Metabolic responses to arsenite in rice seedlings that differed in grain arsenic concentration

© Crop Science Society of America. Arsenic (As) occurs naturally in the environment, and is present in all edible and nonedible plant tissues. Plants have multiple mechanisms to prevent plant injury by heavy metals such as As. These same mechanisms could be used to reduce accumulation of As in rice (Oryza sativa L.) grains. From previous study of 1765 international rice accessions, specific accessions were identified as having exceptionally high grain As concentrations (grain As accumulators) and others low grain As (grain As excluders). This study investigated As uptake, transport, and metabolism in six previously identified lines to determine which physiological responses, if any, were associated with accumulation or exclusion of As in grains. Hydroponically grown seedlings were treated with 0 (controls) or 100 mM arsenite [As(III)], and then whole seedlings were analyzed for concentrations of As plus key compounds involved in heavy metal metabolism. Both grain accumulators and grain excluders actively concentrated As within their roots, and both groups had 10-fold higher As concentrations in roots than leaves. In response to As(III), roots of both grain excluders and grain accumulators increased in cysteine and phytochelatin (PC) production, which suggests PC sequestration of As. In contrast, only grain excluders doubled in leaf glutathione (GSH) concentration by 72 h after As(III) addition. Because PC concentrations remained constant in leaves, it appears that the additional leaf GSH in the grain excluders was not used to produce more PC but may instead be forming As-GSH adducts, which also aid in As sequestration

Validation of a major QTL for salinity tolerance on chromosome 1 of rice in three different breeding populations

The effect of a major quantitative trait locus (QTL) for salinity tolerance in rice, designated as SalTol in a previous study, was tested using three F2 breeding populations. The populations were derived from the following F1 hybrids: 'BRRI dhan40' (susceptible)/ 'IR61920-3B-22-2-1' (highly tolerant); 'BRRI dhan28' (highly susceptible)/ 'IR50184-3B-18-2B-1' (moderately tolerant); and 'Kajalsail' (tolerant)/ 'IR52713-2B-8-2B-1-2' (tolerant). Targeted mapping of the chromosome region containing SolTol (49.6 to 87.1 cM) on chromosome 1 was conducted using 20 SSR and two EST markers. Comparisons of linkage maps of the three populations were very similar to the previous QTL map that identified SolTol. A QTL was only detected for 'BRRI dhan40'/ 'IR61920-3B-22-2-1' population. The SSR marker RM8094 was the most tightly-linked marker (P<0.001); four other markers, RM1287, RM3412, RM493 and CP03970, were also significantly associated with salinity tolerance (P<0.05). An F-3 population of the cross 'BRRI dhan40'/ 'IR61920' was used to reconfirm this result. This was interesting because the tolerant parent in this population was not related to the tolerant parent used for the original mapping population. QTLs were not detected at the SalTol locus for either of the other two populations. This was consistent with the phenotypes of the parents used to construct these populations, and indicates that the SolTol QTL may only be effective in specific populations