Effect of growth regulators and Physiological Gradients on the High frequency plant regeneration from the long-term callus cultures of different germplasms of Rice (Oryza sativa L.)

Callus cultures of rice were initiated from mature embryos of different cultivars on LS medium containing 2 mg/L 2,4-D. Increasing concentrations of 2,4-D and 2,4-5T also increased the frequency of callus initiation in all the cultivars tested. Of different cultivars, Tellahamsa was found to be superior for callus initiation. Genotypic differences for plant regeneration were also observed. Cultivar Tellahamsa showed the highest (65-75%) frequency of plant differentiation followed by DGWG, Yerragaluvadlu, Surekha, Basmati-370, Bala, Chakko amubi, Jaya and IR-8. Callus cultures of rice cultivar Bala grown on a shoot-forming medium (LS + 1 mg/L IAA + 4 mg/L KN + 2% sucrose) were exposed to gibberellic acid and abscisic acid for varying lengths of time and at different periods during culture. Gibberellic acid totally suppressed the organogenesis in callus cultures of rice. The results suggest that if the tissue accumulated sufficient gibberellic acid prior to the initiation of meristemoids and shoot primordia, repression of shoot formation occurred. This repression was not reversed by increasing the levels of IAA and KN in the medium, but abscisic acid could partially overcome the gibberellic acid repression of shoot formation in rice callus. It has been observed in rice that shoots usually emerge from the basal portions of callus. This observation suggested that perhaps physiological gradients of materials were operative during the organ initiation process. To test this hypothesis, starch content and the enzyme activity of malate dehydrogenase in upper and lower portions of shoot-forming and non-shoot-forming callus were determined. Starch began to accumulate in both upper and lower portions of the shoot forming tissues within 4 days of culture. The rate of accumulation however, was faster and more in the lower portion of the callus leading to a peak of accumulation on day 8 in culture, i.e., prior to shoot formation. Non-shoot-forming callus cultures accumulated little starch during the same period of culture. Malate dehydrogenase (MDH) activity was examined in order to know the overall rate of respiration. In the upper segment of shoot-forming callus, the activity of MDH was very high by day 4 but declined continuously thereafter. The rate of activity of the enzyme was significantly higher beyond four days in culture in case of the lower portion of the shoot forming callus. Enzyme activity was lower in the non-shoot-forming portions (both upper and lower) of the callus. The higher rate of enzyme activity for the upper portion of the tissue could be attributed to increased oxygen availability. Thus, the evidence for the idea that concentrations of gradients or physiological gradients of substances into the callus tissue may be the operative factors promoting organ initiation in vitro is presented

Intriguing Role of Proline in Redox Potential Conferring High Temperature Stress Tolerance

Proline is a proteinogenic amino acid synthesized from glutamate and ornithine. Pyrroline-5-carboxylate synthetase and pyrroline-5-carboxylate reductase are the two key enzymes involved in proline synthesis from glutamate. On the other hand, ornithine-δ-aminotransferase converts ornithine to pyrroline 5-carboxylate (P5C), an intermediate in the synthesis of proline as well as glutamate. Both proline dehydrogenase and P5C dehydrogenase convert proline back to glutamate. Proline accumulation is widespread in response to environmental challenges such as high temperatures, and it is known to defend plants against unpropitious situations promoting plant growth and flowering. While proline accumulation is positively correlated with heat stress tolerance in some crops, it has detrimental consequences in others. Although it has been established that proline is a key osmolyte, its exact physiological function during heat stress and plant ontogeny remains unknown. Emerging evidence pointed out its role as an overriding molecule in alleviating high temperature stress (HTS) by quenching singlet oxygen and superoxide radicals. Proline cycle acts as a shuttle and the redox couple (NAD+/NADH, NADP+/NADPH) appears to be highly crucial for energy transfer among different cellular compartments during plant development, exposure to HTS conditions and also during the recovery of stress. In this review, the progress made in recent years regarding its involvement in heat stress tolerance is highlighted

Plant Cell Cultures : Biofactories for the Production of Bioactive Compounds

Plants have long been exploited as a sustainable source of food, flavors, agrochemicals, colors, therapeutic proteins, bioactive compounds, and stem cell production. However, plant habitats are being briskly lost due to scores of environmental factors and human disturbances. This necessitates finding a viable alternative technology for the continuous production of compounds that are utilized in food and healthcare. The high-value natural products and bioactive compounds are often challenging to synthesize chemically since they accumulate in meager quantities. The isolation and purification of bioactive compounds from plants is time-consuming, labor-intensive, and involves cumbersome extraction procedures. This demands alternative options, and the plant cell culture system offers easy downstream procedures. Retention of the metabolic cues of natural plants, scale-up facility, use as stem cells in the cosmetics industry, and metabolic engineering (especially the rebuilding of the pathways in microbes) are some of the advantages for the synthesis and accumulation of the targeted metabolites and creation of high yielding cell factories. In this article, we discuss plant cell suspension cultures for the in vitro manipulation and production of plant bioactive compounds. Further, we discuss the new advances in the application of plant cells in the cosmetics and food industry and bioprinting.Peer reviewe

Genome-wide identification and transcriptional profiling of small heat shock protein gene family under diverse abiotic stress conditions in Sorghum bicolor (L.)

