Liliana Cardemil

Ethylene production and peroxidase activity in aphid-infested barley.

The purpose of this work was to investigate whether ethylene is involved in the oxidative and defensive responses of barley to the aphids Schizaphis graminum (biotype C) and Rhopalophum padi. The effect of aphid infestation on ethylene production was measured in two barley cultivars (Frontera and Aramir) that differ in their susceptibility to aphids. Ethylene evolution was higher in plants infested for 16 hr than in plants infested for 4 hr in both cultivars. Under aphid infestation, the production of ethylene was higher in cv. Frontera than in Aramir, the more aphid susceptible cultivar. Ethylene production also increases with the degree of infestation. Maximum ethylene evolution was detected after 16 hr when plants were infested with 10 or more aphids. Comparing the two species of aphids, Schizaphis graminum induced more ethylene evolution than Rhopalosiphum padi. Infestation with S. graminum increased hydrogen peroxide content and total soluble peroxidase activity in cv. Frontera, with a maximum level of H2O2 observed after 20 min of infestation and the maximum in soluble peroxidase activity after 30 min of infestation. When noninfested barley seedlings from cv. Frontera were exposed to ethylene, an increase in hydrogen peroxide and in total peroxidase activity was detected at levels similar to those of infested plants from cv. Frontera. When noninfested plants were treated with 40 ppm of ethylene, the maximum levels of H2O2 and soluble peroxidase activity were at 10 and 40 min, respectively. Ethylene also increased the activity of both cell-wall-bound peroxidases types (ionically and covalently bound), comparable with infestation. These results suggest that ethylene is involved in the oxidative responses of barley plants induced by infestation.

POLYSACCHARIDES FROM THE ENVELOPES OF HETEROCYSTS AND SPORES OF THE BLUE-GREEN ALGAE ANABAENA VARIABILIS AND CYLINDROSPERMUM LICHENIFORME1

The polysaccharides from the envelopes of heterocysts of Cylindrospermum licheniforme Kütz., and of heterocysts and spores of Anabaena variabilis Kütz., like those from the differentiated cells of Anabaena cylindrica Lemm., have a 1,3‐linked backbone consisting of glucosyl and mannosyl residues in a molar ratio of approximately 3:1. As is the case with A. cylindrica the polysaccharides from A. variabilis and from the heterocysts of C. licheniforme have terminal xylosyl and galactosyl residues as side branches. In addition, the polysaccharide from C. licheniforme resembles that from A. cylindrica in having terminal mannosyl residues as side branches (absent from A. variabilis). The polysaccharides from A. variabilis resemble that from A. cylindrica in having glucose‐containing side branches (absent from the heterocyst polysaccharide from C. licheniforme), but in contrast to the polysaccharides from the other two species they also have terminal arabinosyl residues as side branches. All of the polysaccharides mentioned appear to be structurally related; we present tentative structures for those not previously investigated. In contrast, the envelope of spores of C. licheniforme contains only a largely 4‐linked galactan. The bulk of this envelope is not polysaccharide in nature, and contains aromatic groups.

Effects of water stress and high temperature on photosynthetic rates of two species of Prosopis.

The main aim of this research was to compare the photosynthetic responses of two species of Prosopis, Prosopis chilensis (algarrobo) and Prosopis tamarugo (tamarugo) subjected to heat and water stress, to determine how heat shock or water deficit, either individually or combined, affect the photosynthesis of these two species. The photosynthetic rates expressed as a function of photon flow density (PFD) were determined by the O(2) liberated, in seedlings of tamarugo and algarrobo subjected to two water potentials: -0.3 MPa and -2.5 MPa and to three temperatures: 25 degrees C, 35 degrees C and 40 degrees C. Light response curves were constructed to obtain light compensation and light saturation points, maximum photosynthetic rates, quantum yields and dark respiration rates. The photochemical efficiency as the F(v)/F(m) ratio and the amount of RUBISCO were also determined under heat shock, water deficit, and under the combined action of both stress. Photosynthetic rates at a light intensity higher than 500 micromole photons m(-2)s(-1) were not significantly different (P>0.05) between species when measured at 25 degrees C under the same water potential. The maximum photosynthetic rates decreased with temperature in both species and with water deficit in algarrobo. At 40 degrees C and -2.5 MPa, the photosynthetic rate of algarrobo fell to 72% of that of tamarugo. The quantum yield decreased in algarrobo with temperature and water deficit and it was reduced by 50% when the conditions were 40 degrees C and -2.5 MPa. Dark respiration increased by 62% respect to the control at 40 degrees C in tamarugo while remained unchanged in algarrobo. The photochemical efficiency decreased with both, high temperature and water deficit, without differences between species. RUBISCO content increased in algarrobo 35 degrees C. Water deficit reduced the amount of RUBISCO in both species. The results of this work support the conclusion that in both Prosopis species, the interaction between high temperature and water deficit affects photosynthesis responses greater than each individual stress, and that the interactive effect is more pronounce in algarrobo than in tamarugo.

