Photosynthetic Response of Barley Plants to Soil Flooding

72 to 120 h of soil flooding of barley plants (Hordeum vulgare L. cv. Alfa) led to a noticeable decrease in the rates of CO₂ assimilation and transpiration, and in chlorophyll and dry mass contents. Stomatal conductance decreased following flooding without appreciable changes in the values of intercellular CO₂ concentrations. A drop in the activity of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and of the photorespiratory enzymes phosphoglycollate phosphatase (EC 3.1.3.18) and glycollate oxidase (EC 1.1.3.1) was observed, while the activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) increased in all flooded plants. Flooding of barley plants caused an increase in proline content and in leaf acidity.     

Stomatal characteristics during micropropagation of Wrightia tomentosa

A deviation from usually found characteristics of stomata in Wrightia tomentosa was noted during in vitro propagation. Increase in stomatal frequency in leaves of plants grown in vitro was observed with 29.4 % malformed stomata. The stomata were spherical, wide open, did not close in detached leaves even after 3 h. The leaves exhibited 93.4 % total water loss during 3-h period. Stomatal frequency, percentage of malformed stomata and rate of water loss declined in subsequent rooting phase. Nevertheless, for high survival rate plantlets were hardened under gradually decreasing air humidity either in partially opened glass bottles containing Soilrite™ moistened with 1/4 Murashige and Skoog nutrients or in pots covered with polyethylene bags. The stomatal characteristics of hardened plants were comparable to seedlings. Survival rate was more than 95 %.     

Stomatal and photosynthetic responses ofCichorium intybus leaves to sulfur dioxide treatment at different stages of plant development

Fifty-day-oldCichorium intybus Linn, plants were exposed to 1 ppm sulfur dioxide gas, 2 h per day for 7 consecutive days. Their leaves as well as those from the control plants were sampled at pre-flowering, flowering, and post-flowering stages to study their morphological, physiological, and biochemical responses to SO₂ stress. The number, dimensions, area, and biomass of leaves were less in the treated plants. Length and width of stomatal apertures on both epidermises were greater for leaves exposed to SO₂. The Stomata were longer on the adaxial epidermis, but shorter on the abaxial epidermis, except at the pre-flowering stage. Stomatal widths varied widely. Compared with the controls, the abaxial epidermis on treated leaves showed consistently lower stomatal densities as well as stomatal indices. This was also true for the adaxial epidermis during the post-flowering stage. The photosynthetic rate and stomatal conductance were reduced in the SO₂-exposed plants, but intercellular CO₂ concentrations increased at the pre-flowering stage and, subsequently, declined. Chlorophyll a, carotenoid, and total chlorophyll contents increased at the pre-flowering stage, and then decreased. The level of chlorophyllb was reduced throughout plant development compared with the untreated controls.     

Effect of abscisic acid on photosynthetic parameters during <Emphasis Type="Italic">ex vitro</Emphasis> transfer of micropropagated tobacco plantlets

The aim of this research was to determine whether exogenous abscisic acid (ABA) applied immediately after ex vitro transfer of in vitro grown plants can improve their acclimatization. Tobacco (Nicotiana tabacum L.) plantlets were transferred into pots with Perlite initially moistened either by water or 50 μM ABA solution and they were grown under low (LI) or high (HI) irradiance of 150 and 700 μmol m⁻² s⁻¹, respectively. Endogenous content of ABA in tobacco leaves increased considerably after ABA application and even more in plants grown under HI. Stomatal conductance, transpiration rate and net photosynthetic rate decreased considerably 1 d after ex vitro transfer and increased thereafter. The gas exchange parameters were further decreased by ABA application and so wilting of these plants was limited. Chlorophyll (a+b) and β-carotene contents were higher in ABA-treated plants, but the content of xanthophyll cycle pigments was not increased. However, the degree of xanthophyll cycle pigments deepoxidation was decreased what also suggested less stress in ABA-treated plants. No dramatic changes in most chlorophyll a fluorescence parameters after ex vitro transfer suggested that the plants did not suffer from restriction of electron transport or photosystem damage.     

