Effect of gramine on the feeding behavior of the aphids Schizaphis graminum and Rhopalosiphum padi

The effects of the indole alkaloid gramine on the behavior of the aphids Schizaphis graminum and Rhopalosiphum padi feeding on barley seedlings and on artificial diets were studied. On barley cv. F. Union, which lacks gramine, S. graminum ingested from phloem tissue for 30–80 min and non-phloem for 20–40 min, over a period of 3 h. In cultivar Datil S, gramine was found only in the epidermis and parenchyma mesophyll cells. On this cultivar, the non-phloem wave form of S. graminum was not observed. On F. Union, R. padi ingested non-phloem with short periods of ingestion from phloem. On cv. Datil S, this aphid did not show the non-phloem wave form. In experiments performed with cv. F. Union seedlings that contained exogenous gramine S. graminum did not ingest from phloem. Exogenous gramine was found only in the vascular bundles. It is suggested that gramine content and location may affect the feeding behavior of aphids in barley.

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Résumé Les effects de la gramine sur le comportement alimentaire des pucerons Schizaphis graminum et Rhopalosiphum padi on été étudiés en plantules d'orge (Hordeum distichum) et aussi avec des diètes artificielles à l'aide d'un moniteur électronique. S.graminum se nourri pendant 30–80 minutes à partir du phloème et il a pris 20–40 minutes en se nourrisant d'autres tissues divers, d'un total de 3 heures d'exposition à la plante. Dans la culture Datil S la gramine a été trouvée seulement dans les cellules de l'epidermis et du parenchyme du mesophyle. Dans ce cas, l'onde non-phloematique de S. graminum, n'a été pas observé; le temps pour le première onde X a été plus prolongé par rapport à la culture F. Union. Dans la culture F. Union, R. padi se nourri principalement de tissue non-phloematique (35–100 minutes) et du phloème par des brèves périodes (15–25 minutes). Dans le cas de la culture Datil S ce puceron n'a pas montré l'onde X. D'autre part, quand les plantules de F. Union ont été poussées dans des solution avec gramine, S. graminum ne se nourri pas du phloeme, tandis que R. padi montre un comportement similaire a celui-ce observé avec plantules sans gramine. La gramine absorbé par les plantules a été retrouvée seulement dans les faisceaux vasculaires. D'autre part, la gramine dans des diètes artificielles agit comme repulsif alimentaire à partir de concentrations de 0,5 mM. Avec des diètes contenant 3 mM de gramine l'alimentation des pucerons a été inhibée. Pourtant, ces resultats sugèrent que le contenuet et la localisation de la gramine peuvent modifier le comportement alimentaire des pucerons en plantules d'orge.

     

Robustness of activity of Calvin cycle enzymes after high light and low temperature conditions in Antarctic vascular plants

Only two vascular plants have naturally colonized the Maritime Antarctic: Colobanthus quitensis and Deschampsia antarctica. We propose that one of the reasons of their success in this environment is the robustness of their CO₂ assimilation machinery. In order to understand the mechanisms involved in the positive photosynthetic rates under stressful conditions, we analyzed changes in the activity of two key Calvin cycle enzymes: Ribulose bisphosphate carboxylase oxygenase (Rubisco) and stromal Fructose-1,6-bisphosphatase after high light and low temperature treatments. Our results show that the activity of both enzymes does not decrease after 48 h high light/low temperature treatments, a feature usually observed in plants adapted to harsh environments. The activation state of both enzymes remained high throughout the treatments. This feature has been related to the redox state of the chloroplast, suggesting that both plants maintain their redox balance under high light and/or low temperature conditions assayed. Both plants differed in their responsiveness to cold acclimation as observed by gas exchange and enzymatic measurements. We propose that these differences may be related to microclimate adaptations to the environment they naturally develop in the Maritime Antarctic.     

Effect of dry-matter concentration of milk substitute and method of feeding on intake and performance by lambs

Forty-eight lambs were artificially reared from 1 day old and offered milk substitute reconstituted to give diets containing 10, 16, 22 and 28% dry matter (DM). Three feeding methods were used for each diet: milk substitute available ad libitum (AL); restricted to a mean daily intake of 1300 g liquid milk substitute (RLQ); and restricted to a mean daily intake of 247 g milk substitute DM (RDM).Solid food intake and lamb growth rate were measured both before and after weaning at 28 days.For method AL, decreasing DM concentration in the milk substitute increased intake of the liquid but decreased that of DM. When DM intakes were held constant, neither method of feeding nor DM concentration had an effect on lamb growth, and level of reconstitution of the milk substitute had no effect on its digestibility. Differences in growth rate before weaning were due entirely to differences in intake of milk substitute DM.After weaning, lambs which had received the diet containing 10% DM tended to perform less well than those that had received the other diets.The lambs were slaughtered at 35 kg live weight. There were no effects of treatment on gains of water, fat and protein.     

