Ultrastructural cytology of plastids in pollen grains of certain androgenic and nonandrogenic plants

Summary

An ultrastructural survey of the plastid types from the tetrad stage to early bicellular pollen grains of several angiosperms has been conducted. Most families studied, namely theSolanaceae, Gramineae (Poaceae), Cruciferae (Brassicaceae), Ranunculaceae andLiliaceae, include species known to produce embryoids from pollen grains of cultured anthers (androgenesis), while a few families, such as theScrophulariaceae, Convolvulaceae andChenopodiaceae, mainly consist of recalcitrant or nonandrogenic species. Proplastids were found to be specific to pollen grains of all androgenic species studied, while amyloplasts were characteristic of those of recalcitrant species such asAntirrhinum majus, Convolvulus arvensis, Beta vulgaris andChenopodium album. In all androgenic species, starch accumulation only started at the late bicellular stage, except in tomato andLilium where it started before pollen mitosis. In the recalcitrant species, starch accumulated throughout pollen development with a peak during pollen maturation. Duringin vitro androgenesis, proplastids of the pollen were transformed to amyloplasts and then to chloroplasts, in the cotyledons and leaves of the plantlets formed. The amyloplasts of pollen in recalcitrant species retained their original morphology in culture although the number of starch grains per plastid increased considerably. These results clearly indicate that plastids can be used as a specific marker to identify androgenic species from recalcitrant ones. The question, “Do plastids indicate the ability to perform androgenesis?”, has also been discussed.