Cold tolerance of the photosynthetic apparatus: pleiotropic relationship between photosynthetic performance and specific leaf area of maize seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S-5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (Phi(PSII)) at low temperature, (ii) a population of 226 F-2:3 families from the cross of ETH-DL3 x ETH-DH7, and (iii) a population of 168 F-2:4 families from the cross of Lo964 x Lo1016 were tested at low (15/13 degrees C day/night) or at optimal (25/22 degrees C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13 degrees C the groups of S-5 inbred lines selected for high or low Phi(PSII) differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with Phi(PSII) (r=-0.56, p < 0.05) and SPAD (r=-0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13 degrees C, while co-location was not detected at 25/22 degrees C. The co-selection of SLA and Phi(PSII) in the inbred lines and the co-location of QTL for SLA, SPAD, and Phi(PSII) at 15/13 degrees C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high Phi(PSII) at low temperature leads to a constitutively altered SLA.