Effect of High Solar Radiation Stress on Endogenous Polyamine Content in Six Apple Cultivars (Malus domestica Borkh)

Polyamines are chemical polycations that play a critical role in the response to stress conditions. This study aimed to quantify the levels of free polyamines (putrescine, spermidine, and spermine) and to examine their relationship with oxidative metabolism in the skin of apple (Malus domestica Borkh) fruit exhibiting symptoms of high solar radiation stress. The study focused on fruit from the cultivars ´Gala,´ ´Red Delicious,´ ´Fuji,´ ´Cripp´s Pink,´ ´Golden Delicious,´ and ´Granny Smith,´ comparing fruit with mildly sunburned skin (Sb-1) to those with healthy skin (Sb-0), all collected at commercial harvest time. The results indicated that high solar radiation stress leads to an increase in polyamine content in Sb-1 fruit skin, with cultivar-specific variations. Notably, only the Sb-1 fruit of the ´Red Delicious´ cultivar showed an increase in putrescine. Spermidine levels increased in Sb-1 across all cultivars except ´Golden Delicious,´ while spermine levels significantly increased in the ´Fuji,´ ´Cripp´s Pink,´ and ´Granny Smith´ cultivars. Despite the observed increases in polyamine content, phenolic content, and antioxidant capacity in Sb-1, these changes did not prevent increased lipid peroxidation, alterations in maturity indices, or the manifestation of sunburn symptoms in the affected tissue. These findings contribute to a deeper understanding of the role of polyamines in the response to high solar radiation stress, particularly in apple tissues.