Plasticity of young Moringa oleifera L. plants to face water deficit and UVB radiation challenges

Climatic change challenges are predicted to increase combined episodes of drought, heat and higher UVB-radiation, which will impact crops/plants production. Moringa oleifera is a major source of food/economy in underdeveloped regions, and its tolerance to high UVB radiation (UVB) and water deficit (WD) remains unclear. We exposed two-month old plants to: a) WD for 4 days; b) UVB radiation for 3 days (26.3 kJ m− 2); c) WD + UVB in combination for 4 days (the UVB stress was imposed at the 2nd day of WD). One and ten days after the end of stresses the following parameters were measured: plant growth, water-status, chlorophyll a fluorescence, leaf gas-exchange, pigments, carbohydrates, cell-membrane-stability, phenols, malondialdehyde content and antioxidant capacity (including antioxidant enzymes). Stress exposure did not affect plant water status. One day after the end of the stresses, net CO2 assimilation rate dropped in all treatments, but after 10 days an overall recovery was observed, except in plants exposed to UVB treatment. The plants exposed to UVB showed, in general, more severe effects, increasing pigment content and MDA, while no changes were observed in the total antioxidant capacity (after 1 day). Our data suggest that young M. oleifera plants present some tolerance to WD or UVB radiation and that the combination of the two stresses led to lower stressful responses than the UV stress imposition alone (photosynthesis, pigments, starch and antioxidant capacity). The lower outcome shown in the combined stresses suggest that this species is able to cope multiple stresses, and that a previous acclimation (possibly activating the antioxidant capacity) to one of the stresses may play an important role in this tolerance.