Is a decreased water potential after withholding oxygen to roots the cause of the decline of leaf-elongation rates in Zea mays L. and Phaseolus vulgaris L.?

Leaf-elongation rates of Zea mays L. and Phaseolus vulgaris L. were measured in plants grown for 4 d in nutrient solution bubbled with N₂ and in soil-grown waterlogged Phaseolus plants. Leaf water potential in both species was lower 3–4h after replacing aeration by N₂-bubbling. In Zea, the water potential after 24 h or more was the same in control plants and plants with N₂ treatment. In Phaseolus, the water potential of inundated plants and plants with N₂ treatment was always lower than those of control plants. The leaf-elongation rate of both species was always lower in plants treated with N₂, especially during light periods. In Zea, the elongation rate was lowest in the first 24 h, whilst in Phaseolus it was lowest on the last (fourth) day of treatment. There was no difference between N₂ treatment and inundation experiments. It is concluded that during the first hours of treatment the leaf-elongation rate was reduced as a consequence of the lower water potential. Thereafter, however, elongation rates were lower than could be expected on the basis of the plant's water relations.Abbreviations LER leaf elongation rate - PEG-200 polyethylene-glycol 200 - RWC relative water content     

Interaction of Cytokinins and Abscisic Acid During Regulation of Stomatal Opening in Bean Leaves

Effects of benzyladenine (BA) and abscisic acid (ABA) applied separately or simultaneously on parameters of gas exchange of Phaseolus vulgaris L. leaves were studied. In the first two experimental sets) 100 M ABA and 10 M BA were applied to plants sufficiently supplied with water. Spraying of leaves with ABA decreased stomatal conductance (g _s) and in consequence transpiration rate (E) and net photosynthetic rate (P _N) already 1 h after application, but 24 h after application the effect almost disappeared. 10 M BA slightly decreased gas exchange parameters, but in simultaneous application with ABA reversed the effect of ABA. Immersion of roots into the same solutions markedly decreased gas exchange parameters and 24 h after ABA application the stomata were completely closed. The effect of ABA was ameliorated by simultaneous BA application, particularly after 1-h treatment. In the third experimental set, plants were pre-treated by immersing roots into water, 1 M BA, or 100 M ABA for 24 h and then the halves of split root system were dipped into different combinations of 1 M BA, 100 M ABA, and water. In plants pre-treated with ABA all gas exchange parameters were small and they did not differ in plants treated with H₂O+H₂O, H₂O+BA, or BA+BA. In plants pre-treated with BA or H₂O, markedly lower values of P _N were found when both halves of roots were immersed in ABA. Further, the effects of pre-treatment of plants with water, 1 M BA, 100 M ABA, or ABA+BA on the development of water stress induced by cessation of watering and on the recovery after rehydration were followed. ABA markedly decreased gas exchange parameters at the beginning of the experiment, but in its later phase the effect was compensated by delay in development of water stress. BA also delayed development of water stress and increased P _N in water-stressed leaves. BA reversed the effect of ABA at mild water stress. Positive effects of BA and ABA pre-treatments were observed also after rehydration.     

Alterations in light-induced stomatal opening in a starch-deficient mutant of Arabidopsis thaliana L. deficient in chloroplast phosphoglucomutase activity

