Biologia de Polyphagotarsonemus latus (Banks, 1904) (Acari: Tarsonemidae) em algodoeiro

Leaf discs obtained from the first or second non-cotyledonal leaf of cotton (Gossypium hirsutum L.) seedlings were used for the study of the biology of Polyphagotarsonemus latus on cotton IAC-20 cultivar. Seedlings were grown in pots and placed on a layer of cotton moistened with distilled water. The assays were carried out at 28.5 ± 0.3°C, relative humidity of 71.0 ± 2.6% and a 14 h photophase. The duration of immature phases was 4.1 ± 0.1 days for females and 4.1 ± 0.3 days for males, with a survival of 91.2%. After a pre-oviposition period of 1.1 ± 0.2 days, the females deposited 4.5 ± 0.9 eggs per day during 6.8 ± 1.3 days, i.e., 29.6 ± 7.3 eggs per female. The longevity was 10.0 ± 1.5 days for females and 8.8 ± 1.1 days for males. The intrinsic rate of increase (rm) was 0.323; finite rate of increase (λ) 1.38 individual per female per day; mean generation time (T) 9.54 days and net reproductive rate (Ro) 21.73.

The Decisive Step in Betaxanthin Biosynthesis Is a Spontaneous Reaction1

Experiments were performed to confirm that the aldimine bond formation is a spontaneous reaction, because attempts to find an enzyme catalyzing the last decisive step in betaxanthin biosynthesis, the aldimine formation, failed. Feeding different amino acids to betalain-forming hairy root cultures of yellow beet (Beta vulgaris L. subsp. vulgaris “Golden Beet”) showed that all amino acids (S- and R-forms) led to the corresponding betaxanthins. We observed neither an amino acid specificity nor a stereoselectivity in this process. In addition, increasing the endogenous phenylalanine (Phe) level by feeding the Phe ammonia-lyase inhibitor 2-aminoindan 2-phosphonic acid yielded the Phe-derived betaxanthin. Feeding amino acids or 2-aminoindan 2-phosphonic acid to hypocotyls of fodder beet (B. vulgaris L. subsp. vulgaris “Altamo”) plants led to the same results. Furthermore, feeding cyclo-3-(3,4-dihydroxyphenyl)-alanine (cyclo-Dopa) to these hypocotyls resulted in betanidin formation, indicating that the decisive step in betacyanin formation proceeds spontaneously. Finally, feeding betalamic acid to broad bean (Vicia faba L.) seedlings, which are known to accumulate high levels of Dopa but do not synthesize betaxanthins, resulted in the formation of dopaxanthin. These results indicate that the condensation of betalamic acid with amino acids (possibly including cyclo-Dopa or amines) in planta is a spontaneous, not an enzyme-catalyzed reaction.

Abscisic Acid-Dependent and -Independent Expression of the Carrot Late-Embryogenesis-Abundant-Class Gene Dc3 in Transgenic Tobacco Seedlings1

We studied the expression of three promoter 5′ deletion constructs (−218, −599, and −1312) of the LEA (late embryogenesis abundant)-class gene Dc3 fused to β-glucuronidase (GUS), where each construct value refers to the number of base pairs upstream of the transcription start site at which the deletion occurred. The Dc3 gene is noted for its induction by abscisic acid (ABA), but its response to other plant hormones and various environmental stresses has not been reported previously for vegetative cells. Fourteen-day-old transgenic tobacco (Nicotiana tabacum L.) seedlings were exposed to dehydration, hypoxia, salinity, exogenous ethylene, or exogenous methyl jasmonate (MeJa). GUS activity was quantified fluorimetrically and expression was observed by histochemical staining of the seedlings. An increase in GUS activity was observed in plants with constructs −599 and −1312 in response to dehydration and salinity within 6 h of stress, and at 12 h in response to hypoxia. No increase in endogenous ABA was found in any of the three lines, even after 72 h of hypoxia. An ABA-independent increase in GUS activity was observed when endogenous ABA biosynthesis was blocked by fluridone and plants were exposed to 5 μL L−1 ethylene in air or 100 μm MeJa. Virtually no expression was observed in construct −218 in response to dehydration, salinity, or MeJa, but there was a moderate response to ethylene and hypoxia. This suggests that the region between −218 and −599 is necessary for ABA (dehydration and salinity)- and MeJa-dependent expression, whereas ethylene-mediated expression does not require this region of the promoter.

