一氧化氮对强光胁迫下高羊茅叶片抗氧化系统的调节效应

在强光胁迫下,采用水培法,使用外源NO和去除内源NO措施,研究了NO对2个高羊茅(Arid3和Houndog5)品种的抗氧化系统的调节作用.结果表明,Arid3的内源NO比对照增加201.5%,而Houndog5仅增加21.1%.Houndog5发生严重氧化损伤,电解质渗出率和丙二醛(MDA)含量分别比对照增加72.6%和85.1%,而Arid3受到的伤害较轻,分别比对照增加36.1%和30.1%.使用O.2 mmol·L~(-1)的NO专一清除剂2,4-羧基苯-4,4,5,5-四甲基咪唑-1-氧-3-氧化物(PTIO)清除内源NO,加剧强光胁迫对Arid3与Houndog5氧化伤害.应用0.1 mmol·L~(-1)的外源NO供体硝普钠(SNP)能降低强光胁迫造成的Arid3和Houndog5 叶片脂氧合酶(LOX)活性,降低超氧自由基(O_2)产生速率和质膜相对透性的增加以及MDA和H_2O_2的累积;同时,O.1 mmol·L~(-1)的SNP还能够诱导过氧化物酶(POD)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸氧化物酶(APX)和谷胱甘肽还原酶(GR)活性.而外源NO的保护作用被PTIO逆转.上述结果暗示,NO可能作为一个活性分子诱导抗氧化物酶的活性,减轻强光胁迫下2个高羊茅品种氧化损伤.     

Endogenous nitric oxide mediates He-Ne laser-induced adaptive responses in salt stressed-tall fescue leaves

The aim of this study was to investigate the role of endogenous nitric oxide in protective effects of He–Ne laser on salt stressed-tall fescue leaves. Salt stress resulted in significant increases of membrane injury, reactive oxygen species (ROS) production, polyamine accumulation, and activities of SOD, POD, and APX, while pronounced decreases of antioxidant contents, CAT activity and intracellular Ca²⁺ concentration in seedlings leaves. He–Ne laser illumination caused a distinct alleviation of cellular injury that was reflected by the lower MDA amounts, polyamine accumulation and ROS levels at the stress period. In contrast, the laser treatment displayed a higher Ca²⁺ concentration, antioxidant amounts, NO release, antioxidant enzyme, and NOS activities. These responses could be blocked due to the inhibition of NO biosynthesis by PTIO (NO scavenger) or LNNA (NOS inhibitor). The presented results demonstrated that endogenous NO might be involved in the progress of He–Ne laser-induced plant antioxidant system activation and ROS degradation in order to enhance adaptive responses of tall fescue to prolonged saline conditions.     

Growth rates and assimilate partitioning in the elongation zone of tall fescue leaf blades at high and low irradiance

Tall fescue (Festuca arundinacea Schreb.) leaf blades elongated 33% faster at continuous low than at continuous high irradiance (60 versus 300 micromoles per second per square meter photosynthetic photon flux density) when temperature of the leaf elongation zone was held constant at 21°C. Increased rate of elongation was associated with a near proportional increase in length of the elongation zone (+38%). In contrast, growth in width and thickness was decreased at low irradiance, resulting in only a 12% increase in leaf area production and 5% less total growth-associated water deposition than at high irradiance. At low irradiance dry matter (DM) import into the elongation zone was 28% less, and 55% less DM was used per unit leaf area produced. DM use in synthesis of structural components (i.e. DM less water-soluble carbohydrates) was only 13% less at low irradiance, whereas water-soluble carbohydrates (WSC) deposition was 43% less. The lower rate of WSC deposition at low irradiance was associated with a higher net rate of monosaccharide deposition (+39%), whereas net deposition rates for sucrose (−27%) and fructan (−56%) were less than at high irradiance. Still, at low irradiance, net fructan accumulation accounted for 64% of WSC deposition, i.e. 25% of DM import, demonstrating the high sink strength of the leaf elongation zone.     

