Temperature at night affects the genetic control of acclimation to cold in maize seedlings

Although suboptimal temperatures during maize (Zea mays L) seedling growth are known to result in decreased photosynthetic efficiency due to a combination of temperature and light stress, details remain scant on the impact of low night temperatures on photosynthetic activity. To better understand the role of night temperature on the acclimation of the photosynthetic apparatus to suboptimal temperature, a QTL experiment was conducted with the IBM302 population. Seedlings were grown under optimal temperature (24/22°C, day/night) or under subopti¬mal temperatures (17°C day and 6 or 13°C night). The two parental lines, B73 and Mo17, responded somewhat differently to suboptimal temperatures, as revealed by measurements of the operating quantum efficiency of PS II (Fq’/Fm’), the maximum quantum efficiency of PS II primary photochemistry (Fv/Fm) and leaf greenness (SPAD). While Mo17 showed very little change in response to the temperature at night, B73 exhibited a lower photosyn¬thetic performance at 13°C than at 6°C at night. At 17/6°C the photosynthetic efficiency of both genotypes was similar. These observations were supported by QTL analyses. A major QTL for photosynthesis-related traits was detected on chromosome 5 with the favorable allele contributed by Mo17. This QTL showed a lower additive effect at a temperature of 6°C than at 13°C during the night and appeared to be the major factor explaining the differential response of the parental lines to changes in the temperature at night. As potential candidate genes for this locus, ivr2 (coding for an acid vacuolar invertase) and a2 (coding for an anthocyanidin synthase) were identi¬fied. QTL analyses for invertase activity and anthocyanin content revealed a QTL for invertase activity near the ivr1 gene and a QTL for anthocyanin content close to the r1 locus, both, however, were not related to the major QTL for photosynthesis-related traits. Comparative QTL analyses of photosynthetic traits of this population and other pulished studies revealed conserved QTL regions on chromosomes 6 and 8.