Komarov Botanical Institute
197376 St.-Petersburg, Prof. Popov St., 2
e-mail: gamaleil@fromru.com
The diversity of tissue and cell organization in the leaves of dicots is explained as the mutual effect of light and water fluxes distribution. Equally with certain data about the role of light distribution, the same influence of water flux distribution on the leaf structure is recognized. Dorsiventral leaves of woody plants have an adequate to structure dorsiventral ring of water circulation. Rising flux from the xylem allocates via leaf apoplast with intermediate accumulation in upper epiderma. Descending flux starts and returns to bundle moving from cell to cell along the symplast (ER) of spongy parenchyma, bundle sheath and terminal complexes of the phloem. Isolateral leaves of herbs have a concentric pathway of solute circulation corresponding to the structure. Xylem flux allocates via symplast with water and nitrogen accumulation in paraveinal parenchyma. Water returns to phloem by transit via the apoplast in parallels with phloem exudate formation. Structural features correlated with the model of water circulation in the leaf are described. Numerous lines of leaf evolution well-known for dicots collect to two main topics which are typical for woody and herbaceous forms of dicots. The mechanisms of cell and tissue differentiation under the control of transport fluxes are discussed with special attention to ontogenetic and phylogenetic trends.
