Carbon and nitrogen metabolism in barley plants exposed to UV‐B radiation

Abstract

The effect of UV-B radiation on FW, leaf and stem length, photosynthetic O2 evolution, levels of carbohydrates and nitrates, and extractable activities of some of the enzymes involved in C and N metabolism was evaluated in barley (Hordeum vulgare L. cv. Express) seedlings during the 9 days following transfer to an UV-B enriched environment. The results show that under our experimental conditions UV-B radiation scarcely affects the photosynthetic competence of barley leaves, expressed as RuBP carboxylase (EC 4.1.1.39) activity, O2 evolution rate and chlorophyll content. Nevertheless, this treatment induced significant alterations of the enzyme activity of nitrate reductase (EC 1.6.6.1) and glutamine synthetase (EC 6.3.1.2), although only after a few days of treatment. The effects were not confined to the exposed tissue, but were detectable also at the root level. In fact, nitrate reductase decreased in response to UV-B in both leaf and root tissue, whereas glutamine synthetase was affected only in the root. In contrast, nitrate content was not influenced by the treatment, neither in root nor in leaf tissue, whilst leaf sucrose diminished in exposed plants only on the last day of treatment.

Impact of solar Ultraviolet-B on the proteome in soybean lines differing in flavonoid contents

“…Sullivan and Teramura (1990) found that UV-induced reductions involving PS in soybean occurred only at high internal CO 2 levels, suggesting that UV-B could lead to increased substrate limitations on photosynthesis. Also, some studies indicated that UV-B could reduce the carbohydrate levels in plants (Quaggiotti et al, 2004;Ghisi et al, 2002). Consistent with these results, the enzymes involved in CO 2 assimilation were suppressed by solar UV-B in this study.…”

“…Reduction of this enzyme under stress conditions has been reported, and this may be a protective mechanism because nitric oxide, an intermediate of nitrogen assimilation, is an active radical (Wang et al, 2004). It has been reported that UV-B can decrease nitrogen assimilation in some plants (Quaggiotti et al, 2004;Ghisi et al, 2002;Balakumar et al, 1999). The reduction of enzymes involved in primary nitrogen and carbon metabolism indicates redirection of carbon and nitrogen resources into other pathways, such as those involved in repair or protection processes.…”

RESPONSES IN NITROGEN MASS AND NITROGEN METABOLISM OF WILD SUGARCANE (<I>SACCHARUM SPONTANEUM</I> L.) CLONES TO ENHANCED UV-B RADIATION UNDER FIELD CONDITIONS

“…Enhanced UV-B radiation inhibited growth and decreased nitrate reductase activity in dragon spruce (Picea asperata Mast.) needles (Yao and Liu, 2007) and in young crop seedlings (Ghisi et al, 2002;Niu et al, 2007;Yao and Liu, 2007). A decrease in photosynthesis or NO 3 -content has been observed in some cases (Rajendiran and Ramanujam, 2006;Yao and Liu, 2007).…”

“…Nitrate reductase activity in plants may also depend on temperature, water conditions, light intensity and UV radiation (Niu et al, 2007;Krywult et al, 2008). Nitrate reductase decreased in response to UV-B in both leaf and root tissue of barley plants, whereas glutamine synthetase was affected only in the root (Ghisi et al, 2002). Glutamine synthetase in leaves and roots is a key enzyme in the route of incorporation of inorganic N into organic compounds (Miflin and Lea, 1980).…”

“…Glutamine synthetase in leaves and roots is a key enzyme in the route of incorporation of inorganic N into organic compounds (Miflin and Lea, 1980). Effects of enhanced UV-B radiation on activities of nitrate reductase and glutamine synthetase lead to changes in free animo acid, total protein contents and N assimilation in leaves and roots, depending on photosynthetic functionality and root growth (Ghisi et al, 2002).…”