Concurrent effect of aluminum toxicity and phosphorus deficiency in the root growth of aluminum tolerant and sensitive rice cultivars

Aluminium (Al) toxicity and phosphorus (P) deficiency are the major constraints to plants under acidic soils (pH <= 4.5). In this study, the co-effect of Al toxicity and P deficiency under pH < 4.5 was studied to analyze the root growth, root structure, Al uptake and gene expression in Al-tolerant and-sensitive rice cultivars. About 24.2-28.9% root growth inhibition was recorded in the susceptible cultivars, whereas only 2.69-4.32% was recorded in tolerant cultivars. Whereas, the relative Al uptake in sensitive cultivars ranged from 1.90-to 3.25-fold higher than the control, whereas it was 1.58-to 1.9-fold higher in tolerant cultivars. Higher distortion in root was observed in sensitive cultivars, whereas it was less in tolerant cultivars. In addition, hematoxylin and Evan's blue staining showed high intensity of stain in the root tips of sensitive cultivars as compared to tolerant cultivars, indicating a higher effect of Al toxicity. The OsNRAT1 (Nramp aluminum transporter 1) gene responsible for Al detoxification in rice was highly expressed in roots of tolerant cultivars. From this comparative study, it is inferred that Al toxicity-tolerant rice cultivars possess better efficiency in the maintenance of P deficiency as compared to sensitive cultivars. Thereby, Al toxicity-tolerant rice cultivars can be used in future rice breeding programs as P efficient cultivars.