Bariloche protein symposium argentine society for biochemistry and molecular biology

144
BIOCELL, 27 (Suppl. I), 2003
PL-P42.
ENHANCEMENT OF THE NATURAL DISEASE
RESISTANCE OF POTATOES BY CHEMICALS
Andreu AB
1
, Guevara MG
1
, Wolski EA
1
, Daleo GR
1
, Caldiz DO
2
1
Instituto de Investigaciones Biológicas, UNMDP, cc 1245,
2
McCain Argentina SA, Balcarce. E-mail: [e-mail]
The mechanism involved in systemically induced resistance (SIR)
can be induced nonspecifically in susceptible plants. In response
to pathogens the natural defense mechanism of plants includes
the production of lignin, phytoalexins and the induction of plant
enzymes. The aim of this investigation was to study the induction
of SIR mediated by the chemical activator DL-3-aminobutiric acid
(BABA) and the fungicide Fosetyl-aluminium (Aliette) in
processing potato cultivars with different levels of resistance
against  Phytophthora infestans. For the chemical induction of
resistance, foliage of potato cultivars were sprayed with BABA,
Aliette or water (as a control) and after three days the foliage was
inoculated with P. infestans. After several days, the following
parameters were evaluated: development of disease symptoms in
foliage, protein level of several enzymes, and phenols and
phytoalexin content in post-harvest tuber samples. After application
of the chemicals the highest level of protection against P. infestans
in foliage was observed at early stages of the development of the
crop (30 days after sprouting). An increase in the resistance against
Late Blight was also detected in plant tubers or post-harvest. There
was also an increase in protein level of ß1-3 glucanase and aspartic
protease, as well as in phenols and phytoalexins content in potato
tuber disks post infection. This effect seemed to persist throughout
the whole of plant. This treatment may offer the possibility of
controlling both foliage and tuber blight and could have a major
impact in reducing overwinter survival of P. infestans in tubers.
PL-P43.
EXPRESSION OF ASR GENES DURING
EMBRYOGENESIS AND CELLULAR LOCALISATION OF
TRANSCRIPTS UPON WATER-STRESS IN VEGETATIVE
ORGANS
Frankel, Nicolás; Maskin, Laura; Maldonado, Sara and Iusem,
Norberto.
Laboratorio de Fisiología y Biología Molecular, Facultad de
Ciencias Exactas y Naturales, UBA; IFIBYNE-Conicet; Buenos
Aires, Argentina. E-mail: [e-mail]
Asr genes of  tomato are a family of putative transcription factors
up-regulated during water-stress. Several homologues have been
cloned from different plant species, but little is known about these
genes. Recently, an Asr from grape has been  shown to activate an
hexose transporter promoter. In this work, we analyze the pattern
of expresion of Asr1 and Asr2 during embryogenesis and investigate
the cellular localization of the transcripts in roots and leaves under
normal and stress conditions. Both proteins are detected only in
late embryogenesis (55-70 days post-anthesis). This expression
correlates with the lowest seed water content and the accquisition
of dessication tolerance. However, ASR proteins lack any of the
known late embryogenesis abundant (LEA) protein motifs. In situ
hibrydization assays  showed that Asr1 and Asr2 are specifically
transcribed in companion cells of the leaf phloem under normal
conditions. Upon water-stress, Asr1 and Asr2 presence expands
to surrounding parenchima cells. Asr1 mRNA was not detected in
roots under both normal and stress conditions. In contrast, Asr2
mRNA is present in root phloem under water-stress treatment.
According to our preliminary results, tomato ASR proteins may
form heterodimers or homodimers in their native state.
PL-P44.
MOLECULAR CLONING OF A POTATO LEAF CDNA
ENCODING AN ASPARTIC PROTEASE
Guevara, María G.
1
; Veríssimo, Paula
2
; Pires, Euclides
2
; Faro,
Carlos
2
; Mendieta, Julieta R
1
. and Daleo, Gustavo R.
1
1
IIB, Universidad Nacional de Mar del Plata, Argentina.
2
Departamento Bioquímica, Universidad de Coimbra, Portugal.
[e-mail]
A number of aspartic proteases (APs) cDNA have been isolated
from different plants. The sequence of APs can be divided into
three regions: two of them, an amino-terminal region and a carboxy-
terminal region show high similarity to each other and to enzymes
from mammalian and microbial sources; the third one, a  plant
specific insert (PSI) is present only in precursors of heterodimeric
plant APs. We have cloned a full-length cDNA encoding an potato
leaf  AP (StLAP1). The sequence of the longest clone has 1682 pb,
with three regions in common with all plant APs. The open reading
frame has a capacity to encode a protein of 497 amino acids which
shares 94% sequence identity with AP from tomato. A single band
was detected on gel blots of total RNA probed with the StLAP1.
The size of this mRNA was estimated to be 1.8 Kb which is in
good agreement with the lenght of the cDNA cloned. Also, we
have analyzed by northern blot the expression of  StLAP1 in
different potato leaf cultivars under stress conditions. These
analyses showed that expression levels of StLAP1 were highest in
leaf after mechanical wounding and in potato cultivars resistant
towards  P. infestans after infection with this pathogen. These
results and the results obtained previously about of the
accumulation and the antimicrobial activity of the purified potato
leaf AP (APH2) suggest that this enzyme may have a role in the
defense response of potato.
PL-P45.
STRUCTURAL AND  BIOLOGICAL ACTIVITY
RELATIONSHIP OF AMARANTH STORAGE PROTEINS
Aphalo, Paula; Martínez, Estela Nora and Añón, María Cristina
Centro de Investigación y Desarrollo en Criotecnología de
Alimentos (CIDCA), 47 y 116, La Plata (1900), Argentina. E-mail:
paphalo@.quimica.unlp.edu.ar
Amaranth storage proteins, albumins and globulins show conformational
differences.  Albumins present structural flexibility, with low proportion of
disulfide bridges and low denaturation temperature. Globulins, of high
molecular weight and stabilized by disulfide bridges, include 11S-globulin,
globulin-P and glutelins. Although they share polypeptidic patterns, they
present different aggregation states. Glutelins are highly aggregated whereas
11S-globulins behave as non-polymerized molecules. Globulin-P presents an
intermediate state of aggregation, and contains a characteristic monomeric
polypeptide (P56), which may be a non-processed precursor. The objective of
the present work was to correlate the structural characteristics of amaranth
storage proteins with their biological activity during germination. Storage
proteins (albumins, 11S-globulin, globulin-P and glutelins) were extracted
from Amaranthus hypochondriacus seeds at different hours after imbibition
(h.a.i.) The protein fractions were analyzed by polyacrilamide gel
electrophoresis under denaturing and non-denaturing conditions, gel filtration
chromatography and immunological techniques. Results showed a faster
breakdown on albumins, 11S-globulin and globulin-P. Albumins and globulin-
P lost their reactivity against a rabbit anti-globulin-P polyclonal antiserum at
15 (h.a.i.) indicating the disappearance of conformational epitopes. Conversely,
11S-globulin maintains its reactivity for longer periods of hydrolysis.
Chromatographic and electrophoretic techniques support these structural
differences. Glutelins breakdown was observed after longer periods of
germination. The albumins early mobilization may be the consequence of its
loose structure. The different behavior of globulin-P in comparison with the
other globulins may be associated with the presence of the monomeric P56
polypeptide, which is located on the molecule surface and was shown to be
more easily hydrolyzed.

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