Exogenous silicon leads to increased antioxidant capacity in freezing-stressed pistachio leaves | Tretiranje listov pistacije (Pistacia vera ‘Ahmadaghaii’) s silicijem poveča njihovo antioksidativno sposobnost v mraznem stresu

English. Freezing stress limits photosynthesis and growth of plants. This may be attributed to the enhancement of freezing-associated oxidative damage. In this study, we followed precisely changes in the extent of lipid peroxidation and oxidative damage in leaves of pistachio (Pistacia vera ‘Ahmadaghaii’) plants exposed to foliar-applied silicon (Si) under freezing stress. The foliar-applied Si decreased significantly damaging effects of cold on relative water content (RWC), accompanied by an increase in shoot fresh mass (SFM). In addition, pre-Si treatment caused a significant reduction of the leaf area lost by freezing. There was a remarkable increase in phenylalanine ammonia-lyase (PAL) activity during recovery. Since leaf phenolic content was not affected by supplementary Si, the possibility that exogenously applied Si directly influences the activity of PAL seems thin. In the present work, freezing stress caused great membrane damage, as assessed by lipid peroxidation, but Si application significantly reduced the membrane damage because of an efficient scavenging by superoxide dismutase (SOD) and peroxidase (POD). Under freezing, despite the increasing POD activity, Si-supplied plants accumulated the highest levels of hydrogen peroxide (H2O2) may act as a signal for recovery ability from freezing injury. A positive correlation was found between the concentration of malondialdehyde (MDA) and the percentage of necrotic leaf area. This study suggests that the possible mechanisms for Si enhanced freezing resistance may be attributed to the higher antioxidant defense activity and lower lipid peroxidation through leaf water retention, in addition to its role as a mere physical barrier.

Slovenian. Mrazni stres omejuje fotosintezo in rast rastlin, kar lahko pripišemo povečanju oksidativnih poškodb zaradi zmrzovanja. V raziskavi sta bili spremljani peroksidacija lipidov in oksidativne poškodbe listov pistacije (Pistacia vera ‘Ahmadaghaii’) izpostavljenih mraznem stresu in foliarnem tretmaju s silicijem (Si). Foliarna uporaba silicija je značilno zmanjšala učinke mraza na ravni relativne vsebnosti vode (RWC), kar je povzročilo povečanje sveže mase poganjkov (SFM). Dodatno je predtretiranje s Si povzročilo značilno zmanjšanje izgube listne površine zaradi zmrzovana. Med okrevanjem po mraznem stresu je bila opazno povečana aktivnost fenilalanin amonik-liaze (PAL). Zaradi nespremenjene vsebnosti fenolov v listih po aplikaciji Si je maloverjetno, da bi foliarno dodani Si neposredno vplival na aktivnost PAL. Mrazni stres je povzročil velike poškodbe membran, ki so bile ocenjene s peroksidacijo lipidov, a jih je uporaba Si značilno zmanjšala zaradi učinkovitega antioksidativnega delovanja superoksid dismutaze (SOD) in peroksidaze (POD). Kljub povečanju aktivnosti POD v razmerah zmrzovanja, so s Si-obravnavane rastline kopičile največje količine vodikovega peroksida (H2O2), ki je lahko deloval kot signal za sposobnost okrevanja po poškodbah zaradi zmrzovanja. Ugotovljena je bila pozitivna korelacija med koncentracijo malondialdehida (MDA) in odstotkom nekrotične listne površine. Raziskava kaže, da je možen mehanizen preko katerega Si povečuje odpornost na zmrzovanje večja antioksidativna obramba in manjša peroksidacija lipidov, ki se odraža v večjem zadrževanju vode poleg delovanja Si kot čisto fizikalne prepreke.