Carbon metabolism in sink limited conditions

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In the next five years, we will continue to study the regulation of carbon (C) metabolism in spring ephemerals. 1) Spring ephemerals produce much larger storage organs (bulb or corm) under low than under higher growth temperature, a unique case amongst temperate species. However, the C metabolism of these organs also presents similarities with the C metabolism of other major sinks such as potato tuber or cereal grain. A proteomic approach will be used to identify the main proteins in the storage organ that are modulated by growth temperature. Those proteins more closely related to C metabolism will be further studied. 2) Leaf senescence in spring ephemerals is apparently induced by feedback inhibition once sink growth has slowed down. Starch does not accumulate in the leaves of these species; feedback inhibition appears to use a different pathway than the one already described for starch accumulating species. We will try to identify the cascade of events leading to leaf senescence using different approaches: in vivo chlorophyll fluorescence, gas exchanges, and proteomics. 3) C partitioned to cell wall material in the corms increases with growth temperature. This could be a way to divert some of the C and avoid feedback inhibition under conditions of reduced starch storage capacity. We will analyse cell wall composition and test the hypothesis that hemicelluloses are used as carbohydrate storages when sink growth slows down. Respiratory rates - both through the cytochrome and the alternative pathways - will also be monitored as another pathway that can use extra C in conditions where growth becomes limited by sink activity. Study of the C metabolism of spring ephemerals will help unravel some of the mechanisms that allow them to reach large sizes under low temperatures. This study will also lead to a better understanding of the regulation of C metabolism in sink limited species, i.e. in conditions where carbohydrates are in excess, a situation that species will encounter more often in the future as CO2 concentrations continue to increase.