Thiamine and Indole-3-Acetic Acid Induced Modulations in Physiological and Biochemical Characteristics of Maize ( Zea mays L.) under Arsenic Stress

Arsenic (As) accumulation in plant tissues is an emerging threat to crop productivity and global food security. As-toxicity in soil is increasing at alarming rates through mining, pesticide applications and industrial revolution. Therefore, a novel study was conducted to disclose the role of vitamin B1 (thiamine) and Indole-3-acetic acid (IAA) in maize ( Zea mays L.) against different As stress levels, i.e., 0, 50 and 100 mg/kg sodium arsenite (NaAsO 2 ). Seeds of two contrasting maize varieties Akbar and Pearl were primed with different treatments, i.e., control (non-primed seeds), thiamine (250 ppm), IAA (30 µM) and a mixture of thiamine (250 ppm) + IAA (30 µM). Of both As stress levels (50, 100 mg/kg), a higher As stress level (100 mg/kg) imparts maximum negative impacts on maize growth by decreasing shoot and root nutrient ions—potassium (K), calcium (Ca), phosphorus (P), total phenolics, total soluble proteins—as compared to the control, while increases in catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), malondialdehyde MDA, hydrogen peroxide (H 2 O 2 ), proline, total soluble sugars, free amino acids and ascorbic acid were recorded under As-stress as compared to control. The varietal differences showed that Pearl exhibited tolerance against As-stress as compared to Akbar. However, thiamine and IAA treated seeds of maize manifested remarkable enhancement in plant growth attributes with better chlorophyll, plant water status, enzymatic and non-enzymatic antioxidants activities under imposed As-stress. The growth and biomass significantly increased with priming treatments of thiamine and IAA under both As-stress levels of both varieties that suggests the role of these in As-stress tolerance. Overall, the performance order in improving growth under As-stress of thiamine and IAA treatments was thiamine + IAA > thiamine > IAA observed in both maize varieties.