Biosynthesis of Indol-3-yl-acetyl-myo-inositol Arabinoside in Kernels of Zea mays L

Extracts of immature kernels of Zea mays L. catalyzed the synthesis of indol-3-yl-acetyl-myo-inositol arabinoside from indol-3-yl-acetyl-myo-inositol and UDP-[U-¹⁴C]xylose. The product contained radioactivity which upon hydrolysis with trifluoroacetic acid cochromatographed with arabinose and not xylose. The amount of product from the reaction was proportional to the amount of indol-3-yl-acetyl-myo-inositol added, and the product was positive to Ehmann's reagent for indoles. In addition, the product and authentic indol-3-yl-acetyl-myo-inositol arabinoside had the same R_F or retention time in three chromatographic systems.     

Effects of temperature and water availability on light energy utilization in photosynthetic processes of Deschampsia antarctica

Regional climate change in Antarctica would favor the carbon assimilation of Antarctic vascular plants, since rising temperatures are approaching their photosynthetic optimum (10–19°C). This could be detrimental for photoprotection mechanisms, mainly those associated with thermal dissipation, making plants more susceptible to eventual drought predicted by climate change models. With the purpose to study the effect of temperature and water availability on light energy utilization and putative adjustments in photoprotective mechanisms of Deschampsia antarctica Desv., plants were collected from two Antarctic provenances: King George Island and Lagotellerie Island. Plants were cultivated at 5, 10 and 16°C under well‐watered (WW) and water‐deficit (WD, at 35% of the field capacity) conditions. Chlorophyll fluorescence, pigment content and de‐epoxidation state were evaluated. Regardless of provenances, D. antarctica showed similar morphological, biochemical and functional responses to growth temperature. Higher temperature triggered an increase in photochemical activity (i.e. electron transport rate and photochemical quenching), and a decrease in thermal dissipation capacity (i.e. lower xanthophyll pool, Chl a/b and β carotene/neoxanthin ratios). Leaf mass per unit area was reduced at higher temperature, and was only affected in plants exposed to WD at 16°C and exhibiting lower electron transport rate and amount of chlorophylls. D. antarctica is adapted to frequent freezing events, which may induce a form of physiological water stress. Photoprotective responses observed under WD contribute to maintain a stable photochemical activity. Thus, it is possible that short‐term temperature increases could favor the photochemical activity of this species. However, long‐term effects will depend on the magnitude of changes and the plant's ability to adjust to new growth temperature.     

The role of ABA in freezing tolerance and cold acclimation in barley

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT₅₀, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT₅₀ and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT₅₀ of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT₅₀ decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.     

Comparative study of microbiological and histopathological techniques used for the detection of Helicobacter pylori

This study evaluates the sensitivity, specificity and predictive values of several techniques commonly used for the detection of Helicobacter pylori in an analysis of 105 biopsy specimens (gastric and duodenal). For comparative purposes, the techniques investigated were divided into 2 groups: histopathological and microbiological. The former included hematoxylin-eosin and Giemsa stains, a Gram stain modified for use in tissue, and immunohistochemical techniques. Microbiological analysis was performed using culture, the urease test and the conventional Gram stain. The immunohistochemical techniques proved to be the most sensitive (93%). The modified Gram stain was sufficiently sensitive (92%) and specific (97%) for the detection of the bacterium. When combined with a microbiological technique such as the urease test, this stain showed increased sensitivity (96%) but its specificity was reduced to 94%. This combination of tests is recommended for the detection of H. pylori in biopsy specimens since it is easily performed at low cost and gives excellent results. For economical reasons, it is suggested that the use of immunohistochemical techniques should be restricted to specific cases.     

