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- Title
The Changes in the Tapetum of Pinus banksiana Accompanying Formation and Maturation of the Pollen.
- Authors
DICKINSON, H. G.; BELL, P. R.
- Abstract
As meiosis is completed, and following the synthesis of lipid during meiotic prophase, the tapetum begins to form precursors of sporopollenin. These accumulate in cisternae of the endoplasmic reticulum, resembling large dictyosome vesicles. They are released from the tapetal protoplasts intact, but rupture in the loculus. The liberated precursors polymerize either on lipid droplets in the expanded tapetal walls, forming the orbicules, or on the lipid layer surrounding the loculus, forming the second component of the peritapetal membrane. On rupture of the callose wall condensation also proceeds on the walls of the meiospores, already coated with a thin layer of sporopollenin synthesized by the spore itself. The tapetal protoplasts expand considerably during synthesis of the precursors. Wide channels also form between the protoplasts, and the nuclei undergo irregular divisions. Ribosomes are conspicuous in the tapetal cytoplasm during the sporopollenin synthesis, but protein levels are low. It is proposed that protein is exported to the loculus and untimately incorporated into the developing microspores. In the final phase of microsporogenesis the tapetum fragments, and parts move into the loculus.Protein levels in the tapetum are now high, possible indicating the massive synthesis of hydrolases which accomplish the dissolution of the tissue. Removal of the lipid component of the peritapetal membrane precedes the desiccation of the anther. The surfaces of the mature pollen lack organized or irregular deposits of tapetal debris.
- Publication
Annals of Botany, 1976, Vol 40, Issue 5, p1101
- ISSN
0305-7364
- Publication type
Article