Morphological changes, alteration of photosynthetic parameters and chlorophyll production induced by infection with alfalfa dwarf virus in Medicago sativa plants

In Argentina, infections by alfalfa dwarf virus (ADV) affect the cultivation of alfalfa, which is globally one of the most important forage plants. The main objective of this study was to improve current understanding of the underlying mechanisms related to the dwarfism phenotype developed during viral infection. Hydrogen peroxide production, callose deposition and PR5 gene expression levels were evaluated to determine if ADV induces plant defence responses. At the morphological level, higher epicuticular wax production and an increase in proliferation of cells from the fundamental parenchyma were observed when plants were infected by ADV. Infected plants had reduced photosynthesis, stomatal conductance and transpiration/evaporation rate, but interestingly the production of chlorophylls was induced. Finally, using transcriptional analysis, ADV was observed to negatively affect the expression of genes related to synthesis of auxins, cytokinins and brassinosteroids. These results suggest that ADV infection induces a hormonal imbalance leading to an increase in chlorophyll pigment synthesis, stomatal closure and generation of tissue deformation. Overall, the results show a morphological, physiological and photosynthetic characterization of dwarf plants affected by ADV.