Kernel Maturity Research Articles

Raman Multi-Omic Snapshots of Koshihikari Rice Kernels Reveal Important Molecular Diversities with Potential Benefits in Healthcare.

This study exploits quantitative algorithms of Raman spectroscopy to assess, at the molecular scale, the nutritional quality of individual kernels of the Japanese short-grain rice cultivar Koshihikari in terms of amylose-to-amylopectin ratio, fractions of phenylalanine and tryptophan aromatic amino acid residues, protein-to-carbohydrate ratio, and fractions of protein secondary structures. Statistical assessments on a large number of rice kernels reveal wide distributions of the above nutritional parameters over nominally homogeneous kernel batches. This demonstrates that genetic classifications cannot catch omic fluctuations, which are strongly influenced by a number of extrinsic factors, including the location of individual grass plants within the same rice field and the level of kernel maturation. The possibility of collecting nearly real-time Raman "multi-omic snapshots" of individual rice kernels allows for the automatic (low-cost) differentiation of groups of kernels with restricted nutritional characteristics that could be used in the formulation of functional foods for specific diseases and in positively modulating the intestinal microbiota for protection against bacterial infection and cancer prevention.

New insights into the carotenoid biosynthesis in Torreya grandis kernels

Torreya grandis is a characteristic rare economic tree species in subtropical mountainous areas. The nut has a variety of bioactive compounds, such as polyphenols and vitamins. However, the carotenoids compositions and its regulatory mechanisms underlying carotenoid biosynthesis in kernels remain unknown. Here, the major carotenoids in the kernel were analyzed. The result showed that lutein and β-carotene were the predominant carotenoids in the kernel, while low levels of α-carotenoid and zeaxanthin were detected. Lutein and β-carotene were decreased during the maturation of kernel. Expression analysis by RNA-seq and qRT-PCR indicated that the expressions of TgCYP97A3 and TgLCYB were also reduced during the maturation of kernel. The contents of lutein or β-carotene were obviously increased in tobacco transiently overexpressing TgCYP97A3 or TgLCYB. Moreover, DPPH radical scavenging activity and FRAP were also significantly enhanced. In addition, several MYB and WRKY transcription factors TgMYBS3, TgMYB48 and TgWRKY11 were identified to positively regulate the TgCYP97A3 expression, while TgMYB48, TgWRKY2 and TgWRKY11 could upregulate the TgLCYB expression. The illustration of carotenoids biosynthesis and its molecular mechanism in kernels not only provides a basis for understanding carotenoids biosynthesis in kernels, but also enables the use of molecular biotechnology to develop new health products rich in carotenoids based on T. grandis nuts.

The Accumulation and Biosynthesis of Anthocyanin in Black, White, and Yellow Waxy Corns (Zea mays L. sinensis kulesh) during Kernel Maturation

Waxy corn kernels with different colors have high phenolic content and good application potential in medicine and food healthcare. In our work, the content changes of phenolic and anthocyanins profiles were related to genes in the anthocyanin biosynthesis pathway, and the antioxidant activities of three different colors of waxy corn kernels (black, white, and yellow) were determined during kernel development. Results showed that growing temperature and light intensity could affect the accumulation of phytochemicals and antioxidant activities in waxy corns during maturation. Phenolic and antioxidant activities decreased over kernel maturation, and spring had higher nutrition levels during the best harvest time (20 and 25 days after pollination in the spring and autumn, respectively) for waxy corns. Cyanidin-3-O-glucoside and pelargonidin-3-O-glucoside were the main anthocyanins detected in the black waxy corns. The contents of cyanidin are higher than pelargonidin followed by peonidin in the autumn, while on the other hand, pelargonidin had a slightly higher content compared to cyanidin in the spring. DFR, CF1, and ANS were the key genes affecting anthocyanin accumulation. This work provided information on the best harvest time for the pigment of waxy corn in order to achieve relatively high phenolic profiles and antioxidant activities. It also illustrated the possible relationship between weather conditions, gene expression levels, and phenolic content during kernel development.

