Selenium treatment alters the accumulation of osmolytes in arsenic-stressed rice (Oryza sativa L.).

Arsenic (As), one of the major pollutants in the soil, is an important environmental concern as its consumption can cause adverse health symptoms in living organisms. Its contamination of rice grown over As-contaminated areas is a serious concern in South Asian countries. Selenium (Se) has been reported to influence various osmolytes under metal stress in plants. The present study reports the role of Se in mitigating As stress in rice by modulating osmolyte metabolism. Rice plants grown in As-amended soil (2.5-10 mg kg-1) in pots were treated with sodium selenate (0.5-1.0 mg Se kg-1 soil) in glass house conditions and leaf samples were collected at 60 and 90 days after sowing (DAS). As-treated rice leaves displayed a reduction in relative water content (RWC) and dry weight than control with a maximum reduction of 1.68- and 2.47-fold in RWC and 1.95- and 1.69-fold in dry weight in As10 treatment at 60 and 90 DAS, respectively. Free amino acids (1.38-2.26-fold), proline (3.88-3.93-fold), glycine betaine (GB) (1.27-1.72-fold), choline (1.67-3.1-fold), total soluble sugars (1.29-1.61-fold), and reducing sugars (1.67-2.19-fold) increased in As-treated rice leaves as compared to control at both stages. As stress increased the γ-aminobutyric acid (GABA), putrescine content, and glutamate decarboxylase activity whereas diamine oxidase and polyamine oxidase activities declined by 1.69-1.88-fold and 1.52-1.86-fold, respectively. Se alone or in combination with As improved plant growth, RWC, GB, choline, putrescine, and sugars; lowered proline and GABA; and showed a reverse trend of enzyme activities related to their metabolism than respective As treatments. As stress resulted in a higher accumulation of osmolytes to combat its stress which was further modulated by the Se application. Hence, the current investigation suggested the role of osmoprotectants in Se-induced amelioration of As toxicity in rice plants.

Metabolic adjustments during compatible interaction between barley genotypes and stripe rust pathogen.

Stripe rust is a fungal disease that has devastated the barley production for a long time. The present study focused on the role of ß-glucan, PR proteins, diamine oxidase (DAO), polyamine oxidase (PAO), key enzymes and metabolites of phenol and proline metabolism in the stripe rust resistance of barley. RD2901 with resistant behavior against stripe rust showed increased levels of PR proteins, phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) along with the accumulation of ß-glucan and lignin which strengthen the plant cell wall during plant-pathogen interaction. It also depicted the enhanced activities of glutamate dehydrogenase (GDH) and ornithine aminotransferase (OAT) coupled with the increased amounts of proline, glycine betaine and choline after infection with M-race of P. striiformis f. sp. hordei. On the contrary, the sensitive genotype Jyoti was unable to enhance the activities of most of these enzymes except PAL and OAT so that it showed an increase in lignin and choline contents only. Secondly, the increase in lignin content was less as compared to the tolerant genotype. Hence, it can be inferred that these key metabolites and enzymes of various metabolic pathways may contribute to the resistance of barley against stripe rust pathogen. This study suggested that these key enzymes and their metabolites could serve as markers for the characterization of plant defensive state that is essential for crop protection.

Stripe rust induced defence mechanisms in the leaves of contrasting barley genotypes (Hordeum vulgare L.) at the seedling stage.

Puccinia striiformis f. sp. hordei, the causal organism of stripe rust in barley poses serious threats to its production. The present study examined the seedling response and changes in antioxidant defence system along with NADPH oxidase, hydrogen peroxide, and lipid peroxidation marker-malondialdehyde (MDA) in the four barley genotypes namely Jyoti, RD2900, RD2901, and RD2552 in response to M and G-races of stripe rust pathogen. Disease reaction showed Jyoti as susceptible genotype, RD2901 and RD2552 as resistant, whereas RD2900 behaved differentially to both the races. M-race which is predominant was found to be more virulent than G-race of barley stripe rust pathogen. RD2901 showed an increase in activities of NADPH oxidase, catalase, peroxidase, and enzymes of ascorbate-glutathione pathway along with ascorbate and glutathione pool on inoculation with M-race, which was accompanied by the decrease in hydrogen peroxide and MDA contents. Jyoti, on the other hand, showed an increase in peroxidase and glutathione-S-transferase activities only which were unable to maintain redox homeostasis. The scrutiny of data indicated an increase in ASA/DHA ratio on infection in all the genotypes irrespective of their behaviour towards the races. However, GSH/GSSG ratio significantly declined in Jyoti and increased or remained unaffected in the resistant genotypes which suggested that GSH/GSSG might be playing a vital role in imparting tolerance against stripe rust. Further, correlation studies also revealed that leaf damage was positively correlated with H2O2 and MDA contents.

Antioxidant potential of barley genotypes inoculated with five different pathotypes of Puccinia striiformis f. sp. hordei.

The stripe rust caused by the fungal pathogen, Puccinia striiformis f. sp. hordei in barley (Hordeum vulgare L.) is a global problem that threatens the production of barley. The present study examined the disease reaction, free radical scavenging potential, non-enzymatic antioxidants like total phenols, o-dihydroxy phenols, flavonoids along with total chlorophyll, chlorophyll a, chlorophyll b and total carotenoids of the four barley genotypes viz. Jyoti (susceptible), RD2900, RD2901 and RD2552 (resistant) infected with five different pathotypes (M, G, 57, Q and 24) of P. striiformis f. sp. hordei. The disease reaction showing RD2901 in the category of immune to very resistant genotype followed by RD2552 in immune to resistant and RD2900 as moderately resistant and Jyoti as susceptible, which was well correlated with biochemical studies. RD2901 possessed higher antioxidant potential in terms of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·) scavenging activity, ferric reducing antioxidant power, reducing power and nitric oxide scavenging activity under control conditions and were maintained sufficiently high on inoculation with different pathotypes (M, G, 57, Q and 24) of P. striiformis f. sp. hordei. Further, these free radical scavenging activities showed the positive correlation with total phenols, o-dihydroxy phenols, flavonoids which in turn might be contributing in tolerance behaviour of this genotype. However, Jyoti with sensitive behaviour towards M, G, and 24 pathotypes depicted minimum DPPH activity and reducing power under control conditions.