Coactive role of zinc oxide nanoparticles and plant growth promoting rhizobacteria for mitigation of synchronized effects of heat and drought stress in wheat plants.

This study intended to investigate the potential of the plant growth-promoting rhizobacteria (PGPR) and green synthesized zinc oxide nanoparticles (ZnO-NPs) (fruit extract of Papaya) against heat and drought stress in wheat. The characterization of green-synthesized ZnO-NPs was done through UV-vis spectrophotometry, Fourier-transform infrared spectrometry, X-ray diffraction and scanning electron microscopy. Individual and combination of PGPR (Pseudomonas sp.) and ZnO-NPs (10 ppm) amendments were tested in a pot experiment to upregulate wheat defence system under three stress groups (drought, heat and combined heat and drought stress). Drought and heat stress synergistically caused higher damage to wheat plants than individual heat and drought stress. This observation was confirmed with remarkable higher MDA and hydrogen peroxide (H2O2) content. Treated plants exposed to all stress groups showed an improved wheat growth and stress resistance through better biomass, photosynthetic pigments, nutrients, soluble sugars, protein and indole acetic acid content. Combination of ZnO-NPs and Pseudomonas sp. Protects the plants from all stress groups by producing higher proline, antioxidant enzymes i. e superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase, and abscisic acid. Moreover, higher stress alleviation by this treatment was manifested by marked reduced electrolyte leakage, MDA and H2O2. The findings of current study confirmed that the synergistic actions of PGPR and ZnO-NPs can rescue plants from both single and combined heat and drought stress.

Combined application of zinc oxide nanoparticles and biofertilizer to induce salt resistance in safflower by regulating ion homeostasis and antioxidant defence responses.

Salinity is a key devastating abiotic factor that hinders the development and yield of safflower. The sole and combined application of zinc oxide nanoparticles (ZnO-NPs) and a biofertilizer (BF) to improve salt tolerance in safflower has not been thoroughly explored. The response of safflower plants in a pot experiment to the foliar spray of ZnO-NPs alone and in combination with a BF was thus detected. We determined that a ZnO-NP concentration of 17 mg/L was sufficient to protect safflower against salinity (250 mM NaCl) by increasing the plant productivity, percent water content, and osmolyte levels. Coapplication of ZnO-NPs and Phytoguard protected safflower plants from salinity stress by improving the activities of antioxidant enzymes and decreasing the levels of proline (leaves (61%) and roots (63%)) and malondialdehyde (MDA) (leaves (54%) and roots (65%)). Under salt stress, the Na+ content increased, while seed coating with biofertilizer and ZnO-NP spray significantly decreased the Na+ concentration (74% in leaves and 60% in roots). For the K+ concentration, however, antagonistic outcomes were observed. Additionally, the combined treatment significantly enhanced agronomic parameters such as the number of leaves and pods per plant, capitulum weight, and the number of yellow and wilted leaves per plant under salinity stress. Thus, ZnO-NPs could be an effective bio-source for the protection of safflower plants under salinity stress. Our findings showed that in the combined treatment of ZnO-NPs and biofertilizer, the salinity tolerance was more pronounced than in the single treatment and untreated control. A thorough analysis at the molecular level, however, is still required to understand the mechanism by which ZnO-NPs and BF in safflower plants alleviate salt stress.

Volatile organic compounds produced by Pseudomonas pseudoalcaligenes alleviated drought stress by modulating defense system in maize (Zea mays L.).

Research on plant growth-promoting bacteria (PGPR) revealed an effective role of bacterial volatile organic compounds (VOCs) in stress alleviation. Out of 15 PGPR strains, infection with VOCs from Pseudomonas pseudoalcaligenes' resulted in maximum germination, growth promotion, and drought tolerance in maize plants. The VOCs of P. pseudoalcaligenes caused induced systemic tolerance in maize plants during 7 days of drought stress. The VOCs exposed plants displayed resistance to drought stress by reducing electrolyte leakage and malondialdehyde content and increasing the synthesis of photosynthetic pigments, proline, and phytohormones contents. Maize plants revealed enhanced resistance by showing higher activities of antioxidant defense enzymes both in shoots and roots under drought stress. Activities of antioxidant enzymes were more pronounced in shoots than roots. Gas chromatography and mass spectrophotometric (GC-MS) analysis comparing VOCs produced by the most efficient P. pseudoalcaligenes strain and inefficient strains of Pseudomonas sp. grown in culture media revealed nine compounds that they had in common. However, dimethyl disulfide, 2,3-butanediol, and 2-pentylfuran were detected only in P. pseudoalcaligenes, indicating these compounds are potential candidates for drought stress induction. Further studies are needed to unravel the molecular mechanisms of VOCs-mediated systemic drought tolerance in plants related to each identified VOC.

Co-application of bio-fertilizer and salicylic acid improves growth, photosynthetic pigments and stress tolerance in wheat under drought stress.

Drought stress hampers the growth and productivity of wheat crop worldwide. Thus far, different strategies have been proposed to improve drought tolerance in wheat but the combined application of plant growth-promoting rhizobacteria formulated bio-fertilizer (BF) and salicylic acid (SA) has not been thoroughly explored yet. Therefore, a pot experiment was conducted to observe the effect of SA, BF, and their combination on wheat plants under optimal and drought stress conditions. Seeds priming was done with BF (107 CFU mL-1). After 2 weeks of germination, SA (one mM) was applied as a foliar spray. Drought stress was applied by withholding water supply at three-leaf stage (30 d old plants) for the next 15 d until soil moisture dropped to 10%. Foliar application of SA increased the bacterial population of BF significantly compared to the sole application of BF under irrigated as well as drought stress conditions. Co-application of BF and foliar spray of SA induced drought tolerance in wheat plants by enhancing plant biomass, photosynthetic pigments, relative water content and osmolytes, and activities of the defense-related system. Plants treated with SA and BF together under drought stress had significantly increased leaf water status, Chl a, Chl b, and carotenoids synthesis by 238%, 125%, 167%, and 122%, respectively. Moreover, the co-application of SA and BF showed maximum SOD, POD, APX, and CAT activities by 165%, 85%, 156%, and 169% in the leaves while 153%, 86%, 116% and 200% in roots under drought stress. Similarly, the combined treatment exhibited a pronounced decrease in MDA content by 54% while increased production of proteins and proline by 145% and 149%, respectively. Our results showed that the co-application of SA and BF induced better drought tolerance as compared with the sole application of SA or BF. The results obtained herein suggest that combined application of BF and SA can be applied to the wheat crop to greatly improve drought tolerance in field conditions.