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Carbohydrate Metabolism and Translocation in Healthy and Cocoa Swollen Shoot Virus-Infected Cocoa Plants

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Abstract

Analyses of cocoa swollen shoot virus-infected and healthy cocoa (Theobroma cacao L.) plant tissues were made to determine the effect of virus infection on the metabolism and transport of carbohydrates in affected plants. Starch, sucrose and reducing sugars were found to accumulate in infected tissues. Translocation of photosynthates (mainly as sucrose) to the stem and root system, as estimated by the overnight loss of carbohydrates from the leaves and by 14CO2 tracer experiments, was as efficient in the infected plants as in the healthy. Infected plants showed a higher diurnal turnover of carbohydrates in their leaves and, on unit leaf area basis, higher levels of 14C-labelled assimilates suggesting that they have a greater photosynthetic capacity than the healthy plants. The rate of respiration, as determined by the proportions of organic acids, amino acids and other intermediary metabolites formed from translocated 14C-labelled sugars, was generally higher in infected than in healthy plants. It is concluded from available data showing the presence in infected tissues of mineral nutrients, protein N and amino acids at the same concentrations as in healthy plants, and from the relatively high rates of photosynthesis and respiration that a high rate of metabolic activity is maintained in the host-virus system. Some factors possibly contributing to the stunted growth of infected plants are discussed in the light of these findings.

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