Summary
The frequent occurrence of chalky rice (Oryza sativa L.) grains becomes a serious problem as a result of climate change. The molecular mechanism underlying chalkiness is largely unknown, however. In this study, the temperature‐sensitive floury endosperm11‐2 (flo11‐2) mutant was isolated from ion beam‐irradiated rice of 1116 lines. The flo11‐2 mutant showed significantly higher chalkiness than the wild type grown under a mean temperature of 28°C, but similar levels of chalkiness to the wild type grown under a mean temperature of 24°C. Whole‐exome sequencing of the flo11‐2 mutant showed three causal gene candidates, including Os12g0244100, which encodes the plastid‐localized 70‐kDa heat shock protein 2 (cpHSP70‐2). The cpHSP70‐2 of the flo11‐2 mutant has an amino acid substitution on the 259th aspartic acid with valine (D259V) in the conserved Motif 5 of the ATPase domain. Transgenic flo11‐2 mutants that express the wild‐type cpHSP70‐2 showed significantly lower chalkiness than the flo11‐2 mutant. Moreover, the accumulation level of cpHSP70‐2 was negatively correlated with the chalky ratio, indicating that cpHSP70‐2 is a causal gene for the chalkiness of the flo11‐2 mutant. The intrinsic ATPase activity of recombinant cpHSP70‐2 was lower by 23% at Vmax for the flo11‐2 mutant than for the wild type. The growth of DnaK‐defective Escherichia coli cells complemented with DnaK with the D201V mutation (equivalent to the D259V mutation) was severely reduced at 37°C, but not in the wild‐type DnaK. The results indicate that the lowered cpHSP70‐2 function is involved with the chalkiness of the flo11‐2 mutant.
An experiment was conducted at the experimental field of the Department of Crop Botany and Tea Production Technology, Sylhet Agricultural University, Sylhet, Bangladesh during July-December, 2013 to evaluate the morphological attributes and yield performances of nine genotypes of sweet potato in acidic soil. Among the genotypes, seven were Japanese viz. JSP-1, JSP-2, JSP-3, JSP-4, JSP-5, JSP-6, JSP-7 and two were Bangladeshi like BARI SP-7 and BARI SP-9. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. The results revealed that the genotypes varied considerably in the morphological characters at all growth stages and yield attributing characters. Among all the genotypes, the highest number (6.53), length (10.80 cm), diameter (3.35 cm) and yield (22.83 t haG 1 ) of storage root was recorded in BARI SP-7 followed by JSP-3 which was 5.35, 9.67 cm, 3.28 cm and 20.96 t haG 1 , respectively. On the other hand, BARI SP-9 showed the longest vine length, highest vine number plant 1 which were 298.7 cm and 6.60, respectively but yield was third highest amounting 19.37 t haG 1 . All the Japanese varieties except JSP-3 were not suitable for the acidic soil condition of Sylhet, Bangladesh. Therefore, the genotypes BARI SP-7 and JSP-3 were found suitable for their better growth and yield performance in acidic soils.
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