Comparison of Maize Inbred Lines Differing in Low Temperature Tolerance:Effect of Acclimation at Suboptimal Temperature on Chloroplast Functioning

Acclimation to optimal or suboptimal temperature may influence photosynthetic properties of different maize genotypes in distinct ways. In this study, leaf growth and chloroplast functioning of the second leaves of Penjalinan, an inbred line used in warm tropical regions (CS) and Z7, an inbred line adapted to cool temperate regions (CT), acclimated at near optimal (24/22 degrees C) and suboptimal (15/13 degrees C) temperature, were compared. When acclimated at 24/22 degrees C, there was little difference between CT and CS in pigment content, in photosynthetic capacity, measured as the maximum quantum yield of oxygen evolution under light limiting conditions (Phi(O2)) and the maximum rate of oxygen evolution at light saturation (P-max), both at 24 and 14 degrees C, or in quantum yield of PSII electron transport (Phi(e)) at decreasing temperature. When acclimated at 15/13 degrees C, differences increased or changed in favour of CT, especially when measured at suboptimal temperature (14 degrees C). CS was more sensitive to light independent chilling compared to CT, as indicated by a sharper decrease in time of the maximal rise of chlorophyll fluorescence induction (F-R). A decrease in F-R was accompanied by a smaller decrease in light use efficiency, measured as the ratio of variable to maximal fluorescence (F-v/F-m) of leaf sections kept at 0 degrees C in the dark. When acclimated at 15/13 degrees C, differences in F-R between CT and CS markedly increased compared to leaves acclimated at 24/22 degrees C. Following a chilling period of 24 h, a faster and more complete recovery of F-R at room temperature in the dark was found in leaves acclimated at 15/13 degrees C. CS was also more sensitive to photoinhibition than CT, as indicated by a sharper decrease with time in the potential quantum yield of PSII (F-v/F-m) when leaf disks were subjected to high light intensity (600 mu mol m(-2)s(-1)) at low temperature (0-2 degrees C). Compared to leaves acclimated at 24/22 degrees C, differences between CT and CS increased when acclimated at 15/13 degrees C. Following a photoinhibitory treatment of 2.5 h, the fastest rates of recovery were found in leaves acclimated at 15/13 degrees C. However, differences in F-v/F-m between CT and CS were still evident after 20 of recovery. (C) 1995 Annals of Botany Company