Source and Magnitude of Ammonium Generation in Maize Roots1

Studies with 15N indicate that appreciable generation of NH4+ from endogenous sources accompanies the uptake and assimilation of exogenous NH4+ by roots. To identify the source of NH4+ generation, maize (Zea mays L.) seedlings were grown on 14NH4+ and then exposed for 3 d to highly labeled 15NH4+. More of the entering 15NH4+ was incorporated into the protein-N fraction of roots in darkness (approximately 25%) than in the light (approximately 14%). Although the 14NH4+ content of roots declined rapidly to less than 1 μmol per plant, efflux of 14NH4+ continued throughout the 3-d period at an average daily rate of 14 μmol per plant. As a consequence, cumulative 14NH4+ efflux during the 3-d period accounted for 25% of the total 14N initially present in the root. Although soluble organic 14N in roots declined during the 3-d period, insoluble 14N remained relatively constant. In shoots both soluble organic 14N and 14NH4+ declined, but a comparable increase in insoluble 14N was noted. Thus, total 14N in shoots remained constant, reflecting little or no net redistribution of 14N between shoots and roots. Collectively, these observations reveal that catabolism of soluble organic N, not protein N, is the primary source of endogenous NH4+ generation in maize roots.

Rapid Regulation by Acid pH of Cell Wall Adjustment and Leaf Growth in Maize Plants Responding to Reversal of Water Stress1

The role of acid secretion in regulating short-term changes in growth rate and wall extensibility was investigated in emerging first leaves of intact, water-stressed maize (Zea mays L.) seedlings. A novel approach was used to measure leaf responses to injection of water or solutions containing potential regulators of growth. Both leaf elongation and wall extensibility, as measured with a whole-plant creep extensiometer, increased dramatically within minutes of injecting water, 0.5 mm phosphate, or strong (50 mm) buffer solutions with pH ≤ 5.0 into the cell-elongation zone of water-stressed leaves. In contrast, injecting buffer solutions at pH ≥ 5.5 inhibited these fast responses. Solutions containing 0.5 mm orthovanadate or erythrosin B to inhibit wall acidification by plasma membrane H+-ATPases were also inhibitory. Thus, cell wall extensibility and leaf growth in water-stressed plants remained inhibited, despite the increased availability of (injected) water when accompanying increases in acid-induced wall loosening were prevented. However, growth was stimulated when pH 4.5 buffers were included with the vanadate injections. These findings suggest that increasing the availability of water to expanding cells in water-stressed leaves signals rapid increases in outward proton pumping by plasma membrane H+-ATPases. Resultant increases in cell wall extensibility participate in the regulation of water uptake, cell expansion, and leaf growth.

Cutin Monomers and Surface Wax Constituents Elicit H2O2 in Conditioned Cucumber Hypocotyl Segments and Enhance the Activity of Other H2O2 Elicitors1

Hypocotyls from etiolated cucumber (Cucumis sativus L.) seedlings were gently abraded at their epidermal surface and cut segments were conditioned to develop competence for H2O2 elicitation. Alkaline hydrolysates of cutin from cucumber, tomato, and apple elicited H2O2 in such conditioned segments. The most active constituent of cucumber cutin was identified as dodecan-1-ol, a novel cutin monomer capable of forming hydrophobic terminal chains. Additionally, the cutin hydrolysates enhanced the activity of a fungal H2O2 elicitor, similar to cucumber surface wax, which contained newly identified alkan-1,3-diols. The specificity of elicitor and enhancement activity was further elaborated using some pure model compounds. Certain saturated hydroxy fatty acids were potent H2O2 elicitors as well as enhancers. Some unsaturated epoxy and hydroxy fatty acids were also excellent H2O2 elicitors but inhibited the fungal elicitor activity. Short-chain alkanols exhibited good elicitor and enhancer activity, whereas longer-chain alkan-1-ols were barely active. The enhancement effect was also observed for H2O2 elicitation by ergosterol and chitosan. The physiological significance of these observations might be that once the cuticle is degraded by fungal cutinase, the cutin monomers may act as H2O2 elicitors. Corrosion of cutin may also bring surface wax constituents in contact with protoplasts and enhance elicitation.

