| Rice(Oryza sativa L.)kernel,providing calorific intake to over a half of the world population,is commonly consumed by human being as white rice followed by brown rice.However,rice genotypes with red,purple,or black bran layer,designated as color rice or pigmented rice.Color rice have anthocyanin in its kernel,which is thought to possess antioxidant nature providing ability to resist different environmental stresses along with contributing towards the rice grain quality improvement.Abiotic stress is the key factor affecting crop growth and productivity negatively,worldwide.Accordingly,the present study was carried out to investigate the genetic control and physiological metabolism of anthocyanin biosynthesis as well as its relationship with other grain quality traits so as to improve the production of color rice and role of anthocyanidin(ANDs)in providing tolerance against various stresses.Two rice genotypes,namely 9311 and NPB and their corresponding 9311 bk and NPBrk mutants were used to study the comparative properties of rice kernel in terms of morphological,physiological and grain quality traits.Various pigments profiles were analyzed for all rice genotypes to evaluate the possible link between pigment accumulation and color formation in both the mutants' kernel.1.Differential anthocyanidin accumulation pattern in color rice and its relation to transcriptional expression of genes involved in anthocyanin biosynthesis pathwayANDs pigment accumulation was found abundant in bk mutant followed by rk mutant while it was found in negligible amount for both the wild types.Our results showed that the bk mutant accumulated substantially higher ANDs content as compared to its wild type,same was the case for rk mutant as compared to its corresponding wild type.Transcriptional expression analysis of genes related to anthocyanin biosynthesis revealed that bk mutant showed higher expression level for all the genes involved in ANDs biosynthesis as compared to its wild type which is in line with the higher accumulation of ANDs content in bk mutant.The highest transcription amounts of OsCHI,OsF3'H,and OsDFR were at 21-days post anthesis,which decreased afterward while the OsCHS and OsF3 H were in line with the accumulation of ANDs content in bk mutant kernel.OsDFR and OsANS showed strikingly higher transcripts in bk mutant as compared to wild type,which showed their crucial role in biosynthesis of ANDs pigment in bk mutant.Contrary to this,the transcriptional expression of OsPAL,OsCHS,and OsCHI in rk mutant was lower as compared to its wild type,and transcripts of OsDFR and OsANS were significantly low in rk mutant as compared to bk mutant.Higher transcriptional expression of both the genes proved to be important in ANDs accumulation in bk mutant while these were less related to accumulation of red color pigment in rk mutant.2.Anthocyanidin accumulation in black kernel mutant rice and its contribution to ROS detoxification in response to high temperature at filling stageRice crop productivity is severely affected by high-temperature resulting in limiting plant growth and development.Various reports documented that plants manage with different abiotic stresses through anthocyanin regulation;how anthocyanin cope with high-temperature stress in rice kernels are largely unexplored.In this study,black mutant(9311bk)was studied in comparison with its wild type(9311).We investigate that high-temperature stress induced ROS accumulation in rice grains.More importantly,our results clearly showed the accumulation of anthocyanin in rice grains under high-temperature stress.High-temperature stress affected chlorophyll,carotenoids,flavonoids,polyphenols,and total soluble sugar contents in both genotypes,which showed the toxicity of high temperature in rice grains.We found that high-temperature toxicity induced anthocyanin accumulation in bk mutant through upregulation of anthocyanin biosynthetic genes.The bk mutant showed less ROS accumulation and had higher ROS scavenging antioxidant enzymes activities than its wild type.Furthermore,the activity of antioxidant enzymes was more upregulated in bk mutant than wild type against oxidative damages caused by high-temperature stress.Taken together these results,our study suggested that high-temperature stress-induced anthocyanin accumulation in bk mutant grains by upregulating the anthocyanin biosynthesis genes,anthocyanin alleviated high-temperature induced toxicity in bk mutant kernel.This study provides valuable information to produce anthocyanin genetic engineering crops to cope with hightemperature toxicity in the field environment.3.Effect of nitrogen deficiency at filling stage to kernel anthocyanidin accumulation and its relation to ROS detoxification in filling grains for bk mutant riceNitrogen availability not only affects the protein content of rice kernel but also affects the contents of anthocyanidin(ANDs),flavonoid and polyphenols in color rice kernel.Compared to high nitrogen treatment(HT),the contents of ANDs,flavonoid,and polyphenols in bk mutant under low nitrogen treatment(LN)were significantly decreased,but the contents were more accumulated in bk mutant as compared to its wild type.The transcriptional expression of ANDs biosynthesis genes related to anthocyanin biosynthesis pathway such as OsPAL,OsCHS,OsF3 H,OsF3'H,OsDFR,and OsANS was downregulated in kernel under nitrogen(N)deficiency condition.These results implied that N-deficiency inhibited the expression of anthocyanin-related genes in rice kernel,which led to a substantial decline in the accumulation of ANDs and other pigments in bk mutant kernel.Furthermore,ROS generation in bk mutant was low,and the activities of SOD,CAT,and APX were high as compared to wild type,and the MDA content in bk mutant were detected at lower level than the wild type.These findings illustrated that higher content of ANDs in bk mutant increased its ability to scavenge ROS and proved its resistance ability towards N-deficiency.4.Effect of shading treatment on kernel anthocyanidin accumulation and its relation to ROS detoxification in filling grainsShading condition during grain filling significantly decreased sucrose,anthocyanidin(ANDs)and flavonoid content in rice kernel.ANDs contents in bk mutant decreased under shaded condition,but their accumulation was higher as compared to wild type.The transcriptional expression of anthocyanin biosynthesis genes related to anthocyanin biosynthesis pathway such as OsPAL,OsCHS,OsF3 H,OsF3'H,OsDFR,and OsANS was downregulated in developing kernel under shaded condition indicating that shading treatment is not conducive to pigment accumulation in color rice kernel,which is related to the decrease in sucrose level of filling grain.The bk mutant showed less ROS accumulation and had higher ROS scavenging antioxidant enzymes activities than its wild type.Furthermore,antioxidant enzymes activity was greater in bk mutant than wild type against oxidative damages caused by shading stress.Taken together,our results indicated that grain filling process of bk mutant grains proved to be tolerant towards shading stress. |
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