Radial-growth and wood-anatomical changes in overaged Quercus pyrenaica coppice stands: functional responses in a new Mediterranean landscape

Recent land-use changes in intensively managed forests such as Mediterranean coppice stands might profoundly alter their structure and function. We assessed how the abandonment of traditional management practices in coppice stands, which consisted of short cutting-cycles (10–15 years), has caused overaging (stems are usually much older than when they were coppiced) and altered their wood anatomy and hydraulic architecture. We studied the recent changes of wood anatomy, radial growth, and hydraulic architecture in two stands of Quercus pyrenaica, a transitional Mediterranean oak with ring-porous wood forming coppice stands in W–NW Spain. We selected a xeric and a mesic site because of their contrasting climates and disturbance histories. The xeric site experienced an intense defoliation after the severe 1993–1994 summer drought. The mesic site was thinned in late 1994. We studied the temporal variability in width, vessel number and diameter, and predicted the hydraulic conductivities (K _h) of earlywood and latewood. In the mesic site, we estimated the vulnerability to xylem cavitation of earlywood vessels. Overaging caused a steep decline in latewood production at a cambial age of 14 years., which was close to the customary cutting cycle of Q. pyrenaica. The diameter distribution of vessels was bimodal, and latewood vessels only accounted for 4% of the K _h. Overaging, acting as a predisposing factor in the decline episode, was observed at the xeric site, where most trees did not produce latewood in 1993–1995. At the mesic site, thinned trees formed wider tree-rings, more latewood and multiseriate tree-rings than overaged trees. The growth enhancement remained 8 years after thinning. Most of the hydraulic conductivity in earlywood was lost in a narrow range of potentials, between −2.5 and −3.5 MPa. We have shown how hydraulic conductivity and radial growth are closely related in Q. pyrenaica and how aging modulates this relationship.     

Non weaving spiders on native woodlands and <Emphasis Type="Italic">Eucalyptus</Emphasis> plantations in Western Mexico: diversity and distribution patterns

Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and their wildlife conservation value is relatively unknown. Recent studies have concluded that secondary forests and tree plantations are less diverse than well-developed tropical rain forests. However, introduced Eucalyptus stands harbored similar species richness to surrounding native woodland in temperate woodlands in North America though the identity of the species present may differ. Species composition, as well as dominance curves and differences in community structure add additional insight to understanding faunistic responses to replacement of native woodland by Eucalyptus plantations. Here, we compared species richness, diversity patterns, and the distribution of non-weaving spiders between native woodlands and Eucalyptus plantations in a temperate region of Mexico. We found more Lycosidae species in all plantation stands. Other community attributes were not consistently different between plantations and native woodlands. This is explained by similarities between, and differences within, the understory of the two main vegetation types. Multivariate analyses identified three spider groups and five spider species could be identified as indicators of these groups. A comparison of the number of species of the wandering spiders between the two vegetation types suggests a compensation pattern that is reported here for the first time.     

Identification of 1,4-Benzoxazin-3-ones in Maize Extracts by Gas-Liquid Chromatography and Mass Spectrometry

Gas-liquid chromatography-mass spectrometry (GLC-MS) has been used for the separation, detection, and identification of 1,4-benzoxazin-3-ones (hydroxamic acids and lactams) and benzoxazolinones found in maize (Zea mays L.) extracts. Compounds of interest were partitioned into ethyl acetate from aqueous maize seedling extracts. For analysis by GLC-MS, trimethylsilyl derivatives were prepared, chromatographed on a column of 3% OV-1, and detected in the mass spectrometer. Mass spectra were obtained for all peaks present in extracts of four maize lines. A data comparison system was developed for relating unidentified spectra to the spectra of the reference compounds. Based on spectral comparisons, three hydroxamic acids (2,4-dihydroxy-2H-1, 4-benzoxazin-3(4H)-one; 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one; and 2,4-dihydroxy-7,8-dimethoxy-2H-1,4-benzoxazin-3(4H)-one), three lactams (2-hydroxy-2H-1,4-benzoxazin-3(4H)-one; 2,7-dihydroxy-2H-1,4-benzoxazin-3(4H)-one; and 2-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one), one benzoxazolinone (6-methoxybenzoxazolinone), and two organic acids (malic and aconitic) were identified in the extracts. In addition, one other hydroxamic acid and one other related compound were tentatively identified based on mass spectral evidence.     

Characterization of an 80-kDa dehydrin-like protein in barley responsive to cold acclimation

Barley ( Hordeum vulgare L.) exposed to low temperature increases its freezing tolerance. This increase has been associated with several metabolic changes caused by low temperature, including expression of dehydrins (DHN), a family of proteins induced by dehydration and cold acclimation. DHNs play an undetermined role in dehydration responses during freezing. We have studied the accumulation of an 80-kDa DHN-like protein (P-80) in barley under cold acclimation 6/4°C (day/night), postulating that it is localized in tissues where primary ice nucleation occurs. P-80 was absent in nonacclimated plants and was detectable after 48 h of cold acclimation, reaching a stable level after 6 days. P-80 decreased when plants were returned to 20–25°C. Drought, ABA and high temperature did not increase the levels of P-80, suggesting that its expression could be specifically regulated by cold. Immunolocalization by tissue printing and fresh cross sections of leaves showed the protein to be associated with vascular tissues and epidermis. The localization of P-80 is consistent with our hypothesis because vascular tissue and the epidermis are preferential ice nucleation zones during the onset of freezing. The differential accumulation of P-80 may have an adaptive value by participating in tolerance mechanisms during freeze-induced dehydration.     

