Starch granule size and amylopectin chain length influence starch in vitro enzymatic digestibility in selected rice mutants with similar amylose concentration.

In human diet, the products of starch digestion are a major energy source. Starch is stored as water insoluble granules composed of amylose and amylopectin. The susceptibility of starch granule to digestive enzymes is affected by starch granule size, shape, and composition. In this study, starch characteristics and in vitro enzymatic hydrolysis in three rice (Oryza sativa L.) mutants (RSML 184, RSML 278 and RSML 352) with similar amylose concentration (24.3-25.8%) was compared to parent ADT 43 (21.4%). The three mutants had reduced thousand grain weight and starch concentration but higher protein and dietary fiber concentrations. The mutant RSML 352 had small starch granules and reduced short glucan chains [Degree of polymerization (DP) 6-12] compared to the other two mutants (RSML 184 and RSML 278). The mutant RSML 352 had the highest hydrolytic index (HI) and least concentration of resistant starch (RS) compared to the other two mutants and parent rice ADT 43. The two rice mutants (RSML 184 and RSML 278) had reduced HI and increased RS concentration than the parent ADT 43. The results showed that starch granule size and amylopectin structure influence starch enzymatic digestibility and RS concentration.

EcoTILLING by sequencing reveals polymorphisms in genes encoding starch synthases that are associated with low glycemic response in rice.

BACKGROUND: Glycemic response, a trait that is tedious to be assayed in cereal staples, has been identified as a factor correlated with alarmingly increasing prevalence of Type II diabetes. Reverse genetics based discovery of allelic variants associated with this nutritional trait gains significance as they can provide scope for genetic improvement of this factor which is otherwise difficult to target through routine screening methods. RESULTS: Through EcoTILLING by sequencing in 512 rice accessions, we report the discovery of six deleterious variants in the genes with potential to increase Resistant Starch (RS) and reduce Hydrolysis Index (HI) of starch. By deconvolution of the variant harbouring EcoTILLING DNA pools, we discovered accessions with a minimum of one to a maximum of three deleterious allelic variants in the candidate genes. CONCLUSIONS: Through biochemical assays, we confirmed the potential role of the discovered alleles alone or in combinations in increasing RS the key factor for reduction in glycemic response.

A simple and rapid single kernel screening method to estimate amylose content in rice grains.

INTRODUCTION: In rice breeding programmes large number of grain samples are routinely analysed for amylose content (AC) through a tedious spectrophotometric method that also involves high reagent costs. OBJECTIVE: Here, we propose a rapid and economic screening technique for assessment of AC based on the amylose-iodine complex formation in the cut grains of rice, which we refer to as the cut grain dip (CGD) method. METHODS: The CGD method involves cutting the rice kernels in the middle with a pair of scissors and dipping the cut end in an optimised iodide:iodine (KI-I) solution termed the rapid amylose detection solution (RADS). RESULTS: It was found that the time taken for deep blue colouration by the cut end of the grains after dipping in RADS was proportional to the AC. The CGD method was further validated in a large set of rice mutants with varied AC. CONCLUSION: The proposed method can be used to screen samples for AC rapidly, with a single rice caryopsis, without any costly equipment and can be especially suitable for screening of mutants and segregants with altered AC in large breeding populations.