Département de biologie et Centre d'étude de la forêt, Université Laval, Québec (QC), Canada.
J Exp Bot. 2009;60(15):4235-48. doi: 10.1093/jxb/erp255. Epub 2009 Aug 26.
Mechanisms that allow plants to cope with a recurrent surplus of carbon in conditions of imbalance between source and sink activity has not received much attention. The response of sink growth and metabolism to the modulation of source activity was investigated using elevated CO(2) and elevated O(3) growth conditions in Erythronium americanum. Sink activity was monitored via slice and mitochondrial respiratory rates, sucrose hydrolysis activity, carbohydrates, and biomass accumulation throughout the growth season, while source activity was monitored via gas exchanges, rubisco and phosphoenolpyruvate carboxylase activities, carbohydrates, and respiratory rates. Elevated CO(2) increased the net photosynthetic rate by increasing substrate availability for rubisco. Elevated O(3) decreased the net photosynthetic rate mainly through a reduction in rubisco activity. Despite this modulation of the source activity, neither plant growth nor starch accumulation were affected by the treatments. Sucrose synthase activity was higher in the sink under elevated CO(2) and lower under elevated O(3), thereby modulating the pool of glycolytic intermediates. The alternative respiratory pathway was similarly modulated in the sink, as seen with both the activity and capacity of the pathway, as well as with the alternative oxidase abundance. In this sink-limited species, the alternative respiratory pathway appears to balance carbon availability with sink capacity, thereby avoiding early feedback-inhibition of photosynthesis in conditions of excess carbon availability.
植物在源库活动失衡条件下应对碳过剩的机制尚未得到太多关注。本研究使用提高 CO2 和 O3 浓度的生长条件，以延龄草（Erythronium americanum）为材料，研究了库生长和代谢对源活动调节的响应。通过切片和线粒体呼吸速率、蔗糖水解活性、碳水化合物和整个生长季节的生物量积累来监测库活性，而源活性则通过气体交换、Rubisco 和磷酸烯醇丙酮酸羧化酶活性、碳水化合物和呼吸速率来监测。提高 CO2 浓度通过增加 Rubisco 的底物可用性来提高净光合速率。提高 O3 浓度主要通过降低 Rubisco 活性来降低净光合速率。尽管源活性受到了调节，但处理对植物生长和淀粉积累没有影响。在提高 CO2 浓度下，蔗糖合酶活性在库中更高，而在提高 O3 浓度下则更低，从而调节糖酵解中间产物的池。替代呼吸途径在库中也得到了类似的调节，表现在途径的活性和容量以及交替氧化酶丰度上。在这个库限制的物种中，替代呼吸途径似乎平衡了碳的可用性与库的容量，从而避免了在碳过剩条件下光合作用的早期反馈抑制。
