Danos foto-oxidativos e sistema de defesa antioxidante em dois híbridos de palma de óleo (Elaeis Guineensis jacq.) submetidos ao estresse salino.

Abstract

Considering that oil palm plantations are generally not irrigated and that there is intensive use of fertilizers, it is possible to assume that, during the dry season, reduced water availability combined with the accumulation of salts in the soil can lead to salinization. This condition can affect the physiology and growth of palm trees, as salt stress triggers metabolic changes, including the excessive production of reactive oxygen species. Therefore, the study aimed to evaluate a possible differential response to photooxidative damage to photosystem II and the ability of these plants to adjust antioxidant enzymes (superoxide dismutase, SOD; ascorbate peroxidase, APX; and catalase, CAT) as a primary cellular defense mechanism. To this end, two oil palm hybrids—Tenera and BRS Manicoré—were subjected to saline stress induced by daily irrigation with a NaCl solution, the concentration of which was gradually increased until reaching 400 mM. The experiment was conducted in a 2 × 2 factorial design with four replicates, involving a combination of the two hybrids and two salinity conditions (control, without NaCl addition; and saline stress, with NaCl addition). To evaluate stress tolerance, several parameters were analyzed, such as pre-morning water potential (Ψam), maximum photochemical efficiency of photosystem II (Fv/Fm), maximum photochemical efficiency of photosystem II in the presence of light (F’v/F’m), the ratio of initial fluorescence in the dark to variable fluorescence in the light (F0/F’v), and non-photochemical dissipation coefficient (NPQ), photochemical dissipation coefficient (qP), effective quantum efficiency (ΦPSII), quantification of pigments such as chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophylls (Chl a+b) and chlorophyll a to b ratio (Chl a/b), xanthophylls, carotenoids and anthocyanins were also evaluated. In addition, the levels of malonic aldehyde and hydrogen peroxide were evaluated, and to evaluate the antioxidant system, the activities of SOD, APX and CAT were estimated. Salt stress significantly reduced the water potential in both hybrids, to the same extent. A reduction in the values of Fv/Fm, F'v/F'm and FPSI were also observed, in addition to an increase in qP in both genotypes. The degradation of chloroplast pigments was significant only in the Tenera hybrid. In BRS Manicoré, the non-photochemical dissipation coefficient (NPQ) increased sixfold compared to the control. Regarding oxidative stress markers, malonic aldehyde levels increased in both hybrids. Hydrogen peroxide levels increased in BRS Manicoré but decreased in Tenera. SOD activity increased in both hybrids under stress, while APX and CAT activities were reduced, with this reduction being more significant in Tenera. It is concluded that BRS Manicoré demonstrated greater tolerance to substrate salinity, presenting less damage to the photosynthetic apparatus and greater superoxide dismutase activity, which may be advantageous under prolonged salt stress conditions.