Heavy metals, including a hexavalent form of
chromium (
Cr(VI)) increasing accumulation in agricultural soil, cause a significant reduction in quality, yield, and growth of rice varieties worldwide. Screening for the selection of tolerant varieties is essential for conventional and molecular breeding. Shaheen basmati (SB) and basmati-385 (B-385) rice varieties, a subspecies of indica, show different sensitivity to
Cr(VI), but the underlying mechanisms of this different sensitivity remain elusive. In the current study, we examine the sensitivity of SB and B-385 based on the root, which is the primary organ that encounters water and soil containing
Cr(VI), elongation assay, and
ethylene's possible role (a stress-responsive
phytohormone) in the process. Our results show that SB's seedlings exhibit
hypersensitivity as a higher root elongation inhibition than B-385 under different
Cr(VI) concentrations. Hypersensitive SB consistently expresses a higher level of
ethylene biosynthesis and signaling-related genes than B-385. Moreover,
ethylene signaling antagonist (
silver, Ag) and biosynthesis inhibitor (aminoethoxy vinyl
glycine, AVG) alleviate the difference in
Cr(VI)-induced root growth inhibition between SB and B-385, respectively. Taken together, we conclude that
ethylene mediates difference in sensitivity based on the difference in root growth inhibition in different rice varieties. The difference in
Cr(VI)-induced root growth inhibition in SB and B-385. (A) Root growth of SB is slightly more as compared to B-385 in control conditions in the Hoagland solutions. (B) Seedlings of SB showed
hypersensitivity to 200 μM
Cr(VI) compared to B-385 in terms of primary root growth inhibition, which was higher in SB than B-385. Interestingly,
Cr(VI)-induced relative transcript level of
ethylene biosynthesis, perception, and signaling-related genes was significantly higher in hypersensitive SB than B-385. Current results in association with previous literature show that
Cr(VI)-induced
ethylene biosynthesis is regulating
Cr(VI)-induced
ethylene perception, signaling, and associated
Cr(VI)-induced
ethylene-mediated primary root growth inhibition. Conclusively, the difference in
ethylene quantities in both varieties mediates the difference in root growth inhibition between SB and B-385 (C and E). The difference in
Cr(VI)-induce root growth inhibition between SB and B-385 was significantly alleviated by
ethylene signaling inhibitor (10 μM Ag, as AgNO3) and
ethylene biosynthesis inhibitor (10 μM AVG) treatment in the presence of 200 μM
Cr(VI), respectively. (D)
Ethylene biosynthesis precursor (10 μM ACC) treatment-mediated induced root growth inhibition difference between SB and B-385 was not significant, which may be because of enough quantity of the
Cr(VI)-mediated
ethylene accumulation or unknown limiting factor. Arrows mean addition and an increase in expression, and T-line means suppression or inhibition. The width of the pointers (arrows) is proportional to the gene expression level.