ABSTRACT
Shifting seasons is another emerging feature of global climate change. As a result, areas with normally warm temperature ranges are starting to experience cold waves comprising of prolonged low temperature. In polar areas cold stress or low temperature stress has compelled plants to adapt to those conditions, but crop species of the warmer areas are experiencing chilling or freezing injuries from cold stress due to lack of avoidance mechanisms. Usually injury occurs at temperatures ranges of 2°C to 10°C, but few susceptible species such as rice and sugarcane can experience chilling injury at temperatures as high as 15°C. The damage caused by low temperature stress ranges from abnormalities at cellular level to hindrance during seed emergence, loss of vigour, poor crop stand, and consequently yield losses. Growth is minimized due to the damage caused by cold stress to leaves in the form of decreased leaf cells production, division and elongation with prolonged cell cycle, leaf necrosis, delayed leaf development, leaf wilting, decreased leaf area, slow leaf initiation rate, and increased pathogen and disease incidence. Abnormalities during vegetative growth stages accompanied by chilling-induced damage at flowering stages results in flower abscission, pollen tube distortion, pollen sterility, ovule abortion, poor fruit set, and ultimately reduced yields. Cold stress causes losses at physiological levels where it damages the photosynthetic apparatus and consequently the whole process of photosynthesis as well as gaseous exchange is disturbed. Plant water and nutrient relations are also disturbed due to low temperature. The main mechanism in work that affects plant water relations is reduced transpiration which badly affects root hydraulic function. Disturbed root functions ultimately result in poor nutrient uptake and plant growth is limited due to shortage of water and nutrient supply. To a lesser extent, some plants have undergone evolutionary adaptations to cope with low temperature stress. This avoidance mechanism usually involves physiological processes to prevent sensitive tissues from freezing, accumulation of heat in their bodies in warmer times of the day, undergoing seed or organ dormancy, and making use of leaves to protect their growing meristems. This chapter discusses in detail plant damages caused by low temperature stress, the physiological process that leads to visible losses and plant adaptations that help minimize these losses.
