Aplicação de priming na germinação de sementes e na tolerância ao estresse luminoso de plântulas de espécies nativas da Mata Atlântica

Abstract

Priming is a pre-sowing technique that can induce a higher percentage and speed of seed germination, in addition to enhancing the antioxidant activity of plants under abiotic stress. Therefore, the objective of this study was to investigate germination and biochemical responses influenced by the application of priming to seeds. It was also investigated whether this pre-sowing technique is capable of generating seedlings that are more tolerant to light stress. Seeds from four tree species native to the Atlantic Forest were used: Ceiba speciosa; Astronium fraxinifolium; Tabebuia roseoalba and Myrsine coriacea. The main hypothesis is that seed priming can improve the germination process, initial growth, anatomical parameters, photosynthesis, and the antioxidant defense system, thereby generating plants that are physiologically capable of tolerating the consequences of full sun exposure. To investigate this hypothesis, two experiments were conducted. The first, investigated the effects of priming with water, methionine, and PEG during the germination of seeds from the four species. Germination parameters (final germination percentage (%G) and germination speed index (GSI)) and biochemical parameters (hydrogen peroxide (H2O2), malondialdehyde (MDA), protein content, and antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) were evaluated. The second experiment investigated the effects of priming on the generation of C. speciosa seedlings grown under light stress. The experiment was conducted in a 2x2 factorial scheme, with two light conditions (full sun and 50% shade) and two seed treatments: without priming (control) and with priming with methionine. Initial growth parameters, dry matter, photosynthetic and anatomical parameters, pigment content, and the same biochemical parameters as in the first experiment (H2O2, MDA, proteins, SOD, CAT, and APX). In experiment I, it was observed that priming induced an increase in GSI in T. roseoalba and A. fraxinifolium seeds and increased CAT activity in C. speciosa seeds. M. coriacea seeds had lower MDA content when primed with methionine, lower H2O2 content when primed with water, methionine, or PEG, and higher protein content when hydroprimed. In experiment II, it was found that seedlings grown in full sun had higher H2O2 values and shoot length, regardless of the treatment applied to the seeds. Chlorophyll b and total chlorophyll content was higher in plants conditioned under shade and treated with priming for both light conditions. The anatomical variables analyzed were not statistically significant. Thus, it can be concluded that seed priming influenced the improvement of some parameters, mainly related to the germination process. However, in seedlings, although it induced an increase in chlorophyll b and total chlorophyll content, it did not generate seedlings significantly different from those that did not receive the treatment.