Transport of Sterols to the Plasma Membrane of Leek Seedlings1

To investigate the intracellular transport of sterols in etiolated leek (Allium porrum L.) seedlings, in vivo pulse-chase experiments with [1-14C]acetate were performed. Then, endoplasmic reticulum-, Golgi-, and plasma membrane (PM)-enriched fractions were prepared and analyzed for the radioactivity incorporated into free sterols. In leek seedlings sterols are present as a mixture in which (24R)-24-ethylcholest-5-en-3β-ol is by far the major compound (around 60%). The other sterols are represented by cholest-5-en-3β-ol, 24-methyl-cholest-5-en-3β-ol, (24S)-24-ethylcholesta-5,22E-dien-3β-ol, and stigmasta-5,24(241)Z-dien-3β-ol. These compounds are shown to reside mainly in the PM. Our results clearly indicate that free sterols are actively transported from the endoplasmic reticulum to the PM during the first 60 min of chase, with kinetics very similar to that of phosphatidylserine. Such a transport was found to be decreased at low temperature (12°C) and following treatment with monensin and brefeldin A. These data are consistent with a membrane-mediated process for the intracellular transport of sterols to the PM, which likely involves the Golgi apparatus.

Parallel Changes in H2O2 and Catalase during Thermotolerance Induced by Salicylic Acid or Heat Acclimation in Mustard Seedlings1

Spraying mustard (Sinapis alba L.) seedlings with salicylic acid (SA) solutions between 10 and 500 μm significantly improved their tolerance to a subsequent heat shock at 55°C for 1.5 h. The effects of SA were concentration dependent, with higher concentrations failing to induce thermotolerance. The time course of thermotolerance induced by 100 μm SA was similar to that obtained with seedlings acclimated at 45°C for 1 h. We examined the hypothesis that induced thermotolerance involved H2O2. Heat shock at 55°C caused a significant increase in endogenous H2O2 and reduced catalase activity. A peak in H2O2 content was observed within 5 min of either SA treatment or transfer to the 45°C acclimation temperature. Between 2 and 3 h after SA treatment or heat acclimation, both H2O2 and catalase activity significantly decreased below control levels. The lowered H2O2 content and catalase activity occurred in the period of maximum thermoprotection. It is suggested that thermoprotection obtained either by spraying SA or by heat acclimation may be achieved by a common signal transduction pathway involving an early increase in H2O2.

Dim-Red-Light-Induced Increase in Polar Auxin Transport in Cucumber Seedlings1 : I. Development of Altered Capacity, Velocity, and Response to Inhibitors

We have developed and characterized a system to analyze light effects on auxin transport independent of photosynthetic effects. Polar transport of [3H]indole-3-acetic acid through hypocotyl segments from etiolated cucumber (Cucumis sativus L.) seedlings was increased in seedlings grown in dim-red light (DRL) (0.5 μmol m−2 s−1) relative to seedlings grown in darkness. Both transport velocity and transport intensity (export rate) were increased by at least a factor of 2. Tissue formed in DRL completely acquired the higher transport capacity within 50 h, but tissue already differentiated in darkness acquired only a partial increase in transport capacity within 50 h of DRL, indicating a developmental window for light induction of commitment to changes in auxin transport. This light-induced change probably manifests itself by alteration of function of the auxin efflux carrier, as revealed using specific transport inhibitors. Relative to dark controls, DRL-grown seedlings were differentially less sensitive to two inhibitors of polar auxin transport, N-(naphth-1-yl) phthalamic acid and 2,3,5-triiodobenzoic acid. On the basis of these data, we propose that the auxin efflux carrier is a key target of light regulation during photomorphogenesis.

