Physiological responses and expression of sugar associated genes in faba bean (Vicia faba L.) exposed to osmotic stress.

Faba bean (Vicia faba L.) is the major food legume crop in Tunisia. However, its growth and yield is strongly affected by water-limited environments. In this study, osmotic stress exhibited a negative effect on Bachar and Badii cultivar. Nevertheless, the deteriorating effects of osmotic stress were relatively low on studied parameters of Bachar due to its better efficiency to reduce oxidative damage by increasing enzymatic activities such as catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX), accumulation of total chlorophyll (Chlt), soluble sugars and leaf relative water content (RWC). GC-MS analysis determined a total of 11 soluble carbohydrates induced by osmotic stress and differentially accumulated in the both cultivars. Bachar showed elevated levels of mannose, glucose, galactose, ribose, rhamnose and myo-inositol which might help to maintain osmotic adjustment, membranes and proteins protection from the damaging effect of reactive oxygen species. Sugar metabolism related genes (VfNINV3, VfPHS2, VfFRK4, VfHXK1, VfGPI1, VfSTP1.1, VfpGlcT1.1, VfSTP5.1, VfpGlcT1.2, VfSWEET2.1, VfVINV2, VfSUS1, VfPGM1, VfSUT1.1, VfGPT1, VfSPS1, VfSPP1, VfPHS1, VfSUT4.1 and VfTMT1.1) were differentially expressed in both cultivars demonstrating their important roles in sugar accumulation. Most of these genes were upregulated in the leaves of Bachar under moderate and severe stress, which could lead to increase glycolysis and tricarboxylic acid cycle in order to accelerate energy production, necessary to increase osmotic regulation and consequently enhancing the osmotic stress tolerance in that cultivar. Overall, sugars accumulation ability can be used as a useful indicator for the osmotic stress tolerant potential in faba bean breeding programs. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at (10.1007/s12298-021-00935-1).

Alleviation of drought stress in faba bean (Vicia faba L.) by exogenous application of ß-aminobutyric acid (BABA).

Drought stress is one of the most prevalent environmental factors limiting faba bean (Vicia faba L.) crop productivity. ß-aminobutyric acid (BABA) is a non-protein amino acid that may be involved in the regulation of plant adaptation to drought stress. The effect of exogenous BABA application on physiological, biochemical and molecular responses of faba bean plants grown under 18% PEG-induced drought stress were investigated. The results showed that the application of 1 mM of BABA improved the drought tolerance of faba bean. The application of BABA increased the leaf relative water content, leaf photosynthesis rate (A), transpiration rate (E), and stomatal conductance (gs), thereby decreased the water use efficiency. Furthermore, exogenous application of BABA decreased production of hydrogen peroxide (H2O2), malondialdehyde and electrolyte leakage levels, leading to less cell membrane damage due to oxidative stress. Regarding osmoprotectants, BABA application enhanced the accumulation of proline, and soluble sugars, which could improve the osmotic adjustment ability of faba bean under drought challenge. Interestingly, mended antioxidant enzyme activities like catalase, guaiacol peroxidase, ascorbate peroxidase and superoxide dismutase and their transcript levels may lead to counteract the damaging effects of oxidative stress and reducing the accumulation of harmful substances in BABA-treated faba bean plants. In addition, exogenous BABA significantly induced the accumulation of drought tolerance-related genes like VfMYB, VfDHN, VfLEA, VfERF, VfNCED, VfWRKY, VfHSP and VfNAC in leaves and roots, suggesting that BABA might act as a signal molecule to regulate the expression of drought tolerance-related genes.

Plant growth promoting rhizobacteria modulates the antioxidant defense and the expression of stress-responsive genes providing Pb accumulation and tolerance of grass pea.

To ensure the success of phytoremediation, it is important to consider the appropriate combination of plants and microorganisms. This study was conducted to get a better insight into the underlying molecular and biochemical mechanism of grass pea (Lathyrus sativus L.) induced by plant growth promoting rhizobacteria (PGPR), when exposed for 3, 6, 9, and 14 days to 1 mM Pb in a hydroponic system. The significant positive effect of bacterial inoculation was reproduced in various parameters. Results indicated that inoculation of PGPR significantly increased the accumulation of Pb by 20%, 66%, 43%, and 36% in roots and by 46%, 55%, 37%, and 46% in shoots, respectively after 3, 6, 9, and 14 days of metal exposure compared to the uninoculated plants. The metal accumulation in grass pea plants triggered a significant elevation in the synthesis of non-protein thiols (NPT), particularly in inoculated plant leaves where it was about 3 and 2-fold higher than the uninoculated set on the 6th and the 9th day. Nevertheless, Pb treatment significantly increased oxidative stress and membrane damage in leaves with the highest hydrogen peroxide (H2O2) production and tissue malondialdehyde (MDA) concentration recorded in uninoculated plants. Furthermore, the PGPR inoculation alleviated the oxidative stress, improved significantly plant tolerance, and modulated the activities of antioxidant enzymes (SOD, CAT, APX, GR, DHAR, and MDHAR). Similarly, the expression patterns of LsPCS, LsGCN, LsCNGC, LsGR, and LsGST through qRT-PCR demonstrated that bacterial inoculation significantly induced gene expression levels in leaves 6 days after Pb treatment, indicating that PGPR act as regulators of stress-responsive genes. The findings suggest the key role of PGPR (R. leguminosarum (M5) + Pseudomonas fluorescens (K23) + Luteibacter sp. + Variovorax sp.) in enhancing Pb accumulation, reducing metal toxicity, strengthening of the antioxidant system, and conferring higher Pb tolerance to grass pea plants. Hence, the association Lathyrus sativus-PGPR is an effective tool to achieve the goal of remediation of Pb contaminated sites.

Exogenous application of spermidine mitigates the adverse effects of drought stress in faba bean (Vicia faba L.).

In Tunisia, drought stress is a major environmental factor limiting crop production and causing relatively low and unstable faba bean yields. In the present study, we explored the putative role of spermidine (0.5, 1, 1.5 and 2mM) in ameliorating the effects of drought stress induced by polyethylene glycol (PEG-6000, -0.58MPa) in faba bean seedlings. Drought stress reduced photosynthetic performance, chlorophyll and relative water content in leaves of faba bean variety Badii. Moreover, drought increased proline, electrolyte leakage and malondialdehyde content by inducing reactive oxygen species (hydrogen peroxide) generation in leaves. However, applying spermidine increased the activities of catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase. The results show that the application of spermidine especially at a rate of 1.5mM effectively reduces oxidative damage and alleviates negative effects caused by drought stress. In addition, exogenous spermidine increased the expression of polyamine biosynthetic enzymes' genes (VfADC , VfSAMDC and VfSPDS ), and reduced the expression of VfSPMS suggesting that exogenous spermidine can regulate polyamines' metabolic status under drought challenge, and consequently may enhance drought stress tolerance in faba bean. Real-time quantitative polymerase chain reaction analysis revealed that some drought responsive genes (VfNAC , VfHSP , VfNCED , VfLEA , VfCAT , VfAPX , VfRD22 , VfMYB , VfDHN , VfERF , VfSOD and VfWRKY ) from various metabolic pathways were differentially expressed under drought stress. Overall, these genes were more abundantly transcribed in the spermidine-treated plants compared to untreated suggesting an important role of spermidine in modulating faba bean drought stress response and tolerance.