AOBPreview originally published online on May 21, 2003
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Annals of Botany 92: 137-143, 2003
© 2003 Annals of Botany Company
Girdling Affects Carbohydrate-related Gene Expression in Leaves, Bark and Roots of Alternate-bearing Citrus Trees
1 The Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food, and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel
* For correspondence. E-mail goldsmit{at}argi.huji.ac.il
Received: 10 February 2003; Returned for revision: 10 March 2003; Accepted: 21 March 2003 Published electronically: 21 May 2003
Effects of girdling on carbohydrate status and carbohydrate-related gene expression in citrus trees were investigated. Alternate-bearing Murcott (a Citrus reticulata hybrid of unknown origin) trees were girdled during autumn (25 Sep. 2001) and examined 10 weeks later. Girdling brought about carbohydrate (soluble sugar and starch) accumulation in leaves and shoot bark above the girdle, in trees during their fruitless, off year. Trees during their heavy fruit load, on year did not accumulate carbohydrates above the girdle due to the high demand for carbohydrates by the developing fruit. Girdling caused a strong decline in soluble sugar and starch concentrations in organs below the girdle (roots), in both on and off trees. Expression of STPH-L and STPH-H (two isoforms of starch phosphorylase), Agps (ADP-glucose pyrophosphorylase, small subunit), AATP (plastidic ADP/ATP transporter), PGM-C (phosphoglucomutase) and CitSuS1 (sucrose synthase), all of which are associated with starch accumulation, was studied. It was found that gene expression is related to starch accumulation in all off tree organs. RNA levels of all the genes examined were high in leaves and bark that accumulated high concentrations of starch, and low in roots with declining starch concentrations. It may be hypothesized that changes in specific sugars signal the up- and down-regulation of genes involved in starch synthesis.
Key words: Alternate bearing, carbohydrates, Citrus, girdling, soluble sugar, starch.