Quantitative Phosphoproteomic Analysis Reveals Potential Regulatory Mechanisms of Early Fruit Enlargement in Pecan (Carya illinoinensis)

Pecan (Carya illinoinensis) is a popular tree nut. Its fruit development undergoes slow growth, rapid expansion, core hardening, and kernel maturation stages. However, little is known about how pecan initiates fruit development and enlargement after pollination. In this study, we performed the first large-scale identification of potential phosphorylation sites and proteins at early development of pecan fruit by a label-free phosphoproteomic quantification technique. A total of 2155 phosphosites were identified from 1953 phosphopeptides covering 1311 phosphoproteins in unpollinated pistils and fruits at 5 and 9 weeks after pollination. Of these, 699 nonredundant phosphoproteins were differentially phosphorylated (DP). Furthermore, the phosphorylation intensity of DP proteins in brassinolide (BR) and auxin signaling were analyzed, and the function of CiBZR1 was investigated. Ectopic expression of CiBZR1 resulted in BR response phenotypes with curled leaves and fruit, while enlarged seed size in Arabidopsis. Subcellular localization and transcriptional activation activity assay demonstrated that CiBZR1 distributed in both the nucleus and cytoplasm with transcriptional activity. When two phosphosites mutated, CiBZR1S201P,S205G moved to the nucleus completely, while the transcriptional activity remained unchanged. Taken together, our data reveal extensive phosphoproteins and lay a foundation to comprehensively dissect the potential post-translational regulation mechanism of early development of pecan fruit.

Profiling and Quantification of Anthocyanins in Purple-Pericarp Sweetcorn and Purple-Pericarp Maize

Purple-pericarp sweetcorn accessions, derived from crossing purple-pericarp maize with white shrunken2 sweetcorn, were assessed for differences in anthocyanin profile at both sweetcorn eating stage and at full kernel maturity. The 'Tim1' sweetcorn line developed a similar total anthocyanin concentration to its 'Costa Rica' parent when assessed at sweetcorn-eating stage. At full maturity it surpassed the purple maize parent, but this was mainly due to the presence of starch diluting the anthocyanin concentration of the latter. The anthocyanin/colour relationship was affected by both total anthocyanin concentration and the ratio of cyanidin- to pelargonidin-based anthocyanins. Malonylation of anthocyanins was also found to vary and did not appear to be linked with either cyanidin:pelargonidin ratio or total anthocyanin concentration. In addition, anthocyanin synthesis was affected by kernel maturity at harvest, with colour development increasing in conjunction with a progression of anthocyanin development across the kernel surface. Pigmentation was present in the aleurone, pericarp and vitreous endosperm of kernels of the purple-pericarp maize parent and purple-pericarp sweetcorn accessions when fully mature, but pigmentation was only apparent in the pericarp at sweetcorn-eating stage. Importantly for consumers, anthocyanin pigmentation covered almost the entire kernel surface at sweetcorn-eating stage.

Integrated metabolite analysis and health-relevant in vitro functionality of white, red, and orange maize (Zea mays L.) from the Peruvian Andean race Cabanita at different maturity stages.

