Dissolution of Outer Wall of Pollen Grain during Pollination

THE exine patterning of the wall of the angiosperm pollen grain is established early in the ontogeny of the spore, and the exine pattern seems to be controlled genetically by the haploid microspore 1–6 . The material of the exine, sporopollenin, is remarkably durable and chemically inert, and is one of the most resistant wall polymers produced by plants. Although many feel sporopollenin is a tapetal derivative 3–6 , the exine has been suggested to be wholly a secretion of the microspore protoplast 7 . Heslop-Harrison and Knox have recently reported storage of the hydrolytic enzymes acid phosphatase, ribonuclease, esterase and amylase in pollen walls 8 . We report here further evidence of an enzyme system in the wall of the angiosperm pollen grain and suggest that the enzymes degrade the exine during germination.