Ribeiro Rafael V, Machado Eduardo C, Habermann Gustavo, Santos Mauro G, Oliveira Ricardo F
Laboratório de Fisiologia Vegetal 'Coaracy M. Franco', Centro de Pesquisa e Desenvolvimento em Ecofisiologia e Biofísica, Instituto Agronômico, IAC, PO Box 28, 13012-970, Campinas, SP, Brazil.
Departamento de Botânica, Instituto de Biociências, Univ Estadual Paulista, UNESP, 13506-900, Rio Claro, SP, Brazil.
Funct Plant Biol. 2012 Jun;39(6):471-480. doi: 10.1071/FP11277.
To understand the effect of summer and winter on the relationships between leaf carbohydrate and photosynthesis in citrus trees growing in subtropical conditions, 'Valencia' orange trees were subjected to external manipulation of their carbohydrate concentration by exposing them to darkness and evaluating the maximal photosynthetic capacity. In addition, the relationships between carbohydrate and photosynthesis in the citrus leaves were studied under natural conditions. Exposing the leaves to dark conditions decreased the carbohydrate concentration and increased photosynthesis in both seasons, which is in accordance with the current model of carbohydrate regulation. Significant negative correlations were found between total non-structural carbohydrates and photosynthesis in both seasons. However, non-reducing sugars were the most important carbohydrate that apparently regulated photosynthesis on a typical summer day, whereas starch was important on a typical winter day. As a novelty, photosynthesis stimulation by carbohydrate consumption was approximately three times higher during the summer, i.e. the growing season. Under subtropical conditions, citrus leaves exhibited relatively high photosynthesis and high carbohydrate levels on the summer day, as well as a high nocturnal consumption of starch and soluble sugars. A positive association was determined between photosynthesis and photoassimilate consumption/exportation, even in leaves showing a high carbohydrate concentration. This paper provides evidence that photosynthesis in citrus leaves is regulated by an increase in sink demand rather than by the absolute carbohydrate concentration in leaves.
为了解夏季和冬季对亚热带条件下生长的柑橘树叶片碳水化合物与光合作用之间关系的影响，对‘伏令夏橙’树进行了碳水化合物浓度的外部调控，即让其处于黑暗环境中并评估其最大光合能力。此外，还研究了自然条件下柑橘叶片中碳水化合物与光合作用之间的关系。在两个季节中，将叶片置于黑暗条件下均会降低碳水化合物浓度并提高光合作用，这与当前的碳水化合物调控模型一致。在两个季节中，总非结构性碳水化合物与光合作用之间均存在显著的负相关关系。然而，在典型的夏季，非还原糖是明显调控光合作用的最重要碳水化合物，而在典型的冬季，淀粉则很重要。新颖的是，在夏季（即生长季节），因碳水化合物消耗而导致的光合作用刺激大约高出三倍。在亚热带条件下，柑橘叶片在夏季表现出相对较高的光合作用和较高的碳水化合物水平，以及较高的淀粉和可溶性糖夜间消耗量。即使在碳水化合物浓度较高的叶片中，光合作用与光合同化物消耗/输出之间也存在正相关关系。本文提供的证据表明，柑橘叶片的光合作用是由库需求的增加而非叶片中碳水化合物的绝对浓度所调控。