Fusicoccin Binding to Its Plasma Membrane Receptor and the Activation of the Plasma Membrane H+-ATPase1 : IV. Fusicoccin Induces the Association between the Plasma Membrane H+-ATPase and the Fusicoccin Receptor

Different approaches were utilized to investigate the mechanism by which fusicoccin (FC) induces the activation of the H+-ATPase in plasma membrane (PM) isolated from radish (Raphanus sativus L.) seedlings treated in vivo with (FC-PM) or without (C-PM) FC. Treatment of FC-PM with different detergents indicated that PM H+-ATPase and the FC-FC-binding-protein (FCBP) complex were solubilized to a similar extent. Fractionation of solubilized FC-PM proteins by a linear sucrose-density gradient showed that the two proteins comigrated and that PM H+-ATPase retained the activated state induced by FC. Solubilized PM proteins were also fractionated by a fast-protein liquid chromatography anion-exchange column. Comparison between C-PM and FC-PM indicated that in vivo treatment of the seedlings with FC caused different elution profiles; PM H+-ATPase from FC-PM was only partially separated from the FC-FCBP complex and eluted at a higher NaCl concentration than did PM H+-ATPase from C-PM. Western analysis of fast-protein liquid chromatography fractions probed with an anti-N terminus PM H+-ATPase antiserum and with an anti-14–3-3 antiserum indicated an FC-induced association of FCBP with the PM H+-ATPase. Analysis of the activation state of PM H+-ATPase in fractions in which the enzyme was partially separated from FCBP suggested that the establishment of an association between the two proteins was necessary to maintain the FC-induced activation of the enzyme.

Re-Aeration following Hypoxia or Anoxia Leads to Activation of the Antioxidative Defense System in Roots of Wheat Seedlings1

The response of the ascorbate-glutathione cycle was investigated in roots of young wheat (Triticum aestivum L.) seedlings that were deprived of oxygen either by subjecting them to root hypoxia or to entire plant anoxia and then re-aerated. Although higher total levels of ascorbate and glutathione were observed under hypoxia, only the total amount of ascorbate was increased under anoxia. Under both treatments a significant increase in the reduced form of ascorbate and glutathione was found, resulting in increased reduction states. Upon the onset of re-aeration the ratios started to decline rapidly, indicating oxidative stress. Hypoxia caused higher activity of ascorbate peroxidase, whereas activities of monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase were diminished or only slightly influenced. Under anoxia, activities of ascorbate peroxidase and glutathione reductase decreased significantly to 39 and 62%, respectively. However, after re-aeration of hypoxically or anoxically pretreated roots, activity of enzymes approached the control levels. This corresponds with the restoration of the high reduction state of ascorbate and glutathione within 16 to 96 h of re-aeration, depending on the previous duration of anoxia. Apparently, anoxia followed by re-aeration more severely impairs entire plant metabolism compared with hypoxia, thus leading to decreased viability.

Localization and movement of mineral oil in plants by fluorescence and confocal microscopy

Fluorescence and confocal laser scanning microscopy were explored to investigate the movement and localization of mineral oils in citrus. In a laboratory experiment, fluorescence microscopy observation indicated that when a 'narrow' distillation fraction of an nC23 horticultural mineral oil was applied to adaxial and opposing abaxial leaf surfaces of potted orange [Citrus x aurantium L. (Sapindales: Rutaceae)] trees, oil penetrated steadily into treated leaves and, subsequently, moved to untreated petioles of the leaves and adjacent untreated stems. In another experiment, confocal laser scanning microscopy was used to visualize the penetration into, and the subsequent cellular distribution of, an nC24 agricultural mineral oil in C. trifoliata L. seedlings. Oil droplets penetrated or diffused into plants via both stomata and the cuticle of leaves and stems, and then moved within intercellular spaces and into various cells including phloem and xylem. Oil accumulated in droplets in intercellular spaces and within cells near the cell membrane. Oil entered cells without visibly damaging membranes or causing cell death. In a field experiment with mature orange trees, droplets of an nC23 horticultural mineral oil were observed, by fluorescence microscopy, in phloem sieve elements in spring flush growth produced 4-5 months and 16-17 months after the trees were sprayed with oil. These results suggest that movement of mineral oil in plants is both apoplastic via intercellular spaces and symplastic via plasmodesmata. The putative pattern of the translocation of mineral oil in plants and its relevance to oil-induced chronic phytotoxicity are discussed.

