Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: IV. The Effect of Light Intensity on the Carbon Dioxide Compensation Point

The carbon dioxide compensation point () was found to vary whenmeasured at increasing light intensities, in plants grown ata constant illumination. This response varied with the physiologicalage of the leaf. The also varied when measured at a constantillumination, with plants grown at different light intensities.The activity of the enzymes RuDP carboxylase, nitrate reductase,glycollate oxidase, and catalase was found to be influencedby the light intensity at which the plants were grown. A goodcorrelation was obtained between the measured and the ratioof nitrate reductase: RuDP carboxylase activities, suggestingthat nitrate reductase may be used as an indirect measure ofphotorespiration in plants receiving nitrate as the sole nitrogensource.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: II. Effects of External Concentrations of Carbon Dioxide and Oxygen

Plants grown in a high carbon dioxide environment (< 1 percent) were found to have increased levels of RuDP carboxylase,and suppressed activities of catalase, glycollate oxidase, andnitrate reductase, enzymes all associated with the peroxisome.Similarly, plants grown in low oxygen concentrations showedsuppressed activities of the peroxisomal enzymes. However, underthese conditions RuDP carboxylase activity was also suppressed.These results further suggest that nitrate reductase activityis associated with photorespiration.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: I. Effects of Light Period, Leaf Age, and Position, on Carbon Dioxide Compensation Point ({Gamma})

The carbon dioxide compensation point () was found to vary underconstant environmental conditions, as the duration of lighttreatment increased, and also with leaf age. The activitiesof RuDP carboxylase, catalase, glycollate oxidase, and nitratereductase were found to vary with duration of the light treatmentduring the course of a single day. RuDP carboxylase activity was found to exhibit a rhythmic fluctuationof activity with age, which had a frequency common to all theleaves examined. The activities of RuDP carboxylase, glycollateoxidase, and nitrate reductase in the leaves was found to increasewith ascending leaf position; the activities generally decreasedwith leaf age. The ratio of nitrate reductase activity to RuDPcarboxylase activity was found to give an excellent correlationwith measured T, and the value of nitrate reductase as an indirectmeasure of photorespiration and the relationship between nitrogenmetabolism and photorespiration is discussed.     

Precise Measurements of Carbon Dioxide Exchange by Illuminated Leaves near the Compensation Point

The results of precise measurements of rates of carbon dioxideassimilation at low external concentrations of carbon dioxideand of rates of carbon dioxide output into virtually carbondioxide-freeair show that linear extrapolations of the carbon dioxide intakecurve plotted against the external concentrations of carbondioxide give an exaggerated estimate of the rate of carbon dioxideoutput from illuminated leaves into carbon dioxide-free air. The shape of the exchange curve suggests that the rate of endogenousproduction of carbon dioxide changes at external concentrationsin the region of the carbon dioxide compensation point ().     

Differential Effects of Carbon Dioxide on the Growth Rates of Coleoptiles and the Enclosed Leaves of Hordeum vulgare L. seedlings

Carbon dioxide appears to modulate the growth rates of the barley(Hordeum vulgare L.) coleoptile and the enclosed leaves duringearly germination. Its effect is to stimulate the coleoptileto elongate at a rate equal to or greater than that of the enclosedleaves. Such stimulation was observed directly in barley coleoptilesfloated on CO₂-sarurated water or indirectly using a DCMU solution.This mechanism ensures that the tender leaves remain enclosedwithin the structurally strong coleoptile sheath until the shootpushes through the soil surface. It is suggested that CO₂ respiredby the enclosed leaves effects this modulation: the CO₂ couldpass into the coleoptile chamber and thence into the coleoptilevia stomata present on coleoptile inner walls.     

Effects of Light Intensity on Photosynthetic Carboxylative Phase Enzymes and Chlorophyll Synthesis in Greening Leaves of Hordeum vulgare L

The effects of various light intensities on in vivo increases in activities of phosphoriboisomerase, phosphoribulokinase and ribulose-1, 5-diP carboxylase and on synthesis of chlorophyll were studied in greening leaves of Hordeum vulgare L.

Each enzyme was already present in dark-grown plants, but further increases in activities required both a light treatment of the intact plant and a favorable temperature. The amount of enzymatic activity and chlorophyll developed was governed by light intensity.

Measured activities of phosphoriboisomerase and ribulose 1,5-diP carboxylase were highly correlated with synthesis of chlorophyll at all intensities studied. Measured activity of phosphoribulokinase was correlated with synthesis of chlorophyll only at saturating or near saturating light intensities. At decreasing light intensities the response curves of this enzyme differed from those of chlorophyll and of phosphoriboisomerase and ribulose-1, 5-diP carboxylase. A lag period of phosphoribulokinase increased with decreasing light intensity. After the lag period a rapid rate of increase occurred which did not level off during 48 hours of illumination. Thus, a different control mechanism may be operative in inducing increased activity of this enzyme.

