Effect of a short photoinhibition stress on photosynthesis, chlorophyll a fluorescence, and pigment contents of different maize cultivars. Can a rapid and objective stress indicator be found?

The effect of a short cold stress in combination with photoinhibition stress, similar to a low temperature and a high irradiance situation during early morning in the spring time, was examined on four maize cultivars common for Belgium, that differ in early vigour. After 1 h of 2 °C and 500 µmol(photon) m^-2 s^-1, quantum efficiency and maximum photosynthesis rate at saturating irradiance decreased on average by 11 and 8 %, respectively. For one cultivar, Magister, the decrease was the largest: by 23 and 10 %, respectively. For this cultivar it was combined with a decrease of the water vapour conductance after the stress. The decrease of Fv/Fo due to the cold/light stress was dependent on the cold tolerance (early vigour) of the cultivars. Fv/Fo changed with –45.5 and –40.2 % for the cultivars Ardiles and Banguy, respectively (cultivars with a less good early vigour) in comparison to –36.3 and –35.9 % for Fjord and Magister, which have a good early vigour. Also the ratio of total chlorophylls/total carotenoids changed in dependence on cold tolerance of the cultivars. For more cold tolerant cultivars, the relative amount of total carotenoids (x+c) was higher, indicating a higher protective state. Both the parameter Fv/Fo and the ratio of total chlorophylls to total carotenoids can be used to differentiate the cold tolerant cultivars from the cold non-tolerant ones. Fv/Fo has the advantage because its resolving power is larger and the measurement is less expensive than determination of the pigment ratio.