Seed Treatment with Trichoderma longibrachiatum T6 Promotes Wheat Seedling Growth under NaCl Stress Through Activating the Enzymatic and Nonenzymatic Antioxidant Defense Systems

Salt stress is one of the major abiotic stresses limiting crop growth and productivity worldwide. Species of Trichoderma are widely recognized for their bio-control abilities, but little information is regarding to the ability and mechanisms of their promoting plant growth and enhancing plant tolerance to different levels of salt stress. Hence, we determined (i) the role of Trichoderma longibrachiatum T6 (TL-6) in promoting wheat (Triticum aestivum L.) seed germination and seedling growth under different levels of salt stress, and (ii) the mechanisms responsible for the enhanced tolerance of wheat to salt stress by TL-6. Wheat seeds treated with or without TL-6 were grown under different levels of salt stress in controlled environmental conditions. As such, the TL-6 treatments promoted seed germination and increased the shoot and root weights of wheat seedlings under both non-stress and salt-stress conditions. Wheat seedlings with TL-6 treatments under different levels of NaCl stress increased proline content by an average of 11%, ascorbate 15%, and glutathione 28%; and decreased the contents of malondialdehyde (MDA) by an average of 19% and hydrogen peroxide (H₂O₂) 13%. The TL-6 treatments induced the transcriptional level of reactive oxygen species (ROS) scavenging enzymes, leading to the increases of glutathione s-transferase (GST) by an average of 17%, glutathione peroxidase (GPX) 16%, ascorbate peroxidase (APX) 17%, glutathione reductase (GR) 18%, dehydroascorbate reductase (DHAR) 5%. Our results indicate that the beneficial strain of TL-6 effectively scavenged ROS under NaCl stress through modulating the activity of ROS scavenging enzymes, regulating the transcriptional levels of ROS scavenging enzyme gene expression, and enhancing the nonenzymatic antioxidants in wheat seedling in response to salt stress. Our present study provides a new insight into the mechanisms of TL-6 can activate the enzymatic and nonenzymatic antioxidant defense systems and enhance wheat seedling tolerance to different levels of salt stress at physiological, biochemical and molecular levels.

Irradiation influence on the phenoloxidase pathway and an anti-oxidant defense mechanism in Spodoptera litura (Lepidoptera: Noctuidae) and its implication in radio-genetic 'F 1 sterility' and biorational pest suppression tactics

The present study was conducted to appraise the ontogenic radio-sensitivity of a serious tropical pest, Spodoptera litura (Fabr.). The molecular responses pertaining to the phenoloxidase (PO) pathway and an anti-oxidant defense mechanism were evaluated in order to understand its implication in pest control at pre-harvest and post-harvest intervals. Irradiation exhibited an inverse relationship with age with respect to impact on developmental and transcriptional responses. Transcript abundance of PO cascade enzymes, prophenoloxidase (slppo-2), its activating enzyme (slppae-1) and free-radical scavenging enzymes, superoxide dismutase (slsod) and catalase (slcat) was evaluated upon gamma irradiation alone and the dual-stress of radiation plus microbial challenge. The slppo-2, slppae-1, slsod and slcat transcripts were significantly up-regulated in F 1 L6 larvae (6th-instar) resulting from 100 Gy sub-sterilized male adults and unirradiated female moths. The extent of upregulation was relatively higher in comparison with L6 survivors (6th-instar larvae) developed from irradiated neonates (L1) treated with 100 Gy. Upon Photorhabdus challenge, the transcripts were down-regulated in irradiated L1 suggesting increased larval susceptibility to bacterial infections. Radioresistance increased with the age of the insect, and molecular responses (transcript abundance) of insect defense mechanism were less influenced when older age (F 1 progeny) were irradiated. These findings will help to optimize the gamma dose to be employed in inherited sterility technique for (pre-harvest) pest suppression and (post-harvest) phytosanitation and quarantine, and suggest compatible integration of biorational tactics including nuclear technology.

