Stimulation of ethylene production in detached rice leaves by vanadate

The effect of vanadate on ethylene biosynthesis in detached rice leaves was investigated. Vanadate at pH 5.0–7.0 effectively enhanced ethylene production within 3 h of its application. It promoted the conversion of ACC to ethylene. Treatment with vanadate did not decrease ACC level until late stage of incubation, i.e. at 12 h after incubation. Molybdate, an inhibitor of phosphatase had no or much less stimulatory effect on ethylene production than did vanadate at comparable concentrations. Azide, an inhibitor of F₁-ATPase, inhibited ethylene production in detached rice leaves. FC and vanadate were observed to be synergisticly increased ethylene production in detached rice leaves. In conclusion, plasma membrane H⁺-ATPase does not seem to be involved in ethylene biosynthesis in detached rice leaves.Abbreviations ACC 1-Aminocyclopropane-1-carboxylic acid - FC Fusicoccin     

镍对离体玉米叶片衰老的调节作用

本文研究了镍对离体玉米叶片衰老的调节作用。研究结果表明,玉米叶片在衰老过程中,超氧化物歧化酶（ＳＯＤ）、过氧化物酶（ＰＯＤ）过氧化氢酶（ＣＡＴ）、抗坏血酸过氧化物酶（ＡsＳ－ＰＯＤ）活性和抗坏血酸（ＡsA)含量显著降低,超氧阴离子自由基（Ｏ^-2)产生率显著增加,脂质过氧化作用加剧,丙二醛（ＭＤＡ）含量升高,细胞质膜透性增大。而１０^-2、１０^-3mol.L^-1Ni^2 处理能增强上述保护酶活性和抗氧化剂ＡsA的含量从而能减轻细胞膜脂过氧化使用。２０^-3、１０^-2mol.L^-1Ni^2 处理能显著延缓蛋白质和叶绿素 降解。因此镍能延缓离体玉米叶片的衰老,尤其是以１０^-2mol.L^-1Ni^2 对衰老的延缓作用更大。动态测定结果表明,１０^-2mol.L^-1Ni^2 处理能使衰老滞后２－天。     

Proline accumulation induced by excess nickel in detached rice leaves

The regulation of proline accumulation in detached rice leaves exposed to excess NiSO₄ was investigated. NiSO₄ treatment increased proline and Ni contents but had no effect on relative water content, indicating that proline accumulation in Ni-exposed detached rice leaves was due to Ni uptake per se, rather than to water stress. Proline accumulation caused by NiSO₄ was related to protein hydrolysis, a decrease in proline dehydrogenase activity, and a decrease in proline utilization. It seems that an increase in the content of ammonia and an increase in the activities of Δ¹-pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase play minor if any role in Ni-induced proline accumulation in detached rice leaves.     

Evaluation of light-harvesting complex proteins as senescence-related protein markers in detached rice leaves

Ten light-harvesting complex (Lhc) proteins were investigated to determine which was the most appropriate protein marker of senescence in detached rice leaves. The levels of Lhc proteins were monitored by immunoblot analysis, which was conducted using commercially available antibodies raised against each Lhc protein. Among the Lhc proteins evaluated in this study, Lhca1, Lhcb1, Lhcb2, Lhcb3, and Lhcb5 were not appropriate to be used as senescence markers while others can be used after optimization of the procedure.     

Regulation of nitrate reductase in detached oat leaves by light and oxygen

Regulation of nitrate reductase (NR, EC 1.6.6.1) by oxygen concentration and light was studied in segments of oat ( Avena sativa L. cv. Suregrain) leaves, using the in vivo nitrate reductase assay. The activity of NR decreased after excision in either light or darkness; the addition of cycloheximide prevented this decrease. Treatments that increased tissue permeability (anoxia, Triton X-100) also increased NR activity. There was in general less NR activity in the light than in the dark and also less under aerobic (21–100% O₂) than under anaerobic (0.3% O₂) conditions. Treatments with antioxidants improved the activity in the light, but only at high O₂ levels (21–100% O₂).
The results suggest that NR may be regulated by inhibitory proteins synthesized in either light or darkness, by permeability changes and by light-induced oxidations that occur when O₂ is present. Oxygen may control the activity by stimulating the synthesis of inhibitory proteins in the light and in the dark and by promoting oxidation of SH-groups in the light.     