The high maize (Zea mays L.) diversity in Peru has been recognized worldwide, but the investigation focused on its integral health-relevant and bioactive characterization is limited. Therefore, this research aimed at studying the variability of the primary and the secondary (free and dietary fiber-bound phenolic, and carotenoid compounds) metabolites of three maize types (white, red, and orange) from the Peruvian Andean race Cabanita at different maturity stages (milk-S1, dough-S2, and mature-S3) using targeted and untargeted methods. In addition, their antioxidant potential, and α-amylase and α-glucosidase inhibitory activities relevant for hyperglycemia management were investigated using in vitro models. Results revealed a high effect of the maize type and the maturity stage. All maize types had hydroxybenzoic and hydroxycinnamic acids in their free phenolic fractions, whereas major bound phenolic compounds were ferulic acid, ferulic acid derivatives, and p-coumaric acid. Flavonoids such as luteolin derivatives and anthocyanins were specific in the orange and red maize, respectively. The orange and red groups showed higher phenolic ranges (free + bound) (223.9-274.4 mg/100 g DW, 193.4- 229.8 mg/100 g DW for the orange and red maize, respectively) than the white maize (162.2-225.0 mg/100 g DW). Xanthophylls (lutein, zeaxanthin, neoxanthin, and a lutein isomer) were detected in all maize types. However, the orange maize showed the highest total carotenoid contents (3.19-5.87 μg/g DW). Most phenolic and carotenoid compounds decreased with kernel maturity in all cases. In relation to the primary metabolites, all maize types had similar fatty acid contents (linoleic acid > oleic acid > palmitic acid > α-linolenic acid > stearic acid) which increased with kernel development. Simple sugars, alcohols, amino acids, free fatty acids, organic acids, amines, and phytosterols declined along with grain maturity and were overall more abundant in white maize at S1. The in vitro functionality was similar among Cabanita maize types, but it decreased with the grain development, and showed a high correlation with the hydrophilic free phenolic fraction. Current results suggest that the nutraceutical characteristics of orange and white Cabanita maize are better at S1 and S2 stages while the red maize would be more beneficial at S3.

Genome-wide identification and characterization of the phenylalanine ammonia-lyase gene family in pecan (Carya illinoinensis)

Pecans have high amounts of phenolics and flavonoids and are an important source of natural polyphenols. However, the molecular mechanisms of phenolic biosynthesis in this plant have not been elucidated. Phenylalanine ammonia-lyase (PAL) is the first committed enzyme in the phenylpropane metabolic pathway, is involved in phenolic metabolism, and plays crucial roles in plant growth and development. Nevertheless, knowledge about PALs in pecan has not been fully determined. In the present study, genome-wide CiPALs were identified and characterized, and their expression profiles were evaluated using transcriptome data. In total, seven CiPALs were obtained, and their amino acid lengths ranged from 615 to 760. All of them had predicted locations in the cytoplasm. The open reading frames of CiPAL1∼5 were interrupted by a single intron, while no introns existed in other CiPALs. Different types of cis-elements were identified in the promoter regions of seven CiPALs. Abscisic acid-responsive elements and MeJA-responsive elements were abundant in CiPAL4 and CiPAL5. These two genes were widely expressed in different tissues. CiPALs were differentially expressed during kernel maturation, female flower development, graft union generation and drought stress tolerance, in which CiPAL4 and CiPAL5 exhibited higher expression levels than other genes. Then, the full-length cDNAs of them were cloned. Homology analysis suggested that CiPAL4 and CiPAL5 shared identity values of 89.97% with each other and showed 89.70% and 79.12% identity with AtPAL1, respectively. Phylogenetic analysis indicated that they clustered together with JrPAL3 and JrPAL. Finally, the genetic polymorphisms of CiPAL4 and CiPAL5 were evaluated using seven pecan cultivars, and 13 and 14 mutations were observed in CiPAL4 and CiPAL5, respectively. Therefore, the two CiPALs might play crucial roles in the abiotic stress response and phenolic biosynthesis in pecan. The polymorphism mutations of CiPALs will be useful for genetic study in this plant.

