Growth, structure, stomatal responses and secondary metabolites of birch seedlings ( Betula pendula) under elevated UV-B radiation in the field

Abstract

Three-year-old birch (Betula pendula Roth.) seedlings were exposed, in the field, to supplemental levels of UV-B radiation. Control seedlings were exposed to ambient levels of UV radiation, using arrays of unenergized lamps. A control for UV-A radiation was also included in the experiment. Enhanced UV-B radiation had no significant effects on height growth, and shoot and root biomass of birch seedlings. Leaf expansion rate increased transiently in the middle of the growing period in enhanced UV-B-and UV-A-exposed plants; however, final leaf size and relative growth rate remained unaffected. Leaf thickness and spongy intercellular spaces were increased in UV-B-exposed seedlings along with increased density of glandular trichomes. At the ultrastructural level, enhanced UV-B increased the number of cytoplasmic lipid bodies, and abnormal membrane whorls were found. Both enhanced UV-B and UV-A radiation induced swelling of chloroplast thylakoids. Stomatal density and conductance were significantly increased by elevated UV-B radiation. UV-A radiation increased the length and width of stomata, whereas UV-B radiation had only a marginal effect on stomatal size. UV-A and enhanced UV-B radiation attenuated the appearance of necrotic spots in autumn, probably caused by the fungus Pyrenopeziza betulicola, suggesting a direct harmful effect of UV on pathogens or reduced susceptibility to pathogens in UV-exposed seedlings. Secondary metabolite analysis showed increases in (+)-catechin, quercetin, cinnamic acid derivative, apigenin and pentagalloylglucose in birch leaves under enhanced UV-B radiation. Negative correlations between apigenin, and particularly quercetin concentrations and lipid peroxidation levels indicated an antioxidant role of secondary metabolites in birch leaves exposed to UV-B radiation.

Stomatal Frequency Change Over Altitudinal Gradients: Prospects for Paleoaltimetry

“…Plants at high altitudes may suffer increased vulnerability to the enhanced UV-B levels as the short and cool growing seasons can delay the development of protective epidermis, cuticles and epicuticular wax (DeLucia et al 1992;Turunen and Latola 2005). As a response to enhanced UV-B in experimental settings, most plant species exhibit a decrease in stomatal density (Dai et al 1995;Visser et al 1997;Keiller and Holmes 2001;Poulson et al 2002;Gitz et al 2005), but increases have also been observed (Stewart and Hoddinott 1993;Kostina et al 2001). According to Nogues et al (1998Nogues et al ( , 1999 the increased UV-B radiation at higher altitudes limits stomatal opening, and hence reduces stomatal conductance.…”

Effects of enhanced UV-B radiation on growth and photosynthetic responses of four species of seedlings in subalpine forests of the eastern Tibet plateau

“…Consistent with these results, increase of UV-B radiation led to shrinkage and distortion of leaves in A. mono and S. hemsleyi seedlings, and reduced leaf number and leaf weight of A. mono seedlings. In addition, a common response of deciduous trees to UV-B radiation is thickening leaves due to different anatomic changes such as increased thickness of palisade tissue, induced more spongy mesophyll and intercellular space (Nagel et al, 1998;Kostina et al, 2001). In present study, elevated UV-B radiation enhanced thickness of leaf and spongy mesophyll in S. hemsleyi seedlings.…”

Sustainable Agriculture Reviews

“…Thicker leaves enable plants to attenuate more UV-B radiation and hence to protect palisade layers from deleterious effects of irradiation. Nevertheless, UV-induced ultrastructural changes in birch indicate that increase in leaf thickness did not completely provide protection for palisade mesophyll against UV-B radiation in birch seedling (Kostina et al 2001 ). Nevertheless, UV-induced ultrastructural changes in birch indicate that increase in leaf thickness did not completely provide protection for palisade mesophyll against UV-B radiation in birch seedling (Kostina et al 2001 ).…”

“…Leaf expansion and anatomical development are altered by UV-B in case of many agronomic and tree species. Kostina et al ( 2001 ) reported changes at the ultrastructural level in response to enhanced UV-B exposure in birch seedling (Betula pendula) and observed the rise to numerous cytoplasmic lipid bodies and abnormal membrane whorls. For example, UV-B radiation caused increased leaf thickness in Brassica napus L. (Cen and Bornman 1993 ) whereas, Staxen and Bornman ( 1994 ) reported that Petunia hybrid plants grown without UV-B irradiance had thicker leaves than UV-B-irradiated plants.…”