Noninvasive localization of petroleum-derived spray oil in plants with chemical shift selective magnetic resonance imaging

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) were used to detect petroleum-derived spray oils (PDSOs) in citrus seedlings and trees. The NMR spectrum of the phantom containing 10% (v/v) of a nC24 agricultural mineral oil (AMO) showed the resonance of the water protons at delta = 5 ppm, while the resonance of the oil protons at delta = 1.3 to 1.7 ppm. The peak resolution and the chemical shift difference of more than 3.3 ppm between water and oil protons effectively differentiated water and the oil. Chemical shift selective imaging (CSSI) was performed to localize the AMO within the stems of Citrus trifoliata L. seedlings after the application of a 4% (v/v) spray. The chemical shift selective images of the oil were acquired by excitation at delta = 1.5 ppm by averaging over 400 transients in each phase-encoding step. Oil was mainly detected in the outer cortex of stems within 10 d of spray application; some oil was also observed in the inner vascular bundle and pith of the stems at this point. CSSI was also applied to investigate the persistence of oil deposits in sprayed mature Washington navel orange (Citrus x aurantium L.) trees in an orchard. The trees were treated with either fourteen 0.25%, fourteen 0.5%, four 1.75%, or single 7% sprays of a nC23 horticultural mineral oil (HMO) 12 to 16 months before examination of plant tissues by CSSI, and were still showing symptoms of chronic phytotoxicity largely manifested as reduced yield. The oil deposits were detected in stems of sprayed flushes and unsprayed flushes produced 4 to 5 months after the last spray was applied, suggesting a potential movement of the oil via phloem and a correlation of the persistence of oil deposit in plants and the phytotoxicity. The results demonstrate that MRI is an effective method to probe the uptake and localization of PDSOs and other xenobiotics in vivo in plants noninvasively and nondestructively.

Effects of Photosystem II inhibiting herbicides on mangroves - preliminary toxicology trials

Mangroves are sensitive to the root application of Photosystem II inhibiting herbicides and Avicennia marina is more sensitive than other mangroves tested. Seedlings of four mangrove species, including two salt-excreting species (A. marina and Aegiceras corniculatum) and two salt-excluding species (Rhizophora stylosa and Ceriops australis) were treated with a range of concentrations of the herbicides diuron, ametryn and atrazine. Assessment of responses required the separation of seedlings into two groups: those that had only their roots exposed to the herbicides through the water (A. marina and R. stylosa) and those that had both roots and leaves exposed to herbicides through the water (A. corniculatum and C australis). Salt-excreting species in each group were more susceptible to all herbicide treatments than salt-excluding species, indicating that root physiology was a major factor in the uptake of toxic pollutants in mangroves. Submergence of leaves appeared to facilitate herbicide uptake, having serious implications for seedling recruitment in the field. Each herbicide was ranked by its toxicity to mangrove seedlings from most damaging to least effective, with diuron > ametryn > atrazine. The relative sensitivity of A. marina found in these pot trials was consistent with the observed sensitivity of this species in the field, notably where severe dieback had specifically affected A. marina in the Mackay region, north eastern Australia. (c) 2004 Elsevier Ltd. All rights reserved.

Putrescine-Sensitive (Artifactual) and Insensitive (Biosynthetic) S-Adenosyl-L-Methionine Decarboxylase Activities of Lathyrus sativus Seedlings

The crude extracts of 3-day-old etiolated seedlings of Lathyrus sativus contained two S-adenosyl-L-methionine decarboxylase activities. The artifactual putrescine-dependent activity was due to the H2O2 generated by diamine oxidase (EC 1.4.3.6) of this plant system and was inhibited by catalase. This observation was confirmed by using an electrophoretically and immunologically homogeneous preparation of L. sativus diamine oxidase. In the presence of putrescine, diamine oxidase, in addition to S-adenosylmethionine, decarboxylated L-lysine, L-arginine, L-ornithine, L-methionine and L-glutamic acid to varying degrees. The decarboxylation was not metal-ion dependent. The biosynthetic S-adenosylmethionine decarboxylase (EC 4.1.1.21) was detected after removing diamine oxidase specifically from the crude extracts by employing an immunoaffinity column. This Mg2+ -dependent decarboxylase was not stimulated by putrescine or inhibited by catalase. The enzyme activity was inhibited by semicarbazide, 4-bromo-3-hydroxybenzoylamine dihydrogen phosphate and methylglyoxal-bis (guanylhydrazone). It was largely localized in the shoots of the etiolated seedlings and was purified 40-fold by employing a p-hydroxymercuribenzoate/AH-Sepharose affinity column, which also separated the decarboxylase activity from spermidine synthase.