Pearl millet is one of the most important subsistence crops grown in India and sub-Saharan Africa. In many cereal crops, reduced height is a key trait for enhancing yield, and dwarf mutants have been extensively used in breeding to reduce yield loss due to lodging under intense management. In pearl millet, the recessive d2 dwarfing gene has been deployed widely in commercial germplasm grown in India, the United States, and Australia. Despite its importance, very little research has gone into determining the identity of the d2 gene. We used comparative information, genetic mapping in two F2 populations representing a total of some 1500 progeny, and haplotype analysis of three tall and three dwarf inbred lines to delineate the d2 region by two genetic markers that, in sorghum, define a region of 410 kb with 40 annotated genes. One of the sorghum genes annotated within this region is ABCB1, which encodes a P-glycoprotein involved in auxin transport. This gene had previously been shown to underlie the economically important dw3 dwarf mutation in sorghum. The cosegregation of ABCB1 with the d2 phenotype, its differential expression in the tall inbred ICMP 451 and the dwarf inbred Tift 23DB, and the similar phenotype of stacked lower internodes in the sorghum dw3 and pearl millet d2 mutants suggest that ABCB1 is a likely candidate for d2.
Ageing induces many deteriorative changes to seeds during storage like genetic damage, protein degradation, enzyme inactivation and loss of membrane integrity. In this study, we subject to investigate the alterations in seed coat structure and its permeability properties due to accelerated ageing affecting the subsequent imbibition of soybean [Glycine max (L.) Merr.] seeds. Two contrasting seed coat colour genotypes, JS 335 (white) and Bhatt (black) were selected and artificially aged for 48 and 72 h. The results of seed ageing on permeability, imbibition and germination proved that permeability and imbibition increased but germination decreased in white genotype due to imbibitional injury, whereas germination increased in black genotype due to breaking of hard seed coat imposed dormancy. The hard seeds in the black genotype with a different seed coat structure compared to the white genotype prevented imbibition injury in aged seeds by regulating permeability. Microscopic studies of seed coat structure in aged seeds revealed a thick cuticle with small hilar fissure and compact, dense hourglass cells in black genotype compared to a thin cuticle with large hilar fissure and loosely packed and distorted hourglass cells in white genotype. Thus the altered permeability and imbibition injury in artificially aged seeds is shown to occur mainly as a result of altered and damaged seed coat structure. INTRODUCTIONSeed ageing is an irreversible and inexorable process of a progressive decrease in vigour ultimately leading to the loss of seed viability (Arc et al., 2011;Lehner et al., 2008;Stewart & Bewley, 1980). The rate of seed ageing depends upon the genotype/ species, the conditions prevailing during storage like moisture content, temperature, humidity and seed composition (Roberts, 1973). It has been reported that high moisture content and high temperature accelerate seed deterioration (Ellis & Hong, 1991;Goel et al., 2003) based on which seeds are accelerated to artificially age by exposing them to high humidity and temperature of about 40-45 ˚C and 100% RH (Delouche & Baskin, 1973). Accelerated ageing is shown to induce many deteriorative changes to seeds during storage
The seed coat composition of white (JS 335) and black (Bhatt) soybean (Glycine max (L.) Merr) having different water permeability was studied. Phenols, tannins and proteins were measured, as well as trace elements and metabolites in the seed coats. The seed coat of Bhatt was impermeable and imposed dormancy, while that of JS 335 was permeable and seeds exhibited imbibitional injury. Bhatt seed coats contained comparatively higher concentrations of phenols, tannins, proteins, Fe and Cu than those of JS 335. Metabolites of seed coats of both genotypes contained 164 compounds, among which only 14 were common to both cultivars, while the remaining 79 and 71 compounds were unique to JS 331 and Bhatt, respectively. Phenols are the main compounds responsible for seed coat impermeability and accumulate in palisade cells of Bhatt, providing impermeability and strength to the seed coat. JS 335 had more cracked seed coats, mainly due to their lower tannin content. Alkanes, esters, carboxylic acids and alcohols were common to both genotypes, while cyclic thiocarbamate (1.07%), monoterpene alcohols (1.07%), nitric esters (1.07%), phenoxazine (1.07%) and sulphoxide (1.07%) compounds were unique to the JS 335 seed coat, while aldehydes (2.35%), amides (1.17%), azoles (1.17%) and sugar moieties (1.17%) were unique to Bhatt seed coats. This study provides a platform for isolation and understanding of each identified compound for its function in seed coat permeability.
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