Physio-Biochemical Responses and Cadmium Partitioning Associated with Stress Tolerance in Hulless Barley Genotypes

Among heavy metals, cadmium (Cd) is shown to have adverse consequences for plants. Due to its harmful nature and ability to move through the soil–plant system, it is a very worrying element for soil experts and plant physiologists. In this work, we designed a pot experiment to study the influence of three soil concentrations of cadmium (0, 15, and 30 mg/kg) to explore its physiological impacts, and its portioning in the whole plant of three hulless barley varieties. Our findings demonstrated marked Cd accumulation in roots, leaves, and stems under severe Cd stress (30 mg/kg). Cd stress was also shown to reduce photosynthetic activity, chlorophyll fluorescence (Fv/Fm), and transpiration rates (E). The application of Cd in the soil increased the activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) enzymes, as well as the levels of oxidative stress markers such as malondialdehyde (MDA), hydrogen peroxide (H2O2), and proline. These results reflect the negative effects of cadmium on morpho-physiological traits in barley genotypes. However, the principal component analysis indicated a significant correlation between oxidative stress indicators and enzymatic activities, along with different levels of Cd tolerance between Tombari, Assiya, and Giza 130 genotypes. When exposed to Cd, these varieties shifted a significant amount of energy from growth to produce antioxidant compounds and osmolytes. Despite this, these defenses did not effectively shield the plant from the detrimental effects of oxidative stress induced by Cd accumulation at vegetative stages. Consequently, we highly recommend testing these varieties under Cd-contaminated soil to investigate the rate of cadmium accumulation in the seeds, the harvested part used in human nutrition.