RIP activity in basic protein fractions of tissue extracts from Fragaria x ananassa

Ribosome-inactivating proteins (RIPs) in plants are enzymes which depurinate rRNA, thus inhibiting protein synthesis, as well as other polynucleotide substrates, including nucleic acids from plant viruses. Biological activity, distribution, mechanism of action and physiological role of RIPs are still not completely understood. The aims of our study were to determine the range of RIP activity in tissue extracts of the Fragaria × ananassa strawberry cultivars ‘Dora’ and ‘Record’, of differing susceptibility to soil-borne pathogens, and the influence thereupon of crop management and growth stage. RIP activity was found in every tested tissue, with IC50s ranging from 5 to 150 µg/mL, and sharply increased in leaves during endogenous fruiting. We also determined the effect of exogenous stress by drought on RIP activity in potted plants of the same varieties, observing a marked increase of RIP activity in wilted leaves. The augmented RIP activity found in leaves of plants exposed to endogenous and exogenous stress suggests that it could be a response mechanism and may represent a useful tool in selecting strawberry genotypes resistant to different biotic and abiotic stresses.