Studies of the development of wheat (Triticum aestivum) pollen: formation of the pollen aperture

Abstract

Pollen of Triticum aestivum is described at a series of developmental stages. Observations are recorded on the ultrastructural level and the light microscopy level. The pollen aperture starts to develop at the late tetrad period. The fibrillar coat of the plasma membrane is thinner at the site of the developed pore than in the rest of the wall. The bacules are developed as dense stained patches distributed in the fibrillar matrix. The tectum is formed as a result of deposition of material on the distal surface of the fibrillar matrix. On release of the microspores from the tetrad, development of the foot layer takes place on a trilamellated structure. Additional trilamellated structures are formed and are seemingly associated with the proximal surface of the foot layer in the nonaperture exine. These lamellations are the progenitors of a highly developed endexine in the annulus. At the early vacuolate stage a thick granular–fibrillar layer is developed under the operculum. This layer becomes highly compressed in the vacuolate pollen grain, which indicates that it may function as a cushion that protects the operculum from detaching by elimination of cytoplasmic pressure initiated during pollen vacuolation. Zwischenkörper is developed between the convoluted plasma membrane and the compact granular–fibrillar layer below the operculum. The intine is developed as a thin layer under Zwischenkörper and becomes very thick at the border between the annulus and the nonapertural wall.