Gustavo E. Zúñiga

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.

ANTIOXIDANT COMPOUNDS IN SKIN AND PULP OF FRUITS CHANGE AMONG GENOTYPES AND MATURITY STAGES IN HIGHBUSH BLUEBERRY (Vaccinium corymbosum L.) GROWN IN SOUTHERN CHILE

We evaluated the genotype and maturity effects on antioxidant activity and phenolic compounds of whole, skin and pulp fruits from three highbush blueberry cultivare (cv. Brigitta, cv. Bluegold and cv. Legacy) grown in southern Chile. Total antioxidant activity (TAA) in ripe fruits varied among the cultivare in the order Legacy > Brigitta > Bluegold. We found that TAA in unripe green and fully ripe fruits was high and similar between them, whereas the lowest levels were found in intermediate ripe fruits. The same trend was observed for fruit total phenolic content. This could be attributed to the higher concentrations of phenolic acids (mainly chlorogenic acid) and flavonols (mainly rutin) at immature fruit stages; whereas the high TAA in mature fruits could be explained by the elevated amounts of anthocyanin. All antioxidant compounds were mostly located in the skin. High amounts of delphinidin aglycone were found. HPLC-DAD/MS revealed that the main contents of skin anthocyanins are petunidin-3-glucoside and petunidin-3-arabinnoside followed by malvidin-3-galactoside. It is noticeable that highbush blueberry fruits grown in southern Chile have exceptionally higher antioxidant activity and anthocyanins contents compared with those cultivated in the northern hemisphere.

Non-structural carbohydrates in Deschampsia antarctica Desv. from South Shetland Islands, Maritime Antarctic

Abstract Deschampsia antarctica Desv. (Angiosperm: family Graminaceae) plants were collected from Robert Island, South Shetland Islands, Maritime Antarctic, during February, 1992 and January, 1993, and were extracted with 80% ethanol. Total soluble sugars were analyzed in leaves and roots by colorimetric and HPLC techniques. Compared with other gramineae, the levels of sucrose and fructans were higher. These substances reached their maximum levels by the end of summer. The levels of sucrose and fructans found in February, 1992 were twice the level found in January, 1993. We suggest that the unusually high accumulation of sucrose and fructans may be one of the protective mechanisms against low temperature that has allowed D. antarctica to grow in the Maritime Antarctic.

Effect of infestation by aphids on the water status of barley and insect development

Abstract To compare the effects of aphid infestation with some effects of wounding and drought-stress, several physiological parameters and metabolite concentrations were measured in infested, mechanically wounded or water-stressed young barley plants ( Hordeum vulgare cv Aramir). Barley plants infested with the greenbug ( Schizaphis graminum ) had lower water potentials and CO 2 assimilation than non-infested plants. Abscisic acid content increased by 55% in leaves after 72 hr of infestation. Water potentials and stomatal resistance of barley plants changed only as a consequence of infestation by the greenbug or by drought-stress. Proline concentration increased in leaves subjected to infestation or drought by 11- and 14-fold, respectively. Leaves with artificial damage showed the same reduction in chlorophyll contents as leaves of drought-stressed plants. Greenbug infestation caused higher chlorosis than other treatments. Contents of soluble carbohydrates and proteins decreased 52 and 38% by infestation, 38 and 28% by drought, and 14 and 8% by artificial leaf damage, respectively. To study the influence of these treatments on the quality of barley plants as a food source for the aphids, developmental rates ( 1 D ) and the mean relative growth rates (MRGR) of nymphs reared on these seedlings were compared. New Aphids reared on previously infested seedlings had the lowest MRGR and 1 D ( ca 82 and 68%, respectively) compared to aphids on control plants without previous infestation. Aphids reared on plants subjected to drought also had lower MRGR and 1 D ( ca 89% and 77%). Greenbugs on wounded leaves had similar MRGR and 1 D rates to nymphs reared on control plants. These results show that greenbug infestation of barley produced changes similar to those observed in plants subjected to drought-stress and that aphids feeding on both groups of seedlings had lower developmental and mean relative growth rates. Water-stress caused in barley by aphid infestation or drought would probably affect greenbug development due to the effects of stress on the chemical composition of the plant.

