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. 1983 Nov;73(3):729–734. doi: 10.1104/pp.73.3.729

Effects of Light and Elevated Atmospheric CO2 on the Ribulose Bisphosphate Carboxylase Activity and Ribulose Bisphosphate Level of Soybean Leaves 1

C V Vu 1,2,3, L H Allen Jr 1,2,3, George Bowes 1,2,3
PMCID: PMC1066539  PMID: 16663291

Abstract

Soybean (Glycine max L. Merr. cv Bragg) was grown throughout its life cycle at 330, 450, and 800 microliters CO2 per liter in outdoor controlled-environment chambers under solar irradiance. Leaf ribulose-1,5-bisphosphate carboxylase (RuBPCase) activities and ribulose-1,5-bisphosphate (RuBP) levels were measured at selected times after planting. Growth under the high CO2 levels reduced the extractable RuBPCase activity by up to 22%, but increased the daytime RuBP levels by up to 20%.

Diurnal measurements of RuBPCase (expressed in micromoles CO2 per milligram chlorophyll per hour) showed that the enzyme values were low (230) when sampled before sunrise, even when activated in vitro with saturating HCO3− and Mg2+, but increased to 590 during the day as the solar quantum irradiance (photosynthetically active radiation or PAR, in micromoles per square meter per second) rose to 600. The nonactivated RuBPCase values, which averaged 20% lower than the corresponding HCO3− and Mg2+-activated values, increased in a similar manner with increasing solar PAR. The per cent RuBPCase activation (the ratio of nonactivated to maximum-activated values) increased from 40% before dawn to 80% during the day. Leaf RuBP levels (expressed in nanomoles per milligram chlorophyll) were close to zero before sunrise but increased to a maximum of 220 as the solar PAR rose beyond 1200. In a chamber kept dark throughout the morning, leaf RuBPCase activities and RuBP levels remained at the predawn values. Upon removal of the cover at noon, the HCO3− and Mg2+-activated RuBPCase values and the RuBP levels rose to 465 and 122, respectively, after only 5 minutes of leaf exposure to solar PAR at 1500.

These results indicate that, in soybean leaves, light may exert a regulatory effect on extractable RuBPCase in addition to the well-established activation by CO2 and Mg2+.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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