Effects of Exposure to Short Periods of Suboptimal Temperature during Chill (5 °C) on Gas Exchange and Chlorophyll Fluorescence in Maize Seedlings (Zea Mays L.)

The effect of various periods of exposure to suboptimal temperature ('warm breaks'– WB: 14 °C for 4 h, 1 h and 0 h – control in 24 h cycles) during chilling (5 °C) of maize seedlings on the photosynthesis, the photochemical efficiency of photosystem II (Fv/Fm) and on the injuries of the cell membranes of leaves and water content in plants was compared. The measurements were conducted after 1, 3, 7 and 12 chill cycles. It was found that WB of either length distinctly diminished the chill-induced inhibition of net photosynthesis and the decrease of photochemical efficiency of PSII. The protective effect on WB on these parameters was observed shortly after completion of chilling of the plant as well as an after-effect. Daily warming up of the plants also reduced the leakage of electrolytes and diminished the water deficit of the chilled seedlings. The protective effect of WB on the measured parameters of the plants was greater in the chill-sensitive genotype than in the chill-tolerant one, especially when plants were warmed up for 4 h. The results obtained are an indication that short periods of warm weather during cold spring may diminish the injuries of the photosynthetic apparatus, as well as reduce the disturbance of water status of seedlings, contributing in this way to better condition of maize crops.