Accumulation of HSP70 in Deschampsia antarctica Desv. leaves under thermal stress

The aim of this study was to evaluate the hypothesis that Deschampsia antarctica Desv., the only grass of the Maritime Antarctic, responds to temperatures higher or lower than its optimum for photosynthesis (13°C), with the accumulation of heat shock proteins. The LT50 was determined in plants acclimated at 4°C (cold-acclimated plants) and in plants grown at 13°C (control plants) by membrane damage and by the activity of respiratory dehydrogenases. The LT50 was 48.3°C in both groups of plants when determined by membrane damage. When the LT50 was determined by the activity of respiratory dehydrogenases, this was, without significant difference, 47.8°C in cold-acclimated plants and 46.5°C in control plants. Western blot analyses were performed to investigate the accumulation of HSP70 at different temperatures. The optimal temperature for HSP70 accumulation was 35°C in cold-acclimated and control plants. Cold-acclimated plants subjected to a thermal stress of 35°C accumulated HSP70 protein more than control plants subjected to 35°C. After eight hours of continuous stress at 35°C, the maximum relative content of HSP70 in cold-acclimated plants was 1.9 fold higher than control plants. The threshold temperature for HSP70 accumulation was lower in cold-acclimated plants than in control plants. It is concluded that D. antarctica is able to tolerate heat stress with an LT50 similar to those of heat tolerant plants and that the cold-acclimated plants accumulate higher levels of HSP70 than those grown at 13°C.

Physiological and molecular responses of Prosopis chilensis under field and simulation conditions

Abstract The diurnal courses of CO 2 assimilation and stomatal conductance in spring were determined in trees of Prosopis chilensis growing in Quebrada San Carlos, Vicuna, 4th Region, Chile. These two parameters along with proline content, and the expression of free and conjugated ubiquitin and the heat shock protein (HSP) M r 70 K were determined at the same time intervals in the leaves of six-month-old plants acclimated in a growth chamber with similar conditions to those of Quebrada San Carlos. The expression of the HSPs was studied by Western and immuno dot blot analyses using monoclonal and polyclonal antibodies generated against these types of proteins. The CO 2 assimilation of northwest-facing trees and plants under simulated conditions showed a bimodal response with maxima at 12.00 and 18.00 hr, when the temperature was 25° and the relative humidities were 35 and 33%, respectively; the minimum was around 15.00 hr with a temperature of 35° and a relative humidity of 32%. The low CO 2 assimilation at 35° was not correlated with stomatal closure, but rather with a nyctinastic movement of leaf and foliole petioles, which greatly decreased the foliar area. After 18.00 hr, CO 2 assimilation declined to become zero or negative at 21.00 hr. Proline, the expression of M r 70 K and conjugated ubiquitin also reached a maximum at 35°. The expression of free ubiquitin showed the reverse pattern being high at night, early in the morning and late in the evening. The physiological implications of these responses to temperature stress are discussed.

Regulation of α-amylase isoenzyme expression in Araucaria araucana by gibberellic and abscisic acids

Abstract Expression of α-amylase (EC 3.2.1.1) isoenzymes present in the embryos and mega-gametophytes of Araucaria araucana seedlings was studied under gibberellic acid (GA 3 ) and abscisic acid (ABA) treatments and after 90 hr of imbibition in 20 mM of β-chloroethyltrimethylammonium (CCC), a GA 3 biosynthesis inhibitor. When CCC was used, α-amylase activity in the treated embryos decreased to 28% with respect to the controls. The isoenzymes of R m 0.42 and 0.51 were greatly affected. When the embryos were imbibed simultaneously in the presence of 20 mM CCC and 10 −5 M of GA 3 , α-amylase activity and the expression of isoenzymes were restored with respect to controls. ABA at 10 −4 and 10 −5 M decreased α-amylase activity of embryos to 67 and 81%, respectively. Expression of isoenzymes of R m 0.51 was greatly decreased by ABA but the effect on the others was small. Isoenzyme expression of mega-gametophytic α-amylase was not affected by CCC, GA 3 or ABA treatment.

