Journal Article

Changes in Photosynthetic Rates and Gene Expression of Leaves during a Source–Sink Perturbation in Sugarcane

A. J. McCormick, M. D. Cramer and D. A. Watt

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 1, pages 89-102
Published in print January 2008 | ISSN: 0305-7364
Published online October 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm258
Changes in Photosynthetic Rates and Gene Expression of Leaves during a Source–Sink Perturbation in Sugarcane

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

In crops other than sugarcane there is good evidence that the size and activity of carbon sinks influence source activity via sugar-related regulation of the enzymes of photosynthesis, an effect that is partly mediated through coarse regulation of gene expression.

Methods

In the current study, leaf shading treatments were used to perturb the source–sink balance in 12-month-old Saccharum spp. hybrid ‘N19’ (N19) by restricting source activity to a single mature leaf. Changes in leaf photosynthetic gas exchange variables and leaf and culm sugar concentrations were subsequently measured over a 14 d period. In addition, the changes in leaf gene response to the source–sink perturbation were measured by reverse northern hybridization analysis of an array of 128 expressed sequence tags (ESTs) related to photosynthetic and carbohydrate metabolism.

Key Results

Sucrose concentrations in immature culm tissue declined significantly over the duration of the shading treatment, while a 57 and 88% increase in the assimilation rate (A) and electron transport rate (ETR), respectively, was observed in the source leaf. Several genes (27) in the leaf displayed a >2-fold change in expression level, including the upregulation of several genes associated with C4 photosynthesis, mitochondrial metabolism and sugar transport. Changes in gene expression levels of several genes, including Rubisco (EC 4·1·1·39) and hexokinase (HXK; EC 2·7·1·1), correlated with changes in photosynthesis and tissue sugar concentrations that occurred subsequent to the source–sink perturbation.

Conclusions

These results are consistent with the notion that sink demand may limit source activity through a kinase-mediated sugar signalling mechanism that correlates to a decrease in source hexose concentrations, which, in turn, correlate with increased expression of genes involved in photosynthesis and metabolite transport. The signal feedback system reporting sink sufficiency and regulating source activity may be a potentially valuable target for future genetic manipulation to increase sugarcane sucrose yield.

Keywords: C4 metabolism; array; hexose; photosynthesis; sucrose; Saccharum spp.; source–sink; gene expression

Journal Article.  8830 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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