Physiological and biochemical alterations due to low temperature stress in papaya genotypes

Papaya (Carica papaya L.) being a typical tropical plant, is highly sensitive to low temperature stress. Thepresent experiment was conducted under completely controlled conditions of National Phytotron Facility, ICAR-IARI, New Delhi to investigate the effect of different low temperature regimes on antioxidant enzymes and otherphysiological and biochemical parameters in five papaya genotypes and one distant relative i.e., cold tolerant genus Vasconcellea cundinamarcensis. The outcomes suggested a genotype-specific substantial increase of antioxidant enzymes activities, viz., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR) under the cold treatment regimes. The highest percent increase of SOD, APX, GPX and GR activities were found in the tolerant genotype V. cundinamarcensis, while the highest increase in CAT activity was observed in P-7-9 at the 20^º/10^ºC (day/night) temperature regimeover the control. Low temperature regimes led to increase in membrane injury in papaya leaves possibly throughthe phase transition or oxidative damage of cell membrane due to ROS generation in the photosystem becauseof disruption in the photosynthetis process. The highest increase in the membrane injury index was noted ingenotype Red Lady (79.93%). The photosynthetic rate was severely reduced under the low temperature regimes. The total sugars and total soluble proteins content in papaya leaves were observed to increase under the lowtemperature regimes may be due to cold induced osmotic stress.