Genome-wide Identification and Expression Analysis of NAC Transcription Factor Family Genes during Fruit and Kernel Development in Siberian Apricot

The NAC (NAM, ATAF1/2, and CUC2) family is a group of plant-specific transcription factors that have vital roles in the growth and development of plants, and especially in fruit and kernel development. This study aimed to identify members of the NAC gene (PsNACs) family and investigate their functions in siberian apricot (Prunus sibirica). A total of 102 predicted PsNAC proteins (PsNACs) were divided into 14 clades and the genes were mapped to the eight chromosomes in siberian apricot. The PsNACs of the same clade had similar structures. A synteny analysis showed that the PsNACs had close relationships with the NAC genes of japanese apricot (Prunus mume). An expression pattern analysis of the PsNACs revealed many differences in various tissues and at different stages of fruit and kernel development. All eight PsNACs in clade XI have crucial roles in fruit and kernel development. Seven PsNACs (PsNACs 18, 64, 23, 33, 9, 4, and 50) in clades I, III, VI, VII, and XIII are related to fruit development. Eight PsNACs (PsNACs 6, 13, 46, 51, 41, 67, 37, and 59) in clades I, II, V, VIII, and XIII are involved in fruit ripening. Five PsNACs (PsNACs 6, 94, 41, 32, and 17) in clades I, IV, V, VII, and XI regulated the rapid growth of the kernel. Four PsNACs (PsNACs 50, 4, 67, and 84) in clades I, III, V, and XIII affected the hardening of the kernel. Four PsNACs (PsNACs 17, 82, 13, and 51) in clades II, XI, and IX acted on kernel maturation. We have characterized the NAC genes in siberian apricot during this study. Our results will provide resources for future research of the biological roles of PsNACs in fruit and kernel development in siberian apricot.

Full-length transcriptome analysis of pecan (Carya illinoinensis) kernels

Pecan is rich in bioactive components such as fatty acids (FAs) and flavonoids and is an important nut type worldwide. Therefore, the molecular mechanisms of phytochemical biosynthesis in pecan are a focus of research. Recently, a draft genome and several transcriptomes have been published. However, the full-length mRNA transcripts remain unclear, and the regulatory mechanisms behind the quality components biosynthesis and accumulation have not been fully investigated. In this study, single-molecule long-read sequencing technology was used to obtain full-length transcripts of pecan kernels. In total, 37,504 isoforms of 16,702 genes were mapped to the reference genome. The numbers of known isoforms, new isoforms, and novel isoforms were 9013 (24.03%), 26,080 (69.54%), and 2411 (6.51%), respectively. Over 80% of the transcripts (30,751, 81.99%) had functional annotations. A total of 15,465 alternative splicing (AS) events and 65,761 alternative polyadenylation events were detected; wherein, the retained intron was the predominant type (5652, 36.55%) of AS. Furthermore, 1894 long noncoding RNAs and 1643 transcription factors were predicted using bioinformatics methods. Finally, the structural genes associated with FA and flavonoid biosynthesis were characterized. A high frequency of AS accuracy (70.31%) was observed in FA synthesis-associated genes. This study provides a full-length transcriptome data set of pecan kernels, which will significantly enhance the understanding of the regulatory basis of phytochemical biosynthesis during pecan kernel maturation.

Nondestructive measurement of husk-covered corn kernel layer dynamic moisture content in the field

Corn kernel moisture content is the most frequently used indicator for kernel maturity prediction and determination of the appropriate mechanized harvesting time. Corn varieties with lower moisture contents and thus faster dehydration of the corn kernels after physiological maturity are suitable for high plant density and mechanized harvesting. However, nondestructive measurement of the dynamic moisture content of the husk-covered corn kernel layer before physiological maturity in the field remains challenging at present. Therefore, in this study, a nondestructive measurement method based on the vector reflection coefficient measurement technique is proposed and developed for in situ monitoring of the husk-covered corn kernel layer moisture in the field. Based on the one-port calibration procedure used for the handheld moisture detection device, quadratic regression models were established for the corn kernel layer moisture using impedance parameters from 51 husk-covered corn samples. Results showed that this method enabled nondestructive estimation of the husk-covered corn kernel layer moisture (R2=0.62) with a 3.53% root mean square error (RMSE) using a serial capacitor Cs and the husk moisture (R2=0.85) with a RMSE of 7.12%. Additionally, intact corn ears were measured in the field from the dent stage to the maturity stage using this device to investigate the dynamic moisture contents of the kernels and husks. Results showed that the measured moisture content of kernels before physiological maturity followed exponential decay functions with increasing numbers of days, and the mean difference between the measured kernel moisture contents of the intact corn ears and the oven-drying moisture contents of these kernels is 3.72%. In conclusion, the handheld moisture detection device allows us to measure the moisture of husk-covered corn kernel layers nondestructively before maturity in the field. This study thus provides a new way to obtain corn kernel dehydration curves in situ before maturity and estimate the corn maturity time.

