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Keywords:

  • Chilling damage;
  • CO2 assimilation;
  • development;
  • low temperature stress;
  • photoinhibition;
  • photosynthesis;
  • Zea mays

When plants of Zea mays L. cv. LG11 that have been grown at optimal temperatures are transferred to chilling temperatures (0–12°C) photoinhibition of photosynthetic CO2 assimilation can occur. This study examines how growth at sub-optimal temperatures alters both photosynthetic capacity and resistance to chilling-dependent photoinhibition. Plants of Z. mays cv. LG11 were grown in controlled environments at 14, 17, 20 and 25°C. As a measure of the capacity for photosynthesis under light limiting conditions, the maximum quantum yields of CO2 assimilation (φa.c) and O2 evolution (φa.o) were determined for the laminae of the second leaves at photon fluxes of 50–150 μmol m-2s-1. To determine photosynthetic capacity at photon fluxes approaching light saturation, rates of CO2 uptake (A1500) and O2 evolution (A1500) were determined in a photon flux of 1500 μmol m-2s-1. In leaves developed at 14°C, φ and φ were 26 and 43%, respectively, of the values for leaves grown at 25°C. Leaves grown at 17°C showed intermediate reductions in φ and φ, whilst leaves developed at 20°C showed no significant differences from those grown at 25°C. Similar patterns of decrease were observed for A1500 and A1500.0 with decreasing growth temperature. Leaves developed at 25°C showed higher rates of CO2 assimilation at all light levels and measurement temperatures in comparison to leaves developed at 17 and 14°C. A greater reduction in A1500 relative to A1500.0 with decreasing growth temperature was attributed to increased stomatal limitation. Exposure of leaves to 800–1000 μmol m-2 s-1 when plant temperature was depressed to ca 6.5°C produced a photoinhibition of photosynthetic CO2 assimilation in all leaves. However, in leaves developed at 17°C the decrease in A1500 following this chilling treatment was only 25% compared to 90% in leaves developed at 25°C. Recovery following chilling was completed earlier in leaves developed at 17°C. The results suggest that growth at sub-optimal temperatures induces increased tolerance to exposure to high light at chilling temperatures. This is offset by the large loss in photosynthetic capacity imposed by leaf development at sub-optimal temperatures.