Evolution of cell systems and plant life forms

Abstract

The distribution of photosynthates in the body of vascular plants is examined by the methods of electron and confocal fluorescent microscopy in lifetime dynamics and using fixed preparations. It is shown that system relations of cells are provided by the “trophic tract,” i.e., endoplasmic membrane meshwork, which is induced by photosynthesis and moves along plasmodesmata from photosynthetic cells to meristematic cells consuming photosynthates. The structure and functions of the trophic tract are controlled by the actomyosin contractile apparatus of the cytoskeleton. Climatic cooling and aridization in the Neogene caused the loss of plasticity of the actomyosin complex, elimination of plasmodesmata, and fragmentation of the trophic tract, which were accompanied by partial transition of plants to the distribution of photosynthates through the apoplast. This caused the appearance in the Miocene of perennial and annual herbs, with the trophic tract composed of particular domains without plasmodesmal connections. In contrast to the continuous endoplasmic trophic tract of trees, the apoplastic tract of herbs is inefficient, since transdomain transport of sugar along the apoplast is connected with high energy consumption. However, it is free from the influence of cold temperatures and deficiency in water or mineral supply. The cost for phylogenetic adaptogenesis of vascular plants to the Neogene climatic cooling and aridization is a fourfold increase in genome size. The morphofunctional consequences are reduction of cell systems and life forms in connection with the energy problems induced by fragmentation of the trophic tract.