Effects of High Night Temperature on Crassulacean Acid Metabolism (CAM) Photosynthesis of Kalanchoë pinnata and Ananas comosus

Abstract

The effects of the night temperature on CO2 exchange rate and organic acid accumulation in the leaves of two crassulacean acid metabolism (CAM) plants, Kalanchoë pinnata and Ananas comosus (pineapple), were examined under a fixed day-temperature condition of 30°C. With the increase of the night temperature, the CO2 exchange rate decreased in both species, and K. pinnata completely lost nocturnal CO2 uptake under a high night temperature (30/37°C in day/night) condition (HNT). Malate accumulation in the leaves of pineapple and K. pinnata in the morning decreased with increasing night temperature, but that in the afternoon was not influenced by the night temperature. Diurnal changes of ten kinds of metabolites were investigated under HNT. Pineapple accumulated a large amount of nocturnal malate under HNT, but K. pinnata did not. Four kinds of hexose-phosphate (hexose-P) were accumulated at the same levels during the day/night cycle under HNT in both plant species. Nocturnal accumulation of oxaloacetate (OAA) was observed but phosphoenolpyruvate (PEP) was kept at a high level both in day and night under HNT in both plant species. The concentrations of malate required for 50% inhibition of the activities of day and night forms of PEP carboxylase (PEPC) from the pineapple leaves were 1.2 and 0.7 mM, respectively, whereas those from the K. pinata leaves were 3.7 and 2.0 mM, respectively. In both plants, NAD-MDH activity in vitro increased with increasing temperature. It is therefore suggested that under HNT, phosphorylation may not be the major factor controlling PEPC activity in pineapple, and therefore CAM mode in pineapple was maintained under HNT. The nighttime phosphorylation of PEPC in K. pinnata would disappear under HNT leading to the loss of nocturnal malate accumulation.