Invertase in leaves: conundrum or control point?

The distribution and activity of invertase in mature source leaves is discu ssed in relation to the anabolic and catabolic processes that occur in such tissues. Anomalously high levels of extractable activity are not, at first sight, consistent with the perceived anabolic function of leaves. The mech anisms of sucrose breakdown in leaves are discussed with particular referen ce to the ways in which in vivo activity could be modulated by factors such as product inhibition or developmental control. The possible roles of inve rtase in leaves are discussed in relation to (a) the metabolism of sucrose in heterotrophic tissues (epidermis and vasculature); (b) sensing changes i n assimilate abundance and transducing these into altered patterns of gene expression and (c) the metabolism of oligosaccharides based upon sucrose. E vidence is presented that indicates a significant degree of tissue-level co mpartmentation in the activity of invertase.