Stomatal responses to light of Arabidopsis thaliana wild-type plants and mutant plants deficient in starch (phosphoglucomutase deficient) were compared in gas exchange experiments. Stomatal density, size and ultrastructure were identical for the two phenotypes, but no starch was observed in guard cells of the mutant plants whatever the time of day. The overall extent of changes in stomatal conductance during 14 h light–10 h dark cycles was similar for the two phenotypes. However, the slow endogenous stomatal opening occurring in darkness in the wild type was not observed in the mutant plants. Stomata in the mutant plants responded much more slowly to blue light (70 μmol m^?2 s^?1) though the response to red light (250 μmol m^?2 s^?1) was similar to that of wild-type plants. In paradermal sections, stomatal responses to red light (300 μmol m^?2 s^?1) were weak for wild-type plants as well as for mutant plants. Stomatal opening was greater under low blue light (75 μmol m^?2 s^?1) than under red light for the two genotypes. However, in mutant plants, a high chloride concentration (50 mol m^?3) was necessary to achieve the same stomatal aperture as observed for the wild-type plants. These results suggest that starch metabolism, via the synthesis of a counter-ion to potassium (probably malate), is required for full stomatal response to blue light but is not involved in the stomatal response to red light.     

Rehydration of Sugar Beet Plants after Water Stress: Effect of Cytokinins

The possibility to improve the recovery of sugar beet plants after water stress by application of synthetic cytokinins N⁶-benzyladenine (BA) or N⁶-(m-hydroxybenzyl)adenosine (HBA) was tested. Relative water content (RWC), net photosynthetic rate (P_N), transpiration rate (E), stomatal conductance (g_s), chlorophyll (Chl) a and Chl b contents, and photosystem 2 efficiency characterized by variable to maximal fluorescence ratio (F_v/F_m) were measured in control plants, in water-stressed plants, and after rehydration (4, 8, 24, and 48 h). Water stress markedly decreased parameters of gas exchange, but they started to recover soon after irrigation. Application of BA or HBA to the substrate or sprayed on leaves only slightly stimulated recovery of P_N, E, and g_s in rehydrated plants, especially during the first phases of recovery. Chl contents decreased only under severe water stress and F_v/F_m ratio was not significantly affected by water stress applied. Positive effects of BA or HBA application on Chl content and F_v/F_m ratio were mostly not observed.     

Mycorrhizal promotion of host stomatal conductance in relation to irradiance and temperature

Colonization of roots and soil by arbuscular mycorrhizal (AM) fungi sometimes promotes stomatal conductance (g _s) of the host plant, but scientists have had difficulty predicting or manipulating the response. Our objective was to test whether the magnitude of AM influence on g _s is related to environmental conditions: irradiance, air temperature or leaf temperature. Stomatal conductances of two groups of uncolonized sorghum plants were compared to g _s of plants colonized by Glomus intraradices (Gi) or Gigaspora margarita (Gm) in 31 morning and afternoon periods under naturally varying greenhouse conditions. Stomatal conductance of Gi and Gm plants was often markedly higher than g _s of similarly sized nonAM plants. AM promotion of g _s was minimal at the lowest irradiances and lowest air and leaf temperatures, but was substantial at intermediate irradiance and temperatures. AM promotion was again low or absent at the highest irradiances and temperatures. Magnitude of AM promotion of g _s was not a function of absolute g _s. Promotion of g _s by Gi and Gm was remarkably similar. Differing phosphorus fertilization did not affect g _s.     

过表达IbOr基因甘薯增强抗旱性的生理机制

以超表达甘薯橙色基因(IbOr)的转基因甘薯(TS)以及非转基因甘薯(NT)为实验材料,通过15%聚乙二醇6000(PEG-6000)模拟干旱条件,研究转基因与非转基因甘薯幼苗在水分胁迫不同时间的光合系统,膜脂过氧化及抗氧化防御系统中主要指标的变化情况,探讨转基因甘薯耐旱性的生理机制。结果显示:(1)随PEG-6000胁迫时间延长,甘薯叶片的叶绿素、类胡萝卜素含量及其叶片净光合速率、气孔导度、胞间CO2浓度、蒸腾速率都显著降低,但转基因株系降低幅度小于非转基因植株。(2)在正常供水和水分胁迫下,超表达IbOr基因甘薯叶片中O-·2、MDA含量均低于非转基因甘薯,即转基因甘薯具有较低的活性氧水平且脂膜受损伤较小。(3)PEG-6000胁迫24h后,甘薯叶片中SOD、POD酶活性均增加,48h达到最大值,且转基因甘薯中2种酶活性显著高于非转基因甘薯。研究表明,过表达IbOr基因可以有效减轻甘薯在水分胁迫条件下受损害的程度,且可能主要通过提高甘薯的抗氧化胁迫能力来完成。     

