INVESTIGADORES
SCARPECI Telma Eleonora
congresos y reuniones científicas
Título:
AMINO ACID METABOLISM IN RIPENING FRUITS OF LYCOPERSICON ESCULENTUM
Autor/es:
ESTELA M. VALLE; SANTIAGO BORTOLOTTI; TELMA E. SCARPECI; SILVANA B. BOGGIO
Lugar:
Reims, Francia
Reunión:
Simposio; 6º International Symposium on Inorganic Nitrogen Assimilation; 2001
Institución organizadora:
INRA-Versalles
Resumen:
The relative molar content
of free amino acids in tomato (Lycopersicon
esculentum Mill.) fruits changed at different developing stages (1). The ripening of tomato is characterized by a
dramatic increase in the glutamate content and the tasty cv. Cherry had the
highest relative glutamate molar content (52 %) of all the tested tomato fruit
cultivars. The events triggering this
process and the metabolic pathways involved are still poorly understood. Measurements of nitrogen-assimilating enzyme
activities in pericarp extracts of mature green and red fruits showed a
decrease in glutamine synthetase (GS), alanine aminotransferase and glutamate
decarboxylase during fruit ripening and an increase in glutamate dehydrogenase
(GDH) and aspartate aminotransferase activities during this transition
(2). Ferredoxin-glutamate synthase was
barely detected in these fruits.
Western blot analysis revealed that while GS was principally present in
green fruit extracts, GDH was almost exclusively observed in the extracts of
red fruits, suggesting an opposite pattern of induction between GS and GDH. The activity and protein variations of GS
and GDH levels during fruit ripening were also observed in their RNAm
levels. The ripening process involves the chloroplasts differentiation into
chromoplasts and is accompanied by the coordinated regulation of complex
gene expression patterns. To further
study this reciprocal pattern of induction between GS and GDH, experiments were
performed in tomato green flesh (gf),
a stay-green mutant, which is deficient in the chloroplast degradation
machinery. The enzymatic activity,
protein and mRNA of GS were present at similar levels in green as well as in
ripe gf fruits indicating a
correlation in GS expression with the presence of chloroplasts. GDH protein and transcripts, on the other
hand, were observed in green and to some extend in ripe fruits. These results suggest that the expression of
GDH and GS are likely controlled by different mechanisms in tomato fruits.
References: 1. Valle et al. (1998)
Plant Cell Physiol 39: 458-461. 2. Boggio
et al. (2000) Plant Sci (2000) 159: 125-133