INVESTIGADORES
SALERNO Graciela Lidia
artículos
Título:
Carbon Cycling in Anabaena sp. PCC 7120. Sucrose Synthesis in the Heterocysts and Possible Role in Nitrogen Fixation
Autor/es:
CUMINO, ANDREA C.; MARCOZZI, CLARISA; BARRERIRO, ROBERTO; SALERNO, GRACIELA L.
Revista:
PLANT PHYSIOLOGY.
Editorial:
American Society of Plant Biologists
Referencias:
Año: 2007 vol. 143 p. 1385 - 1397
ISSN:
0032-0889
Resumen:
Nitrogen (N)
available to plants mostly originates from N2 fixation carried out
by prokaryotes. Certain cyanobacterial species contribute to this energetically
expensive process related to carbon (C) metabolism. Several filamentous strains
differentiate heterocysts, specialized N2-fixing cells. To
understand how C and N metabolism are regulated in photodiazotrophically grown organisms,
we investigated the role of sucrose (Suc) biosynthesis in N2
fixation in Anabaena sp. PCC 7120
(also known as Nostoc sp. PCC 7120).
The presence of two Suc-phosphate synthases (SPS), SPS-A and SPS-B, directly
involved in Suc synthesis with different glucosyl donor specificity, seems to
be important in the N2-fixing filament. Measurement of enzyme
activity and polypeptide levels plus reverse transcription-polymerase chain
reaction experiments showed that total SPS expression is greater in cells grown
in N2 versus combined N conditions. Only SPS-B, however, was seen to
be active in the heterocyst, as confirmed by analysis of green fluorescent
protein reporters. SPS-B gene expression is likely controlled at the
transcriptional initiation level, probably in relation to a global N regulator.
Metabolic control analysis indicated that the metabolism of glycogen and Suc is
likely interconnected in N2-fixing filaments. These findings suggest
that N2 fixation may be spatially compatible with Suc synthesis and
support the role of the disaccharide as an intermediate in the reduced C flux
in heterocystforming cyanobacteria.