Francisco J. Pérez

Difference in hydroxamic acid content in roots and root exudates of wheat (Triticum aestivum L.) and rye (Secale cereale L.): Possible role in allelopathy.

Hydroxamic acids (Hx) produced by some cereal crops have been associated with allelopathy. However, the release of Hx to the soil by the producing plant-an essential condition for a compound to be involved in allelopathy-has not been shown. GC and HPLC analysis of roots and root exudates of wheat (Triticum aestivum L.) and rye (Secale cereale L.) cultivars, with high Hx levels in their leaves, demonstrated the presence of these compounds in the roots of all cultivars analyzed and in root exudates of rye. Moreover, bioassays employing root exudates collected from wheat and rye seedlings demonstrated that only rye exudates inhibited root growth of wild oats,Avena fatua L., a weed whose root growth is inhibited by Hx. These results suggest that rye could potentially interfere with the growth ofAvena fatua in nature and that this interference could be due to the release of Hx to the soil by way of roots.

Allelopathic effect of hydroxamic acids from cereals on Avena sativa and A.fatua

Abstract 2,4-Dihydroxy-7-methoxy- 1,4-benzoxazin-3-one (DIMBOA), the main hydroxamic acid of wheat, and its decomposition product 6-methoxy-benzoxazolin-2-one (MBOA), inhibited 50% root growth of wild oat, Avena fatua at concentrations of 0.7 and 0.5 mM respectively. 6-Methoxy-benzoxazolin-2-one also inhibited seed germination of A. fatua at all concentration tested. It stimulated root growth in A. sativa at concentrations below ca 1.5 mM and inhibited it at higher concentration. Pulse experiments with DIMBOA indicated that it decomposed to MBOA in A. fatua seeds within a period of 48 hr. Uptake by A. fatua seeds of MBOA, DIMBOA and water showed similar kinetic patterns. However MBOA was taken up preferentially to DIMBOA. The MBOA uptake depends on the after-ripening of the seed. The potential exploitation of hydroxamic acids from wheat as allelochemicals in the control of A. fatua is discussed.

Ascorbic acid and flavonoid-peroxidase reaction as a detoxifying system of H2O2 in grapevine leaves

Biosynthesis of both ascorbic acid (AsA) and peroxidase activity were induced by light in cv. Sultana grapevine leaves. Induced peroxidase activity mainly involved basic isoenzymes of pI 9.8 and 9.6 and catalyzed the oxidation of flavonoids like quercetin and kaempferol and derivatives of hydroxycinnamic acids such as ferulic and p-coumaric acids, but not AsA. However, the peroxidase-dependent oxidation of ferulic acid and quercetin was temporarily suppressed by AsA as long as it remained in the reaction medium. Kinetics and spectroscopic results indicated that AsA was oxidized to dehydroascorbic acid only in the presence of phenols or flavonoids, and did not interfere with the catalytic activity of the peroxidase. Ascorbate peroxidase isoenzymes (APx), whose activities are widely considered central for detoxification of H2O2 in most plant cells, were not detected in grape leaves extracts. The significance of light stimulus on peroxidase activity and leaf AsA content is discussed in terms of a flavonoid-redox cycle proposed as an alternative system to detoxify H2O2 in grapevine leaves.

Root exudates of wild oats : allelopathic effect on spring wheat

Abstract Root exudates from the undisturbed root system of wild oats Avena fatua were collected by a modification of the Tang and Young method. Exudates inhibited root and coleoptile growth of spring wheat seedlings ( Triticum aestivum ). Scopoletin, coumarin, p -hydroxybenzoic and vanillic acid were tentatively identified from the root exudates by HPLC.

An Improved Chemiluminescence Method for Hydrogen Peroxide Determination in Plant Tissues

As a consequence of the increasing importance of hydrogen peroxide in plant metabolism, more efficient methods are required for accurate determinations of its concentration in plant tissue and organs. Here we present a highly sensitive chemiluminescence (CL) method based on the Co (II) catalysed oxidation of luminol by H2O2. The replacement of ferricyanide, the traditional catalyst of luminol luminescence by Co (II), enhanced the sensitivity of the reaction towards H2O2 in three orders of magnitude. Thus, plant extracts can be diluted to such a level that quenching effects of phenols and ascorbic acid (ASA), which are normally present at high concentrations in plant tissues is avoided, and therefore, pre-treatments with PVP and ascorbate oxidase to remove these quenchers from plant-extracts become unnecessary. To exemplified the high performance of the method, measurements of H2O2 were carried out in PVP treated and non-treated extracts of grapevine leaf, a plant tissue that contain high levels of phenols and ASA. Moreover, increases in H2O2 levels were detected in disc-leaf treated with aminotriazole, a specific Cat inhibitor, showing the importance of Cat as a H2O2 scavenging enzyme in leaves of grapevine.

