title: Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with "antisense" rbcS : IV. Impact on photosynthesis in conditions of altered nitrogen supply.
abstract: The effect of nitrogen supply during growth on the contribution of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) to the control of photosynthesis was examined in tobacco (Nicotiana tabacum L.). Transgenic plants transformed with antisense rbcS to produce a series of plants with a progressive decrease in the amount of Rubisco were used to allow the calculation of the flux-control coefficient of Rubisco for photosynthesis (CR). Several points emerged from the data: (i) The strength of Rubisco control of photosynthesis, as measured by CR, was altered by changes in the short-term environmental conditions. Generally, CR was increased in conditions of increased irradiance or decreased CO2. (ii) The amount of Rubisco in wild-type plants was reduced as the nitrogen supply during growth was reduced and this was associated with an increase in CR. This implied that there was a specific reduction in the amount of Rubisco compared with other components of the photosynthetic machinery. (iii) Plants grown with low nitrogen and which had genetically reduced levels of Rubisco had a higher chlorophyll content and a lower chlorophyll a/b ratio than wild-type plants. This indicated that the nitrogen made available by genetically reducing the amount of Rubisco had been re-allocated to other cellular components including light-harvesting and electron-transport proteins. It is argued that there is a "luxury" additional investment of nitrogen into Rubisco in tobacco plants grown in high nitrogen, and that Rubisco can also be considered a nitrogen-store, all be it one where the opportunity cost of the nitrogen storage is higher than in a non-functional storage protein (i.e. it allows for a slightly higher water-use efficiency and for photosynthesis to respond to temporarily high irradiance).
authors.affiliation: Lehrstuhl für Pflanzenphysiologie, Postfach 101251, W-8580, Bayreuth, FRG.
authors.forename: W P
authors.initials: WP
authors.lastname: Quick
authors.forename: K
authors.initials: K
authors.lastname: Fichtner
authors.forename: E D
authors.initials: ED
authors.lastname: Schulze
authors.forename: R
authors.initials: R
authors.lastname: Wendler
authors.forename: R C
authors.initials: RC
authors.lastname: Leegood
authors.forename: H
authors.initials: H
authors.lastname: Mooney
authors.forename: S R
authors.initials: SR
authors.lastname: Rodermel
authors.forename: L
authors.initials: L
authors.lastname: Bogorad
authors.forename: M
authors.initials: M
authors.lastname: Stitt