     

Regulation of Fructan Metabolism in Leaves of Barley (Hordeum vulgare L. cv Gerbel)

Excised primary leaf blades of barley (Hordeum vulgare L. cv Gerbel) rapidly synthesized large quantities of fructan in the light and, upon transfer to the dark, they rapidly degraded it again. In the course of such a light/dark cycle the activities of sucrose-sucrose-fructosyltransferase (SST), fructan hydrolase, and invertase were measured in cell-free extracts of the blades. SST activity increased 20-fold within 24 hours in the light and disappeared again upon transfer to the dark during a similar period of time. Cycloheximide inhibited the increase of SST activity in the light indicating de novo synthesis. The loss of SST activity in the dark, however, was unaffected by cycloheximide. No SST activity appeared in the light if photosynthesis was inhibited by lowering the CO₂ concentration in the atmosphere. However, SST activity and fructan synthesis were induced even in the dark and at a low CO₂ concentration when the leaf blades were immersed in a solution of sucrose. Several other sugars, maltose and fructose in particular, had the same effect. Trehalose induced SST activity but no fructan synthesis occurred. The activities of fructan hydrolase and invertase changed little during the light/dark cycle. It is suggested that the control of SST activity in conjunction with the supply of photosynthates plays a key role in the regulation of fructan metabolism.     

Effect of Inorganic Nitrogen lons on Photosynthesis and Carbon Dioxide Compensation Concentration of Themeda triandra and Zea mays

Vacuum infiltration of nitrate and ammonium ions into nitrogen-starvedleaf tissue of Themeda triandra and Zea mays increased the carbondioxide compensation point well in excess of the level normallyassociated with C₄ photosynthetic pathway plants. The net photosyntheticrate was stimulated by the nitrate ions and but slightly inhibitedby the ammonium ions. These effects were immediate. The ionsincreased the Themeda triandra carbon dioxide compensation pointand had no effect on that of Zea mays when these plants weregrown on fertilized soil. The dark respiration rates of nitrogen-starvedThemeda triandra leaves were unaffected by the infiltrationof inorganic nitrogen ions. The results suggest that photosynthesisand photorespiration are directly influenced by inorganic nitrogenions. Themeda triandra, Zen mays, net photosynthetic rate, carbon dioxide compensation points, inorganic nitrogen stimulation     

Effects of Mechanical Impedance on Root Growth in Barley (Hordeum vulgare L.): III. OBSERVATIONS ON THE MECHANISM OF RESPONSE

The effects of mechanical stress on whole root systems was investigatedusing beds of solid glass spheres (ballotini) continuously suppliedwith aerated nutrient solution. As noted in earlier experiments,increased mechanical impedance slowed root extension and alteredcell size and number; it also caused distortion of the rootapex, stimulated growth of lateral shoot meristems, and inducedthe formation of nodal roots. The development of lateral branchroots was enhanced and where root axes curved around ballotinilateral roots formed preferentially on the outer (convex) sidewhereas root hairs developed on the inner (concave) side. After roots were relieved from mechanical stress at least 3d elapsed before the rate of extension growth equalled thatof unimpeded plants. When intact Zea mays root apices first made contact with ballotinitheir elongation was slowed by 70% for about 10 min; where rootcaps were removed before the roots made contact, no such effectswere seen. We discuss the general nature of the mechanism of response tomechanical stress.     

The Effects of X-rays on the Embryonal Growth and Development of Hordeum vulgare L.

The effects of softer X-rays as an external agent on the developingembryos were manifested by a number of abnormalities such asenlargement and vacuolation of cells, disturbances in cell walls,disintegration of cells leading to the formation of cavities,disturbances in distribution of meristematic tissues, a numberof proliferations in different parts of the embryo, and retardedgrowth of the embryo during the early post-radiation period.In addition to these, deeply stained globular cytoplasmic bodieswere observed in radiated embryonic cells. Very similar kindsof abnormalities were produced by softer X-rays starting from400 r. and including 800 r. The frequency of occurrence anddegree of proliferations in embryos irradiated with 800 r.,however, were relatively higher than those produced by 400 r.and 500 r. Treatments with 300 r. units of irradiation inducedonly the appearance of deeply stained globular bodies withincytoplasm and no effects were visible with dosages below 300r. Comparative measurements of cell- lengths of the treatedand control embryos at undifferentiated as well as at differentiatedstages showed an increase in cell-lengths within radiated embryos.Radiated embryos showed defective pattern of germination. HarderX-rays were found to be less effective in inducing embryonicabnormalities than softer rays when equal calculated dosagesof the two were applied to the flowering spikes of Hordeum vulgareL.     

