
%0 Journal Article
%A Bowes, George 
%A Rao, Srinath K. 
%A Estavillo, Gonzalo M. 
%A Reiskind, Julia B. 
%T C<emph type="8">4</emph> mechanisms in aquatic angiosperms: comparisons with terrestrial C<emph type="8">4</emph> systems
%J Functional Plant Biology
%D 2002/03/19
%V 29
%N 3
%P 379-392
%K C3&#8211;C4 intermediate, C4 photosynthesis, CO2 concentrating mechanism, Egeria, Eleocharis, Hydrilla, Kranz anatomy, NADP-ME, Neostapfia, Orcuttia, phosphoenolpyruvate carboxylase, Rubisco, Sagittaria, Thalassiosira, Tuctoria, Udotea.
%R https://doi.org/10.1071/PP01219
%U https://www.publish.csiro.au/paper/PP01219 
%X Aquatic C4 photosynthesis probably arose in response to dissolved CO2 limitations, possibly before its advent in terrestrial plants. Of over 7600 C4 species, only about a dozen aquatic species are identified. Amphibious Eleocharis species (sedges) have C3&#8211;C4 photosynthesis and Kranz anatomy in aerial, but not submersed, leaves. Aquatic grasses have aerial and submersed leaves with C4 or C3&#8211;C4 photosynthesis and Kranz anatomy, but some lack Kranz anatomy in the submersed leaves. Two freshwater submersed monocots, Hydrilla verticillata and possibly Egeria densa, are C4 NADP-malic enzyme (NADP-ME) species. A marine macroalga, Udotea flabellum (Chlorophyta), and possibly a diatom, are C4, so it is not confined to angiosperms. Submersed C4 species differ from terrestrial in that &#946;-carboxylation is cytosolic with chloroplastic decarboxylation and Rubisco carboxylation, so the C4 and Calvin cycles operate in the same cell without Kranz anatomy. Unlike terrestrial plants, Hydrilla is a facultative C4 that shifts from C3 to C4 in low &#91;CO2&#93;. It is well documented, with C4 gas exchange and pulse-chase characteristics, enzyme kinetics and localization, high internal &#91;CO2&#93;, relative growth rate, and quantum yield studies. It has multiple phosphoenolpyruvate carboxylase isoforms with C3-like sequences. Hvpepc4 appears to be the photosynthetic form induced in C4 leaves, but it differs from terrestrial C4 isoforms in lacking a C4 signature Serine. The molecular mass of NADP-ME (72 kDa) also resembles a C3 isoform. Hydrilla belongs to the ancient Hydrocharitaceae family, and gives insight to early C4 development. Hydrilla is an excellent &#8216;minimalist&#8217; system to study C4 photosynthesis regulation without anatomical complexities. 
