Poster: Photosynthesis

Abs # 351: Regulation of photosynthesis during Arabidopsis leaf development

Presenter:	Stessman, Dan , djstess@iastate.edu
Authors	Stessman, Dan  (A)   Miller, Adam  (B)   Spalding, Martin  (A)   Rodermel, Steven  (A)
Affiliations:	(A): Iowa State University (B): Lorrain County Community College

Previous investigations in our laboratory have focused on the source strength regulation of tobacco leaf development, or specifically, that variations in leaf carbohydrate production affect the onset and duration of senescence. This study examines the changes in photosynthetic parameters of a single Arabidopsis leaf grown under continuous light. The goal was to test whether developmental-dependent alterations in photosynthesis and gene expression are correlated with alterations in carbon partitioning, carbohydrate pool sizes, or activities of hexokinase, vacuole acid invertase, or cell wall acid invertase. We found that photosynthetic rates, gene expression, pigment levels, and total soluble protein amount decline from the first time point measured, even before full leaf expansion has been attained. In contrast, flux of ¹⁴CO₂ into hexoses increases during leaf expansion, then declines in the fully expanded leaf. The total starch level also increases, but begins to decline before the leaf is fully expanded. Hexokinase, vacuole acid invertase, and cell wall acid invertase activities do not change until late in leaf senescence, when they increase dramatically. This increase corresponds with an increase in the hexose pool size of senescent leaves, as well as SAG gene expression. Taken together, these results suggest that acid invertase and hexokinase activities do not control the partitioning of label into hexoses during development, since this increase in hexose is not reflected in the flux and partitioning of ¹⁴CO₂. We conclude that our data are not readily compatible with a simple model for leaf development, whereby alterations in photosynthetic rates are mediated by hexose flux or by hexose pool sizes. Yet these factors may contribute to the control of gene expression.