Development and validation of rapid and cost-effective protocol for estimation of amylose and amylopectin in maize kernels

High amylopectin in waxy maize synergistically affects seed germination and seedling vigour over traditional maize genotypes

Waxy maize grains rich in amylopectin have emerged as a popular food and industrial raw materials. Here, a set of waxy inbreds having recessive waxy1 (wx1) gene derived through marker-assisted selection (MAS), and their original versions were evaluated for germination, seed vigour index-I and vigour index-II, electrical conductivity (EC) and enzymatic activities viz., dehydrogenase (DH), esterase (EST), peroxidase (POX), superoxide dismutase (SOD) and α-amylase (AMY). Waxy inbreds under study possessed average 97.8% amylopectin compared to 72.4% in original inbreds. Waxy versions showed 15.2% more test weight, 4.3% increase in germination, 22.7% higher seed vigour index-I and 28.3% higher seed vigour index-II, respectively, over the original inbreds. Further, activity of DH, EST, POX, SOD and AMY of MAS-derived waxy inbreds was more than that of original inbreds, whereas EC was less in improved inbreds compared to originals. Amylopectin exhibited strong positive correlations (r = 0.69 to 0.97**) with seed germination, vigour index-I and -II, DH, SOD, POX, EST and AMY activity. However, amylopectin showed negative correlation of - 0.82** with EC. Seed germination and seed vigour indices were also positively correlated with all enzymatic activities (r = 0.58 to 0.92**). The analysis revealed that waxy inbreds possess better seed vigour and enzymatic activities over traditional inbreds. This is the first report of synergistic effects of wx1 gene on seed germination, vigour and enzymatic activities in maize endosperm.

Development of novel gene-based markers for waxy1 gene and their validation for exploitation in molecular breeding for enhancement of amylopectin in maize

Waxy corn possessing high amylopectin is widely employed as an industrial product. Traditional corn contains ~ 70-75% amylopectin, whereas waxy corn with the mutant waxy1 (wx1) gene possesses ~ 95-100% amylopectin. Marker-assisted breeding can greatly hasten the transfer of the wx1 allele into normal corn. However, the available gene-based marker(s) for wx1 are not always polymorphic between recipient and donor parents, thereby causing a considerable delay in the molecular breeding program. Here, a 4800 bp sequence of the wx1 gene was analyzed among seven wild-type and seven mutant inbreds employing 16 overlapping primers. Three polymorphisms viz., 4 bp InDel (at position 2406 bp) in intron-7 and two SNPs (C to A at position 3325 bp in exon-10 and G to T at position 4310 bp in exon-13) differentiated the dominant (Wx1) and recessive (wx1) allele. Three breeder-friendly PCR markers (WxDel4, SNP3325_CT1, and SNP4310_GT2) specific to InDel and SNPs were developed. WxDel4 amplified 94 bp among mutant-type inbreds, while 90 bp was amplified among wild-type inbreds. SNP3325_CT1 and SNP4310_GT2 revealed the presence-absence polymorphisms with an amplification of 185 bp and 189 bp of amplicon, respectively. These newly developed markers showed 1:1 segregation in both BC1F1 and BC2F1 generations, while 1:2:1 segregation was observed in BC2F2. The recessive homozygotes (wx1wx1) of BC2F2 identified by the markers possessed significantly higher amylopectin (97.7%) compared to the original inbreds (Wx1Wx1: 72.7% amylopectin). This is the first report of novel wx1 gene-based markers. The information generated here would help in accelerating the development of waxy maize hybrids.

Shading affects the starch structure and digestibility of wheat by regulating the photosynthetic light response of flag leaves

Heavy haze-induced decreases in solar radiation represent an important factor that affects the structural properties of starch macromolecules. However, the relationship between the photosynthetic light response of flag leaves and the structural properties of starch remains unclear. In this study, we investigated the impact of light deprivation (60 %) during the vegetative-growth or grain-filling stage on the leaf light response, starch structure, and biscuit-baking quality of four wheat cultivars with contrasting shade tolerance. Shading decreased the apparent quantum yield and maximum net photosynthetic rate of flag leaves, resulting in a lower grain-filling rate and starch content and higher protein content. Shading decreased the starch, amylose, and small starch granule amount and swelling power but increased the larger starch granule amount. Under shade stress, the lower amylose content decreased the resistant starch content while increasing the starch digestibility and estimated glycemic index. Shading during the vegetative-growth stage increased starch crystallinity, 1045/1022 cm^-1 ratio, starch viscosity, and the biscuit spread ratio, while shading during the grain-filling stage decreased these values. Overall, this study indicated that low light affects the starch structure and biscuit spread ratio by regulating the photosynthetic light response of flag leaves.