Physiological and molecular analysis of pitaya (Hylocereus polyrhizus) reveal up-regulation of secondary metabolites, nitric oxide, antioxidant defense system, and expression of responsive genes under low-temperature stress by the pre-treatment of hydrogen peroxide.

Low-temperature events are one of the leading environmental cues that considerably reduce plant growth and shift species biodiversity. Hydrogen peroxide (HO) is a signaling molecule that has a distinguished role during unfavorable conditions and shows outstanding perspectives in low-temperature stress. Herein, we elucidated the protective role and regulatory mechanism of HO in alleviating the deleterious effects of low-temperature stress in pitaya plants. Micropropagated pitaya plants were cultured in Murashige and Skoog media supplemented with different levels of HO (0, 5, 10, and 20 mM) and then exposed to low-temperature stress (5 °C for 24 h). HO at 10 mM, improved low-temperature stress tolerance by relieving oxidative injuries and ameliorating growth parameters in terms of fresh weight (66.7%), plant length (16.7%), and pigments content viz., chlorophyll a (157.4%), chlorophyll b (209.1%), and carotenoids (225.9%). HO counteracted the low-temperature stress by increasing amino acids (224.7%), soluble proteins (190.5%), and sugars (126.6%). Simultaneously, secondary metabolites like ascorbic acid (ASA), anthocyanins, phenolics, flavonoids, total antioxidant (TOA), and proline were also up-regulated by HO (104.9%, 128.8%, 166.3%, 141.4%, and 436.4%, respectively). These results corresponded to the stimulative role triggered by HO in boosting the activities of catalase (22.4%), ascorbate peroxidase (20.7%), superoxide dismutase (88.4%), polyphenol oxidase (60.7%), soluble peroxidase (23.8%), and phenylalanine ammonia-lyase (57.1%) as well as the expression level of HpCAT, HpAPX, HpSOD, HpPPO, and HpPAL genes, which may help to moderate low-temperature stress. In conclusion, our findings stipulate new insights into the mechanisms by which HO regulates low-temperature stress tolerance in pitaya plants.