Physiological responses of the leaves of a high-altitude plant Picrorhiza kurroa to cold stress

Abstract

Plants growing at high elevations experience different environmental stresses, such as drought, salt, and cold. Among them, cold stress is the most prevalent one that affects the plants differently. Plants undergo biochemical, metabolic, molecular, and physiological changes under cold stress; hence, they adopt various mechanisms to tolerate it. The antioxidant defence system, osmotic regulators, and photosynthetic pigments in the plant provide them with stress tolerance. The present study is conducted on a high-altitude plant, Picrorhiza kurroa, which grows in such environmental conditions, to study the physiological parameters that provide a coping mechanism against cold stress. For this study, the leaves were collected from Pothivasa (2200 m.a.s.l) and Tungnath (3600 m.a.s.l) in Rudraprayag, Uttarakhand, India. The photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), lipid peroxidation, antioxidant enzymes, namely, superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase, and osmoprotectants (protein, soluble sugar, and proline) present in the leaves were determined to visualize the impact of cold stress. It was revealed that the concentration of photosynthetic pigments increased with elevation. The activity of enzymes was analyzed, and they were observed to decrease with altitude. The malondialdehyde concentration, an indicator of lipid peroxidation, is higher in Pothivasa and lower in Tungnath. There is a significant increase in the osmoprotectants’ content along the altitudinal gradient. Therefore, the leaves from both sampling locations revealed the physiological changes that occurred in them to adapt to the cold stress conditions.