H2O2 is involved in the dormancy-breaking effect of hydrogen cyanamide in grapevine buds

Hydrogen cyanamide (HC) is widely used to induce the breakage of endodormancy (ED) in grape and other deciduous fruit crop, though its mechanism of action is poorly understood. Applications of HC to grapevine buds produce oxidative stress and transient respiratory disturbances which are related to the breakage of ED. Moreover, since the expression and activity of catalase (Cat) is inhibited by HC, enhancements in the levels of H2O2 have also been associated to the breakage of ED in grapevine buds. Here, we reported that increases in H2O2 level in HC-treated grapevine buds are due to the inhibition of Cat activity and enhancement of the respiratory activity of buds. In addition, exogenous applications of H2O2 partially reproduced the inducing effect of HC in the breakage of ED, thus providing further support for the hypothesis that H2O2 mediates the effects of HC. On the other hand, Mit isolated from both control and HC-treated buds respired equally well when NADH was used as a respiratory substrate, but when succinate was used as an electron donor Mit respiration was non-detected, suggesting that the stimulatory effect of HC on bud respiration is related to metabolic alterations leading to increase of the concentration of NADH rather than to changes in Mit functionality.

Use of the dynamic model for the assessment of winter chilling in a temperate and a subtropical climatic zone of Chile

A B S T R A C T Accumulated chilling was estimated by applying three different models to the hourly autumn-winter temperature records from Santiago (33°34 S lat; 625 m.a.s.l.) and Vicuna (30°02´ S lat; 643 m.a.s.l.) for the years 2005 and 2006. The model of chilling hours, currently used in Chile as an agroclimatic indicator, was of limited use for effectively contrasting a subtropical condition (Vicuna) with a temperate area such as Santiago. The application of the Utah model gave negative values from March to May, and even up to June in Vicuna, since in this model the chilling effect is “negated” by warmer temperatures. However, a modified version of the Utah model named Positive Chilling Units (PCU), in which negative values are omitted, showed differences in the accumulated chilling between both regions, although these differences were of small magnitude and were noted only from July onwards. The Dynamic Model, which considers that chilling is irreversibly accumulated as quantum or Chill Portions (CP), showed that chilling in Santiago doubled that of Vicuna, and that these differences in location were already expressed at the beginning of autumn, confirming, thus, the suitability of the model for subtropical conditions. In this work the advantages of the dynamic model over other models are discussed.

Near-Universal Prevalence of Pneumocystis and Associated Increase in Mucus in the Lungs of Infants With Sudden Unexpected Death

We demonstrate that Pneumocystis reaches a >90% prevalence peak at 3–5 months of age and associates with increased mucus (MUC5AC), suggesting airway epithelium stimulation in infants during this age range. Host ability to clear mucus would determine pathogenic expression.

On the mechanism of dormancy release in grapevine buds: a comparative study between hydrogen cyanamide and sodium azide

Sodium azide (NaN3), a well-known inhibitor of mitochondrial respiration, stimulated bud-dormancy release in grapevines similar to hydrogen cyanamide (HC), while HC, a well-known dormancy release agent, inhibited the O2 uptake in isolated grape bud mitochondria similarly to NaN3. Additionally, both chemicals induced transcript expression of the antioxidative enzyme glutathione reductase and glucose-6-phosphate-dehydrogenase (G6PD), therefore upregulated the ascorbate-glutathione cycle (AGC) and the pentose phosphate pathway, respectively. As a result of AGC activation, the ratio of reduced to oxidized glutathione (GSH/GSSG) increased. Both stimuli also upregulated the transcription of 1,3-β-d-glucanase, a key enzyme in dormancy release. Together, these data support mechanistic connection between impaired Mit function and dormancy release, and suggests that as a consequence of O2 deprivation, increases in glycolysis and in ethanolic fermentation could be responsible for activation of downstream stages in the dormancy release mechanisms.

Diferulate and lignin formation is related tobiochemical differences of wall-bound peroxidases

Abstract Purified cell walls from oat coleoptiles contain ionically and covalently bound peroxidaseactivity which correspond to 06% of the total peroxidase activity in the coleoptile Ionicallywall-bound peroxidases showed a 2–3-fold higher efficacy than peroxidases in the covalentfraction in the use of H 2 O 2 and phenolic substrates that are precursors of diferulate bridges andlignin The NADH oxidase activity in both fractions was effectively enhanced by p -coumaric acidand the ionic fraction showed a higher efficacy over the covalent one for NADH utilization in thepresence of this phenol Moreover the isoelectrofocusing pattern revealed marked differences inisoform composition for ionically and covalently bound wall peroxidases A cationic group ofisoperoxidases (pI∼96) was present only in the ionic fraction while the covalent fraction wasenriched with anionic forms (pI∼40–65) In excised coleoptiles incubated for 24 h the ionicallywall-bound peroxidase activity increased by 50% over covalently bound activity for 4 h ofincubation The increase of peroxidase activity preceded the accumulation of diferulic acid andlignin in oat cell walls Thus the evidence here reported suggest a possible functional differenceof peroxidase wall fractions studied related to diferulate and lignin synthesis in oat coleoptiles ©1998 Elsevier Science Ltd All rights reserved