Distribution of hydroxamic acids in zea mays tissues

The hydroxamic acid content of leaves of cereals correlates well with resistance to aphids. In maize these compounds were absent from xylem exudates and guttation drops. Lateral veins of leaves of 7-day-old maize plants contained 8 mmol/kg fr. wt. while the entire leaf contained only 4.2 mmol/kg fr. wt. In leaves of 20-day-old plants, these amounts decreased by ca one-third. In mesocotyls, the cortex and central vascular cylinder contained 1.3 and 2.2 mmol/kg fr. wt, respectively. In 12-day-old wheat plants, the complete leaves and their veins contained 2.4 and 6.4 mmol/kg fr. wt respectively. Thus, the concentration of hydroxamic acid was always higher in the vascular bundles.     

Light energy partitioning in photosystems I and II during development of Nothofagus nitida growing under different light environments in the Chilean evergreen temperate rain forest

Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the shade. Nonetheless, older seedlings are commonly found at full sun. We tested the hypothesis that light capture and photochemical and non-photochemical energy dissipation of both photosystems PSI and PSII adjust with ontogeny and brighter environment. Light energy partitioning in both photosystems was studied in seedlings of different developmental stages (small 9.7 cm, tall 36 cm) under contrasting light environments (8–200 and 1,800–2,043 μmol photons m⁻² s⁻¹) in the Chilean evergreen temperate forest. Higher A _max, dark respiration, and light compensation and saturation points in sun seedlings of both developmental stages were accompanied by higher rates of electron transport. These seedlings also showed a high fraction of open PSII reaction centres and similar non-photochemical quenching at high-light in both photosystems, showing no effect of developmental stage in these parameters. Conversely, light capture, total thermal dissipation after photoinhibition, active down-regulation of antenna efficiency, and state transitions were higher in smaller seedlings than in taller ones. These changes maintain photostasis, preventing photodamage, while favouring a more oxidized quinone pool. There is an independent effect of seedling development and light acclimation on this transition from shade to sun during early ontogeny. This transition reflects short-term responses of the photosynthetic apparatus to light and longer term responses that depend on seedling developmental stage.     

Effect of cold acclimation on the photosynthetic performance of two ecotypes of Colobanthus quitensis (Kunth) Bartl

The effects of cold acclimation of two ecotypes (Antarctic and Andes) of Colobanthus quitensis (Kunth) Bartl. Caryophyllaceae on their photosynthetic characteristics and performance under high light (HL) were compared. Non-acclimated plants of the Antarctic ecotype exhibited a higher (34%) maximal rate of photosynthesis than the Andes ecotype. In cold-acclimated plants the light compensation point was increased. Dark respiration was significantly increased during the exposure to 4 degrees C in both ecotypes. Cold-acclimated Antarctic plants showed higher Phi(PSII) and qP compared with the Andes ecotype. In addition, the Antarctic ecotype exhibited higher heat dissipation (NPQ), especially in the cold-acclimated state, which was mainly associated with the fast relaxing component of non-photochemical quenching (NPQ(F)). By contrast, the Andes ecotype exhibited a lower NPQ(F) and a significant increase in the slowly relaxing component (NPQ(s)) at low temperature and HL, indicating higher sensitivity to low temperature-induced photoinhibition. Although the xanthophyll cycle was fully operational in both ecotypes, cold-acclimated Antarctic plants exposed to HL exhibited higher epoxidation state of the xanthophyll cycle pigments (EPS) compared with the cold-acclimated Andes ecotype. Thus, the photosynthetic apparatus of the Antarctic ecotype operates more efficiently than that of the Andes one, under a combination of low temperature and HL. The ecotype differences are discussed in relation to the different climatic conditions of the two Colobanthus.     

Intraspecific variation in Pinus pinaster PSII photochemical efficiency in response to winter stress and freezing temperatures

As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT₅₀, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site. P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (F_v/F_m), quantum yield of non-cyclic electron transport (Φ_PSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT₅₀ was closely related to the minimum winter temperatures of the population''s range. The dark-adapted F_v/F_m ratio discriminated clearly between interior and coastal populations.In conclusion, variations in F_v/F_m, Φ_PSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT₅₀) than coastal populations that typically experience mild winters. Therefore, LT₅₀, as estimated by F_v/F_m, is a reliable indicator of frost tolerance among P. pinaster populations.