Journal of Cereal Science 95 (2020) 103018 Available online 10 June 2020 0733-5210/© 2020 Elsevier Ltd. All rights reserved. Effect of high temperature stress during ripening on the accumulation of key storage compounds among Japanese highly palatable rice cultivars Tsutomu Ishimaru a, b, * , Masayuki Miyazaki c , Takanari Shigemitsu d , Masaru Nakata b , Masaharu Kuroda b , Motohiko Kondo a, e , Takehiro Masumura d a NARO Institute of Crop Science, NARO, 2-1-18 Kannondai, Tsukuba, Ibaraki, 305-8518, Japan b Hokuriku Research Station, Central Region Agricultural Research Center, National Agriculture and Food Research Organization (CARC/NARO), 1-2-1 Inada, Joetsu, Niigata, 943-0193, Japan c Fukuoka Agricultural Research Center, Chikushino, Fukuoka, 818-8549, Japan d Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Shimogamo, Sakyo-ku, Kyoto, 606-8522, Japan e Graduate School of Bioagricultural Sciences, Nagoya University, Furo Chikusa, Nagoya, 464–8601, Japan A R T I C L E INFO Keywords: 13 kDa prolamin Starch properties Grain appearance High temperature stress Rice ABSTRACT High temperature stress during ripening increases the frequency of chalky grains, resulting in a lower market value for rice (Oryza sativa L.). Changes in starch properties and the accumulation pattern of storage proteins are proposed to be related to the occurrence of chalky grains. This study investigated changes in the accumulation of key storage compounds in the grains of Japanese highly palatable rice cultivars, subjected to high temperature stress when grown in a growth chamber and the feld. The 13 kDa prolamin content was signifcantly reduced in a highly heat-sensitive cultivar, Tsukushiroman, whereas the 13 kDa prolamin content was not affected in a heat- tolerant cultivar, Genkitsukushi, even in a high temperature chamber condition (31/26 � C day/night), when compared with the control chamber condition (26/21 � C day/night) for both genotypes. In addition, grains grown in feld conditions revealed that severely chalky grains had less 13 kDa prolamin than perfect grains in all fve genotypes. Changes in amylose content and the distribution of amylopectin chain lengths did not explain the difference in grain appearance both for chamber and feld experiments. These results strongly suggest that physiological processes linked with the synthesis of 13 kDa prolamin are associated with grain appearance in Japanese highly palatable under high temperature stress. 1. Introduction High temperature stress during ripening reduces the grain quality of rice (Oryza sativa L.). The proportion of chalky grains signifcantly in- creases when rice plants are subjected to average mean temperatures over 27 � C during the frst 20 days after heading (Wakamatsu et al., 2007). A high frequency of chalky grains degrades grain appearance and the market value, resulting in reductions in rice head yield and farmer income (Lyman et al., 2013). Due to occasional decreases in the levels of perfect grains because of recent increases in air temperatures (Hamachi et al., 2012; Ishimaru et al., 2018; Lanning et al., 2011), integrated studies on seed physiology under high temperature stress conditions, improved cultivation techniques, and the development of heat-tolerant rice cultivars to ensure high frequencies of perfect grains have been strongly promoted (See reviews, Fitzgerald et al., 2009; Ishimaru et al., 2016; Mitsui et al., 2016; Morita et al., 2016; Sreenivasulu et al., 2015). Starch and storage proteins are the major storage compounds ac- counting for 75–85% and 7–9% of the dry weight of rice grains, respectively. The chalky phenotype is attributed to loosely packed am- yloplasts resulting from aberrant starch accumulation (Ishimaru et al., 2009; Tashiro and Wardlaw, 1991; Yamakawa et al., 2007). Accumu- lation of some storage compounds responds extremely to high temper- atures. For example, the amylose content is reduced in grains grown under high temperature stress (Lin et al., 2010; Miyazaki et al., 2013; Yamakawa et al., 2007). High temperature stress alters the fne structure of amylopectin; the distribution of short chain-length molecules de- creases, whereas that of long chain-length amylopectin increases (Umemoto et al., 1999; Yamakawa et al., 2007). A reduction in the Abbreviations: BiP, endosperm luminal binding protein; ER, endoplasmic reticulum; SDS-PAGE, Sodium dodecyl sulfate-Polyacrylamide gel electrophoresis. * Corresponding author. Hokuriku Research Station, CARC/NARO, 1-2-1 Inada, Joetsu, Niigata, 943-1093, Japan. E-mail address: cropman@affrc.go.jp (T. Ishimaru). Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: http://www.elsevier.com/locate/jcs https://doi.org/10.1016/j.jcs.2020.103018 Received 29 April 2020; Received in revised form 21 May 2020; Accepted 21 May 2020