CEFOBI   05405
CENTRO DE ESTUDIOS FOTOSINTETICOS Y BIOQUIMICOS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Fumarate and cytosolic pH coordinate the synthesis or comsuption of C4 organic acid in Arabidopsis thaliana
Autor/es:
ARIAS, C. L.; ANDREO, C. S.; DRINCOVICH, M. F.; GERRARD WHEELER, M. C.
Lugar:
Mar del Plata
Reunión:
Congreso; XXIX Reunión Argentina de Fisiología Vegetal; 2012
Institución organizadora:
Sociedad Argentina de Fisiología Vegetal
Resumen:
A.
thaliana is a plant species that
accumulates high levels of organic acids and uses them as carbon, energy and
reducing power sources. Among the enzymes that metabolize these compounds one
of the most important is malic enzyme (ME), which is present as a multigene
family. In this regard, NADP-ME2 is located in the cell cytosol of all Arabidopsis
organs being able to catalyze both the forward (oxidative decarboxylation of
malate) and reverse (reductive carboxylation of pyruvate) ME reactions. Particularly,
both NADP-ME2 activities are regulated by fumarate. However, it is unclear
which one is prevailing in vivo and
whether this metabolite may influence the direction of the reaction in any
condition. In the present work, an analysis at several pHs was performed using
the recombinant enzyme. The results indicated a pH-dependence of the fumarate modulation
with opposite behavior on the two activities analyzed. In contrast to the high
activation by fumarate observed at pH 7.5, the decarboxylation is not longer
activated at pH 7. Instead, in the latter situation, fumarate acted as an
inhibitor. Furthermore, the degree of activation for the carboxylation is close
10 times higher at pH 7 than at pH 7.5. Thus, at pH 7 a strong preference of
the reverse reaction over the forward one was observed, while at pH 7.5 the
opposite is true. Thereby, the concerted and specific fumarate regulation of
both reactions by changes in the cytosolic pH would direct the net flux through
this key metabolic point, leading to the synthesis or the degradation of C4
compounds according to the physiological context. The cellular conditions are a
reflection of the highly varying environments at which plants are exposed. In
this regard, a possible mechanism involving diurnal-nocturnal pH fluctuations,
NADP-ME2 and the cytosolic fumarase isoform that convert ME substrate into ME
modulator is discussed.