THE ROLE OF SOLAR UV-B IN GROWTH REGULATION OF CRESS (Lepidium sativum L.) SEEDLINGS

Abstract— Action spectra for growth reduction within the 260 nm to 305 nm waveband were measured for hypocotyls and roots of young etiolated cress ( Lepidium sativum ) seedlings. The action spectra show increasing photon effectiveness with decreasing wavelength and resemble those due to DNA damage. Using short term irradiations, photoreceptors absorbing in the visible range were found to be without influence. As no photoreactivation could be found and the seedlings showed no outward signs of damage, this growth effect may be due to a UV photoreceptor. A modeling calculation was carried out to estimate the effectiveness of solar UV-B on this response both under present conditions and under reduced ozone levels. Even under present conditions, solar UV-B could be involved in regulating growth during the period immediately after germination.