Role of the tapetum in pollen and spore dispersal

Abstract

Group-specific functions linked to the dispersal of pollen and spores are reported in all the groups of land plants. Anthocerotopsida tapetal cells envelop developing meiocytes and spores; after exine formation their walls thicken, the cytoplasm starts to degenerate, and elaters from more than one tapetal cell are formed. Elaters aid spore dispersal from the sporangium. In some Marchantiopsida the tapetal cells form elaters but each originates from one cell. In Equisetophyta, the spores have two or four elaters composed of lignin and connected with the exine. They are formed with the aid of the tapetal cytoplasm once exine is complete. The elaters of this group (called also adpressors) differ from the above in that they adhere to and originate connected with the exine. In Polypodiophyta like Lecanopteris mirabilis, the spores have superficial strands which facilitate adhesion to dispersing ants. One of the main features of Spermatophyta parietal tapetum is to produce orbicules. In strictly anemophilous species pollenkitt is not produced and pollen grains are dispersed individually. Since both exine and orbicules consist of sporopollenin, they have the same electrostatic charges. This is believed to aid expulsion from the anther at anthesis. Pollenkitt is a degeneration product of amoeboid and periplasmodial tapetum in Magnoliophyta. It forms a layer on pollen grains and has at least four different functions related to dispersal: (1) it causes the grains to unite in clumps and (2) to adhere to pollinator bodies; (3) it protects the pollen grain cytoplasm from sunlight; and (4) the oily and perfumed components attract pollinators.