Chalky part differs in chemical composition from translucent part of japonica rice grains as revealed by a notched-belly mutant with white-belly

Abstract

Background: Chalkiness has a deleterious influence on rice appearance and milling quality. We identified a notched-belly mutant with a high percentage of white-belly, and thereby developed a novel comparison system that can minimize the influence of genetic background and growing conditions. Using this mutant, we examined the differences in chemical composition between chalky and translucent endosperm, with the aim of exploring relations between occurrence of chalkiness and accumulation of starch, protein and minerals.

Results: Comparisons showed a significant effect of chalkiness on chemical components in the endosperm. In general, occurrence of chalkiness resulted in higher total starch concentration and lower concentrations of the majority of the amino acids measured. Chalkiness also had a positive effect on the concentrations of As, Ba, Cd, Cr, Mn, Na, Sr and V, but was negatively correlated with those of B, Ca, Cu, Fe and Ni. By contrast, no significant chalkiness effect on P, phytic acid-P, K, Mg or Zn was observed. In addition, substantial influence of the embryo on endosperm composition was detected, with the embryo showing a negative effect on total protein, amino acids such as Arg, His, Leu, Lys, Phe and Tyr, and all the 17 minerals measured, excluding Ca, Cu, P and Sr.

Conclusion: An inverse relation between starch and protein as well as amino acids was found with respect to chalkiness occurrence. Phytic acid and its colocalized elements K and Mg were not affected by chalkiness. The embryo exerted a marked influence on chemical components of the endosperm, in particular minerals, suggesting the necessity of examining the role of the embryo in chalkiness formation. © 2016 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Keywords: chalkiness; chemical composition; minerals; phytic acid; rice.

Figure 1

Experimental scheme for chemical analysis of translucent and chalky grains. T₁ and T₂ are the upper and bottom half part of translucent grain, respectively. C₁ and C₂ are the upper and bottom half part of chalky grain, respectively. T₁, T₂ and C₁ are translucent, while C₂ is opaque. T₁ accounts for 47.06% of the translucent grains, and T₂ for 52.94%. C₁ consists of 42.48% chalky grains, and C₂ 57.52%. The embryos of C₂ and T₂ were removed.

Figure 2

SEM images of endosperm transverse sections from the upper and bottom half parts of grains with white‐belly (C₁ and C₂) and without white‐belly (T₁ and T₂). (A, B, C) Translucent tissues of T₁, T₂, and C₁, respectively. (D, E F) Chalky tissues of bottom half part of C₂. Large and small white arrows indicate compound starch granules and single starch granules, respectively. Large black arrows indicate traces of smaller protein bodies (PBI) removed during sample preparation. Small black arrows indicate that micro‐pores occur on the surface of the compound starch granules, which show evidence of α‐amylase attack.

Figure 3

Differences in chain length distribution of amylopectin between chalky grains (C_g) and translucent grains (T_g) as revealed by HPAEC‐PAD.