Protective Role of Melatonin and IAA in the Regulation of Resistance of Potato Regenerants to Cold Stress

Potato is the fourth most important food crop. Recently, negative effects of a temperature drop on field crops have been increasingly frequently recorded. The elucidation of the mechanisms of plant tolerance to cold contributes to the development of measures to reduce crop yield losses from prolonged low temperatures. Potato health can be improved with the help of microclonal propagation. We studied short-term treatments of roots with indole-3-acetic acid (IAA) or melatonin (Mel) as a stimulus to activate the protective responses of potato regenerants to the later effects of hypothermia. The effect of 4-h treatment of roots with 0.1 μM IAA or Mel solutions on the cold tolerance of Solanum tuberosum L. regenerant plants in aquaculture was investigated. Two lines of regenerants obtained in vitro from the apical (AR) and middle part (MR) of the shoot of sterile plants of different growth intensity were used as a study object. It was found that hypothermia (4 °C, 3 days) most affected the actively growing plant organs: leaves and roots in MR, and leaves, stems, and stolons in AR. The most damaged AR leaves retained severe dehydration and elevated oxidative status during natural recovery, despite increased superoxide dismutase intensity and free proline levels. Pretreatment of plants with individual hormones increased their resistance to damaging hypothermia, manifested by changes in metabolic and growth responses. IAA pretreatment exerted a greater positive effect than Mel pretreatment. IAA treatment stimulated the root and leaf growth recovery in MR by reducing oxidative stress and restoring constitutive water levels at increased free proline, ascorbic acid, and the sum of flavonoids and phenolic compounds. Possible reasons for the differences between AR and MR hormone restoration therapy are discussed.