Physiology and Molecular Biology of Plants

Eight Saltol quantitative trait locus (QTL) linked simple sequence repeat (SSR) markers of rice (Oryza sativa L.) were used to study the polymorphism of this QTL in 142 diverse rice genotypes that comprised salt tolerant as well as sensitive genotypes. The SSR profiles of the eight markers generated 99 alleles including 20rare alleles and 16 null alleles. RM8094 showed the highest number (13) of alleles followed by RM3412 (12), RM562 (11), RM493 (9) and RM1287 (8) while as, RM10764 and RM10745 showed the lowest number (6) of alleles. Based on the highest number of alleles and PIC value (0.991), we identified RM8094 as suitable marker for discerning salt tolerant genotypes from the sensitive ones. Based upon the haplotype analysis using FL478 as a reference (salt tolerant genotypes containing Saltol QTL), we short listed 68 rice genotypes that may have at least one allele of FL478 haplotype. Further study may confirm that some of these genotypes might have Saltol QTL and can be used as alternative donors in salt tolerant rice breeding programmes.

In recent years, there has been a considerable and renewed upsurge in research to ascertain the physiological and biochemical role of Nitric oxide (NO) in plants. The present investigation is focused to study the role of NO on neck bending associated with senescence and postharvest performance in isolated flowers of Calendula officinalis. The flower buds harvested at one day before anthesis stage were supplied with sodium nitroprusside (SNP) as a source of NO at different concentrations viz., 50, 100, 150 and 200 µM. A distinct set of flowers held in distilled water designated the control. The investigation revealed that SNP delayed the senescence in flowers of C. officinalis significantly manifested by prolonged longevity. The maximum longevity of 12 days was recorded in flowers supplemented with 100 µM SNP. The flowers held in distilled water (control) displayed early senescence symptoms and lasted for 6 days only. Our research suggested that improved flower longevity by SNP was commensurate with delayed neck bending, inhibition of bacterial growth in the vase, increased solution uptake, high membrane stability, besides an up-regulated activities of antioxidant enzymes in the tissue samples. In addition, the treated flowers exhibited increased content of  sugar fractions, total phenols and soluble proteins in the petal tissues compared to control. Further, 100 µM SNP was observed as most effective treatment and increased the longevity of flowers by 6 days. The concentration above 150 µM provoked early senescence compared to control, whereas concentration lower than 100 µM was less efficacious in improving the postharvest life and longevity of cut Calendula flowers.

Haloxylon persicum (Bunge ex Boiss & Buhse), is one of the hardy woody desert shrubs, which is now endangered and/or nearing extinction. Urban landscape development and overgrazing are the major threats for the erosion of this important plant species. For conserving the species, it is critical to develop an efficient in vitro regeneration protocol for rapid multiplication of large number of regenerants. Leaf explants, cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of thidiazuron (TDZ) (0.5, 1, 2 µM), showed significant difference in bud sprouting and adventitious shoot induction. The highest shoot bud formation was recorded on MS medium supplemented with 0.5 µM TDZ. Shoot tip necrosis (STN), observed after first subculture of shoot buds in same medium, increased in severity with subculture time. Application of calcium (4 mM) and boron (0.1 mM) in combination with kinetin (10 µM) in the subculture medium significantly reduced the intensity of STN. On an average eight shoots/explant were produced by alleviating this problem. ISSR marker analysis revealed monomorphic banding pattern between progenies and parents, indicating the true to type nature of the clones and its parents.

Among legumes, lentil serves as an imperative source of dietary proteins and are considered an important pillar of global food and nutritional security. The crop is majorly cultivated in arid and semi-arid regions and exposed to different abiotic stresses. Drought stress is a polygenic stress that poses a major threat to the crop productivity of lentils. It negatively influenced the seed emergence, water relations traits, photosynthetic machinery, metabolites, seed development, quality, and yield in lentil. Plants develop several complex physiological and molecular protective mechanisms for tolerance against drought stress. These complicated networks are enabled to enhance the cellular potential to survive under extreme water-scarce conditions. As a result, proper drought stress-mitigating novel and modern approaches are required to improve lentil productivity. The currently existing biotechnological techniques such as transcriptomics, genomics, proteomics, metabolomics, CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/cas9), and detection of QTLs (quantitative trait loci), proteins, and genes responsible for drought tolerance have gained appreciation among plant breeders for developing climate-resilient lentil varieties. In this review, we critically elaborate the impact of drought on lentil, mechanisms employed by plants to tolerate drought, and the contribution of omics approaches in lentils for dealing with drought, providing deep insights to enhance lentil productivity and improve resistance against abiotic stresses. We hope this updated review will directly help the lentil breeders to develop resistance against drought stress.

