Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with ?antisense? rbcS

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).

Energy dissipation is an essential mechanism to sustain the viability of plants: The physiological limits of improved photosynthesis

“…Therefore, it was assumed that the carboxylation is the rate limiting step (Hartmann and Harpel, 1994). Although this view has been revisited because the overexpression of Rubisco did not increase the carboxylation efficiency in transgenic plants (Quick et al, 1992) it is obvious that the carbon flux through the Calvin cycle is far too low compared to the absorption capacity of the plants. A rough estimate from the rate constants and the stoichiometry of the cytochrome f, which is involved in the rate limiting step of the ETR chain (Wilhelm and Wild, 1984), and the RubisCo (as a representative of the whole Calvin cycle) shows that the ETR is potentially up to 10 times high (Raines, 2003).…”

Photosynthetic Pigments, Photosynthesis and Plastid Ultrastructure in RbcS Antisense DNA Mutants of Tobacco {Nicotiana tabacum)

“…The antisense mutants have been used for a wide variety of molecular, bio chemical and physiological studies to examine the mechanisms that regulate Rubisco biosynthesis, and to investigate the control that Rubisco exerts on photosynthesis, plant growth and development (reviewed by Stitt and Schulze, 1994;Rodermel, 1999 Investigations of pigment composition and content in the antisense mutants have focused on chlorophyll. These studies revealed that chloro phyll levels are reduced in plants with very low amounts of Rubisco, but that Chi a/C hi b ratios are only weakly affected in these plants (Quick et al, 1991(Quick et al, , 1992; Jiang and Rodermel, 1995). While this suggests that the composition of the thylakoid membrane is relatively refractory to changes in Rubisco content, chlorophyll fluorescence and flu orescence quenching measurements demonstrated that photosynthesis is inhibited in the antisense plants, especially in mutants with sharp reductions in Rubisco (Quick et al, 1991;1992;Stitt et al, 1991).…”

“…These studies revealed that chloro phyll levels are reduced in plants with very low amounts of Rubisco, but that Chi a/C hi b ratios are only weakly affected in these plants (Quick et al, 1991(Quick et al, , 1992; Jiang and Rodermel, 1995). While this suggests that the composition of the thylakoid membrane is relatively refractory to changes in Rubisco content, chlorophyll fluorescence and flu orescence quenching measurements demonstrated that photosynthesis is inhibited in the antisense plants, especially in mutants with sharp reductions in Rubisco (Quick et al, 1991;1992;Stitt et al, 1991). These experiments further showed that the mutants are photoinhibited at lower light inten sities than in the wild-type (WT), although the precise mechanisms were not investigated.…”

“…The studies of Stitt and his group (Quick et al, 1991(Quick et al, , 1992Stitt et al, 1991) , 1997; 2000). Photosynthetic rates also change markedly as a function of leaf nodal position on the canopy, with rates falling progressively as one moves down the canopy from fully-expanded leaves at the top of the plant to fully-expanded leaves at the base of the plant (Jiang and Rodermel, 1995).…”

Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis

“…Models are a useful tool for identifying these targets (Zhu et al, 2007;von Caemmerer, 2013). Based on studies of steady-state models of photosynthesis, as well as experimental work, several targets for improvement of photosynthesis have been postulated, including the introduction of CO2 concentrating mechanisms in C3 plants (von Caemmerer et al, 2012), increasing concentrations of SBPase (Zhu et al, 2007;Rosenthal et al, 2011) or Rubisco (Quick et al, 1992;Makino, 2003), bypassing photorespiration (Kebeish et al, 2007;von Caemmerer et al, 2012), increasing mesophyll conductance (Flexas et al, 2013), improving Rubsico kinetic properties (Whitney et al, 2001), or redistribution of chlorophyll within the canopy . However, given that different photosynthetic processes may also limit CO2 assimilation under fluctuating irradiance, additional targets can be identified that could contribute to further improvements of biomass production under natural conditions.…”