Response of photosynthesis and respiration to temperature under water deficit in two evergreen Nothofagus species

Respiration and photosynthesis were studied in two Nothofagus species with different drought tolerance in order to evaluate the effect of water deficit on foliar carbon balance and the possible role of the alternative pathway on respiratory adjustment. We propose that under severe water deficit the more drought‐tolerant species N. dombeyi is able to decrease its respiration more than the less drought‐tolerant species N. nitida, thus carbon gain could be maintained when photosynthesis is suppressed by drought. Dark respiration (R_d) and carbon assimilation under saturating light (A_sat) were evaluated under seasonal field conditions and during drying and re‐watering cycles under glasshouse. In addition, respiratory pathway changes were evaluated by oxygen isotope fractionation. In the field, N. dombeyi displayed greater light‐saturated photosynthetic capacity than N. nitida, but R_d did not differ between species during summer. In the glasshouse, N. dombeyi displayed an unchanged rate of R_d and increased carbon loss under severe water deficit. Nothofagus nitida displayed a more flexible respiratory response to water deficit, with a lower thermal sensitivity of respiration (decrease in Q₁₀) and a decrease in R_d. This contributed to maintaining leaf carbon balance during the water deficit period. Respiratory electron flow was mainly via the cytochrome pathway for both species and under all treatments, indicating no strong participation of alternative respiration. Our results suggest that under severe water stress, N. dombeyi could be more injured than N. nitida and that the lack of control in the carbon loss under prolonged periods of drought could be limiting for its survival.     

Ecophysiological plasticity and local differentiation help explain the invasion success of Taraxacum officinale (dandelion) in South America

Plasticity and local adaptation have been suggested as two main mechanisms that alien species use to successfully tolerate and invade broad geographic areas. In the present study, we try answer the question if the mechanism for the broad distributional range of T. officinale is for phenotypic plasticity, ecotypic adaptation or both. For this, we used individuals of T. officinale originated from seeds collected in five localities along its latitudinal distribution range in the southern‐hemisphere. Seedlings were acclimated at 5 and 25°C for one month. After the acclimation period we evaluated ecophysiological and cytogenetic traits. Additionally, we assessed the fitness at each temperature by recording the seed output of individuals from different localities. Finally, we performed a manipulative experiment in order to assess the tolerance to herbivory and competitive ability between T. officinale from all origins and Hypochaeris scorzonerae a co‐occurring native species. Overall, individuals of T. officinale showed high plasticity and ecotypic adaptation for all traits assessed in this study. Changes both in physiology and morphology observed in T. officinale from different origins were mostly correlated, enhancing their ecophysiological performance in temperatures similar to those of their origin. Additionally, all localities showed the same chromosome number and ploidy level. On the other hand, all individuals showed an increase the seed output at 25°C, but those from northern localities increased more. T. officinale from all origins was not significantly affected by herbivory while native showed a negative effect. On the other hand, T. officinale exerted a strong negative effect on the native species, but this former not effected significantly to the invasive T. officinale. High plasticity and local adaptation in all ecophysiological traits, seed‐set and the low cytogenetic variability in T. officinale suggests that both strategies are present in this invasive plant species and are not mutually exclusive. Finally, higher tolerance to herbivory and competitive ability suggests that T. officinale could perform successfully in environments with different climatic conditions, and thus colonize and invade South‐America.     

Effect of lactose and glycerol on the motility, normal apical ridge, chromatin condensation and chromatin stability of frozen boar spermatozoa

The effect of lactose and glycerol concentration, as well as the equilibration time with glycerol was studied on motility, normal apical ridge (NAR), and chromatin state of boar spermatozoa after the freezing and thawing process. In the first experiment, samples were frozen in first and second extenders containing different concentrations of lactose (11, 12 and 14%). In the second experiment samples were frozen using second extenders with different concentrations of glycerol (4, 6, 8 and 10%) and were incubated at 5 degrees C for 0 and 30 min. Motility, motility after caffeine treatment, NAR, chromatin condensation and stability (susceptibility to de-condense after heparin treatment) were evaluated. The results indicated that freezing spermatozoa in extenders with increasing concentrations of lactose adversely affected motility but provided a protective effect on acrosomes. Increased lactose concentration induced higher chromatin condensation but maintained the same stability. Increasing the glycerol concentration in the second extender from 4-6 to 8% led to higher motility and NAR as well as lower chromatin condensation and stability. When 30 min equilibration time was allowed after dilution with the same extenders, spermatozoa showed higher NAR and lower chromatin condensation and stability. The longer equilibration time was detrimental for motility when freezing in the 8% glycerol extender but favourable when using the 4% glycerol extender. Compared to the 8% glycerol, spermatozoa frozen in the 10% glycerol extender showed similar motility and increased chromatin condensation and stability, as well as low values of NAR that did not improve by longer incubation time.