Salz- und Überflutungstoleranz von Puccinellia peisonis

Abstract

Summary Flooding-tolerance of Puccinellia is at least partly afforded by a well-developed aerenchyma, which is continuous from the apical to the proximal region of the root. Intercellular spaces between the inner cortex and the endodermis are small, thereby forming a unicellular layer of parenchymatous cortical cells immediately adjacent to the endodermal cells. Suberization of the endodermis (secondary stage) begins near the root apex, but passage cells persist as far as 100–150 mm behind the apex. Fine structure of cells of the inner cortex is comparable with that of endodermal passage cells, which are rich in cytoplasm and organelles. Remarkably, the cells of the inner cortex differentiate, at later stages of development, into a second endodermis (including secondary and tertiary stage), external to the original one. Passage cells in this additional endodermis are located in the same radial position as those of the original endodermis. It is therefore likely that the inner cortical cells of Puccinellia roots function as a second physiological barrier to the transport of solutes into the stele. Salt tolerance of Puccinellia would then be mediated by a close cooperation of aerenchyma, inner cortical and passage cells, and by xylem parenchyma cells, regulating symplasmic ion transport through root tissues into the xylem vessels.