Abstract
Effect of high temperature (HT) on anthocyanin (ANS) accumulation and its relationship with reactive oxygen species (ROS) generation in color rice kernel was investigated by using a black kernel mutant (9311bk) and its wildtype (WT). 9311bk showed strikingly higher ANS content in the kernel than WT. Just like the starch accumulation in rice kernels, ANS accumulation in the 9311bk kernel increased progressively along with kernel development, with the highest level of ANS at kernel maturity. HT exposure evidently decreased ANS accumulation in 9311bk kernel, but it increased ROS and MDA concentrations. The extent of HT-induced decline in kernel starch accumulation was genotype-dependent, which was much larger for WT than 9311bk. Under HT exposure, 9311bk had a relatively lower increase in ROS and MDA contents than its WT. This occurrence was just opposite to the genotype-dependent alteration in the activities of antioxidant enzymes (SOD, CAT and APX) in response to HT exposure, suggesting more efficiently ROS detoxification and relatively stronger heat tolerance for 9311bk than its WT. Hence, the extent of HT-induced declines in grain weight and kernel starch content was much smaller for 9311bk relative to its WT. HT exposure suppressed the transcripts of OsCHS, OsF3’H, OsDFR and OsANS and impaired the ANS biosynthesis in rice kernel, which was strongly responsible for HT-induced decline in the accumulation of ANS, C3G, and P3G in 9311bk kernels. These results could provide valuable information to cope with global warming and achieving high quality for color rice production.
Highlights
Rice (Oryza sativa L.) is one of the most important cereal crops in the world, especially in Asian countries
The insignificant difference in polyphenol content was found between 9311bk and WT (Figure 2C). These results clearly indicated that the black color of 9311bk kernels was chemically derived from the ANS accumulation, rather than the polyphenol and other pigment
The possible reason for the elevated heat tolerance of color rice could be explained by the combination of two factors: Firstly, ANS biosynthesis and its accumulation in plant tissues may play an important role in protecting plant against reactive oxygen species (ROS) damage, because of ANS being widely considered as antioxidant molecules in plant cells [28]
Summary
Rice (Oryza sativa L.) is one of the most important cereal crops in the world, especially in Asian countries. The kernel color of rice is considered as one of most important traits for the improvement of grain quality, due to its potential biological and pharmacological applications. Previous studies have confirmed that the phenotype of rice kernel is attributed to the accumulation of anthocyanins in pericarps [2]. Anthocyanins are natural colorants belonging to the category of bioflavonoids, which may be divided into two types of chemical compounds: anthocyanins (ANS) and anthocyanidins [3]. Two types of anthocyanins share a common basic core structure, namely the flavylium ion structure [2,3].
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