Enzymology of Fructan Synthesis in Grasses: Properties of Sucrose-Sucrose-Fructosyltransferase in Barley Leaves (Hordeum vulgare L. cv Gerbel)

Fructan synthesis was induced in excised primary leaf blades of Hordeum vulgare L. cv Gerbel by illumination in 30 millimolar fructose. This treatment induced a 26-fold increase of sucrose-sucrose-fructosyltransferase (SST, EC 2.4.1.99) activity within 24 hours. Acid invertase (EC 3.2.1.26) activity remained about constant. By preparing protoplasts from induced leaves, approximately 80% of the invertase activity was removed with the cell walls while SST was retained. The protoplast homogenate was used to partially purify and characterize SST. Acid precipitation (pH 4.75) and anion exchange chromatography (fast protein liquid chromatography on Mono `Q') resulted in a recovery of about 80% of total SST activity. The principal activity (SST 1), accounting for 85% of the activity recovered, was purified about 200-fold. It was essentially free of invertase activity and catalyzed the synthesis of a trisaccharide which co-chromatographed with isokestose (1F-β-fructosylsucrose). The remaining 15% of SST activity (SST 2) was purified about 35-fold. It retained substantial invertase activity and catalyzed the synthesis of only one trisaccharide which co-chromatographed with kestose (6F-β-fructosylsucrose). It is concluded that barley leaves which store mainly fructan of the phlein type (β-2-6 polyfructosylsucrose), nevertheless contain sucrose-sucrose 1F-β-d-fructosyltransferase as the key enzyme of fructan synthesis.     

Effects of High Temperature and Water Deficit on Photosystem II in Hordeum vulgare Leaves of Various Ages

Structural and functional characteristics of photosystem II (PSII) were examined in leaves of 4-, 7-, and 11-day-old barley seedlings exposed to high temperature (40°C, 3 h) and water deficit (replacement of nutrient medium with 3% PEG 6000 solution, 45 h). In young seedlings, the effective quantum yield of PSII photochemical reactions decreased upon heat treatment but did not change after dehydration. Both stressful factors diminished the Q _B-reducing capacity of PSII in 4- and 7-day-old plants. This was caused by the increase in the reduction level of plastoquinone and by the impairment of the Q _B-binding site of the D1 protein. The increase in the content of plastoquinol after the heat shock was due to the impaired oxidizing capacity of cytochrome f (Cyt f). The dehydration did not alter the content of functionally active Cyt f but elevated the microviscosity of the lipid bilayer in thylakoid membranes, which presumably impeded the lateral diffusion of plastoquinones and reduced their reoxidation rate. The heating and dehydration of old leaves reduced the amount of -type PSII reaction centers, thereby inhibiting the linear electron transport. It is concluded that PSII responses to heat treatment and water deficit are subject to variations depending on leaf age. Measurements of the redox potentials for plastoquinones, Cyt f, and cytochrome b ₅₅₉ upon senescence, hyperthermia, and water deficit allowed us to propose that heat and water stresses activate cyclic electron transport around PSII.     

不同辐照度下高浓度锰对黄瓜叶片活性氧产生和抗氧化酶活性的影响

高浓度锰处理提高了黄瓜叶片中H2O2含量和O-2·的产生速率,导致膜脂过氧化;与自然辐照度相比,1/2辐照度使高浓度锰胁迫下黄瓜叶片活性氧和丙二醛(MDA)的积累均显著降低。高浓度锰处理导致细胞溶质和叶绿体中过氧化氢酶(CAT)活性降低,而其他抗氧化酶的活性升高,尤其是自然辐照度下叶绿体中抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)活性的提高幅度比1/2辐照度下更大。高浓度锰处理使自然辐照度下线粒体中抗氧化酶的活性明显升高,而在1/2辐照度下该处理对该酶活性没有显著影响。     

Carbon and Nitrogen Assimilation by Vicia faba L. at Low Temperature: the Importance of Concentration and Form of Applied-N

Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m^–3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m^–3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m^–3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO₂uptake and not an increased CO₂, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation     

Potential cultivation of Hordeum vulgare L. in soils with high mercury background concentrations

Experimental work was carried out under close-to-real conditions to study mercury uptake by Hordeum vulgare L. cultivated in lysimeter experiments. The soil in the lysimeter experiment was obtained from a test plot located near Almadén (Spain) and had a mean mercury content of 22.9 mg kg(-1). A sequence of four crops was sown starting in autumn 2000 and repeated on a yearly basis until 2004. The first crop was grown in the field prior to the extraction of 5 one-cubic-meter lysimeters. The succeeding crops were sown in the lysimeter experiments at the CIEMAT Research Centre (Madrid, Spain). Samples of root and shoot were obtained during the four seasons. Concentrations of mercury at plant maturity in roots vary between I and 3 mg kg(-1) and in straw and grain the concentrations range from 72 to 480 microg kg(-1) and from 5 to 257 microg kg(-1), respectively. In order to assess the potential risk for human health and animal feed, an evaluation of the mercury content in the edible part of the crop has been carried out. According to legislation, there is no human health intoxication risk with a balanced consumption; otherwise, the forage use would have to be controlled.     

