Regulation of photosynthesis by sugars in sugarcane leaves

A.J. Mccormick, Michael Cramer, D.A. Watt

    Research output: Contribution to journalArticle

    43 Citations (Scopus)

    Abstract

    In sugarcane, increased sink demand has previously been shown to result in increased photosynthetic rates that are correlated with a reduction in leaf hexose concentrations. To establish whether sink limitation of photosynthesis is a result of sugar accumulation in the leaf, excision and cold-girdling techniques were used to modify leaf sugar concentrations in pot-grown sugarcane. In excised leaves that were preincubated in darkness for 3 h, sucrose accumulation was reduced but accumulated again upon transfer to the light, while hexose concentrations remained lower than in controls (7.7 μmol mg−1 FW versus 18.6 μmol mg−1 FW hexose in controls). These results were associated with a 66% and 59% increase in photosynthetic assimilation (A) and electron transport rate (ETR), respectively, compared to controls maintained in the light. Similar increases in photosynthesis were observed when dark-treated leaves were supplied with 5 mM sorbitol, but not when supplied with 5 mM sucrose. Further analyses of 14C-labeled sugars indicated rapid turnover between sucrose and hexose. Cold-girdling (5 °C) increased sucrose and hexose levels and resulted in a decline of photosynthetic rates over 5 d (48% and 35% decline in assimilation rate and ETR, respectively). These sugar-induced changes in photosynthesis were independent of changes in stomatal conductance. This study demonstrates that the down-regulation of photosynthesis in response to culm sugar accumulation reported previously could be due to the knock-on effect of accumulation of sugar in leaf tissue, and supports the contention that hexose, rather than sucrose, is responsible for the modulation of photosynthetic activity.
    Original languageEnglish
    Pages (from-to)1817-1829
    JournalJournal of Plant Physiology
    Volume165
    Issue number17
    DOIs
    Publication statusPublished - 2008

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    Saccharum
    Hexoses
    Photosynthesis
    hexoses
    sugarcane
    Sucrose
    photosynthesis
    sugars
    sucrose
    leaves
    girdling
    Electron Transport
    electron transfer
    assimilation (physiology)
    Light
    Sorbitol
    Darkness
    sorbitol
    stomatal conductance
    Down-Regulation

    Cite this

    Mccormick, A.J. ; Cramer, Michael ; Watt, D.A. / Regulation of photosynthesis by sugars in sugarcane leaves. In: Journal of Plant Physiology. 2008 ; Vol. 165, No. 17. pp. 1817-1829.
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    abstract = "In sugarcane, increased sink demand has previously been shown to result in increased photosynthetic rates that are correlated with a reduction in leaf hexose concentrations. To establish whether sink limitation of photosynthesis is a result of sugar accumulation in the leaf, excision and cold-girdling techniques were used to modify leaf sugar concentrations in pot-grown sugarcane. In excised leaves that were preincubated in darkness for 3 h, sucrose accumulation was reduced but accumulated again upon transfer to the light, while hexose concentrations remained lower than in controls (7.7 μmol mg−1 FW versus 18.6 μmol mg−1 FW hexose in controls). These results were associated with a 66{\%} and 59{\%} increase in photosynthetic assimilation (A) and electron transport rate (ETR), respectively, compared to controls maintained in the light. Similar increases in photosynthesis were observed when dark-treated leaves were supplied with 5 mM sorbitol, but not when supplied with 5 mM sucrose. Further analyses of 14C-labeled sugars indicated rapid turnover between sucrose and hexose. Cold-girdling (5 °C) increased sucrose and hexose levels and resulted in a decline of photosynthetic rates over 5 d (48{\%} and 35{\%} decline in assimilation rate and ETR, respectively). These sugar-induced changes in photosynthesis were independent of changes in stomatal conductance. This study demonstrates that the down-regulation of photosynthesis in response to culm sugar accumulation reported previously could be due to the knock-on effect of accumulation of sugar in leaf tissue, and supports the contention that hexose, rather than sucrose, is responsible for the modulation of photosynthetic activity.",
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    Regulation of photosynthesis by sugars in sugarcane leaves. / Mccormick, A.J.; Cramer, Michael; Watt, D.A.

    In: Journal of Plant Physiology, Vol. 165, No. 17, 2008, p. 1817-1829.

    Research output: Contribution to journalArticle

    TY - JOUR

    T1 - Regulation of photosynthesis by sugars in sugarcane leaves

    AU - Mccormick, A.J.

    AU - Cramer, Michael

    AU - Watt, D.A.

    PY - 2008

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    N2 - In sugarcane, increased sink demand has previously been shown to result in increased photosynthetic rates that are correlated with a reduction in leaf hexose concentrations. To establish whether sink limitation of photosynthesis is a result of sugar accumulation in the leaf, excision and cold-girdling techniques were used to modify leaf sugar concentrations in pot-grown sugarcane. In excised leaves that were preincubated in darkness for 3 h, sucrose accumulation was reduced but accumulated again upon transfer to the light, while hexose concentrations remained lower than in controls (7.7 μmol mg−1 FW versus 18.6 μmol mg−1 FW hexose in controls). These results were associated with a 66% and 59% increase in photosynthetic assimilation (A) and electron transport rate (ETR), respectively, compared to controls maintained in the light. Similar increases in photosynthesis were observed when dark-treated leaves were supplied with 5 mM sorbitol, but not when supplied with 5 mM sucrose. Further analyses of 14C-labeled sugars indicated rapid turnover between sucrose and hexose. Cold-girdling (5 °C) increased sucrose and hexose levels and resulted in a decline of photosynthetic rates over 5 d (48% and 35% decline in assimilation rate and ETR, respectively). These sugar-induced changes in photosynthesis were independent of changes in stomatal conductance. This study demonstrates that the down-regulation of photosynthesis in response to culm sugar accumulation reported previously could be due to the knock-on effect of accumulation of sugar in leaf tissue, and supports the contention that hexose, rather than sucrose, is responsible for the modulation of photosynthetic activity.

    AB - In sugarcane, increased sink demand has previously been shown to result in increased photosynthetic rates that are correlated with a reduction in leaf hexose concentrations. To establish whether sink limitation of photosynthesis is a result of sugar accumulation in the leaf, excision and cold-girdling techniques were used to modify leaf sugar concentrations in pot-grown sugarcane. In excised leaves that were preincubated in darkness for 3 h, sucrose accumulation was reduced but accumulated again upon transfer to the light, while hexose concentrations remained lower than in controls (7.7 μmol mg−1 FW versus 18.6 μmol mg−1 FW hexose in controls). These results were associated with a 66% and 59% increase in photosynthetic assimilation (A) and electron transport rate (ETR), respectively, compared to controls maintained in the light. Similar increases in photosynthesis were observed when dark-treated leaves were supplied with 5 mM sorbitol, but not when supplied with 5 mM sucrose. Further analyses of 14C-labeled sugars indicated rapid turnover between sucrose and hexose. Cold-girdling (5 °C) increased sucrose and hexose levels and resulted in a decline of photosynthetic rates over 5 d (48% and 35% decline in assimilation rate and ETR, respectively). These sugar-induced changes in photosynthesis were independent of changes in stomatal conductance. This study demonstrates that the down-regulation of photosynthesis in response to culm sugar accumulation reported previously could be due to the knock-on effect of accumulation of sugar in leaf tissue, and supports the contention that hexose, rather than sucrose, is responsible for the modulation of photosynthetic activity.

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