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Title: THE EXCEPTIONAL LOW TEMPERATURE TOLERANCE OF C4 PHOTOSYNTHESIS IN MISCANTHUS X GIGANTEUS CORRESPONDS TO A LOWER ACTIVATION ENERGY OF RUBISCO

Author
item NAIDU, SHAWNA - UNIVERSITY OF ILLINOIS
item SZAREJKO, JOHN - UNIVERSITY OF ILLINOIS
item RAMIG, KELLY - UNIVERSITY OF ILLINOIS
item Portis Jr, Archie
item LONG, STEPHEN - UNIVERSITY OF ILLINOIS

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2005
Publication Date: 7/16/2005
Citation: Naidu, K.M., Szarejko, S.L., Ramig, K.M., J.M., Portis Jr, A.R., Long, S.P. 2005. The exceptional low temperature tolerance of c4 photosynthesis in miscanthus x giganteus corresponds to a lower activation energy of rubisco [abstract]. Plant Biology Annual Meeting. Paper No. 262. Available: http://abstracts.aspb.org/pb2005/public/P43/7406.html.

Interpretive Summary:

Technical Abstract: Among the few cold-tolerant C4 species, the grass Miscanthus x giganteus is exceptional in being one of the most productive. In replicated trials in SE Britain (52oN) it achieved annual net primary productivities >27 t/ha dry matter, the highest plant productivity recorded in Britain. When grown at 14oC, photosynthesis in Zea mays leaves is severely (~80%) reduced relative to leaves grown at 25oC, and this corresponds with decreased content of phosphoenol-pyruvate carboxylase (PEPc), pyruvate orthophosphate dikinase (PPDK), and 1-5 ribulose bisphosphate carboxylase/oxygenase (Rubisco). Metabolic control of light-saturated C4 photosynthesis has been shown to reside with these enzymes. Although M. x giganteus uses the same NADP-Malic enzyme C4 dicarboxylic acid pathway as Z. mays, when grown at 14oC its leaves show high photosynthetic rates and no reduction in amounts of these enzymes relative to leaves grown at 25oC. While higher protein content may contribute to higher photosynthetic capacity at low temperature, enzyme adaptation may also play a role. Does such adaptation exist in M. x giganteus and does it relate to in vivo properties of photosynthesis? We measured the temperature response (5-40oC) of in vitro enzyme function in crude protein extracts from M. x giganteus and Z. mays leaves collected from the field in July/August (~22oC average daytime air temperature). Additionally, the temperature response (5-35oC) of PEP carboxylation and PEP regeneration capacity (Vpr) in vivo were determined on intact leaves from plants grown in controlled environments (25oC). Activation energies (Ea) were derived from these responses. At low temperature (5-15oC), there was no significant difference with species in Ea for PPDK, while Ea of PEPc (p < 0.05) and Rubisco (p < 0.1) were significantly lower in M. x giganteus. Additionally, Ea of Vpr was significantly lower (p < 0.1) than in Z. mays. Therefore, this capacity would decline less in M. x giganteus with temperature. At light saturation and normal CO2 concentration, C4 photosynthesis is limited by Vpr. The in vitro analysis showed that of the two enzymes assumed to exert metabolic control on Vpr, only Rubisco and not PPDK had significantly lower Ea. Therefore, we conclude that in addition to maintenance of protein contents in leaves grown at low temperature, a greater Kcat for Rubisco at low temperature may be critical to the ability of M. x giganteus to realize high photosynthesis at sub-optimal temperatures.