The small heat shock proteins (sHsps/Hsp20s) are the molecular chaperones that maintain proper folding, trafficking and disaggregation of proteins under diverse abiotic stress conditions. In the present investigation, a genome-wide scan revealed the presence of a total of 47 sHsps in Sorghum bicolor (SbsHsps), distributed across 10 subfamilies, the major subfamily being P (plastid) group with 17 genes. Chromosomes 1 and 3 appear as the hot spot regions for SbsHsps, and majority of them were found acidic, hydrophilic, unstable and intron less. Interestingly, promoter analysis indicated that they are associated with both biotic and abiotic stresses, as well as plant development. Sorghum sHsps exhibited 15 paralogous and 20 orthologous duplications. Expression analysis of 15 genes selected from different subfamilies showed high transcript levels in roots and leaves implying that they are likely to participate in the developmental processes. SbsHsp genes were highly induced by diverse abiotic stresses inferring their critical role in mediating the environmental stress responses. Gene expression data revealed that SbsHsp-02 is a candidate gene expressed in all the tissues under varied stress conditions tested. Our results contribute to the understanding of the complexity of SbsHsp genes and help to analyse them further for functional validation

Pearl Millet Mapping Population Parents: Performance and Selection Under Salt Stress Across Environments Varying in Evaporative Demand

It is vital to screen the germplasm of crop plants for salt stress tolerance so as to utilize them in breeding programs. Accordingly, in the present study, twenty diverse inbred lines, parents of mapping populations of pearl millet were chosen to determine the phenotypic contrasts for seed yield, which can open the way for developing salt tolerance QTLs. Parents were grown in two summer seasons (late and early) with VPD ≥ 2 kPa, and one rainy season with VPD < 2 kPa, during flowering and grain filling under saline (150 and 200 mM) and non-saline (0 mM) conditions. Salinity delayed flowering time by a fortnight in the summer seasons but only 5–6 days in the low VPD rainy season. Salinity decreased grain yield by 86% in late-summer and 80% in early-summer, but less than 70% in rainy season. GY penalty was higher than vegetative biomass under saline conditions especially in summer season when the evaporative demand was very high. It appears that reproduction and grain filling are sensitive to high temperature that can compound the effect of salinity and high VPD. GY of inbreds under salinity was not better in comparison with non-saline conditions. DOF and grain density (thousand grain weight) were found as important correlated traits under salinity. Also, GY was affected significantly if VPD increased during flowering time

Drought Stress Tolerance Mechanisms in Barley and Its Relevance to Cereals

In the changing environment, water is the major limiting factor for crop productivity throughout the world, and there is every need to generate climate-resilient crops. Since drought is a complex phenomenon, we need to dissect various mechanisms at the physiological, biochemical, and molecular levels in order to generate crop plants with better drought tolerance but without any yield penalties. Accumulated literature points out that improvement at both source and sink levels are needed to elevate final yields under water deficit conditions. Here, we summarize the current status of plant adaptation mechanisms and the strategies that we need to carve for generating drought stress-tolerant crops like barley

Changes in timing of water uptake and phenology favours yield gain in terminal water stressed chickpea AtDREB1A transgenics

