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Dep. of Plant Agriculture, Univ. of Guelph, Guelph, ON, N1G 2W1, Canada
* Corresponding author (mtollena{at}uoguelph.ca)
Maize (Zea mays L.) leaf photosynthesis during the grain-filling period is affected by low (
4°C) night temperatures. Three factors that are potentially involved in this phenomenon were examined: (i) duration of cold exposure, (ii) acclimation prior to exposure to light, and (iii) level of incident photosynthetic photon flux density (PPFD) following cold exposure. Studies were carried out with plants grown hydroponically under both field and controlled-environment conditions. Three hybrids (‘Pride 5’, ‘Pioneer 3902’, and ‘Cargill 1877’) were used in the field experiments and Pioneer 3902 was used in controlled-environment experiments. Plants were exposed to 4°C in the dark for either 2 or 16 h and, subsequently, acclimated for either 0 or 1 h in the dark before exposure to high PPFD. Four incident PPFD levels (400, 650, 1200, and 2000 µmol m-2 s-1) after cold exposure were examined. Both duration of cold exposure and acclimation after cold exposure affected the reduction in leaf carbon exchange rate (CER). Leaf CER was reduced by 18.0% after a 2-h exposure and by 30.4% after a 16-h exposure to 4°C, and leaf CER was reduced by 20.4 and 28.0% for 1- and 0-h acclimation, respectively. Dark-adapted Fv/Fm (Fv = variable fluorescence; Fm = maximum chlorophyll fluorescence), that is, maximum quantum efficiency of Photosystem II, was 0.71 after cold exposure during the night compared with 0.81 for the control. The Fv/Fm was affected by duration of cold exposure (0.74 and 0.68 for 2- and 16-h exposure, respectively) but not by acclimation. Reduction in leaf photosynthesis after cold exposure was linearly related to the incident PPFD level. Results support the contention that the reduction in CER due to low night temperature is not associated with photoinhibition.
Abbreviations: CER, carbon exchange rate • LED, light-emitting diode • PPFD, photosynthetic photon flux density • PSII, Photosystem II
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