The senescence of detached leaves of tropaeolum

The senescence of detached Tropaeolum majus leaves was compared with that described earlier for Avena. Tropaeolum was chosen as being not only a dicot but also as having a nearly circular leaf, thus needing only the smallest minimum of wounding, since wounding delays the loss of chlorophyll and protein in darkness. Tropaeolum resembles Avena in that closing the stomata osmotically or with ABA causes rapid senescence in light. As in Avena also, n-hexanol and α,α′-dipyridyl delay senescence in darkness but cause `bleaching' of chlorophyll in light. Unlike Avena, however, kinetin and gibberellic acid, which delay senescence in the dark in both species, do so in Tropaeolum without causing any significant stomatal opening. The senescence of Tropaeolum leaves is actually promoted by fusicoccin, which powerfully delays senescence in Avena, although fusicoccin does cause stomatal opening in darkness in both species. Thus, many of the phenomena of senescence are alike in the monocot and dicot, but there are several significantly different responses to the senescence-modifying reagents. It is concluded that while stomatal closure accelerates senescence in both species, stomatal opening is not directly linked to the prevention of leaf senescence.     

Adventitious rooting of detached Arabidopsis thaliana leaves

Arabidopsis thaliana Heyhn is a model species in biochemical, physiological and molecular studies for which a plethora of mutants is available. This work aimed at developing a system for rooting of detached leaves, and evaluating time course of several relevant biochemical parameters during rooting assays with and without auxins. The rooting pattern was of the direct type (without callus formation) in all of the treatments and ecotypes analyzed and was rather stable. Considering the different parameters examined, peroxidase activity and contents of phenolic compounds and soluble sugars appeared as the most distinct biochemical markers of the rooting process in this system.     

Hormonal activity in detached lettuce leaves as affected by leaf water content

The interrelationship between water deficiency and hormonal makeup in plants was investigated in detached leaves of romaine lettuce (Lactuca sativa L. cv. `Hazera Yellow'). Water stress was imposed by desiccating the leaves for several hours in light or darkness at different air temperatures and relative humidity. In the course of desiccation, a rise in abscisic acid content and a decline in gibberellin and cytokinin activity were observed by gas-liquid chromatography, by both the barley endosperm bioassay and radioimmunoassay and by the soybean callus bioassay. Gibberellin activity began to decline in the stressed leaves before the rise in abscisic acid, the rate of this decline being positively correlated with the rate of increase in leaf water saturation deficit. Recovery from water stress was effected by immersing the leaf petioles in water while exposing the blades to high relative humidity. This resulted in a decrease in leaf water saturation deficit, a reduction in abscisic acid content, and an increase in gibberellin and cytokinin activity.     

Translocation of assimilates and phosphate in detached bean leaves

¹⁴C-assimilates were accumulated by the veins in the blades and transported basipetally into the petioles of detached leaves of Red Kidney bean (Phaseolus vulgaris L.). Neither process was greatly affected by mild moisture stress, age of fully enlarged leaves, or period in the dark prior to exposure to ¹⁴CO₂. However, both vein loading and transport into petioles were greatly reduced by oxygen deficiency. The basipetal transport of ³²PO₄ also did not appear to be greatly reduced by 6 or 8 days of darkness prior to the application of phosphate-³²P, followed by a transport period of 1 day in the dark. Endothall at 5 × 10⁻³ m was effective in stopping basipetal flow of ³²P. It is considered that transport in leaves may be powered by forces in the plasmodesmata of the cell walls between the border parenchyma and phloem.     