Ploidy effects on anatomy and gas exchange of tall fescue leaves

A growth chamber study was designed to interpret differences in CO₂ exchange rate (CER) and leaf diffusive resistance among 4X, 6X, 8X, and 10X ploidy levels of tall fescue (Festuca arundinacea, Schreb). Mesophyll cell size, stomatal density, number of major and minor veins, and bundle cap size of leaf blades were evaluated. Diffusive resistance tended to decrease and CER to increase with increasing ploidy level. Mean stomatal density decreased from 43.6 per square millimeter to 30.6 per square millimeter as ploidy level increased from 4X to 8X. The 10X ploidy level exhibited the highest stomatal density, 47.2 per square millimeter. Major veins decreased from a mean of 14.2 to 10.2, and minor veins increased from a mean of 4.2 to 6.6, per leaf blade as ploidy increased from 4X to 10X. Total number of veins decreased significantly from a mean of 18.4 to 15.7 as ploidy increased from 4X to 8X.     

Measurement of a growth-induced water potential gradient in tall fescue leaves

Spatial distribution of cell turgor pressure, cell osmotic pressure and relative elemental growth rate were measured in growing tall fescue leaves ( Festuca arundinacea ). Cell turgor pressure (measured with a pressure probe) was c . 0.55 MPa in expanding cells but increased steeply (+0.3 MPa) in cells where elongation had stopped. However, cell osmotic pressure (measured with a picolitre osmometer) was almost constant at 0.85 MPa throughout the leaf. The water potential difference between the growth zone and the mature zone (0.3 MPa) was interpreted as a growth-induced water potential gradient. This and further implications for the mechanism of growth control are discussed.     

Interactive role of nitric oxide and calcium chloride in enhancing tolerance to salt stress

Nitric oxide (NO), a small diffusible, ubiquitous bioactive molecule, acts as prooxidant as well as antioxidant, and also regulates remarkable spectrum of plant cellular mechanisms. The present work was undertaken to investigate the role of nitric oxide donor sodium nitroprusside (SNP) and/or calcium chloride (CaCl(2)) in the tolerance of excised mustard leaves to salt stress. After 24h, salt stressed leaves treated with SNP and/or CaCl(2), showed an improvement in the activities of carbonic anhydrase (CA) and nitrate reductase (NR), and leaf chlorophyll (Chl) content, leaf relative water content (LRWC) and leaf ion concentration as compared with the leaves treated with NaCl only. Salinity stress caused a significant increase in H(2)O(2) content and membrane damage which is witnessed by enhanced levels of thiobarbituric acid reactive substances (TBARS) and electrolyte leakage. By contrast, such increases were blocked by the application of 0.2mM SNP and 10mM CaCl(2) to salt stressed leaves. Application of SNP and/or CaCl(2) alleviated NaCl stress by enhancing the activities of antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) and by enhancing proline (Pro) and glycinebetaine (GB) accumulation with a concomitant decrease in H(2)O(2) content, TBARS and electrolyte leakage, which is manifested in the tolerance of plants to salinity stress. Moreover, application of SNP with CaCl(2) was more effective to reduce the detrimental effects of NaCl stress on excised mustard leaves. In addition to this, ameliorating effect of SNP was not effective in presence of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide]. To put all these in a nut shell, the results advocate that SNP in association with CaCl(2) plays a role in enhancing the tolerance of plants to salt stress by improving antioxidative defence system, osmolyte accumulation and ionic homeostasis.     

Agrobacterium-mediated high efficiency transformation of tall fescue (Festuca arundinacea)

Tall fescue (Festuca arundinacea) is the predominant cool-season pasture grass in the USA. Embryogenic calluses were induced from seeds/caryopsis of elite tall fescue cultivars Jesup and Kentucky-31, and were broken up into small pieces and used for Agrobacterium tumefaciens-mediated transformation. Agrobacterium strains LBA4404 and EHA105 harboring pCAMBIA vectors or the super-binary vector pTOK233 were used to infect the embryogenic callus pieces. The number of hygromycin resistant calluses obtained per dish of infected callus pieces was in the range of 2.0-5.8, and the number of transgenic plants recovered per dish of infected callus pieces was in the range of 0.4-1.7. When transformation efficiency was calculated based on the number of transgenic plants recovered and the number of original intact calluses used, the transformation frequency was in the range of 1.9-8.7%. The use of the easily available pCAMBIA vectors could produce equivalent results as the superbinary vector pTOK233. The transgenic nature of the regenerated plants was demonstrated by Southern hybridization analysis using undigested and digested genomic DNA samples. Expression of the transgenes was confirmed by northern hybridization analysis, GUS staining, and detection of GFP signals. Fertile transgenic plants were obtained after vernalization in the greenhouse. Progeny analysis revealed Mendelian inheritance of the transgenes.     

