Response of rice (Oryza sativa L.) callus under influence of polyethylene glycol

Abstract:

Water stress resulting from water scarcity is a major factor limiting crop production in Iraq. The present study aimed to evaluate the effect of adding Polyethylene Glycol-1500 (PEG-1500) used to induce water stress on the growth of embryogenic callus in the rice cultivar 'Anbar 33', as well as on some physiological and biochemical traits associated with water stress tolerance in vitro. PEG-1500 was added to the MS growth medium at concentrations of (0, 5, 10, and 20) g/L to investigate its impact on callus growth, relative water content, somatic embryogenesis, cellular membrane integrity (electrolyte leakage), proline and carbohydrate content. The study found that increasing the PEG concentration resulted in a significant reduction in the fresh weight of embryogenic callus; at a concentration of 20 g/L, the weight recored to 0.14 g compared to 0.22 g in the control treatment. A significant decrease in relative water content was also observed with PEG treatments at 10 and 20 g/L, reaching 73.4% and 67.8% respectively, compared to 94.2% in the control. Furthermore, the results indicated that PEG-induced water stress at concentrations of 10 and 20 g/L negatively affected somatic embryo formation, as the number of somatic embryos decreased from 30.6 in the control treatment to 18.6 and 14, respectively. Increased water stress levels led to a significant rise in electrolyte leakage at concentrations of 10 and 20 g/L compared to the control, indicating greater damage to cell membranes. Conversely, PEG treatment stimulated the accumulation of both proline and carbohydrates. The results indicate that water stress limits embryogenic callus growth and the efficiency of somatic embryogenesis, while enhancing the accumulation of osmolytes compounds such as proline and carbohydrates, reflecting their role in adaptation to water deficient conditions in the growth medium,