Abscisic acid and jasmonic acid affect proteinase inhibitor activities in barley leaves

Proteinase inhibitor (PI) accumulation has been described as a plant defense response against insects and pathogens. The induction of PIs is known to be regulated by endogenous chemical factors including phytohormones. We studied the induction of barley chymotrypsin and trypsin inhibitory activities by aphid infestation, mechanical wounding, abscisic acid (ABA) and jasmonic acid (JA). Wounding experiments led to a minimal accumulation of PI activity (16% over controls) compared to that found in barley seedlings infested by aphids, where chymotrypsin inhibitor activity showed a two-fold increment. No systemic induction could be detected in healthy leaves of an infested or mechanically injured plant. Exogenous ABA applied on barley leaves increased the chymotrypsin inhibitory activity, while JA only increased trypsin inhibitory activity locally and systemically when applied exogenously. Our data suggest that two different mechanisms may be regulating the induction of these two types of inhibitors.

Cold-acclimation limits low temperature induced photoinhibition by promoting a higher photochemical quantum yield and a more effective PSII restoration in darkness in the Antarctic rather than the Andean ecotype of Colobanthus quitensis Kunt Bartl (Cariophyllaceae)

BackgroundEcotypes of Colobanthus quitensis Kunt Bartl (Cariophyllaceae) from Andes Mountains and Maritime Antarctic grow under contrasting photoinhibitory conditions, reaching differential cold tolerance upon cold acclimation. Photoinhibition depends on the extent of photodamage and recovery capability. We propose that cold acclimation increases resistance to low-temperature-induced photoinhibition, limiting photodamage and promoting recovery under cold. Therefore, the Antarctic ecotype (cold hardiest) should be less photoinhibited and have better recovery from low-temperature-induced photoinhibition than the Andean ecotype. Both ecotypes were exposed to cold induced photoinhibitory treatment (PhT). Photoinhibition and recovery of photosystem II (PSII) was followed by fluorescence, CO2 exchange, and immunoblotting analyses.ResultsThe same reduction (25%) in maximum PSII efficiency (Fv/Fm) was observed in both cold-acclimated (CA) and non-acclimated (NA) plants under PhT. A full recovery was observed in CA plants of both ecotypes under dark conditions, but CA Antarctic plants recover faster than the Andean ecotype.Under PhT, CA plants maintain their quantum yield of PSII, while NA plants reduced it strongly (50% and 73% for Andean and Antarctic plants respectively). Cold acclimation induced the maintenance of PsaA and Cyt b6/f and reduced a 41% the excitation pressure in Antarctic plants, exhibiting the lowest level under PhT. xCold acclimation decreased significantly NPQs in both ecotypes, and reduced chlorophylls and D1 degradation in Andean plants under PhT.NA and CA plants were able to fully restore their normal photosynthesis, while CA Antarctic plants reached 50% higher photosynthetic rates after recovery, which was associated to electron fluxes maintenance under photoinhibitory conditions.ConclusionsCold acclimation has a greater importance on the recovery process than on limiting photodamage. Cold acclimation determined the kinetic and extent of recovery process under darkness in both C. quitensis ecotypes. The greater recovery of PSII at low temperature in the Antarctic ecotype was related with its ability to maintain PsaA, Cyt b6/f and D1 protein after photoinhibitory conditions. This is probably due to either a higher stability of these polypeptides or to the maintenance of their turnover upon cold acclimation. In both cases, it is associated to the maintenance of electron drainage from the intersystem pool, which maintains QA more oxidized and may allow the synthesis of ATP and NADPH necessaries for the regeneration of ribulose 1,5-bisphosphate in the Calvin Cycle. This could be a key factor for C. quitensis success under the harsh conditions and the short growing period in the Maritime Antarctic.