Role of calcium ion in protection against heat and high irradiance stress-induced oxidative damage to photosynthesis of wheat leaves

Cross stress of heat and high irradiance (HI) resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus of wheat leaves during grain development. Pre-treatment with calcium ion protected the photosynthetic system from oxidative damage by reducing O^-. ₂ production, inhibiting lipid peroxidation, and retarding electrolyte leakage from cell. Therefore, high F_v/F_m [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], F_m/F₀ (another expression for the maximal photochemical efficiency of PS2), Φ_PS2 (actual quantum yield of PS2 under actinic irradiation), q_P (photochemical quenching coefficient), and P _N (net photosynthetic rate) were maintained, and lower q_NP (non-photochemical quenching coefficient) of the leaves was kept under heat and HI stress. EGTA (a chelant of calcium ion) and LaCl₃ (a blocker of Ca²⁺ channel in cytoplasmic membrane) had the opposite effect. Thus Ca ion may help protect the photosynthetic system of wheat leaves from oxidative damage induced by the cross stress of heat and HI.     

夏季高光下入侵植物三裂叶蟛蜞菊叶片变红的生理功能

三裂叶蟛蜞菊(Wedelia trilobata)是世界最有害的100种外来入侵种之一, 现已在我国东南沿海地区广为分布, 并造成危害。我们对其野外种群的观察发现, 在夏季光照强烈的生境中, 其叶片常常有变红的现象。本研究针对这一现象, 从叶片花色素苷含量的变化入手, 探讨了三裂叶蟛蜞菊叶片变色的原因及其生理功能。结果表明, 红叶中的花色素苷含量显著高于绿叶(P<0.05), 夏季高光照诱导的花色素苷的积累是叶片由绿色变为红色的主要原因。由于花色素苷含量较高, 红叶的总抗氧化能力增强, 在甲基紫精(MV)光氧化处理过程中, 红叶的最大光量子产量(F_v/F_m)和实际光量子产量分别下降了28.2%和79.1%, 显著低于绿叶的下降幅度(70.9%和93.8%)。这一结果表明, 三裂叶蟛蜞菊在夏季遭受强光胁迫时, 叶片由绿色变为红色增强了对氧化逆境的耐受能力, 而相同环境下的本地蟛蜞菊(W. chinensis)并没有叶片变红的现象, 暗示这可能是入侵植物三裂叶蟛蜞菊抵御和适应夏季高光的一种特殊的生理机制。     

Ectopic overexpression of AtHDG11 in tall fescue resulted in enhanced tolerance to drought and salt stress

Tall fescue (Festuca arundinacea Schreb.) is a cool-season perennial grass, which has been conventionally grown in the temperate area. However, as a major type of cool-season turf grass, its growth has been extended to the sub-tropical climate or even to the transitional climate between the sub-tropical and the tropical, and, in some cases, to heavily salinized lands. The extended growth imposes a serious challenge to its tolerance to the abiotic stress, particularly to drought, salt and high temperature. Here, we report a successful introduction of Arabidopsis AtHDG11 into the tall fescue via Agrobacterium-mediated transformation. The ectopic overexpression of AtHDG11 under the control of CaMV 35S promoter with four enhancers resulted in significantly enhanced tolerance to drought and salt stress. No obvious adverse effects on growth and development were observed in the transgenic plants. The enhanced stress tolerance was associated with a more extensive root system, a lower level of malondialdehyde, a nearly normal Na⁺/K⁺ ratio, a higher level of proline and a kinetically accelerated induction of SOD and CAT activities observed in the transgenic plants during drought and/or salt stress, indicating that an enhanced ROS scavenging capability might play a significant role in the acquired tolerance to the abiotic stress. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Ya-Jun Cao and Qiang Wei contributed equally to this work.     

Relationship between postillumination burst of CO2 and enhancement of respiration in tall fescue leaves

The postillumination burst (PIB) of CO₂ and light-enhanced dark respiration (LEDR) depending on oxygen concentration, temperature, respiratory substrates and photorespiratory inhibitor aminoacetonitrile (AAN) were investigated in detached leaves of tall fescue (Festuca arundinacea) using a closed circuit system with an infrared gas analyzer. No PIB was observed in 1 % O₂ under temperature over the range from 15 °C to 35 °C. The rate of LEDR was about twice as low in 1 % O₂ as that in 21 and 50 % O₂ under all temperatures applied. The PIB was absent and LEDR decreased at 21 % O₂ following illumination of leaves for 1 hour at 1 % O₂. When 200 mM glycine or malate solutions were introduced into the leaves of tall fescue, the magnitudes of PIB increased by about 60 and 40 % and rate of LEDR by about 70 % and 40 %, respectively. Pyruvate and succinate were less effective in promotion of PIB and LEDR. AAN had a small stimulatory effect on PIB and LEDR (about 20 % and 10 %, respectively). The dependences between magnitudes of PIB and rates of LEDR were highly correlated (r=0.94). The results presented indicate that atmospheric concentration of oxygen during the period of photosynthesis of tall fescue leaves was necessary not only for occurrence of PIB and LEDR but also for production of substrate(s) (glycine and/or malate) for these phenomena.     

