Abstract
Temperature is one of the most critical factors affecting cassava metabolism and growth. This research was conducted to investigate the effects of short-term exposure to extreme cool (15 degrees C) and hot (45 degrees C) temperature on photosynthesis, biochemical and proteomics changes in potted plants of two cassava cultivars, namely Rayong 9 and Kasetsart 50. One-month-old plants were exposed to 15, 30, and 45 degrees C for 60 min in a temperature chamber under light intensity of 700 mu mol m(-2) s(-1). Compared to the optimum temperature (30 degrees C), exposure to 15 degrees C resulted in 28% reduction in stomatal conductance (gs) and 62% reduction in net photosynthesis rate (P-n). In contrast, gs under 45 degrees C increased 2.61 folds, while P-n was reduced by 50%. The lower P-n but higher electron transport rate (ETR) of the cold-stressed plants indicated that a greater proportion of electrons was transported via alternative pathways to protect chloroplast from being damaged by reactive oxygen species (ROS). Moreover, malondialdehyde (MDA) contents, a marker related to the amount of ROS, were significantly higher at low temperature. Proteomics analysis revealed some interesting differentially expressed proteins (DEPs) including annexin, a multi-functional protein functioning in early events of heat stress signaling. In response to low-temperature stress, AP2/ERF domain-containing protein (a cold-related transcription factor) and glutaredoxin domain-containing protein (a component of redox signaling network under cold stress) were detected. Taken together, both cultivars were more sensitive to low than high temperature. Moreover, Rayong 9 displayed higher P-n under both temperature stresses, and was more efficient in controlling ROS under cold stress than Kasetsart 50.