Variations in photosynthetic gas exchange, stomatal traits and photosystem (PS) II activity were investigated in three popular rice (Oryza sativa L.) landraces namely Kalajeera, Machakanta and Haladichudi from Koraput, India and compared with high yielding modern varieties (IR 64 and IR 42) to judge the possibility of using them in crop improvement programmes. The leaf CO2 photosynthetic rate (PN), stomatal conductance (gs), water use efficiency and carboxylation efficiency were significantly higher in traditional landraces as compared to the high yielding variety. In contrast, the transpiration rate, internal CO2 concentration, special analysis device (SPAD) index and chlorophyll were higher in high yielding varieties. In addition, the traditional landraces showed better stomatal traits such as stomatal density (SD), stomatal size (SS) and stomatal index. Further, multiple correlations between different gas-exchange characteristics and other physiological traits revealed that the PN was not dependent on the leaf pigment content or PS II activity. However, it was dependent on stomatal traits like gs, SD and SS. Taken together, the traditional landraces such as Kalajeera, Machakanta and Haladichudi had superior PN and stomatal efficiency compared to the high yielding variety under prevailing environmental condition. Further research is required to elucidate the genetic diversity of these popular landraces compared to high-yielding ones in relation to photosynthesis efficiency for future crop improvement programmes.

Hydroponically grown 12-day-old rice (Oryza sativa L. cv. BRRI dhan47) seedlings were exposed to 150 mM NaCl alone and combined with 0.5 mM MnSO4. Salt stress resulted in disruption of ion homeostasis by Na+ influx and K+ efflux. Higher accumulation of Na+ and water imbalance under salinity caused osmotic stress, chlorosis, and growth inhibition. Salt-induced ionic toxicity and osmotic stress consequently resulted in oxidative stress by disrupting the antioxidant defense and glyoxalase systems through overproduction of reactive oxygen species (ROS) and methylglyoxal (MG), respectively. The salt-induced damage increased with the increasing duration of stress. However, exogenous application of manganese (Mn) helped the plants to partially recover from the inhibited growth and chlorosis by improving ionic and osmotic homeostasis through decreasing Na+ influx and increasing water status, respectively. Exogenous application of Mn increased ROS detoxification by increasing the content of the phenolic compounds, flavonoids, and ascorbate (AsA), and increasing the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD), and catalase (CAT) in the salt-treated seedlings. Supplemental Mn also reinforced MG detoxification by increasing the activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) in the salt-affected seedlings. Thus, exogenous application of Mn conferred salt-stress tolerance through the coordinated action of ion homeostasis and the antioxidant defense and glyoxalase systems in the salt-affected seedlings.

Mulberry (Morus alba L.) leaves are known as an ideal vegetable with good antioxidant effect, which can bring delicious taste and multiple health benefits. In the present study, the effects of 4-Chlorophenoxyacetic acid sodium salt (4-CPANa) treatment on growth and content of flavonoid compounds in mulberry leaves were investigated. Moreover, the changes in the expression levels of genes involved in flavonoid biosynthetic pathways, and the accumulation of important secondary metabolites including rutin (Rut), chlorogenic acid (ChA), isoquercitrin (IQ) and astragalin (Ast), were investigated in mulberry leaves. The results showed that 4-CPANa treatment could significantly promote the differentiation and growth of mulberry, increased shoot number, bud number, leaf fresh weight and leaf area of mulberry compared with control. Besides, the contents of ChA, Rut, IQ and Ast were significantly increased after 4-CPANa (5 mg/L) treatment. Further analysis revealed that 5 mg/L 4-CPANa strongly induced the expression of flavonoid biosynthesis-related genes including flavonoid 3-O-glucosyltransferase (F3GT) gene, chalcone synthase (CHS) gene, 4-xoumarate-CoA ligase (4CL) and phenylalanine ammonia lyase (PAL) gene. In conclusion, exogenous spraying of 4-CPANa provides a new way to improve the medicinal quality and development of mulberry leaf food with high value.