Expression profile of protein fractions in the developing kernel of normal, Opaque-2 and quality protein maize

Maize protein quality is determined by the composition of its endosperm proteins, which are classified as nutritionally poor zeins (prolamin and prolamin-like) and nutritionally rich non-zeins (albumin, globulin, glutelin-like, and glutelin). Protein quality is considerably higher in opaque-2 mutants due to increased content of non-zeins over zeins. However, the opaque-2 endosperm is soft, which leads to poor agronomic performance and post-harvest infestation. Endosperm modification of opaque-2 had led to the development of Quality Protein Maize (QPM), which has higher protein quality along with hard kernel endosperm. The present study was planned to analyze the expression dynamics of different protein fractions in the endospem of developing maize kernel in normal, opaque-2 and QPM in response to the introgression of endosperm modifiers. Results revealed that albumin and globulin content decreases, whereas, prolamin, prolamin-like, glutelin-like, and glutelin content increases with kernel maturity. It has been observed that opaque-2 mutation affects protein expression at initial stages, whereas, the effect of endosperm modifiers was observed at the intermediate and later stages of kernel development. It has also been noted that prolamin, glutelin, and glutelin-like fractions can be used as quick markers for quality assessment for differentiating QPM varieties, even at the immature stage of kernel development. Overall, the present study implicates the role of different protein fractions in developing and utilizing nutritionally improved maize varieties.

Response of Malt Barley (Hordeum Distichum L) Varieties to Different Row Spacing under Contrasted Environments of North Gondar, Ethiopia

A field experiment was conducted in north Gondar to investigate the response of malt barley varieties to different inter-row spacing under contrasted environment. The experiment was laid out using randomized complete block design with three replications. The treatments were three different inter-row spacing (i.e., 20, 25, and 30 cm), six malt barley varieties (i.e., Holker, HB1963, Sabine, Ibone174/03, EH1847, and Freygebse), and two locations (Miligebsa and Kino). The result sowed that days to 50% heading, days to 90% physiological maturity, plant height, spike length, and number of kernels per spike were significantly ( p < 0.01 ) affected by the main effect of location and varieties. Similarly, effective tiller number, biomass yield, grain yield, and straw yield were significantly ( p < 0.01 ) influenced by the main effect of variety, inter-row spacing, and location. Important interaction was also observed between varieties × inter-row spacing × location on days to 50% heading, spike length, biomass yield, grain yield, and straw yield. Location × variety interaction significantly influences the days to 90% physiological maturity and effective tiller number. Similar significant ( p < 0.05 ) trend was also observed between varieties with inter-row spacing on effective tiller number and thousand kernel weight even at p < 0.01 level of significance. It was found that optimization of row spacing was found to be influenced by location and varietal difference. Hence, on the basis of the result, it can be inferred that 25 cm row spacing combined with the varieties “HB1963,” “Hollker,” and “Sabine” was optimum for maximum yielding potential under potential environment (Miligebsa).

Accumulation of phenolics, antioxidant and antiproliferative activity of sweet corn (Zea mays L.) during kernel maturation

SummaryPhenolic profiles and gene expression pattern in their synthetic pathway, total antioxidant activities and antiproliferative activities in two genotypes of sweet corn (YT16 and YT28) during kernel maturation were analysed. Results showed that increasing trends of phenolics and flavonoids in the two genotypes of kernels from 10 to 30 days after pollination (DAP). Gallic acid, chlorogenic acid, p‐coumaric acid and ferulic acid were identified and quantified as the main phenolic compounds in both genotypes of kernels. High expressing levels of C4O and PAL resulted in the increasing phenolic contents. Higher expressing levels of CHS in YT28 led to higher flavonoid contents than that in YT16. The phenolic contents, antioxidant capacities and antiproliferative abilities of the two genotypes of sweet corn were competitive comparing to many fruits and vegetables. In addition, the maturation process of sweet corn could raise the kernel’s bioactive ability as well as nutritional values.

