Effects of Enhanced UV-B Radiation on Germination, Seedling Growth, Leaf Anatomy and Pigments of Some Crop Plants

Abstract

Summary Cucumis sativus , Phaseolus vulgaris and Raphanus sativus seedlings were continuously irradiated with different levels of UV-B by using cut-off filter systems at a constant irradiance of visible light for up to 12 days. The rate of germination decreased under the highest UV-B irradiance to about 60% of the value of control seeds irradiated with small amounts of UV-B. With rising UV-B levels the growth of hypocotyls was increasingly inhibited. In Cucumis even the lowest level of UV-B irradiation prevented the elongation of hypocotyls. Fresh weight, dry weight and leaf area were smaller in all plants exposed to UV-B. The greatest effect was obtained on leaf area whereas dry weight was only slightly decreased. The contents of photosynthetic pigments were reduced to a similar extent as leaf area. Accumulation of flavonoids increased in radish seedlings, but decreased in cucumber and bean seedlings. Thickness of abaxial and adaxial epidermis of cucumber cotyledons was reduced, whereas the palisade parenchyma became thicker. The leaf surface structure was progressively damaged with increasing UV-B irradiance as shown by SEM pictures. The stomatal number on both sides was markedly lower in UV-B irradiated cucumber cotyledons. Enhanced levels of UV-B irradiation caused reduced growth and pigment accumulation in all plant species investigated. Cucumis, as the most UV-B sensitive plant, was already markedly affected by moderate UV-B irradiation levels.