LAUSR

BACKGROUND AND AIMS UV-B radiation damages the DNA, cells, and photosynthetic apparatus of plants. Plants commonly prevent this damage by synthetizing UV-B protective compounds. Recent laboratory experiments in Arabidopsis and cucumber indicate that plants can also respond to UV-B stress with endopolyploidy. Here we test the generality of this response in natural plant populations, considering their monocentric or holocentric chromosomal structure. METHODS We measured the endopolyploidy index (flow cytometry) and the concentration of UV-B protective compounds in leaves of 12 herbaceous species (1007 individuals) from forest interiors and neighboring clearings where they were exposed to increased UV-B radiation (103 forest+clearing populations). Then we analyzed the data using phylogenetic mixed models. KEY RESULTS Concentration of UV-B protectives increased with UV-B doses estimated from hemispheric photographs of the sky above sample collection sites, but the increase was more rapid in species with monocentric chromosomes. Endopolyploidy index increased with UV-B doses and with concentrations of UV-B absorbing compounds only in species with monocentric chromosomes, while holocentric species responded negligibly. CONCLUSIONS Endopolyploidy seems to be a common response to increased UV-B in monocentric plants. Low sensitivity to UV-B in holocentric species might relate to their success in high-UV stressed habitats and corroborates the hypothesized role of holocentric chromosomes in plant terrestrialization.