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 photosy nthetic properties of different maize genotypes in distinct ways. In t his study, leaf growth and chloroplast functioning of the second leave s 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) te mperature, were compared. When acclimated at 24/22 degrees C, there wa s little difference between CT and CS in pigment content, in photosynt hetic capacity, measured as the maximum quantum yield of oxygen evolut ion under light limiting conditions (Phi(O2)) and the maximum rate of oxygen evolution at light saturation (P-max), both at 24 and 14 degree s C, or in quantum yield of PSII electron transport (Phi(e)) at decrea sing temperature. When acclimated at 15/13 degrees C, differences incr eased or changed in favour of CT, especially when measured at suboptim al temperature (14 degrees C). CS was more sensitive to light independ ent chilling compared to CT, as indicated by a sharper decrease in tim e of the maximal rise of chlorophyll fluorescence induction (F-R). A d ecrease in F-R was accompanied by a smaller decrease in light use effi ciency, 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 acclimate d at 15/13 degrees C, differences in F-R between CT and CS markedly in creased 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 i ndicated by a sharper decrease with time in the potential quantum yiel d of PSII (F-v/F-m) when leaf disks were subjected to high light inten sity (600 mu mol m(-2)s(-1)) at low temperature (0-2 degrees C). Compa red to leaves acclimated at 24/22 degrees C, differences between CT an d CS increased when acclimated at 15/13 degrees C. Following a photoin hibitory 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