Rehydration of dry corn preserves the desirable bacterial community during ensiling.

This study evaluated the rehydration approach of mature corn grains as an alternative for high-moisture corn grain silage production in distinct corn hybrids, storage period, cultivation locations and kernel maturity at plant harvest. High-moisture corn was used as a control. The dry matter content and pH of the silage were measured, and the bacterial community associated with corn grains pre- and post-ensiling was also assessed through 16S rRNA high-throughput sequencing. The decrease in pH value was directly linked to an ecological microbial succession of Enterobacteriales and Actinomycetales to Lactobacillales in the silage at 120 days after storage, either in rehydrated or high-moisture corn. These results were similar for both maize production locations and hybrids tested. Finally, the similarity between the ensiling processes including rehydrated corn and the high-moisture corn grain silages proves the reliability of the rehydration approach as an alternative for the maintenance of a successful bacterial community structure and composition capable of producing high-quality silages from dent and flint corn hybrids in tropical conditions.

Effects of hybrid, kernel maturity, and storage period on the bacterial community in high-moisture and rehydrated corn grain silages

This study evaluated changes in the bacterial community in high-moisture and rehydrated corn grain silage, and their correlation with fermentation quality attributes in distinct corn hybrids, the storage period, and kernel maturity at plant harvest. Most silages achieved good fermentation (pH<4.2). Rehydrated corn had a higher pH across all storage periods evaluated and increased dry matter losses. Leuconostoc and Lactococcus were the dominant genera in fresh material, while Lactobacillus and Acetobacter were prevalent in silages. Clostridium and Enterococcus prevailed in rehydrated corn after 120 days storage, and Clostridium was highly and positively correlated with acetone, butyric acid, and 2,3-butanediol contents. The storage period and kernel maturity were the most important factors responsible for changes in the bacterial community of silages. Results confirmed the existence of a specific bacterial microbiome that was unique for each maturity and storage time. Variations in these factors also affected the fermentation quality through influencing the bacterial community.

Didymella corylicola sp. nov., a new fungus associated with hazelnut fruit development in Italy

A new fungal species constantly associated with hazelnut (Corylus avellana) fructification starting from its primordia is described. The fungus is associated with hazelnut fruit during all their developmental stages, being consistently more present in spring (March–June). A 4-year survey has been conducted, from young fruit formation to full kernel maturity including also the post-harvest phase, to collect fungi associated with damaged/discoloured kernels. A collection of 60 isolates of a new species has been obtained in this study, which is here described as Didymella corylicola sp. nov. Multi-locus phylogenies based on four genomic loci (nuITS and LSU rDNA, RPB2 and TUB2) in combination with morphological data confirmed the fungus to represent a new species of Didymella (Didymellaceae). The occurrence of D. corylicola sp. nov. might have an impact on the quality of hazelnut production by contributing to kernel defects.

Changes of Phytochemical Contents in Sweet and Waxy Corn (Zea mays L.) as Affected by Cultivars and Growth Stages

