Oxidative stress due to high solar radiation increases free polyamines content in apple skin
The North Patagonia region in Argentina provides predisposing climatic conditions for the development of photo-oxidative sunburn in apples. Polyamines (PAs), especially putrescine (Put), spermidine (Spd), and spermine (Spm), participate in plant antioxidant responses under stressful environmental conditions. The aim of this work was to study free individual PAs levels and oxidative metabolism in apple skin with sunburn damage. At commercial harvest, 'Granny Smith' apples (Malus domestica Borkh) with a slight sunburn side (SS) were selected. Thiobarbituric acid reactive substances (TBARs), antioxidant activity (DPPH radical scavenging), chlorophyll content, and free individual PA levels were then evaluated on the SS and the healthy side (HS) of apple peels. Maturity indices were also determined for both sides of the fruits. Results showed that antioxidant capacity increased from 31.4% in HS to 40.8% in SS, while lipid peroxidation was higher in SS (59.7 nmol g‑1 FW) than in HS (43.8 nmol g‑1 FW). Meanwhile, total chlorophyll content was reduced from 62.5 µg g‑1 FW in HS to 28.5 µg g‑1 FW in SS. Put was the most abundant PA in both HS and SS skin tissues, followed by Spm and Spd. High solar radiation stress increased total free PA levels in fruit peel. Spd and Spm content increased 64 and 41%, respectively, in SS samples compared to HS, while no significant differences were found in Put levels. SS samples showed higher flesh firmness and soluble solids content than HS, while starch index and titratable acidity did not differ significantly. Although the role of PA metabolism during stress conditions in plants remains incompletely characterized, our data as well as previous research suggest that Spd and Spm accumulation may be an integral part of the apple fruit response to photo-oxidative sunburn.
Vita, L.I., Venturino, A. and Colavita, G.M. (2020). Oxidative stress due to high solar radiation increases free polyamines content in apple skin. Acta Hortic. 1289, 19-26
sunburn, abiotic stress, antioxidants