Ozone treatment affects pigment precursor metabolism in pine seedlings |
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| Authors: | Y Shamay V I Raskin A S Brandis H E Steinberger J B Marder A Schwartz |
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| Institution: | Department of Agricultural Botany, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel;Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel;Department of Plant Sciences, The Weizmann Institute of Science, P.O. Box 12, Rehovot 76100, Israel |
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| Abstract: | Five‐week‐old seedlings of Pinus halepensis Mill. and Pinus brutia Ten. were exposed to air polluted with ozone (O3) (250 nl l?1, 12 h day?1 for 4 days) or to ambient air containing ca 10–20 nl l?1 O3, in the light (180 μmol m?2 s?1 photosynthetic photon flux density PPFD], 12 h day?1) and then fed for 24 h in the light (100 μmol m?2 s?1 PPFD) with various radioactive precursors of chlorophyll (Chl) and carotene biosynthesis: 5‐4‐14C]‐aminolevulinic acid (14C‐ALA), l ‐14C(U)]‐glutamic acid (14C‐Glu), or d ,l ‐2‐14C]‐mevalonic acid (14C‐MVA). Pigments were then extracted from cotyledons and fully expanded needles. Chl a and carotene were separated by thin‐layer chromatography and high‐performance liquid chromatography and their specific activities were determined. 14C‐ALA and 14C‐Glu labels were incorporated into Chl a and carotene. Exposure to O3 did not inhibit incorporation of 14C‐ALA into Chl a molecules, but hydrolysis of Chl a showed that O3 inhibited phytol labelling of Chl a. Labelling of carotene was also inhibited by O3, but not when 14C‐MVA was used as the label. These data suggest that O3 treatment inhibits (directly or indirectly) the biosynthesis of isoprenoids from products of ALA and Glu metabolism in the plastid, but not from MVA in the cytosol. This inhibition was more prominent when 14C‐ALA was used as the label than when 14C‐Glu was the labelling precursor. A significant increase in pheophorbide a, a tetrapyrrole component of Chl a labelling, and a concomitant decrease in phytol labelling was observed following incubation of O3‐treated pine seedlings with 14C‐ALA and 14C‐Glu. Stronger inhibition of carotene biosynthesis and activation of Chl a tetrapyrrole labelling by 14C‐ALA (in comparison with 14C‐Glu) indicated that exposure to O3 inhibits the conversion of ALA to Glu as the first step in ALA catabolism. These results also suggested a more intensive Glu metabolism (in comparison with ALA) for carotene biosynthesis in the cytosol, as well as cooperation between two pathways of isopentenyl diphosphate biosynthesis. |
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