Structures of the plant trophic tract: Plastid stromules and cell-wall plasmodesmata

Plastid stromules and cell-wall plasmodesmata are special plant-cell stsructures. They were discovered a century and a half apart: stromules at the beginning of the 21st century and plasmodesmata the end of the 19th. The former and latter are intra- and intercellular fragments, respectively, of endoplasmic reticulum, which is a network for photosynthesis distribution in the plant body. Methods and history of discovery, structural similarities and differences, and series of functional interpretations are discussed. The origins of both structures are connected with photosynthesis and photosynthate export. Their tubular structure and transport function are similar. The mobility of both is under control of the actomyosin cytoskeleton. The temperature regimes of formation and functioning also are the same. Photosynthesis is possible at 0°C and even lower. The structures of the exporting network—stromules and plasmodesmata—do not form below 10°C, and after 20°C the numbers of the former and latter significantly increase in relation to growth of cytoskeleton plasticity. The structural and functional continuity of stromules and plasmodesmata are postulated as the mobile trophic tract of vascular plants.