An analysis of resistance to water flow through wheat and tall fescue leaves during pressure chamber efflux experiments

Abstract. This is a physical analysis of water movement in wheat ( Triticum ) and tall fescue ( Festuca arundinacea ) leaves placed in the Scholander pressure chamber. It takes into account the efflux resistances of water movement through the xylem and water flow across the cell membranes. Xylem resistance was estimated using Poiseuille's law.
Leaves which had been pressurized in the chamber were embedded, sectioned, examined under a light microscope and photographed. Cells were intact but distorted and xylem vessels were intact. Cells in portions of the blade squeezed by the chamber sealing grommet were crushed, but xylem vessels remained intact.
By applying pressure several tenths of a megapascal in excess of the balance pressure, water was forced from each leaf through the severed end which protruded from the chamber. Efflux curves were drawn by plotting the total water expressed as a function of time after the pressure increase. Water efflux from the shortest wheat leaf lasted only 10 min while efflux from the longest continued for up to 40 min. The efflux from a tall fescue leaf which was rehydrated and cut to a shorter length was much more rapid than efflux from the original leaf.
Experiments combined with mathematical analysis suggested that the effect of leaf length on efflux is related to a high resistance to water flow through vascular bundles. Xylem resistance would be sufficient to produce this effect if it were 10 times greater than that predicted by Poiseuille's law. Both the observations of water flow from the cut end of the leaf and the mathematical model suggested very little water flows from bundles with vessels of diameter less than 12 μm. The apparent explanation is high resistance to water flow through these small diameter vessels.     

Does irradiance influence the tolerance of marine phytoplankton to high pH?

The effect of irradiance on the tolerance to high pH of the two marine protists Heterocapsa triquetra and Nitzschia navis-varingica were investigated by conducting a series of pH drift experiments. In order to select appropriate levels of irradiance for the pH drift experiments, the photosynthetic activity and the growth rates of the two species were investigated at irradiances from 5 to 250 µmol photons m^-2 s^-1. Irradiances of 20, 35, 80 and 250 µmol photons m^-2 s^-1 were subsequently selected for further studies, because they represented conditions from severely light limited to fully light saturated with respect to photosynthesis and growth. At all four light levels, the pH limits for growth were 9.29-9.42 for H. triquetra and 9.54-9.77 for N. navis-varingica. The pH limit for growth was not positively correlated to irradiance in either of the species. We therefore conclude that low light does not reduce the pH tolerance of the protists studied.     

Translocation of photoassimilate from leaves of two popyploid genotypes of tall fescue differing in photosynthetic rates

The photosynthetic rate of a decaploid genotype (1-16-2) of tall fescue ( Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6-802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the ¹⁴C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h⁻¹) in both genotypes. Recent ¹⁴C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the ¹⁴C, respectively, at 6 h, and 79 and 49% of the ¹⁴C, respectively, at 24 h. Partitioning of ¹⁴C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total ¹⁴C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.     

Hemoglobins dioxygenate nitric oxide with high fidelity

Distantly related members of the hemoglobin (Hb) superfamily including red blood cell Hb, muscle myoglobin (Mb) and the microbial flavohemoglobin (flavoHb) dioxygenate nitric oxide (.NO). The reaction serves important roles in .NO metabolism and detoxification throughout the aerobic biosphere. Analysis of the stoichiometric product nitrate shows greater than 99% double O-atom incorporation from Hb(18)O(2), Mb(18)O(2) and flavoHb(18)O(2) demonstrating a conserved high fidelity .NO dioxygenation mechanism. Whereas, reactions of .NO with the structurally unrelated Turbo cornutus MbO(2) or free superoxide radical (-O.(2)) yield sub-stoichiometric nitrate showing low fidelity O-atom incorporation. These and other results support a .NO dioxygenation mechanism involving (1) rapid reaction of .NO with a Fe(III-)O.(2) intermediate to form Fe(III-)OONO and (2) rapid isomerization of the Fe(III-)OONO intermediate to form nitrate. A sub-microsecond isomerization event is hypothesized in which the O-O bond homolyzes to form a protein caged [Fe(IV)O .NO(2)] intermediate and ferryl oxygen attacks .NO(2) to form nitrate. Hb functions as a .NO dioxygenase by controlling O(2) binding and electrochemistry, guiding .NO diffusion and reaction, and shielding highly reactive intermediates from solvent water and biomolecules.     

