Zinc priming and foliar application enhances photoprotection mechanisms in drought-stressed wheat plants during anthesis

Drought is one of most important limiting factors in wheat productivity worldwide. The need to increase drought tolerance during anthesis is of the utmost importance for high yield potentials and yield stability. Photosynthesis is one of the major physiological processes affected by drought. Damages in the photosynthetic apparatus may also arise due to non-regulated dissipation of excessive energy. Zinc (Zn)is an indispensable micronutrient for plants and is required for a wide range of physiological and biochemical processes. In this work we evaluated the stress mitigation effects of Zn seed priming alone and coupled with Zn foliar application in wheat plants submitted to severe drought during anthesis, followed by a recovery period. Under such severe drought stress, photosynthesis was constrained by both stomatal and non-stomatal limitation. Severe drought also induced an increase in non-regulated energy dissipation and hindered a full recovery of the plant's photosynthetic processes after rewatering. We also report possible activation of transposable elements due to drought stress and Zn application. Yield was severely decreased by drought and Zn treatments were unable to counteract this effect. Although unable to oppose the reduction of net photosynthesis, Zn treatments positively enhance photoprotection. At the end of drought period, Zn priming alone and coupled with Zn foliar application increased, respectively, over 2- and 3- fold the regulated dissipation of excess energy. Zn treatments lessened the non-regulated energy dissipation caused by drought, protected the plants against irreversible damages to the photosynthetic apparatus and enabled a better recovery of wheat plants after stress relief.