Peroxidases in the cell walls of seeds and seedlings of Araucaria araucana

Abstract Two major proteins present in the cell walls of the embryo and megagametophyte tissues of Araucaria araucana seeds were partially purified, characterized and identified as peroxidases. These two proteins have M r s of 83 and 145 × 10 3 , a pI of 10.5, an optimal pH of 5.0 and a buoyant density of 1.333 g ml −1 . Kinetic studies of these peroxidases define a K m app. of 13.6 mM for H 2 O 2 and 3.4 mM for o -phenylenediamine ( o -PDA). The V max is 525 μmol o -PDA oxidized min −1 mg −1 . After oxidation with periodic acid the peroxidases react on gels with dansylhydrazine, demonstrating that the proteins are glycosylated. The sugar components linked to the proteins are galactose, glucose, xylose and mannose. Galactose comprises more than 60% of the sugar residues in both peroxidases. The other sugar contents show significant quantitative differences between the peroxidases. Expression of the peroxidases increases upon wounding of the seed tissues. The two proteins were differently expressed during seed germination. They also showed a different susceptibility to degradation when the proteins were heated in the presence of 5 M urea.

Field studies on the photosynthesis of two desert Chilean plants: Prosopis chilensis and Prosopis tamarugo

Photosynthetic parameters were investigated in relation to light intensity (PAR and UV-B) in two Chilean Prosopis sp., Prosopis chilensis and Prosopis tamarugo in their natural habitats. The objective of this work was to compare the photosynthetic responses and to determine the degree of adaptation of both species to visible- and UV-radiation stress. One of the study sites was Refresco in the Atacama Desert, where P. tamarugo is an endemic plant and P. chilensis was introduced, and the other was Peldehue in the valley of Central Chile where only P. chilensis is present. Due to latitude, light intensity (UV-B and PAR) is higher in Refresco than in Peldehue. The parameters investigated in both species were photosystem II fluorescence, CO(2) assimilation, stomatal conductance, photosynthetic pigment composition, flavonoid absorption patterns and composition of chlorophyll-protein complexes. Fluorescence studies, CO(2) assimilation and stomatal conductance studies demonstrated that photosynthetic activity is more efficient and stable throughout the day in P. tamarugo than in P. chilensis in Refresco. Chlorophyll-protein complexes also seemed to be more stable in P. tamarugo than in P. chilensis. Photosynthetic pigment analyses indicated possible photodamage in P. chilensis trees in Refresco, but not in Peldehue. Such photodamage was absent in P. tamarugo. There was a considerable change in the flavonoid pattern between noon and afternoon hours in both species at both study sites. The physiological implications of these changes indicate that P. tamarugo is more adapted to high solar radiation than P. chilensis.

Cell wall proteins in seedling cotyledons of Prosopis chilensis

Four cell wall proteins of cotyledons of Prosopis chilensis seedlings were characterized by PAGE and Western analyses using a polyclonal antibody, generated against soybean seed coat extensin. These proteins had M(r)s of 180,000, 126,000, 107,000 and 63,000, as determined by SDS-PAGE. The proteins exhibited a fluorescent positive reaction with dansylhydrazine suggesting that they are glycoproteins; they did not show peroxidase activity. The cell wall proteins were also characterized by their amino acid composition and by their amino-terminal sequence. These analyses revealed that there are two groups of related cell wall proteins in the cotyledons. The first group comprises the proteins of M(r)s 180,000, 126,000, 107,000 which are rich in glutamic acid/glutamine and aspartic acid/asparagine and they have almost identical NH2-terminal sequences. The second group comprises the M(r) 63,000 protein which is rich in proline, glycine, valine and tyrosine, with an NH2-terminal sequence which was very similar to that of soybean proline-rich proteins.

Cell kinetics, stomatal differentiation, and diurnal rhythm in Allium cepa☆

Abstract Cell kinetics parameters were obtained for the three mitotic divisions leading to formation of stomata in the epidermis of the cotyledon of Allium cepa seedlings. Analysis of mitotic frequencies throughout the course of development showed that the asymmetrical divisions started at about 50 hr after germination, and the symmetrical divisions were first seen a few hours later. Guard mother cell divisions started around 70 hr after germination. The maximal frequency of both symmetrical and asymmetrical division was found between 3 and 5 days after germination, and the highest frequencies of GMC divisions were observed between 6 and 8.5 days. All divisions ceased after 11 days. The three cell populations analyzed displayed diurnal fluctuations of their mitotic frequencies which were characteristic of the type of cell division measured and seemed independent of the region of the cotyledon in which they took place. The symmetrical divisions displayed two diurnal peaks—one at about 0400 and the other at 1600 hr—and the asymmetrical mitoses showed a single peak at about 2200 hr. Atypical asymmetrical divisions were observed in some guard mother cells, suggesting a different developmental sequence for some of the stomatal complexes.