Relationship of photosynthetic acclimation to changes of Rubisco activity in field-grown winter wheat and barley during growth in elevated carbon dioxide
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- Sicher, R.C. & Bunce, J.A. Photosynthesis Research (1997) 52: 27. doi:10.1023/A:1005874932233
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The responses of photosynthesis, Rubisco activity, Rubisco protein, leaf carbohydrates and total soluble protein to three carbon dioxide treatments were studied in winter wheat [Triticum aestivum (L.)] and barley [Hordeum vulgare (L.)]. Barley and wheat plants were grown in small field plots during 1995 and 1996 in clear, acrylic chambers (1.2–2.4 m2) and were provided with continuous carbon dioxide fertilization at concentrations of 350, 525 and 700 μmol mol−1. Photosynthetic rates of barley penultimate leaves and wheat flag leaves measured at growth carbon dioxide concentrations decreased with leaf age in all three CO2 treatments during 1995 and 1996. Photosynthetic acclimation to elevated CO2 was observed on seven of eight measurement dates for barley and ten of eleven measurement dates for wheat over both years. Initial Rubisco activity, total soluble protein and Rubisco protein in barley penultimate leaves and wheat flag leaves also decreased with leaf age. Total Rubisco activity was not used because of enzyme degradation. There was a significant CO2 treatment effect on initial Rubisco activity, total soluble protein and Rubisco protein for wheat in 1995 and 1996 and for barley in 1995. Responses of barley penultimate leaf Rubisco activity and leaf protein concentrations to elevated carbon dioxide were nonsignificant in 1996. A significant CO2 treatment effect also was detected when means of Rubisco activity, soluble protein and Rubisco protein for wheat flag leaves were combined over harvests and years. These three flag leaf parameters were not significantly different in the 350 and 525 μmol mol−1 CO2 treatments but were decreased during growth in 700 μmol mol−1 CO2 relative to the other two CO2 treatments. Ratios of photosynthesis at 700 and 350 μmol mol−1 were compared to ratios of Rubisco activity at 700 and 350 μmol mol−1 using wheat flag leaf data from 1995 and 1996. Regression analysis of these data were linear [y = 0.586 + 1.103t x (r2 = 0.432)] and were significant at P ≤ 0.05. This result indicated that photosynthetic acclimation was positively correlated with changes of initial Rubisco activity in wheat flag leaves in response to CO2 enrichment. Effects of elevated CO2 on wheat leaf proteins during 1995 and 1996 and on barley during 1995 were consistent with an acceleration of senescence.