诱抗处理对甜瓜叶片防卫酶活性的影响

以黄河蜜幼苗为材料,分析了化学诱导物处理后甜瓜叶片中几丁质酶(CHI)、β-1,3葡聚糖酶(GLU)、苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)活性的变化.结果显示:经5种化学诱导物处理后,甜瓜叶片PAL活性快速增加,于处理后第6天出现活性高峰;苯丙噻二唑(BTH)、水杨酸(SA)、草酸(OAA)和硅酸钠(Na2SiO3)处理后GLU活性变化与PAL相似,PPO活性在测定期内持续升高;磷酸氢二钾(K2HPO4)处理对GLU和PPO活性无明显影响;SA处理后叶片CHI活性明显升高,其它诱导物处理对CHI活性无明显影响.结果表明,防卫酶(特别是GLU和PPO)活性表达增强是BTH、OAA、SA和Na2SiO3等诱导物处理系统诱导甜瓜幼苗白粉病抗性增强的重要生化机制.     

Effects of Salicylic Acid on the Structure of Second Leaves of Hordeum Vulgare L.

The structure and ultrastructure of the second leaves of 10-d-old barley plants (Hordeum vulgare L. cv. Alfa) was investigated after long-term treatment with salicylic acid (SA) in concentrations of 0.1, 0.5 and 1.0 mM. The treatment induced: 1) suppressed bulliform cells formation in the adaxial epidermis (1.0 mM SA); 2) reduction of apoplast in the mesophyll (0.5 and 1.0 mM SA); 3) formation of invaginations (0.1 and 0.5 mM SA) and proliferations (0.5 mM SA); and 4) thylakoid destruction and coagulation of the stroma (1.0 mM SA).     

多胺对裸大麦离体叶片活性氧代谢的影响

裸大麦离体叶片分别在光照和暗诱导下,以腐胺(Put)、亚精胺(Spd)和精胺(Spm)等 3种多胺,分别用2 mmol/L、0.5 mmol/L、和 0.2 mmol/L3种浓度处理,均使丙二醛(MDA)累积减少,延缓过氧化氢酶和SOD活性的下降。以 CaCl_2(5 mmol/L)+Spd(0.5mmol/L)处理,可降低Spd(0.5 mmol/L)的效应。因此多胺延缓离体叶片衰老与活性氧代谢有关,并且进入细胞时,与Ca发生竞争。     

Gas Exchange of Algae: III. Relation between the Concentration of Carbon Dioxide in the Nutrient Medium and the Oxygen Production of Chlorella pyrenoidosa

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.     

Effects of Carbon Dioxide on Metabolism by the Glycollate Pathway in Leaves

When solutions of [¹⁴C]glycollate, glycine, serine, glycerate,or glucose were supplied to segments of wheat leaves throughtheir cut bases in the light, most of the ¹⁴C was incorporatedinto sucrose in air but in CO₂-free air less sucrose was made.The synthesis of sucrose was decreased because metabolism ofserine was partly blocked. Sucrose synthesis from glucose andglycerate in CO₂-free air was decreased but to a smaller extent;relatively more CO₂ was evolved and serine accumulated. Theeffects of DCMU and light of different wavelengths on metabolismby leaves of L-[U-¹⁴C]serine confirmed that simultaneous photosyntheticassimilation of carbon was necessary for the conversion of serineto sucrose. Of various products of photosynthesis fed exogenouslyto the leaves -keto acids were the most effective in promotingphotosynthesis of sucrose and release of ¹⁴CO₂ from ¹⁴C-labelledserine. This suggests that in CO₂-free air the metabolism ofserine may be limited by a shortage of -keto acid acceptorsfor the amino group. In CO₂-free air added glucose stimulatedproduction of CO₂ and sucrose from D-[U-¹⁴C]- glycerate andno competitive effects were evident even though glucose is convertedrapidly to sucrose under these conditions. In addition to asupply of keto acid, photosynthesis may also provide substratesthat can be degraded and provide energy in the cytoplasm forthe conversion of glycerate to sugar and phosphates and sucrose.