Regulation and Localization of Key Enzymes during the Induction of Kranz-Less, C4-Type Photosynthesis in Hydrilla verticillata

Abstract

Kranz-less, C4-type photosynthesis was induced in the submersed monocot Hydrilla verticillata (L.f.) Royle. During a 12-d induction period the CO2 compensation point and O2 inhibition of photosynthesis declined linearly. Phosphoenolpyruvate carboxylase (PEPC) activity increased 16-fold, with the major increase occurring within 3 d. Asparagine and alanine aminotransferases were also induced rapidly. Pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (ME) activities increased 10-fold but slowly over 15 d. Total ribulose-1,5-bisphosphate carboxylase/oxygenase activity did not increase, and its activation declined from 82 to 50%. Western blots for PEPC, PPDK, and NADP-ME indicated that increased protein levels were involved in their induction. The H. verticillata NADP-ME polypeptide was larger (90 kD) than the maize C4 enzyme (62 kD). PEPC and PPDK exhibited up-regulation in the light. Subcellular fractionation of C4-type leaves showed that PEPC was cytosolic, whereas PPDK and NADP-ME were located in the chloroplasts. The O2 inhibition of photosynthesis was doubled when C4-type but not C3-type leaves were exposed to diethyl oxalacetate, a PEPC inhibitor. The data are consistent with a C4-cycle concentrating CO2 in H. verticillata chloroplasts and indicate that Kranz anatomy is not obligatory for C4-type photosynthesis. H. verticillata predates modern terrestrial C4 monocots; therefore, this inducible CO2-concentrating mechanism may represent an ancient form of C4 photosynthesis.

Induction of a C4-Like Mechanism of CO2Fixation in Egeria densa, a Submersed Aquatic Species

“…In this species after a 12-d induction period, the CO 2 compensation point declines, together with the O 2 inhibition of photosynthesis (Magnin et al, 1997). With this effect, PEPC, Asn, and Ala aminotransferases activities increase very rapidly (with the major increase in 3 d), with a slower but considerable increase of NADP-malic enzyme (NADP-ME) and pyruvate phosphate dikinase activities (Magnin et al, 1997). In contrast, the levels of Rubisco remain constant during this period.…”

“…These effects produce gasexchange and biochemical modifications that demonstrate a shift from C 3 to C 4 photosynthesis in the leaves (Bowes and Salvucci, 1989), but without having the characteristics of a typical Kranz anatomy . In this species after a 12-d induction period, the CO 2 compensation point declines, together with the O 2 inhibition of photosynthesis (Magnin et al, 1997). With this effect, PEPC, Asn, and Ala aminotransferases activities increase very rapidly (with the major increase in 3 d), with a slower but considerable increase of NADP-malic enzyme (NADP-ME) and pyruvate phosphate dikinase activities (Magnin et al, 1997).…”

Biochemical and biophysical CO2 concentrating mechanisms in two species of freshwater macrophyte within the genus Ottelia (Hydrocharitaceae)

“…However, NAD-ME actitvity was not measured and the activity of NADP-ME was about half that of PEPC so it is not impossible that NAD-ME is also involved in decarboxyation in this species. H. verticillata is also assumed to belong to the NADP-ME sub-group (Bowes 2011;Bowes et al 2002) but much more evidence is available to support this contention since physiological characteristics changed in parallel to NADP-ME activity and oxygen inhibition measurements are consistent with high concentrations of CO 2 being generated in the chloroplast where NADP-ME is located (Magnin et al 1997;Reiskind et al 1997). In H. verticillata, the ratio of NAD-ME to NADP-ME is about five, much less than that found in the two species of Ottelia studied here (Table 4).…”

The Role of the C4 Pathway in Carbon Accumulation and Fixation in a Marine Diatom

“…The absence of upstream targeting sequences adjacent to the genes for PEPCase and PPDK in T. pseudonana is consistent with cytoplasmic localizations. The localization of PEPCase in the cytoplasm provides the necessary intracellular compartmentalization for simultaneous carbon fixation by PEPCase and Rubisco in a single cell (Magnin et al, 1997;Voznesenskaya et al, 2002). PEPCKase localization cannot be evaluated with certainty from the gene targeting sequence of T. pseudonana, but its activity was found to follow that of Rubisco in crude cell fractions of T. weissflogii (Reinfelder et al, 2000) and PEPCKase protein was immunolocalized within the chloroplast of the marine diatom Skeletonema costatum (Cabello-Pasini et al, 2001).…”