Flashes of UV-C light, a newcomer among plant resistance inducers and stimulants of plant tolerance against abiotic stress, with unique features

Abstract: Whereas UV-C light at low intensity can be used for disinfecting crops, flashes of UV-C light at high intensity have been proven to be effective for stimulating defenses of several plants of economic importance against a large range of diseases, paving the way for the use of them as a plant resistance inducer (PRI) in greenhouse and field conditions. Several studies have confirmed that flashes of UV-C light, applied at 7 to 15 days intervals, can be used to substantially reduce symptoms of powdery mildew in tomato, strawberry and rose production (in greenhouse conditions) and of powdery mildew and downy mildew of grapevine grown in vineyard conditions. Ongoing research aims at understanding the way flashes of UV-C light are perceived by plants and the signaling and regulatory pathways they trigger. Here we provide evidence that flashes of UV-C light stimulate expression of the genes of the salicylic acid (SA)/NPR1 pathway, as well as genes involved in systemic acquired resistance, and notably synthesis of N-hydroxy-pipecolic acid. Interestingly, stimulation of plant immunity by flashes of UV-C light does not come at the price of reduced growth, a common feature among SA analogs or SA or PRIs stimulating SA biosynthesis in plants. Preliminary observations even suggest that they have the potential of stimulating plant tolerance against different forms of abiotic stress, which is consistent with what is known about the hub role of NPR1 in immune and tolerance responses triggered by SA.