Abstract
Elevated CO2 affects plant growth and photosynthesis, which results in changes in plant respiration. However, the mechanisms underlying the responses of plant respiration to elevated CO2 are poorly understood. In this study, we measured diurnal changes in the transcript levels of genes encoding respiratory enzymes, the maximal activities of the enzymes and primary metabolite levels in shoots of Arabidopsis thaliana grown under moderate or elevated CO2 conditions (390 or 780 parts per million by volume CO2, respectively). We examined the relationships between these changes and respiratory rates. Under elevated CO2, the transcript levels of several genes encoding respiratory enzymes increased at the end of the light period, but these increases did not result in changes in the maximal activities of the corresponding enzymes. The levels of some primary metabolites such as starch and sugar phosphates increased under elevated CO2, particularly at the end of the light period. The O2 uptake rate at the end of the dark period was higher under elevated CO2 than under moderate CO2, but higher under moderate CO2 than under elevated CO2 at the end of the light period. These results indicate that the changes in O2 uptake rates are not directly related to changes in maximal enzyme activities and primary metabolite levels. Instead, elevated CO2 may affect anabolic processes that consume respiratory ATP, thereby affecting O2 uptake rates.
Highlights
The atmospheric CO2 concentration has drastically increased in recent decades, and it is expected to increase to double the level that it was before the industrial revolution during this century
Our objectives were as follows: (i) to compare changes in the transcript levels of genes encoding respiratory enzymes in plants grown under elevated CO2 with those in plants grown under moderate CO2, and determine whether changes in gene transcript levels correspond to changes in activities of the enzymes they encode; (ii) to determine which primary metabolites accumulate under elevated CO2; and (iii) to evaluate whether the limiting factor for respiratory rates changes under elevated CO2
The relative growth rate (RGR) of shoots grown under elevated CO2 was higher than that of shoots grown under moderate CO2, except on day 28
Summary
The atmospheric CO2 concentration has drastically increased in recent decades, and it is expected to increase to double the level that it was before the industrial revolution during this century. In most of the C3 species examined so far, the photosynthetic rate on a leaf area basis increases under elevated CO2, the extent of the increase varies among species and among different experimental conditions (Long et al 2004, Leakey et al 2009a). Meta-analyses have shown that respiratory rates on a leaf area basis generally increase under elevated CO2 (Wang and Curtis 2002, Leakey et al 2009a); this is partly attributed to a greater leaf mass per area (LMA) in plants grown under elevated CO2. The respiratory rates on a mass basis are often lower in plants grown under elevated CO2 than in those grown under ambient CO2 (Wang and Curtis 2002, Gonzalez-Meler et al 2004).
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