Regulation of ammonium-induced proline accumulation in detached rice leaves

Accumulation of proline in response to NH₄Cl was studied indetached leaves of rice (Oryza sativa cv. Taichung Native1). Increasing concentrations of NH₄Cl from 50 to 200mMprogressively increased proline content and this was correlated with theincrease in ammonium content. Proline accumulation induced by NH₄Clwas related to proteolysis, an increase in ornithine--aminotransferaseactivity, a decrease in proline dehydrogenase activity, and a decrease inproline utilisation and could not be explained by NH₄Cl-inducedmodification in ¹-pyrroline-5-carboxylate reductase activity.The content of glutamic acid was decreased by NH₄Cl, whereas theincrease in arginine and ornithine contents was found to be associated with theincrease in proline content in NH₄Cl-treated detached rice leaves.     

Regulation of sucrose-phosphate-synthase activity in spinach leaves by protein level and covalent modification

A dot-blot technique was developed using monoclonal antibodies to measure, rapidly and accurately, the amount of sucrose-phosphate synthase (SPS; EC 2.4.1.14) protein present in a crude extract from spinach (Spinacia oleracea L. cv. Dark Green Bloomsdale) leaves; this was compared with SPS activity in this material. During leaf development, increased SPS activity followed closely the increase in enzyme-protein level, indicating denovo synthesis or altered turn-over rates for SPS. In contrast, activation of SPS by illumination of leaves or by mannose treatment of leaf discs in the dark (M. Stitt et al. Planta 174, 217–230) occurred without a significant change in the level of enzyme protein. Since conditions which altered SPS activity did not affect immunoprecipitation or mobility of the 120-kilodalton (kDa) subunit of the enzyme during denaturing gel electrophoresis, some form of protein modification other than proteolysis must be involved. Overall, the results indicate that regulation of SPS activity can involve changes in the level of enzyme protein and-or covalent modification.Abbreviations kDa kilodalton - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - SPS sucrosephosphate synthase Cooperative investigations of the U.S. Department of Agriculture, Agricultural Research Service, and the North Carolina Agricultural Reseach Service, Raleigh. Paper No. 11789 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7643, USA     

Induction of pathogenesis-related proteins by spermidine exogenously supplied to detached tobacco leaves

Continuous treatment with spermidine or 1-aminocyclopropane-1-carboxylic acid stimulated ethylene production and ethylene-forming enzyme activity and accelerated chlorophyll breakdown in detached tobacco leaves. The treatments also induced the production of eleven major acidic pathogenesis-related proteins, which were also produced during the hypersensitive reaction to tobacco necrosis virus. A delay between the onset of the stimulated ethylene increase and the detection of PR-proteins was found; ethylene production was stimulated after a few hours of treatment, whereas one, three and all the eleven PR-proteins were detected by polyacrylamide gel electrophoresis of fluid extracts after 2, 4 and 6 days of treatments, respectively. The possible causal relationship between stimulation of ethylene production and PR-protein accumulation is discussed.     

Chilling injury and recovery in detached and attached leaves measured by chlorophyll fluorescence

Smillie, R. M., Nott, R., Hetherington, S. E. and Öyustt, G. 1987. Chilling injury and recovery in detached and attached leaves measured by chlorophyll fluorescence Chilling injury was compared in detached and attached leaves chilled at 0 or 0.5°C by measuring the decrease in induced chlorophyll fluorescence in vivo. The fluorescence parameter measured was F_R, the maximal rate of rise of induced chlorophyll fluorescence emission after irradiating dark-adapted leaves. The plants used were bean, Phaseolus vulgaris L. cv. Pioneer, and maize, Zea mays L. cvs hybrid GH 390 and Northern Belle. Leaves were detached and placed on wet paper and covered with thin polyethylene film to prevent water loss during chilling. Leaves left attached on plants were treated similarly. When chilled in this way at 100% relative humidity, the chilling-induced decrease in F_R was the same in detached and attached leaves. For the attached leaves, the same result was obtained whether just a single leaf was chilled or the whole plant. Expression of chilling injury was greatest in fully turgid leaves and comparisons can be invalid unless the water status of the detached and attached leaves are the same. Problems arising from diurnal fluctuations in water potential of plants grown in a glasshouse were circumvented by placing leaves on the wet filter paper under polyethylene film prior to chilling, which allowed high water potentials to be regained, or mist sprays in the glasshouse were employed. Determinations of the time course for changes in F_R of maize (cv. Northern Belle) during chilling at 0°C showed that F_R decreased exponentially, at the same rate (time to 50% decrease in F_R was 9.3 h) in detached and attached leaves. Chilling injury was largely reversible for the first 20 h of chilling stress as both detached and attached leaves recovered their pre-chilling values of F_R after a further 20 h at 20°C in darkness. Leaves chilled for 48 h showed partial recovery, while those chilled for 72 h did not recover. Recovery was impeded by light. Inability to recover from chilling as indicated by measurements of F_R was paralleled by the incidence of visible symptoms of injury. It is concluded that detached and attached leaves behave similarly during chilling and short-term recovery, provided a similarity in treatments is rigorously maintained.     