Effects of PEG-induced water stress onin vitro hardening of ‘Valiant’ grape

Polyethylene glycol was added to the rooting medium ofmicropropagated grape shoots to induce water stress. At the end of the rooting stage, plantlets treated with 2% polyethylene glycol were compared with untreated control plantlets and greenhouse-grown plants. Leaves of treated plantlets had the highest deposition of epicuticular wax, followed by those of the greenhouse and control. Stomatal index did not vary among treatments. However, differences in leaf epidermal cell configuration were observed among treatments. The morphological changes of treated plantlets, including substantial deposition of epicuticular wax and modified leaf surface anatomy were associated with increasedex vitro survival after four weeks in the greenhouse.     

Foraging by the aphid parasitoid Ephedrus cerasicola for patchily distributed hosts

Females of the aphid parasitoid Ephedrus cerasicola were released into small glasshouses containing 20–25 paprika plants (Capsicum annuum L.), either aphid-free (controls) or infested with different numbers of Myzus persicae (Sulzer), i.e. from 0 to about 1000 aphids per plant. The number of parasitoids per plant were counted 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 8 h and about 24 h after the release. During the last inspection (24 h) the parasitoids were removed. In the aphid-infested houses, the parasitoids soon gathered on the most heavily infested plants (500–1000 aphids per plant), while the aphid-free and low-infested plants (50–200 aphids per plant) were almost free from parasitoids. In the aphid-free houses, a significantly lower portion of the released parasitoids were found on the plants, and they did not show any preference for certain plants. The percentage parasitism, based on mummies on the plants, was rather density independent after a slight peak on plants with about 50 aphids. No superparasitism was found by dissection of aphids.

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Résumé Des femelles de l'aphidophage Ephedrus cerasicola ont été lachées dans de petites serres contenant 20 à 25 pieds de paprika (Capsicum annuum), contaminés par des effectifs de 0 (témoins) à 1000 pucerons (Myzus persicae) par pied. Le nombre de parasitoïdes par plante a été rélevé 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 8 h, et environ 24 h après leur libération. Les E. cerasicola adultes ont été retirés lors de la dernière inspection (24 h). Dans les serres infestées, les femelles se rassemblent sur les plantes les plus contaminées (500 à 1000 pucerons par pied), tandis que les plantes sans pucerons ou faiblement contaminées (50 à 200 par plante) n'en avaient presque pas. Dans les serres sans pucerons, des femelles en proportion significativement plus faible ont été trouvées sur les plantes, sans qu'elles aient manifesté une préférence pour certaines d'entre elles. Le taux de parasitisme, d'après le nombre de momies par plante, est apparu plutôt indépendant de la densité, après un faible pic pour les plantes avec environ 50 pucerons. Les dissections de pucerons n'ont révélé aucun superparasitisme.

     

Photosynthetic and leaf morphological characteristics in Leucaena leucocephala as affected by growth under different neutral shade levels

Morphological and physiological measurements on individual leaves of Leucaena leucocephala seedlings were used to study acclimation to neutral shading. The light-saturated photosynthetic rate (P_{n max}) ranged from 19.6 to 6.5 mol CO₂ m^–2 s^–1 as photosynthetic photon flux density (PPFD) during growth decreased from 27 to 1.6 mol m^–2 s^–1. Stomatal density varied from 144 mm^–2 in plants grown in high PPFD to 84 mm^–2 in plants grown in low PPFD. Average maximal stomatal conductance for H₂O was 1.1 in plants grown in high PPFD and 0.3 for plants grown in low PPFD. Plants grown in low PPFD had a greater total chlorophyll content than plants grown in high PPFD (7.2 vs 2.9 mg g^–1 on a unit fresh weight basis, and 4.3 vs 3.7 mg dm^–2 on a unit leaf area basis). Leaf area was largest when plants were grown under the intermediate PPFDs. Leaf density thickness was largest when plants were grown under the largest PPFDs. It is concluded that L. leucocephala shows extensive ability to acclimate to neutral shade, and could be considered a facultative shade plant.Abbreviations the initial slope of the photosynthesis vs PPFD curve - P_{n max} the light-saturated photosynthetic rate - PPFD photosynthetic photon flux density     

