Protein Pellicle of Stigmatic Papillae as a Probable Recognition Site in Incompatibility Reactions

Abstract

ANGIOSPERM pollen grains carry extracellular proteins in two sites: in the inner wall layer, the cellulosic intine, and in cavities in the outer exine, the sculptured part of the wall composed of sporopollenin^1–3. The intine proteins, which include several acid hydrolases, are synthesised by the spore and inserted during growth; they are therefore gametophytic in origin. The exine proteins, in contrast, are produced in the tapetum, the nurse tissue of the anther, and injected into the exine cavities during the maturation of the pollen grains; they are thus sporophytic. The enzymic wall proteins seem to be concerned with germination, penetration of the stigma surface and the early growth of the pollen tube. Other fractions are involved in the recognition responses which control breeding behaviour, playing a part in both interspecific⁴ and intraspecific^5,6 incompatibility systems.