PGPB Improve Photosynthetic Activity and Tolerance to Oxidative Stress in Brassica napus Grown on Salinized Soils

Abstract

Soil salinization, one of the most common causes of soil degradation, negatively affects plant growth, reproduction, and yield in plants. Saline conditions elicit some physiological changes to cope with the imposed osmotic and oxidative stresses. Inoculation of plants with some bacterial species that stimulate their growth, i.e., plant growth-promoting bacteria (PGPB), may help plants to counteract saline stress, thus improving the plant’s fitness. This manuscript reports the effects of the inoculation of a salt-sensitive cultivar of Brassica napus (canola) with five different PGPB species (separately), i.e., Azospirillum brasilense, Arthrobacter globiformis, Burkholderia ambifaria, Herbaspirillum seropedicae, and Pseudomonas sp. on plant salt stress physiological responses. The seeds were sown in saline soil (8 dS/m) and inoculated with bacterial suspensions. Seedlings were grown to the phenological stage of rosetta, when morphological and physiological features were determined. In the presence of the above-mentioned PGPB, salt exposed canola plants grew better than non-inoculated controls. The water loss was reduced in inoculated plants under saline conditions, due to a low level of membrane damage and the enhanced synthesis of the osmolyte proline, the latter depending on the bacterial strain inoculated. The reduction in membrane damage was also due to the increased antioxidant activity (i.e., higher amount of phenolic compounds, enhanced superoxide dismutase, and ascorbate peroxidase activities) in salt-stressed and inoculated Brassica napus. Furthermore, the salt-stressed and inoculated plants did not show detrimental effects to their photosynthetic apparatus, i.e., higher efficiency of PSII and low energy dissipation by heat for photosynthesis were detected. The improvement of the response to salt stress provided by PGPB paves the way to further use of PGPB as inoculants of plants grown in saline soils.

Role of Polyamines in the Response to Salt Stress of Tomato

“…There are many controversies about the effect of salinity on the amount of chlorophyll. Many researchers have reported that salinity reduces chlorophyll in salt-sensitive plants and increases it in salt-tolerant plants [38][39][40]. Our data agree with those showing a decrease of chlorophyll in plants exposed to salt stress and non-primed [38], while priming treatment with PAs improved the tolerance of tomato plants to salt stress with respect to chlorophyll maintenance.…”

“…PAs might be positive activators of non-enzymatic protective pathways, reducing the production of radical species, such as DPPH, ferric tripyridyl-triazine or potassium ferrocyanide. To increase antioxidant activity, plants can also enhance the synthesis of osmolytes, such as proline, and secondary metabolites, such as phenols and flavonoids [26,39,40], which are species-specific and associated with plant protection against both abiotic and biotic stresses. Although the synthesis of secondary metabolites increases when plants are grown under salt stress conditions, many studies pay particular attention to only a few target compounds.…”

Photosynthesis and chlorophyll fluorescence of Iranian licorice (Glycyrrhiza glabra l.) accessions under salinity stress

“…After exposure to salinity, it is usual that the photosynthetic rate decreases in response to a decline in leaf area, gas exchange, and also feedback suppression of unused photosynthates (Ilangumaran and Smith, 2017). As observed in the present study, under the effect of salinity, PGPB led to a higher photosynthetic efficiency in licorice plants (by increasing osmolyte production, reduction in membrane damage, higher antioxidant activity, all to protect photosynthetic apparatus) (Rossi et al, 2021), as were similar cases observed in maize plants (Zea mays L.) (Hafez et al, 2021) and pistachio trees (Pistacia vera) (Khalilpour et al, 2021).…”

Co-Inoculation of Plant-Growth-Promoting Bacteria Modulates Physiological and Biochemical Responses of Perennial Ryegrass to Water Deficit

“…Although, in our study, an increase in non-photochemical quenching was observed when plants were inoculated with PGPB, other studies have found contrasting results that were also associated with a beneficial effect of the bacteria [ 31 ]. Because of the great variability in the responses of plants to water deficit, both an increase and a decrease in heat dissipation can indicate a positive effect of PGPB inoculation.…”