Effects of drought on water content and photosynthetic parameters in potato plants expressing the trehalose-6-phosphate synthase gene of Saccharomyces cerevisiae

Two transgenic potato lines, T1 and T2, expressing the trehalose-6-phosphate synthase (TPS1) gene of yeast were isolated. In our experimental approach, we applied two novelties, namely the fusion of the drought-inducible promoter StDS2 to TPS1 and a marker-free transformation method. In contrast to the expected drought-induced expression, only a very low constitutive TPS1 expression was detected in the transgenic lines, probably due to chromosomal position effects. The observed expression pattern, however, was sufficient to alter the drought response of plants. Detached leaves of T1 and T2 showed an 8 h delay in wilting compared to the non-transformed control. Potted plants of T1 and T2 kept water 6 days longer than control plants and maintained high stomatal conductance and a satisfactory rate of net photosynthesis. During drought treatment, CO₂ assimilation rate measured at saturating CO₂ level was maintained at maximum level for 6–9 days in transgenic plants while it decreased rapidly after 3 days in the wild type plants. Under optimal growth conditions, lower CO₂ fixation was detected in the transgenic than in the control plants. Stomatal densities of T1 and T2 leaves were reduced by 30–40%. This may have contributed to the lower CO₂ fixation rate and altered drought response. Ibolya Stiller, and Sándor Dulai contributed equally to this work.     

The effect of kinetin on stomata of the grass Anthephora pubescens Nees

Transpiration from excised leaves of Anthephra pubescens Nees was enhanced by 1 and 10 mmol m^-3 kinetin. Stomatal opening in isolated epidermal strips of A. pubescens under CO₂-free air and in the absence of K⁺ was enhanced by 10 mmol m^-3 kinetin.Abbreviations ABA abscisic acid     

Effect of temperature stress on the endogenous cytokinin content in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh plants

The levels of three endogenous cytokinin equivalents: zeatin (Z), iso-pentenyladenine (iP) and dihydrozeatin (dZ) in two Arabidopsis thaliana (L.) Heynh genotypes — wild type (wt) and ethylene-insensitive mutant (eti5), were compared using enzyme immunoassay (ELISA). Cytokinin content was measured after exposure to low (4 °C for 24 h in darkness) or high temperature (38 °C for 24 h in darkness). Measurements were performed immediately and 24, 48 and 120 h after treatments. It was found that at normal growth conditions eti5 plants contained more endogenous cytokinins compared to the wild type. At both temperature treatments mutant plants had decreased total cytokinin levels. Wild-type plants treated with high temperature (HT) exhibited reduced total cytokinins (with the exception of rates at 48 h), while low temperature (LT) treatment resulted in elevated total amount of the studied equivalents (except at 24 h). The obtained results suggested that HT had greater effect on cytokinin levels than LT since it caused more profound changes in the total content. We assume that this was due to the natural chilling tolerance of Arabidopsis plants.     

