OBJECTIVETo reveal the effects of UV-B radiation on the growth of medical plant Mentha piperita, simulate an enhanced UV-B radiation and evaluate intensity of radiation on the photosynthesis of M. piperita.

METHODThree different levels of UV-B radiation were set in the experiment which included: natural light control (0 W x m(-2)), light UV-B radiation stress (0.15 W x m(-2)) and heavy UV-B radiation stress (0.35 W x m(-2)). The chloroplast ultrastructure, photosynthesis indexes and chlorophyll fluorescence parameters of the M. piperita were observed under the three treatments.

RESULTAlthough the chloroplast ultrastructure was destroyed to some degree under the light UV-B radiation stress, F(v)/(F)m, F(v)/F(o), qP, phiPS II and ETR could resume to the comparative level of natural light control. At the same time, qN increased firstly and decreased thereafter. But under the high strength UV-B radiation stress, the photosynthetic structures were badly destroyed, which could not recover through protecting mechanism by itself.

CONCLUSIONIt was showed that M. piperita was able to protect photosynthetic structures by increasing respiration and dissipation when photosynthetic capacity reduced under light UV-B radiation stress. It is demonstrated that M. piperita has high adaptation to light UV-B radiation stress, which is kind of promising medical plant for area with higher UV-B radiation.