From seeds to plants: the use of priming to improve salt tolerance in sorghum

Abstract

Various environmental conditions can restrict the germination and establishment of plants, with high salinity being one of the most critical. This condition arises from the high concentration of ions in the soil, leading to essential metabolic alterations that affect both germination and plant development. Salinity induces two types of stress: (i) osmotic stress, caused by the reduction of the osmotic potential in the soil solution, and (ii) ionic stress, resulting from ion dissociation, which damages membranes and other cellular structures. In semi-arid and arid regions, there is an urgent need to cultivate species with some level of salt tolerance. Sorghum (Sorghum bicolor (L.) Moench), although moderately tolerant, exhibits critical stages such as germination and seedling establishment, which are highly sensitive to salinity effects. A promising approach to mitigating these effects is the priming technique, which enhances germination and plant development. This study investigated the hypothesis that priming with antioxidant molecules and growth regulators provides better conditions for sorghum germination and growth under salt stress. To understand the tolerance mechanisms, experiments were conducted both in laboratories and greenhouse conditions. In the first chapter, the response of seeds from four sorghum varieties subjected to priming with ascorbic acid, abscisic acid, and hydropriming was evaluated under different NaCl concentrations and osmotic stress induced by PEG-6000. Tests analyzed parameters such as germination percentage, germination speed index, and the mean time for 50% seed germination. In the second chapter, biochemical analyses were performed on two contrasting cultivars (BRS-332 and DKB 540), assessing carbohydrate and amino acid metabolism, hydrogen peroxide and malondialdehyde levels, and antioxidant enzyme activity. The third chapter involved greenhouse experiments in which plants grown from seeds treated with priming were monitored over 65 days under salt stress. Parameters such as chlorophyll a fluorescence, gas exchange, and markers related to salt tolerance identified in the seeds were analyzed during different phenological stages. The results showed that the cultivars exhibit distinct tolerance mechanisms to osmotic and salt stress. Priming induced positive effects, particularly through the accumulation of proline and sugars, which facilitated osmotic adjustment and mitigated oxidative stress in seeds, seedlings, and adult plants. These effects can be attributed to "priming memory," a phenomenon that allows the recovery of metabolic alterations induced by the initial treatment, resulting in better maintenance of photosynthetic metabolism and reduced impacts of salt stress across different phenological stages. In conclusion, priming is an effective tool for enhancing sorghum tolerance to salt stress, contributing to the development of sustainable strategies that enable cultivation in saline areas. This approach broadens productive potential and agricultural resilience in adverse regions, making it a valuable technique for ensuring food security and sustainable agricultural practices in the face of environmental challenges.