Terminal drought causes major yield loss in chickpea, so it is imperative to identify genotypes with best suited adaptive traits to secure yield in terminal drought-prone environments. Here, we evaluated chickpea (At) rd29A:: (At) DREB1A transgenic events (RD2, RD7, RD9 and RD10) and their untransformed C235 genotype for growth, water use and yield under terminal water-stress (WS) and well-watered (WW) conditions. The assessment was made across three lysimetric trials conducted in contained environments in the greenhouse (2009GH and 2010GH) and the field (2010F). Results from the greenhouse trials showed genotypic variation for harvest index (HI), yield, temporal pattern of flowering and seed filling, temporal pattern of water uptake across crop cycle, and transpiration efficiency (TE) under terminal WS conditions. The mechanisms underlying the yield gain in the WS transgenic events under 2009GH trial was related to conserving water for the reproductive stage in RD7, and setting seeds early in RD10. Water conservation also led to a lower percentage of flower and pod abortion in both RD7 and RD10. Similarly, in the 2010GH trial, reduced water extraction during vegetative stage in events RD2, RD7 and RD9 was critical for better seed filling in the pods produced from late flowers in RD2, and reduced percentage of flower and pod abortion in RD2 and RD9. However, in the 2010F trial, the increased seed yield and HI in RD9 compared with C235 came along only with small changes in water uptake and podding pattern, probably not causal. Events RD2 (2010GH), RD7 (2010GH) and RD10 (2009GH) with higher seed yield also had higher TE than C235. The results suggest that DREB1A, a transcription factor involved in the regulation of several genes of abiotic stress response cascade, influenced the pattern of water uptake and flowering across the crop cycle, leading to reduction in the percentage of flower and pod abortion in the glasshouse trials

Genome-wide Identification and Characterization of Hsp70 gene family in Pearl millet (Pennisetumglaucum)

Heat shock proteins (Hsps) are a class of molecular chaperons which are crucial for protein folding, assembly, and translocation in many normal cellular processes. They stabilize proteins and membranes, and can assist in protein refolding under stress conditions in plants. Pearl millet (Pennisetum glaucum) is highly abiotic stress tolerant, but its Hsps have not been characterized. In the present study, PgHsp70 genes were retrieved and gene information analyzed in order to characterize their structure, localization and functions. Genome-wide screening using the tools of bioinformatics identified 18 PgHsp70 genes in the pearl millet genome which have been categorized into four subfamilies depending on their cellular localization such as endoplasmic reticulum, mitochondria, chloroplast and cytoplasm. Number of introns ranged from 0-11 in PgHsp70 family genes and the genes are located across 1 to 7 chromosomes. Phylogenetic analysis of Hsp70s revealed that they are closely related to Sorghum Hsp70s. Promoter analysis showed the presence of cisacting elements such as GCN4, HSE, LTR, MBS, ABRE, MYB, and TC Aassociated with abiotic stress conditions indicating the involvement of these genes in the abiotic stress. Under vapour pressure deficit (VPD) conditions, leaf and root tissues of VPD-sensitive ICMR 1152 line, showed mild expression and in the presence of high VPD, VPD-insensitive ICMR1122 PgHsp70 genes showed high expression in leaf and root tissues in comparison with VPD-sensitive line. Gene PgcHsp70-1 displayed high transcript level under high VPD conditions. These results expand our horizon of understanding of the structure and function of Hsp70s, especially under abiotic stress conditions which can further be validated and employed in breeding programs and genetic engineering

Genome-scale identification, classification, and tissue specific expression analysis of late embryogenesis abundant (LEA) genes under abiotic stress conditions in Sorghum bicolor L.

Late embryogenesis abundant (LEA) proteins, the space fillers or molecular shields, are the hydrophilic protective proteins which play an important role during plant development and abiotic stress. The systematic survey and characterization revealed a total of 68 LEA genes, belonging to 8 families in Sorghum bicolor. The LEA-2, a typical hydrophobic family is the most abundant family. All of them are evenly distributed on all 10 chromosomes and chromosomes 1, 2, and 3 appear to be the hot spots. Majority of the S. bicolor LEA (SbLEA) genes are intron less or have fewer introns. A total of 22 paralogous events were observed and majority of them appear to be segmental duplications. Segmental duplication played an important role in SbLEA-2 family expansion. A total of 12 orthologs were observed with Arabidopsis and 13 with Oryza sativa. Majority of them are basic in nature, and targeted by chloroplast subcellular localization. Fifteen miRNAs targeted to 25 SbLEAs appear to participate in development, as well as in abiotic stress tolerance. Promoter analysis revealed the presence of abiotic stress-responsive DRE, MYB, MYC, and GT1, biotic stress-responsive W-Box, hormone-responsive ABA, ERE, and TGA, and development-responsive SKn cis-elements. This reveals that LEA proteins play a vital role during stress tolerance and developmental processes. Using microarray data, 65 SbLEA genes were analyzed in different tissues (roots, pith, rind, internode, shoot, and leaf) which show clear tissue specific expression. qRT-PCR analysis of 23 SbLEA genes revealed their abundant expression in various tissues like roots, stems and leaves. Higher expression was noticed in stems compared to roots and leaves. Majority of the SbLEA family members were up-regulated at least in one tissue under different stress conditions. The SbLEA3-2 is the regulator, which showed abundant expression under diverse stress conditions. Present study provides new insights into the formation of LEAs in S. bicolor and to understand their role in developmental processes under stress conditions, which may be a valuable source for future research