Modulation of carbon and nitrogen metabolism, and of nitrate reductase, in untransformed and transformed Nicotiana plumbaginifolia during CO 2 enrichment of plants grown in pots and in hydroponic culture

Abstract

hydroponic culture have greater access to N than those grown in pots. Regardless of the culture method, CO 2 enrichment has a direct eect on NR mRNA stability.Abbreviations: Asn = asparagine; Asp = aspartate; Gln = glutamine; Glu = glutamate; GS = glutamine synthetase; GUS = b-glucuronidase; NR = nitrate reductase; PEPCase = phospho-

The nitrate and ammonium nitrate supply have a major influence on the response of photosynthesis, carbon metabolism, nitrogen metabolism and growth to elevated carbon dioxide in tobacco

“…these processes lag behind carbon fixation and growth in elevated [CO 2 ], two recent studies show that amino acid levels remain high in elevated [CO 2 ] in well-fertilized plants (Ferrario-Mery et al 1997;Geiger et al 1998), even increasing in young seedlings where the growth stimulation is very marked (Geiger et al 1998).…”

“…Firstly, without information about the changes in the major nitrogen-containing metabolites it will be impossible to understand how nitrogen assimilation metabolism is stimulated to meet the increased requirement for reduced nitrogen during faster growth in elevated [CO 2 ]. Secondly, since increased rates of plant growth in elevated [CO 2 ] may exacerbate an existing or incipient nitrogen limitation (Hocking & Meyer 1991a;Coleman, McConnaughay & Bazzaz 1993;Rogers et al 1996aRogers et al , 1996bFerrario-Mery et al 1997), investigations of nitrogen metabolism are urgently needed in parallel with investigations of photosynthesis, carbohydrate metabolism and growth, in order to distinguish between direct effects of enhanced [CO 2 ] and increased levels of carbohydrates, and indirect effects due to an accentuated nitrogen limitation.…”

“…There is conflicting evidence with respect to the effect of elevated [CO 2 ] on nitrate reductase (NR) activity. Although elevated [CO 2 ] led to a small increase of NR activity in mustard (Maeskaya et al 1990) and Vigna radiata (Sharma & Sen Gupta 1990), it produced a two-fold decrease of NR activity in wheat (Hocking & Meyer 1991a), maize (Purvis, Peters & Hageman 1974), and a 15-25% decrease in Nicotiana plumbaginifolia (Ferrario-Mery et al 1997). It also led to a decrease of nitrite reductase activity in lettuce (Besford & Hand 1989).…”

“…The decreased concentration of total and organic nitrogen and decreased activity of NR in elevated [CO 2 ] (see above) might therefore be due to a depletion of nitrate in the soil and plant, rather than a fundamental inability to increase nitrate uptake and assimilation to match the increased rates of photosynthesis in elevated [CO 2 ]. Indeed, there are reports that the nitrogen content does not decrease so markedly in elevated [CO 2 ] in well-fertilized plants (Rogers et al 1996a(Rogers et al , 1996bFerrario-Mery et al 1997).As a second example, although growth in elevated [CO 2 ] sometimes results in a sustained stimulation of photosynthesis (Idso & Kimball 1992;Gunderson, Norby & Wullschleger 1993;Teskey 1995), this initial stimulation is often partially or completely reversed (Stitt 1991;Oechel et al 1993;Sage 1994;Nie et al 1995;Jacob et al 1995). This phenomenon is termed photosynthetic 'acclimation'.…”

“…However, in many other studies with a range of species including wheat (Hocking & Meyer 1991a;Mitchell et al 1994;McKee & Woodward 1994;Rogers et al 1996b;Fangmeier et al 1997), cotton (Wong 1979;Rogers et al 1996a), Xanthium occidentale (Hocking & Meyer 1985), Eucalyptis grandis (Conroy, Milham & Barlow 1992) (Wong 1979;Hocking & Meyer 1991a, 1991bPettersson et al 1993;Rogers et al 1993;McKee & Woodward 1994;Jacob et al 1995;Poorter et al 1997), elevated [CO 2 ] should promote more growth in nitrogen-limiting conditions. Although the increased nitrogen use efficiency in elevated [CO 2 ] is partly due to a decrease of the nitrate content (Purvis et al 1974; Yelle, Gosselin & Trudel 1987;Hocking & Meyer 1985;Hocking & Meyer 1991b;Poorter et al 1997), growth in elevated [CO 2 ] also typically leads to a lower organic nitrogen concentration (see above), indicating that organic nitrogen use efficiency is also improved (Wong 1979;Curtis et al 1989;Garbutt et al 1990;Coleman et al 1991;Hocking & Meyer 1991a, 1991bColeman & Bazzaz 1992;Gries et al 1993;Pettersson et al 1993;Pettersson & MacDonald 1994;Körner & Miglietta 1994;Ferrario-Mery et al 1997;Poorter et al 1997).In the following experiments our main aims were therefore (i) to analyse the effect of elevated [CO 2 ] on plant nitrogen status in plants growing at a range of nitrogen supplies, by mo...…”