Changes in oxidative patterns during dormancy break by warm and cold stratification in seeds of an edible fruit tree

The transition from seed dormancy to germination is triggered by environmental factors, and in pomegranate (Punica granatum) seeds higher germination percentages are achieved by warm + cold stratification rather than by cold stratification alone. Our objective was to define the pattern of internal oxidative changes in pomegranate seeds as dormancy was being broken by warm + cold stratification and by cold stratification alone. Embryos isolated from seeds after 1-42 days of warm stratification, after 56 days of warm stratification + 7, 28 or 56 days of cold stratification, and after 1-84 days of cold stratification alone, were used in biochemical tests. Hydrogen peroxide (H2O2), nitric oxide (NO), proline, lipid peroxidation, protein carbonylation, and activities of the scavenging enzymes superoxide dismutase (SOD), hydrogen peroxide enzyme and peroxidase in the embryos were assessed by colorimetric methods. Our results indicated that warm + cold stratification had a stronger dormancy-breaking effect than cold stratification (85% versus 50% germination), which may be attributed to a higher yield of H2O2, NO, lipid peroxidation and protein carbonylation in warm + cold stratification. Furthermore, warm + cold stratification-induced H2O2 change led to greater changes (elevation followed by attenuation) in activities of the scavenging enzymes than that induced by cold stratification alone. These results indicated that restriction of the level of reactive oxygen species change within a positive and safe range by such enzymes promoted seed germination. In addition, a relatively strong elevation of proline during warm + cold stratification also contributed to dormancy breakage and subsequent germination. In conclusion, the strong dormancy alleviating effect of warm + cold stratification on pomegranate seeds may be attributed to the corresponding active oxidative change via H2O2, NO, proline, malondialdehyde, protein carbonylation and scavenging enzymes.

The Ayurvedic drug, Ksheerabala, ameliorates quinolinic acid-induced oxidative stress in rat brain

One of the mechanisms of neurotoxicity is the induction of oxidative stress. There is hardly any cure for neurotoxicity in modern medicine, whereas many drugs in Ayurveda possess neuroprotective effects; however, there is no scientific validation for these drugs. Ksheerabala is an ayurvedic drug which is used to treat central nervous system disorders, arthritis, and insomnia. The aim of our study was to evaluate the effect of Ksheerabala on quinolinic acid-induced toxicity in rat brain. The optimal dose of Ksheerabala was found from a dose escalation study, wherein it was found that Ksheerabala showed maximum protection against quinolinic acid-induced neurotoxicity at a dose of 15 µL/100 g body weight/day, which was selected for further experiments. Four groups of female albino rats were maintained for 21 days as follows: 1. Control group, 2. Quinolinic acid (55 µg/100 g body weight), 3. Ksheerabala (15 µL/100 g body weight), 4. Ksheerabala (15 µL/100 g body weight) + Quinolinic acid (55 µg/100 g body weight). At the end of the experimental period, levels of lipid peroxidation products, protein carbonyls, and activities of scavenging enzymes were analyzed. The results revealed that quinolinic acid intake caused enhanced lipid and protein peroxidation as evidenced by increased levels of peroxidation products such as malondialdehyde, hydroperoxide, conjugated dienes, and protein carbonyls. On the other hand, the activities of scavenging enzymes such as catalase, superoxide dismutase (SOD), glutathione peroxidase, and glutathione reductase as well as the concentration of glutathione were reduced. On coadminstration of Ksheerabala along with quinolinic acid, the levels of all the biochemical parameters were restored to near-normal levels, indicating the protective effect of the drug. These results were reinforced by histopathological studies.

Drought stress and reactive oxygen species: Production, scavenging and signaling

As sessile organisms, plants have evolved mechanisms that allow them to adapt and survive periods of drought stress. One of the inevitable consequences of drought stress is enhanced ROS production in the different cellular compartments, namely in the chloroplasts, the peroxisomes and the mitochondria. This enhanced ROS production is however kept under tight control by a versatile and cooperative antioxidant system that modulates intracellular ROS concentration and sets the redox-status of the cell. Furthermore, ROS enhancement under stress functions as an alarm signal that triggers acclimatory/defense responses by specific signal transduction pathways that involve H(2)O(2) as secondary messenger. ROS signaling is linked to ABA, Ca(2+) fluxes and sugar sensing and is likely to be involved both upstream and downstream of the ABA-dependent signaling pathways under drought stress. Nevertheless, if drought stress is prolonged over to a certain extent, ROS production will overwhelm the scavenging action of the anti-oxidant system resulting in extensive cellular damage and death.