Role of ethylene in the senescence of detached rice leaves

The role of ethylene in the senescence of detached rice leaves in relation to their changes in 1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene production was studied. In freshly excised rice leaf segments, ACC level and ethylene production rates were very low. Following incubation, the rates of ethylene production increased and reached a maximum in 12 h, and subsequently declined. The rise of ethylene production was associated with a 20- to 30-fold increase in ACC level.

Ethylene seems to be involved in the regulation of the senescence of detached rice leaves. This conclusion was based on the observations that (a) maximum ethylene production preceded chlorophyll degradation, (b) ACC application promoted chlorophyll degradation, (c) inhibitors of ethylene production and ethylene action retarded chlorophyll degradation, and (d) various treatments such as light, cycloheximide, α,α-dipyridyl, Ni²⁺, and cold temperature, which retarded chlorophyll degradation, also inhibited ethylene production.

Abscisic acid promoted senescence but significantly decreased ethylene production, whereas benzyladenine retarded senescence but promoted ethylene production. This is interpreted to indicate that abscisic acid treatment increased the tissue sensitivity to ethylene, whereas benzyladenine treatment decreased it.

     

Ammonium in relation to proline accumulation in detached rice leaves

Ammonium accumulation in relation to prolineaccumulation in detached rice leaves under stressconditions was investigated. Ammonium accumulation indark-treated detached rice leaves preceded prolineaccumulation. Ammonium accumulation caused by waterstress coincided closely with proline accumulation indetached rice leaves. Exogenous NH₄Cl andmethionine sulfoximine (MSO), which caused anaccumulation of ammonium in detached rice leaves,increased proline content. It was found that prolinein NH₄Cl- or MSO-treated rice leaves is lessutilized than in water-treated rice leaves (controls). These results are in agreement with the observationthat a decrease in proline utilization contributes tothe accumulation of proline in dark-treated and waterstressed rice leaves. Although ammonium contentincreased in Cd- and Cu-treated rice leaves, theincrease in ammonium content was only observed afterthe increase in proline content.     

Effects of salicylate on stomatal resistance in detached tobacco leaves

Salicylate administered to detached tobacco (Nicotiana tabacum L.) leaves kept in the light rapidly induced an increase in stomatal resistance. This effect was not the result of water stress. Both the concentration of salicylate and the duration of the application to leaves affected the extent of the stomatal response. Application of salicylate for short periods showed that, once the stomatal response started, it was maintained for long period of time in the absence of further supply. K⁺ or Ca²⁺ were able to lower the stomatal resistance induced by salicylate, but only when both the ions were administered together with salicylate the stomatal closure was prevented. The results suggest that salicylate elicits some alterations interfering with the control of, stomatal movements, possibly affecting the integrity of cell membranes.     

Changes in putrescine accumulation induced by agents affecting cytosolic pH in detached rice leaves

Effects of compounds that influenced cytosolic pH on the level of putrescine in detached rice leaves were examined. Permeant weak acids, isobutyric acid and propionic acid, increased the level of putrescine in detached rice leaves. Procaine and trisodium citrate, known to be permeant weak bases, on the other hand, decreased the level of putrescine. It seems possible that the level of putrescine in detached rice leaves is regulated by the cytosolic pH.