9507681 Koch Adaptive plasticity of form is one of the most remarkable features of multicelled plants. At least one contributor to this flexibility appears to be the sensitivity of specific plant genes to sugar levels (ie. photosynthate availability). Among these are the genes for sucrose metabolizing enzymes. Import of translocated sucrose by growing organs can be strongly affected by the capacity for sucrose metabolism, which is catalyzed by only two known pathways in plant (invertase and the reversible sucrose synthase reaction). Under previous NSF grant, Dr. Koch has demonstrated that genes encoding both these enzymes in maize are carbohydrate-responsive, providing a potential mechanism for coarse adjustment of capacity for sucrose use relative to its overall availability. In addition, the newly cloned isozyme genes for invertase exhibit a differential carbohydrate responsiveness with surprising similarity to that observed among isozyme genes of sucrose synthase. In this project, Dr. Koch will address the significance of these developments using a combined molecular, genetic and physiological approach. Probes for an invertase gene family (putatively soluble) provide an opportunity to address the relationship between sugar-responsive gene expression and the widespread role of soluble invertases in initial growth by newly expanding sink tissues.
