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Source: Van Oosten & Besford (1995), Van Oosten et al. (1995).

* Plants were grown at different atmospheric CO2 concentrations: control, 350 mmol CO2 mol-1; high, 700 mmol CO2 mol-1.

Source: Van Oosten & Besford (1995), Van Oosten et al. (1995).

* Plants were grown at different atmospheric CO2 concentrations: control, 350 mmol CO2 mol-1; high, 700 mmol CO2 mol-1.

less. Via a signal-transduction pathway, which also involves phytohormones, the sugar-sensing mechanism regulates the transcription of nuclear encoded photosynthesis-associated genes (Rolland et al. 2006). Among the first photosynthetic proteins that are affected are the small subunit of Rubisco and Rubisco activase. Upon longer exposure, the level of thylakoid proteins and chlorophyll is also reduced (Table 17).

The down-regulation of photosynthesis at elevated CO2 has led to the discovery of sugar-sensing in plants, but it has recently become clear that the signaling pathway is intricately involved in a network regulating acclimation to other environmental factors, including light and nutrient availability as well as biotic and abiotic stress (Rolland et al. 2002). Down-regulation of photosynthesis in response to long-term exposure to elevated CO2 has important global implications. The capacity of terrestrial ecosystems to sequester carbon appears to be saturating, leaving a larger proportion of human carbon emissions in the atmosphere, and accelerating the rate of global warming (Canadell et al. 2007).

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