Expression of Cry1Ac in Transgenic Tobacco Plants Under the Control of a Wound-Inducible Promoter (AoPR1) Isolated from Asparagus officinalis to Control Heliothis virescens and Manduca sexta

Expression of cry1Ac gene from Bacillus thuringiensis (Bt) was evaluated under the control of a wound-inducible AoPR1 promoter from Asparagus officinalis in transgenic tobacco plants. The leaves of transgenic plants were mechanically wounded to evaluate the activity of the AoPR1 promoter in driving the expression of Cry1Ac protein at the wound site. Our results indicate that mechanical wounding of transgenic plants was effective in inducing the expression of Cry1Ac protein. As a result of this induction, the accumulated levels of Cry1Ac protein increased during 6–72 h post-wounding period. The leaves of transgenic tobacco plants were evaluated for resistance against Heliothis virescens and Manduca sexta in insect bioassays in two different ways. The detached tobacco leaves were either fed directly to the insect larvae or they were first mechanically wounded followed by a 72 h post-wounding feeding period. Complete protection of mechanically wounded leaves of transgenic plants was observed within 24 h of the bioassay. The leaves of transgenic plants fed directly (without pre-wounding) to the larvae achieved the same level of protection between 24 and 72 h of the bioassay.     

Stomatal acclimation to increased CO2 concentration in a Florida scrub oak species Quercus myrtifolia Willd

Native scrub‐oak communities in Florida were exposed for three seasons in open top chambers to present atmospheric [CO₂] (approx. 350 μmol mol^?1) and to high [CO₂] (increased by 350 μmol mol^?1). Stomatal and photosynthetic acclimation to high [CO₂] of the dominant species Quercus myrtifolia was examined by leaf gas exchange of excised shoots. Stomatal conductance (g_s) was approximately 40% lower in the high‐ compared to low‐[CO₂]‐grown plants when measured at their respective growth concentrations. Reciprocal measurements of g_s in both high‐ and low‐[CO₂]‐grown plants showed that there was negative acclimation in the high‐[CO₂]‐grown plants (9–16% reduction in g_s when measured at 700 μmol mol^?1), but these were small compared to those for net CO₂ assimilation rate (A, 21–36%). Stomatal acclimation was more clearly evident in the curve of stomatal response to intercellular [CO₂] (c_i) which showed a reduction in stomatal sensitivity at low c_i in the high‐[CO₂]‐grown plants. Stomatal density showed no change in response to growth in high growth [CO₂]. Long‐term stomatal and photosynthetic acclimation to growth in high [CO₂] did not markedly change the 2·5‐ to 3‐fold increase in gas‐exchange‐derived water use efficiency caused by high [CO₂].     

Responses of cowpeas (Vigna unguiculata (L.) Walp.) to progressive soil drought

Summary Greenhouse-grown cowpeas, Vigna unguiculata (L.) Walp., were subjected either to well-watered or to progressive soil drought conditions between 10–40 days after emergence. Stomatal closure was found to correlate with the progressive drying of soil while leaf water potentials were not very different from the well-watered plants. Reduction in leaf turgor resulted in a reduced rate of leaf extension but increased that of root. Stomatal conductance and transpiration rates of soil-drought plants were similar to well-watered plants in the morning, but were greatly reduced in the afternoon till evening. It is suggested that the maintenance of transpiration rates per unit leaf area of soil-drought cowpeas in the morning is due to the reduction in the leaf area per plant and possibly the hydration of the plants in the night through enhanced root growth.     

Induced responses in three alkaloid-containing plant species

In this paper we test three plant species for the inducibility of their alkaloid production. The plants were heavily damaged by cutting off 50% of their leaf surface using a pair of scissors. The cut-off leaf tips were used as controls for possible diurnal fluctuations. After 3, 6, 12, 24 and 48 h, respectively, the leaf bases of the damaged plants were harvested and the alkaloid concentration was measured. In Senecio jacobaea the pyrrolizidine alkaloid (Pa) concentration in damaged plants decreased within 6–12 h after damage. Within 24 h after damage the Pa concentration of Cynoglossum officinale doubled compared to control values. Indole alkaloid production in Catharanthus roseus was found not to be induced in this experiment. The responses are discussed in a functional context. We hypothesize that the nature of the response is not a feature of the type of secondary metabolite, but is related to whether the plants are damaged mainly by generalist or by specialist herbivores.