Morpho-physiological analysis of tolerance to aluminum toxicity in rice varieties of North East India

<div><p>Aluminum (Al) is the third most abundant metal in earth crust, whose chemical form is mainly dependent on soil pH. The most toxic form of Al with respect to plants is Al³⁺, which exists in soil pH <5. Acidic soil significantly limits crop production mainly due to Al³⁺ toxicity worldwide, impacting approximately 50% of the world’s arable land (in North-Eastern India 80% soil are acidic). Al³⁺ toxicity in plants ensues root growth inhibition leading to less nutrient and water uptake impacting crop productivity as a whole. Rice is one of the chief grains which constitutes the staple food of two-third of the world population including India and is not untouched by Al³⁺ toxicity. Al contamination is a critical constraint to plant production in agricultural soils of North East India. 24 indigenous Indica rice varieties (including Badshahbhog as tolerant check and Mashuri as sensitive check) were screened for Al stress tolerance in hydroponic plant growth system. Results show marked difference in growth parameters (relative growth rate, Root tolerance index, fresh and dry weight of root) of rice seedlings due to Al (100 μM) toxicity. Al³⁺ uptake and lipid peroxidation level also increased concomitantly under Al treatment. Histochemical assay were also performed to elucidate uptake of aluminum, loss of membrane integrity and lipid peroxidation, which were found to be more in sensitive genotypes at higher Al concentration. This study revealed that aluminum toxicity is a serious harmful problem for rice crop productivity in acid soil. Based on various parameters studied it’s concluded that Disang is a comparatively tolerant variety whereas Joymati a sensitive variety. Western blot hybridization further strengthened the claim, as it demonstrated more accumulation of Glutathione reductase (GR) protein in Disang rice variety than Joymati under stressed condition. This study also observed that the emergence of lethal toxic symptoms occurs only after 48h irrespective of the dose used in the study.</p></div

Relationship between root length and relative root reduction (%) of 24 genotypes of rice varieties at 100 μM Al concentration for 48h.

<p>The graphical representation was created using ggplot 2 package of R program.</p

Effect of four aluminum concentrations on root relative water content (%) of 24 rice genotypes at 48 h in the hydroponic assay.

<p>Effect of four aluminum concentrations on root relative water content (%) of 24 rice genotypes at 48 h in the hydroponic assay.</p

Correlation between different parameters of 24 rice varieties at 48h.

<p>Correlation between different parameters of 24 rice varieties at 48h.</p

Expression analysis of <i>Os</i>NRAT1 under stressed and unstressed condition.

<p>Expression analysis of <i>Os</i>NRAT1 under stressed and unstressed condition.</p

Histochemical detection of aluminum uptake in root tips of rice seedlings.

<p>Microscopic views of hematoxylin stained root tips. Intense stained colour represent hematoxylin-Al complexes by the root cells at 48h.</p