Effects of ultraviolet irradiation on growth and pigmentation in seedlings

Dark-germinated seedlings of maize, radish, soybean, cucumber and eggplant were grown for 2 or 3 days under ultraviolet light, and the differential effects of UV according to wavelength regions were evaluated. Although the effectiveness of UV irradiation differed somewhat depending on the plant species, generally, four wavelength regions having different effects were discerned. The region from 287 to 302 nm was phytotoxic, causing bronzing (radish), epinasty and blazing (cotyledon, cucumber), formation of brown flecks (soybean), and also severe growth inhibition in hypocotyls. The region from 300 to 338 nm greatly promoted anthocyanin formation and inhibited the shoot elongation. The region from 330 to 370 nm inhibited shoot elongation and promoted cotyledon growth as well as chlorophyll formation. The effects of the region from 384 to 400 nm were generally weak, but in maize coleoptile, radish and soybean hypocotyls this region exerted a distinct inhibition, stronger than the region of 330-370 nm, and in chlorophyll formation in maize coleoptile this region was the most effective of those tested. The above-stated shoot growth inhibition and anthocyanin formation caused by UV were generally greater than those caused by blue or red light, but growth promotion in the cotyledons was smaller.