NEW DELHI: The power of touch extends even to plants, new research reveals. Gently rubbing plants with your fingers can make them less susceptible to disease according to a paper in the open access scientific journal, BMC Plant Biology.Scientists from the universities of Fribourg in Switzerland and Milan in Italy found that rubbing leaves of thale cress plants (Arabidsopsis thaliana) between the thumb and forefinger activates an innate defence mechanism. Within minutes, biochemical changes occur, causing the plant to become more resistant to grey mould fungus (Botrytis cinerea) — a common infestation.Rubbing leaves is a form of mechanical stress. Plants frequently have responses to mechanical stress. Some responses are well-known, like the snapping shut of a Venus flytrap , the folding leaflets of a touch-me-not plant (Mimosa pudica). But there are several unseen responses too. Plants launch an arsenal of 'invisible' responses to mechanical stress , including changes at the molecular and biochemical level.Rubbing thale cress leaves triggered a host of internal changes. Genes related to mechanical stress were activated. Levels of reactive oxygen species increased and the protective outer layer of the leaf became more permeable, presumably to aid the escape of various biologically active molecules that were detected and which are thought to contribute to the observed immune response. This data could also suggest that the mechanical stress is perceived by mechano-sensors that subsequently initiate resistance.Similar effects occur when plants are physically wounded. The same team of scientists had earlier showed how physically wounding thale cress increases levels of reactive oxygen species, also triggering a strong, transient immunity to the grey mould fungus. Here they show primarily the same thing, but in response to an extremely gentle form of wounding — mechanical stimulation by touch — that unlike wounding, leaves cells intact.Wounding and rubbing exemplify how plants can react to a situation that in principle could cause them to become more vulnerable. Instead, they react to touch by deploying a carefully orchestrated defence response — an evolutionary skill that presumably boosts survival.