Change in ultrastructure of apical cells in wheat shoots in ontogenesis

Electron microscopy and morphometric studies were made of apical meristem cells of a shoot of wheat (Triticum aestivum L., variety Saratovskaya-29) at various phases of ontogenesis: vegetative, prefloral, and beginning of flowering (from seed embryo to the beginning of formation of the head). It was demonstrated that during this period there are changes in cytoplasmic structures, their number, proportions, and internal structures. Changes were disclosed which were linked to the hereditary course of growth and differentiation of the apex, that is, changes that were evidently ontogenetic (dynamics of lipid drops, of the Golgi apparatus, endoplasmic reticulum, and to some degree, the structure of plastids and mitochondria). It was demonstrated that in the course of the vegatative phase, changes in activity of the apex meristem and its various zones are connected with comparatively small quantitative changes in content of basic organelle cytoplasm, and their structural transformations are more significant. The activation of the apex in the pre-floral phase is linked to an increase in formation of membrane systems, increase in the functional activity of organelles, and increase in the formation of ribosomes and their density in the cytoplasm which provides conditions for a transition of the apex to generative differentiation.