Abstract

The remarkable resistance of pollen and spore exines to biological decay and non-oxidative chemical attack is a major contributor to the existence of the science of Palynology. The particular type of chemical material which has these properties, called sporopollenin, has been isolated from a wide variety of pollen grains and spores of both higher and lower plants. Early chemical work by Zetzsche and co-workers produced a method for isolation of a standard sporopollenin preparation and established that the polymer was highly unsaturated, contained hydroxyl and C-methyl groups, and that these properties were similar for all the types of sporopollenin examined whether from a recent or fossil source. Later work by Shaw and co-workers has indicated that sporopollenins are oxidative polymers of carotenoids and/or carotenoid esters. Synthetic analogues may be prepared by ionic catalysed oxidative polymerisation of various types of carotenoids; and the products are very similar to the natural materials. The relationship between carotenoids and sporopollenin has been further confirmed by comparison of ozonisation and potash fusion products and by labelling experiments. The biosynthesis of sporopollenin in the sporogenous tissue is seen to resemble a typical suspension polymerisation process in which the globules undergoing polymerisation are known as orbicules. The polymerising globules which will contain carotenoids are laid down on the microspore sac in a manner which is governed by the pre-formed architecture of the sac which in this way operates as a template.

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