Background: Sweet and waxy corn (Zea mays L.) are high in phytochemicals which vary depending on several factors including corn cultivars and the maturation stage. Methods: Five commercial sweet and waxy corn cultivars were grown and their major phytochemical compositions were investigated at the milk, late milk, and soft dough stages. Phytochemicals in corn samples harvested from each kernel maturation stage were determined as total phenolic compounds, anthocyanins, tocopherols, and carotenoids. Results: Significant interactions between the corn cultivars and maturation stage were detected for all phytochemical compositions, with changes in their concentration during seed development. Total phenolic compounds and total anthocyanins were highest in the dark purple waxy variety (316.74 mg GAE/100 g of DW and 522.21 mg CGE/100 g of DW, respectively) in which cyanidin was the major anthocyanin. Carotenoid compositions were also affected by corn type and harvesting stage. The yellow sweet cultivars indicated higher levels of carotenoids than other colors, with lutein as the major carotenoid at concentrations from 0.05 to 8.46 µg/g of DW. Contents of γ-tocotrienol, γ-tocopherol, and α-tocopherol were observed in all five corn cultivars with similar influences of the maturation stage. Conclusion: Results suggested that the phytochemical contents of all five corn types showed diverse reliance regarding cultivars and maturity stages. The purple waxy and yellow sweet corn cultivars contained a high level of phytochemicals. This would open up a useful opportunity for the functional food industry as consumption of these corn cultivars would afford health benefits to consumers.

Anthocyanin composition and changes during kernel development in purple-pericarp supersweet sweetcorn

The current study reports the anthocyanin profile of purple ‘supersweet’ sweetcorn, recently developed from purple Peruvian maize, and the effect of kernel maturity on anthocyanin accumulation. Twenty anthocyanin compounds, consisting of cyanidin-, peonidin-, and pelargonidin-based glucosides, were identified and quantified in purple- and reddish-purple-pericarp sweetcorn accessions. For the first time, four isomers of cyanidin-3-malonylglucoside, four isomers of pelargonidin-3-malonylglucoside and two to three isomers each of cyanidin-3-dimalonylglucoside, peonidin-3-malonylglucoside and pelargonidin-3-dimalonylglucoside, were identified in the new pigmented sweetcorn. While cyanidin-based glucosides predominated in the purple-pericarp accession, pelargonidin-based glucosides predominated in the reddish-purple accession. Total anthocyanin concentration increased significantly (p < 0.05) during the optimum sweetcorn eating period (23 to 28 DAP) and continued to increase as the kernels further matured (>28 DAP). As kernels continued to mature, pigment coverage across the pericarp progressively increased from a small spot at the stigma end of the kernel, to gradually spreading over the entire kernel.

Temporal profiling of essential amino acids in developing maize kernel of normal, opaque-2 and QPM germplasm.

Maize, an important cereal crop, has apoor quality of endosperm protein due to the deficiency of essential amino acids, especially lysine and tryptophan. Discovery of mutants such as opaque-2 led to the development of nutritionally improved maize with a higher concentration of lysine and tryptophan. However, the pleiotropic effects associated with opaque-2 mutants necessitated the development of nutritionally improved hard kernel genotype, the present-day quality protein maize (QPM). The aim of present study was to analyze and compare the temporal profile of lysine and tryptophan in the developing maize kernel of normal, opaque-2 and QPM lines. A declining trend in protein along with tryptophan and lysine content was observed with increasing kernel maturity in the experimental genotypes. However, opaque-2 retained the maximum concentration of lysine (3.43) and tryptophan (1.09) at maturity as compared to QPM (lysine-3.05, tryptophan-0.99) and normal (lysine-1.99, tryptophan-0.45) lines. Opaque-2 mutation affects protein quality but has no effect on protein quantity. All maize types are nutritionally rich at early stages of kernel development indicating that early harvest for cattle feed would ensure a higher intake of lysine and tryptophan. Two promising lines (CML44 and HKI 1105) can be used for breeding high value corn for cattle feed or human food in order to fill the protein inadequacy gap. Variation in lysine and tryptophan content within QPM lines revealed that differential expression of endosperm modifiers with varying genetic background significantly affects nutritional quality, indicating that identification of alleles affecting amino acid composition can further facilitate QPM breeding program.

Anthocyanin Accumulation in Black Kernel Mutant Rice and its Contribution to ROS Detoxification in Response to High Temperature at the Filling Stage.

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.