Seasonal effects on the relationship between photosynthesis and leaf carbohydrates in orange trees

Author(s)

Ribeiro, Rafael V. ^[1] ; Machado, Eduardo C. ^[1] ; Habermann, Gustavo ^[2] ; Santos, Mauro G. ^[3] ; Oliveira, Ricardo F. ^[4]

Affiliation

^[1] IAC, Ctr Pesquisa & Desenvolvimento Ecofisiol & Biofis, Lab Fisiol Vegetal Coaracy M Franco, Inst Agron, BR-13012970 Campinas, SP - Brazil

^[2] Univ Estadual Paulista, UNESP, Inst Biociencias, Dept Bot, BR-13506900 Rio Claro, SP - Brazil

^[3] Univ Fed Pernambuco, Dept Bot, BR-50670901 Recife, PE - Brazil

^[4] Univ Sao Paulo, Escola Super Agr Luiz de Queiroz, Dept Ciencias Biol, BR-13418900 Piracicaba, SP - Brazil

• Document type: Journal article
• Source: FUNCTIONAL PLANT BIOLOGY; v. 39, n. 6, p. 471-480, 2012.
• Web of Science Citations: 15

Abstract

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. (AU)

• FAPESP's process: 05/57862-8 - Flowering and fruiting in Valencia orange tree: anatomical, physiological, biochemical and molecular aspects
• Grantee: Marcelo Carnier Dornelas
• Support Opportunities: Research Projects - Thematic Grants