INVESTIGADORES
MAIALE Santiago Javier
congresos y reuniones científicas
Título:
Molecular and biochemical approximation of polyamine roles in tolerance mechanisms to salt stress in Lotus spp
Autor/es:
ROSALÍA PAZ; DIEGO H SÁNCHEZ; FERNANDO PIECKENSTAIN; SANTIAGO MAIALE; ANALÍA SANNAZZARO; JUAN CRUZ CUEVAS; AMALIA CHIESA; GONZALO BONA; OSCAR A RUIZ
Reunión:
Workshop; Taller interdisciplinario de Lotus y sus simbiontes; 2005
Institución organizadora:
IIB-INTECH
Resumen:
Lotus
glaber is the most important legume in the saline-alkaline lowlands of the
Salado River basin. This region (approximately 9,000,000 ha), located
in Buenos Aires Province (Argentina) is devoted to the breeding of beef cattle.
In order to increase forage yield and improve the quality of their pastures,
regional farmers utilize L. glaber, whose adaptability to saline soils is
well-known. The economic importance of this legume has led to an increasing
number of studies regarding the physiological basis of its salt tolerance.
Polyamines are aliphatic amines of low molecular weight charged positively at
physiological pH. The distribution of these positive charges permits their
interaction with proteins, membrane lipids and DNA. Its well known that the
activity of the plant enzymes of polyamine biosynthesis is induced under
abiotic stress, including salinization. With this idea in mind, we evaluated
the effect of salt stress in polyamine pathway in Lotus glaber. As proline is a
traditional stress marker in plants, we evaluate their levels under similar
stress conditions. To understand the response of L. glaber to salt stress, we
evaluated 15 old days seedlings germinated and growth under 0, 25, 50 and 75 mM NaCl. We observed a
progressive accumulation of Na+ and loosening of K+. Simultaneously we observed
an increasing in proline levels and accumulation in Spm, coincidently with a
diminishing in Spd levels. In addition, we analyzed a natural population
of L. glaber collected from lowlands of Salado River Basin. We isolated 103
genotypes of L. glaber and cloned them by nodal cutting. Thirty days old
genotypes were exposed to 300
mM NaCl (n=5), and death days average was determined. A
Gaussian distribution was obtained. The time survival varied from 12 till 30
days. Five genotypes of each extreme were selected and cloned and sub irrigated
with 0 and 150 mM
NaCl. Based on their differential relative growth rates the genotypes were
classified in sensitive and tolerant. We concluded that the preliminary
classification based on average days of survival-time under strong saline
conditions are not representative of their tolerance physiological conditions
because some genotypes identified firstly as sensible were tolerant and
viceversa. Analysis in polyamine content demonstrated that spermine
accumulates less in tolerant genotypes than in sensible. Simultaneously,
proline presents a progressive accumulation in both genotypes but was smaller
in tolerant ones. Complementary and taking in to account the results obtained,
we generate Lotus corniculatus transgenic plants that overexpressing under
control of the constitutive promoter CaMV35S, a putative gene of spermidine
synthase previously cloned from tobacco. The lines obtained presented
constitutive high levels of Spd and Spm than controls non-transformed.
Moreover, we observed that these transgenic plants under saline stress showed a
decreasing in the spermidine concentrations and an increment in the spermine
levels suggesting activation in the spermine synthase activity. Under similar
conditions the proline levels diminished. Actually, we are working in the
generation of Lotus spp transgenic plants that potentially overexpressing
regulatory enzymes in the polyamine biosynthesis under control of a promoter
inducible by stress. This promoter denominated RD29A was cloned from
Arabidopsis thaliana and is under evaluation in our lab. Binary vectors
harboring the sequence of arginine decarboxylase (ADC) under control of this
promoter was assayed successfully in hairy roots of Lotus corniculatus,
suggesting a conservative stress signaling pathway between species.