Modulation of Photosynthesis and ROS Scavenging Response by Beneficial Bacteria in Olea europaea Plantlets under Salt Stress Conditions

Climate change consequences for agriculture involve an increase of saline soils which
results in lower crop yields due to increased oxidative stress in plants. The present study reports the
use of Plant Growth Promoting Bacteria (PGPB) as a tool to modulate plant innate mechanisms of
adaptation to water stress (salinity and drought) in one year-old olive plantlets var. Arbosana and
Arbequina. Integration of external changes in plants involve changes in Reactive Oxygen Species
(ROS) that behave as signals to trigger plant adaptative mechanisms; however, they become toxic
in high concentrations. For this reason, plants are endowed with antioxidant systems to keep ROS
under control. So, the working hypothesis is that specific beneficial strains will induce a systemic
response able to modulate oxidative stress and improve plant adaptation to water stress. Ten
strains were assayed, evaluating changes in photosynthesis, pigments, ROS scavenging enzymes and
antioxidant molecules, osmolytes and malondialdehyde, as oxidative stress marker. Photosynthesis
and photosynthetic pigments were the most affected variables. Despite the specific response of each
variety, the favorite targets of PGPBs to improve plant fitness were photosynthetic pigments and the
antioxidant pools of glutathione and ascorbate. Our results show the potential of PGPBs to improve
plant fitness modulating oxidative stress.