SOLUBILITY OF POLLEN EXINES

The sporopollenin of pollen exines of Ambrosia trifida is soluble in fused potassium hydroxide, in strong oxidizing solutions, and in certain organic bases. It is insoluble in other organic and inorganic acids and bases, in lipid solvents, and in detergents. The outer exine layer of gymnosperm and angiosperm pollen dissolves in 2-aminoethanol. The inner exine layer, as well as the exine of pteridophyte spores, is insoluble. The exine dissolution process in 2-aminoethanol involves swelling and disintegration of exine structures, leaving some residual globules. Sporopollenin shares some solubility properties with lignin and cutin but appears to be chemically distinct from these substances.