Evaluation of Enzymatic and Non-enzymatic Antioxidant Defense Responses of Durum Wheat (Triticum durum Desf.) in Coping with Boron Stress

Abstract

Wheat, one of the world's most important agricultural products, plays a vital role in meeting the nutritional needs of our growing global population. However, arid and semi-arid regions face a potential threat from boron (B) toxicity. While boron is an essential nutrient for plant growth and development, its excessive presence can be toxic. It disrupts physiological processes, causing chlorosis and necrosis, ultimately leading to yield loss or plant death. Although B deficiency is a problem in the soils of many countries, Türkiye is one of the few experiencing B toxicity problems in its agricultural areas. This study investigated the physiological and biochemical responses of durum wheat to various B concentrations (0-20 mg L-1) under controlled air-conditioned cabin conditions. Durum wheat exhibited a decrease in chlorophyll content, phenolic content, and antiradical capacity at B doses exceeding 10 mg L-1. However, carotene content increased steadily with increasing B concentrations. The activities of antioxidant enzymes, including superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione S-transferase (GST), increased up to a B dose of 15 mg L-1. Catalase (CAT) and glutathione reductase (GR) activities increased up to 10 mg L-1 B dose but decreased at higher B levels. Proline content increased tenfold up to a B dose of 10 mg L-1, indicating an attempt to mitigate stress. Conversely, malondialdehyde (MDA) accumulation increased continuously (approximately 150%) with increasing B doses, suggesting membrane damage. Despite being considered B-sensitive, this study demonstrated that durum wheat can effectively cope with B stress up to a B dose of 10 mg L-1 under controlled conditions. Beyond this threshold, physiological and biochemical changes indicate a decline in stress tolerance. Many osmoregulators, carotenes, alkaloids, flavonoids, tocopherols, phenolic compounds, non-protein amino acids, and several unidentified metabolites are activated to support antioxidant defense. The SOS pathway and the released ROS force gene regulatory systems come into play. Following these, the ROS released in the organism are neutralized, and ionic homeostasis and cellular stress resistance are achieved.