In the many previous studies of plants' response to salt, iron and other stresses, "the plant is generally taken as a single, homogeneous entity", Benfey said. "We've asked if that is appropriate, and the answer is a very loud and clear no."

Benfey examined cells taken from the roots of the model mustard plant Arabidopsis after they were exposed to high salt or low iron. Genomic profiles of root cells taken from the various zones revealed highly specific reactions to each of the stresses.

Out of the thousands of plant genes, only 244-those that set cells' identity-held steady with either stress. The results show that the vast majority of plant genes rise and fall in activity as a reaction to the prevailing environment.

"It shows that there are core genes and there are responsive genes - there is both a hard-wired part and a part that is extremely sensitive to the environment," Benfey said.

And, he added, the precise divide between the two might depend on where exactly you happen to look. The findings of the study have appeared in Science Express, the online version of the journal Science