Carbon metabolism in sink limited conditions

在接下来的五年里，我们将继续研究春季短暂植物碳(C)代谢的调节。1)春季短命植物在较低的生长温度下比在较高的生长温度下产生更大的存储器官(鳞茎或球茎)，这在温带物种中是独一无二的。然而，这些器官的C代谢也与其他主要汇的C代谢相似，如马铃薯块茎或谷类。蛋白质组学方法将被用来鉴定贮藏器官中受生长温度调节的主要蛋白质。那些与碳代谢关系更密切的蛋白质将被进一步研究。2)一旦库生长减慢，春季短命植物叶片衰老明显是由反馈抑制引起的。淀粉不会在这些物种的叶片中积累；反馈抑制似乎使用了一种不同于已描述的淀粉积累物种的途径。我们将尝试使用不同的方法来确定导致叶片衰老的一系列事件：体内叶绿素荧光、气体交换和蛋白质组学。3)球茎中分配给细胞壁物质的C随生长温度的升高而增加。这可能是一种转移部分C的方法，并在淀粉储存量降低的情况下避免反馈抑制。我们将分析细胞壁的组成，并测试半纤维素被用作碳水化合物储存的假设，当库生长放缓时。呼吸速率--通过细胞色素和替代途径--也将作为另一种途径进行监测，这种途径可以在生长受到库容量活动限制的情况下利用额外的C。对春季短命生物碳代谢的研究将有助于解开一些使它们在低温下达到大型体型的机制。这项研究还将有助于更好地了解碳汇受限物种中碳代谢的调节，即在碳水化合物过剩的条件下，随着二氧化碳浓度的继续增加，物种未来将更频繁地遇到这种情况。

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.