Chemical Structure of the Exine of Pollen Walls and a New Function for Carotenoids in Nature

Abstract

RECENT communications^1,2 have confirmed and extended the observation of Zetzsche et al.³ that there is a close chemical similarity between the nitrogen-free walls of a wide variety of pollen and spores. In particular the walls of Lycopodium clavatum and Pinus silvestris, which were studied in most detail, were found to consist of (a) an almost pure cellulose intine (10–15 per cent by weight of the wall) which retained the original shape of the wall after removal of the exine (sporopollenin of Zetzsche) by oxidation; (b) an ill-defined “xylan” fraction (10 per cent); (c) a fraction regarded as lignin-like (10–15 per cent) because the walls produced phenolic acids when fused with potassium hydroxide; (d) a major fraction (55–65 per cent, the exine) which is very resistant to most chemical reagents but readily oxidized to a mixture of mono arid dicarboxylic acids containing eighteen carbon atoms or less.