Mecanismos fisiológicos de resistência a salinidade conferidos pelo porta-enxerto em mudas enxertadas de videira

Abstract

The objective of this study was to evaluate the role of rootstocks on biochemical and physiological mechanisms of resistance to salinity involved in ionic homeostasis, photosynthetic efficiency and oxidative protection in grapevine seedlings. Two studies were carried out, an initial experiment characterizing growth and ionic partitioning in rootstocks and the other with grafted seedlings using the most resistant rootstocks identified (Experiment I). Experiment I was performed in a 4 x 3 factorial assay, consisting of four rootstocks (IAC 313, IAC 572, Paulsen and SO4) exposed to three concentrations of NaCl (0, 40 and 80 mM) in the nutrient solution for 26 days. Experiment II was performed in a 4 x 3 factorial, consisting of four types of grafted seedlings (grafts/rootstocks: BRS Vitória/IAC 313, BRS Vitória/IAC 572, BRS Vitória/Paulsen, BRS Vitória/SO4) increasing NaCl (0, 40 and 80 mM) in the solution for 15 days. The ionic homeostasis was studied by the accumulation and partition of Na+, Cl- and K+ K+/Na+ ratio, the photosynthetic efficiency by the gas exchanges and photochemical activity. Oxidative disturbances were evaluated based on damage markers (membrane lipid peroxidation) and enzymatic activity (SOD, APX and POX) and non-enzymatic activity (ASA and GSH). The results showed that the vines presented different physiological responses to the saline stress, finding a contrast between the studied rootstocks. The rootstocks IAC 313 and IAC 572 have a better tolerance, whereas Paulsen and SO4 are more sensitive, presenting a better growth and greater reductions in the photosynthetic parameters associated to the lower content of K+ in the leaves. The rootstocks IAC 313 and IAC 572, when tested both as rootstocks and grafted on BRS Vitória, showed no reduction of K+ content in the leaves and in roots reduced in a small proportion in response to salinity when compared to SO4 and Paulsen, suggested that if these materials are used in the production of seedlings will result in plants more tolerant to salt stress. The seedlings grafted on IAC 313 under salinity showed higher photosynthetic efficiency associated with better K+/Na+ homeostasis and photochemical activity, indicated by ETR and qP. The activity of the SOD, POX and APX enzymes was differentially modulated by NaCl in the grafted seedlings, as well as the content of ASA and GSH. In general, the results show characteristics associated with sensitivity and/or tolerance to salinity, in grapevine rootstocks and in grafted seedlings. In this study, these characteristics were attributed to the rootstock, but the data indicate only part complexity of the physiological mechanisms in the grafting process that are still little known, especially in saline conditions.