Browning in Annona cherimola fruit: Role of polyphenol oxidase and characterization of a coding sequence of the enzyme

Cherimoya (Annona cherimola Mill.) fruit is an attractive candidate for food processing applications as fresh cut. However, along with its desirable delicate taste, cherimoya shows a marked susceptibility to browning. This condition is mainly attributed to polyphenol oxidase activity (PPO). A general lack of knowledge regarding PPO and its role in the oxidative loss of quality in processed cherimoya fruit requires a better understanding of the mechanisms involved. The work carried out included the cloning of a full-length cDNA, an analysis of its properties in the deduced amino sequence, and linkage of its mRNA levels with enzyme activity in mature and ripe fruits after wounding. The results showed one gene different at the nucleotide level when compared with previously reported genes, but a well-conserved protein, either in functional and in structural terms. Cherimoya PPO gene (Ac-ppo, GenBank DQ990911) showed to be present apparently in one copy of the genome, and its transcripts could be significantly detected in leaves and less abundantly in flowers and fruits. Analysis of wounded matured and ripened fruits revealed an inductive behavior for mRNA levels in the flesh of mature cherimoya after 16 h. Although the highest enzymatic activity was observed on rind, a consistent PPO activity was detected on flesh samples. A lack of correlation between PPO mRNA level and PPO activity was observed, especially in flesh tissue. This is probably due to the presence of monophenolic substrates inducing a lag period, enzyme inhibitors and/or diphenolic substrates causing suicide inactivation, and proenzyme or latent isoforms of PPO. To our knowledge this is the first report of a complete PPO sequence in cherimoya. Furthermore, the gene is highly divergent from known nucleotide sequences but shows a well conserved protein in terms of its function, deduced structure, and physiological role.

Effects of NaCl on glycine-betaine and on aphids in cereal seedlings

Abstract The effect of NaCl on the aphid Schizaphis graminum was studied on seedlings and with artificial diets. Wheat and barley seedlings irrigated with saline Hoagland solution (0–700 mM NaCl) accumulated ions in their leaves. Glycine-betaine, also accumulated in wheat and barley seedlings with increasing salt levels. The population growth rate of the aphid S. graminum in wheat decreased with the amount of salt accumulated by leaves. In barley, however, population growth rate of aphids reached a minimum at 50 mM NaCl, increasing at higher NaCl concentration. Survival of aphids feeding from artificial diets with NaCl decreased (LD50  65 mM). Glycine-betaine, however, increased both survival and reproduction in salt treated and untreated aphids. In addition, ingestion time of aphids feeding in artificial diets also decreased (ED 50  105 mM). These results show that accumulation of NaCl by cereals is more deleterious to aphids in wheat than in barley. This could be partly explained by the higher glycine-betaine accumulation in barley leaves.

Induced plant secondary metabolites for phytopatogenic fungi control: a review

Pathogenic fungi constitute one of the main infectious agents in plants, causing alterations during developmental stages including post-harvest. Phytopathogenic fungi are controlled by synthetic fungicides; however, the use of these is progressively restricted due to both, the harmful effects of pesticides on the environment and human health and the appearance of highly resistant fungal strains. Therefore, there is a great demand for novel natural fungicides. Higher plants are rich source of bioactive secondary metabolites of wide variety such as tannins, terpenoids, saponins, alkaloids, flavonoids, and other compounds, reported to have in vitro antifungal properties. Thus, secondary metabolites with antifungal activity represent an alternative for achieving a sustainable control of phytopathogenic fungi and to reduce the heavy reliance of synthetic pesticides used to control them. Plant antifungal metabolites may be preformed inhibitors that are present constitutively in healthy plants (phytoanticipins), or they may be synthesized de novo in response to pathogen attack or another stress conditions (phytoalexins). These molecules may be used directly or considered as a precursor for developing better fungicidal molecules. This review presents a selection of antifungal agents induced in plants during fungal attack that can be potentially used for phytopathogenic fungi control in crops.

Lipid content in leaves of Deschampsia antarctica from the maritime antarctic

Abstract Deschampsia antarctica plants were collected in Robert Island, Maritime Antarctica, and frozen in liquid nitrogen. Polar lipids and the composition of fatty acids in phospholipids and galactolipids were analysed in leaves and roots. Compared to other Gramineae, no unusual contents in polar lipids and in the degree of unsaturation of fatty acids in most lipid fractions were found. The highest unsaturation ratio (unsaturated/saturated fatty acids) of 3.3 was found in the phosphatidylinositol fraction. Although summer environmental temperatures in Robert Island are usually around 0°, leaves often reach higher temperatures, which are near their photosynthetic optimum.