Physiological and Structural Ontogeny of the Source Leaf
A leaf is transformed during ontogenesis from a heterotrophic, to an autotrophic, organ. Initial dependence on phloem imported nutrients is lost as increasing photosynthetic capacity enables the lamina to satisfy its own carbon requirements, and to export excess photosynthate. This transition is interesting from both a practical and a theoretical viewpoint. The leaf becomes an asset to the carbon economy of the plant only when it is autotrophic and has begun to export. Theoretically, the study of conditions which contribute to the start of assimilate flow should provide insight into the mechanisms of vein loading and long-distance transport.
KeywordsMature Leaf Intermediary Cell Sieve Tube Sieve Element Minor Vein
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