assayed using MU-butyrate substrate shows hi gh activity in stigma papillae. A similar esterase from Tropaeolum pol len has been shown to possess active cutinase activity. The esterase a ctivity in anther tissue is due to a 24 kD enzyme with substrate speci ficity toward acetate esters. Both enzymes require sulfhydryl groups f or their catalytic activity, Immunogold labelling of antibodies raised against these esterases localised the proteins at the subcellular lev el. Antibodies for MU-butyrate hydrolase gave a positive signal in the cell walls of mature stigma papillae and in the tapetum and microspor es during early stages of anther development. In the mature anther, a positive signal in the cytoplasm of pollen grains with some detectable localisation in the exine layer of the pollen wall was obtained. Simi lar results were obtained with acetate hydrolase antibodies. These est erases are thus spatially and temporally regulated in stigma and anthe r tissues.