Hyperauxinity in diseased leaves affected by Mal de Rio Cuarto Virus (MRCV)

One of the symptoms of the Mal de Rio Cuarto disease caused by the Maize Ri o Cuarto Virus (MRCV) is the presence of leaf galls named enations. The rel ationships between enation vascular histology, endogenous indole-3-acetic a cid (IAA) levels and in vitro IAA-oxidative decarboxylation catalyzed by pe roxidases in affected leaves compared to healthy ones, and the presence of the virus in the enation, were investigated. Increased levels of IAA were found in young affected leaves, 36 days post-i nfection, in correlation with alterations of vascular tissues, especially a t the xylem. Low levels of IAA oxidase specific activity in soluble peroxid ase fractions of affected leaves at this stage could be correlated with the highest IAA concentration of these fractions. However, similar IAA concent rations were detected in mature healthy leaves and in those with well-devel oped enations (62 days post-infection) where no further histological change s occurred. In well developed enations high IAA concentrations coexisted wi th high enzyme activities of soluble and ionically bound to cell wall perox idase fractions. The virus presence was localized by TEM in the parenchyma phloem cells of enations.