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Lookup NU author(s): Dr Johan Ceusters,
Emerita Professor Anne Borland
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Despite the increased energetic costs of CAM compared with C-3 photosynthesis, it is hypothesized that the inherent photosynthetic plasticity of CAM allows successful acclimation to light-limiting conditions. The present work sought to determine if CAM presented any constraints to short and longer term acclimation to light limitation and to establish if and how metabolic and photosynthetic plasticity in the deployment of the four phases of CAM might facilitate acclimation to conditions of deep shade. Measurements of leaf gas exchange, organic acids, starch and soluble sugar (glucose, fructose, and sucrose) contents were made in the leaves of the constitutive CAM bromeliad Aechmea 'Maya' over a three month period under severe light limitation. A. 'Maya' was not particularly tolerant of severe light limitation in the short term. A complete absence of net CO2 uptake and fluctuations in key metabolites (i.e. malate, starch or soluble sugars) indicated a dampened metabolism whilst cell death in the most photosynthetically active leaves was attributed to an over-acidification of the cytoplasm. However, in the longer term, plasticity in the use of the different phases of gas exchange and different storage carbohydrate pools, i.e. a switch from starch to sucrose as the major carbohydrate source, ensured a positive carbon balance for this CAM species under extremely low levels of irradiance. As such, co-ordinated plasticity in the use of C-3 and C-4 carboxylases and different carbohydrate pools together with an increase in the abundance of light-harvesting complexes, appear to underpin the adaptive radiation of the energetically costly CAM pathway within light-limiting environments such as wet cloud forests and shaded understoreys of tropical forests.
Author(s): Ceusters J, Borland AM, Godts C, Londers E, Croonenborghs S, Van Goethem D, De Proft MP
Publication type: Article
Publication status: Published
Journal: Journal of Experimental Botany
Print publication date: 22/09/2010
ISSN (print): 0022-0957
ISSN (electronic): 1460-2431
Publisher: Oxford University Press
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