干旱区生态环境知识资源中心

Development of the structures providing for communication routes in the course of plant ontogenesis proceeds as functional source-sink relations are elaborated. Recent evidence concerning the structure of the transport system presumes that radial (parenchymal) transport zones maintain control over the development and functioning of the transport system throughout the plant lifespan. The specific domain organization of parenchyma assimilate transport is discussed in particular using data on the apoplast and endoplast structures in leaf parenchyma. These structures were shown to correlate with the time-course of photosynthesis and assimilate export under normal conditions and when the photosynthesis/export rates were severely affected in experiments. The relation of photosynthesis to the structural patterns of transport routes in parenchyma of various vascular plant species was analyzed using published data and evidence collected by the author in the Transaltai Gobi. The species composition of the flora of this desert is reduced along the aridity gradient due to the elimination, first, of the advanced species which developed a specialized system of assimilate translocation from the leaf (type 1), and, next, of the advanced species which employ rapid assimilate export via apoplast (type 2). The extremely arid ecotopes are inhabited by species with a primitive, archaic (non-specialized) organization of communication routes in parenchyma (type 0), low photosynthesis and metabolism, slow growth, and long intervals of arrested development. The distribution of plant species on the basis of two classes of traits characteristic of the photosynthetic capacity and the pattern of the export system is discussed in relation to plant life strategies in increasingly arid ecotopes.