Poster: Photosynthesis (carbon)
Abs #
229: Activity, expression and localization of NADP-ME isoforms in a C4 system that lacks Kranz anatomy
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Presenter: |
Estavillo, Gonzalo M., monsa@ufl.edu |
Authors | Estavillo, Gonzalo M. (A) Rao, Srinath K. (A) Reiskind, Julia B. (A) Bowes, George (A) | | Affiliations: |
(A): Department of Botany, University of Florida
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Hydrilla verticillata is a facultative C4 plant that switches from a C3 to a C4 system under low CO2. In the C4 leaf NADP-malic enzyme (NADP-ME) concentrates CO2 in the chloroplast for fixation by Rubisco. Increased NADP-ME activity and protein accompanying C4 induction are reported. Three full-length cDNAs encoding NADP-ME were sequenced from Hydrilla: HvMe1, HvMe2, and HvMe3. The objective of this research is to determine which isoform operates in the C4 cycle. Activity analyses, expression profiles and localization studies were performed. NADP-ME activity was three-fold higher in C4 than in C3 leaf extracts during the first four hours of light. Anti-NADP-ME against rice chloroplastic recombinant enzyme recognized a 64-66 kD band from chloroplasts of both light harvested leaf types. Two bands of higher mass were detected primarily in the cytoplasmic fraction when probed with anti-NADP-ME against the maize chloroplastic recombinant C4 enzyme. HvMe2 transcripts were detected only in C4 leaves. Expression occurred with two hours light exposure and had a half-life of 60 minutes. In contrast, HvMe1 and HvMe3 were expressed in both C3 and C4 leaves, and the timing and regulation differed from HvMe2. Expression of HvMe3 appeared to be constitutive and not light regulated. However, HvMe1 transcripts transiently appeared after four and one hours in the light in C3 and C4 plants, respectively. Circumstantial evidence from the presence of HvMe2 mRNA in C4 plants and its deduced pI (8.9), suggest that this may be the isoform responsible for decarboxylation in C4 Hydrilla leaves. Kinetic studies with recombinant protein are underway to further characterize the roles of the three Hydrilla NADP-ME isoforms. Supported by USDA NRICGP 98-35306-6449 and 2002-35318-12540.
