Poster: Temperature Responses
Abs #
191: Alternative electron sinks do not play a role in the cold-tolerance of C4 photosynthesis in Miscanthus x giganteus
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Presenter: |
Naidu, Shawna L., shawna@uiuc.edu |
Authors | Naidu, Shawna L. (A) Long, Stephen P. (A) | | Affiliations: |
(A): University of Illinois at Urbana-Champaign
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Miscanthus x giganteus is unique among C4 species in its remarkable ability to maintain high photosynthetic productivity at low temperature. Efficient conversion of radiation into net carbon fixation requires minimum diversion of absorbed energy to non-photosynthetic processes, e.g. photorespiration or the Mehler reaction. Low temperature-grown Zea mays has been reported to exhibit large alternative electron sinks, which may protect against photodamage in chilling conditions. Do such alternative electron sinks play a role in cold-tolerant C4 photosynthesis in M. x giganteus? Zea mays and M. x giganteus were grown and measured at 25/20ºC or 14/10ºC (day/night). Chlorophyll fluorescence and gas exchange were measured simultaneously on the exact same attached leaf segment (n=7-9) with the same light source. Cold-grown leaves had 29% (M. x giganteus) and 81% (Z. mays) lower rates of light-saturated photosynthesis (Asat) than warm-grown leaves. In both species this was concurrent with decreased operating efficiency of whole chain electron transport through PSII (fPSII), decreased maximum quantum efficiency of PSII (Fv'/Fm’), and decreased efficiency of open PSII centers ((Fm’-Fs)/Fv’). Response patterns were similar in both species, but decreases in Z. mays were always much larger. For both species at both temperatures, the linear relationship between fPSII and the efficiency of CO2 assimilation (fCO2) had a zero intercept suggesting an absence of non-photosynthetic electron sinks. Photorespiration was inferred only in warm-grown Z. mays, at trace levels (Asat 4% greater in low O2). These data suggest that alternative electron sinks are negligible in both warm- and cold-gown M. x giganteus and Z. mays, and that thermal de-excitation was greater in Z. mays at low temperature.