Effects of endophytic fungi on some drought tolerance mechanisms of tall fescue in a hydroponics culture

Neotyphodium, a seed-transmissible nonpathogenic fungal endophyte (symbiont) is considered beneficial because endophyte-infected grasses are more drought-tolerant, produce more dry matter, utilize soil nitrogen more efficiently, and deter insects. In this study, the effects of endophytes on physiological mechanisms of drought tolerance in tall fescue (Festuca arundinacea Schreb.) were studied in a greenhouse. Two clonally propagated genotypes of tall fescue (F. arundinacea Schreb.), naturally containing endophyte (EI), and their endophyte-free ramets (EF) were tested at three water stress treatments exerted by PEG 6000 in a hydroponics system. Relative water content (RWC), cell membrane stability (CMS), proline and chlorophyll contents in plant leaves were measured during water stress treatments. After harvest, K⁺, Ca²⁺, and Mg²⁺ contents were measured in plant roots and shoots. After 20 days under stress conditions, plants were transferred to basal hydroponics medium, and their survival after stress relief was evaluated. The results showed that endophyte considerably contributes to host grass water stress tolerance. Both genotypes of EI and EF plants did not differ in RWC, but, regardless of the infection status, genotype 75 had the higher RWC than genotype 83. EI clones of both genotypes maintained slightly higher chlorophyll content and membrane stability than EF clones, although these differences were not significant. The EI plants of genotype 83 concentrated significantly more proline than EF plants, but in the genotype 75, differences between EI and EF clones were not significant. Plant mineral absorption was also influenced by the endophyte presence. EI clones had the higher concentrations of K⁺ in the shoots of both genotypes. The Mg²⁺ and Ca²⁺ contents in EF plants of both genotypes were higher than EI plants in the roots, but in the shoots there were no differences between EI and EF clones. EI clones survived longer after stress removal. These results strongly suggest that Neotyphodium endophytes exert their effects on tall fescue drought tolerance through alteration of various physiological mechanisms involved. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 563–570. This test was submitted by the authors in English.     

Photoinhibition and xanthophyll cycle activity in bayberry (Myrica rubra) leaves induced by high irradiance

The effect of high irradiance (HI, photosynthetically active photon flux density of 1 300 μmol m⁻² s⁻¹) on net photosynthetic rate (P _N), chlorophyll fluorescence parameters, and xanthophyll cycle components were studied in fruit tree bayberry leaves. HI induced the photoinhibition and inactivation of photosystem 2 (PS2) reaction centres (RCs), which was characterized by decreased P _N, maximum yield of fluorescence after dark adaptation (F_m), photochemical efficiency of PS2 (F_v/F_m) and quantum yield of PS2 (Φ_PS2), and increased reduction state of Q_A (1-q_P) and non-photochemical quenching (NPQ). Initial fluorescence (F₀) showed a decrease after the first 2 h, and subsequently increased from the third hour exposure to HI. Furthermore, a greater increase in the ratio (F_i-F₀)/(F_p-F₀) which is an expression of the proportion of the Q_B non-reducing PS2 centres, whereas a remarked decrease in the slope of F_i to F_p which represents the rate of Q_A reduction was observed in leaves after HI exposure. Additionally, HI caused an increase in the pool size of the xanthophyll cycle pigments and sustained elevated contents of zeaxanthin (Z), antheraxanthin (A), and de-epoxidation state (DES) at the end of the irradiation period. During HI, decreased F_m, F_v/F_m, Φ_PS2, NPQ, slope of F_i to F_p, V+A+Z, and DES, and increased F₀, 1-q_P, ratio (F_i-F₀)/(F_p-F₀), and V were observed in dithiothreitol (DTT)-fed leaves compared to control ones under the same conditions. Hence photoinhibition caused by HI in bayberry was probably attributed to inactivation of PS2 RCs, and photoprotection from photodamage were mainly related to the xanthophyll cycle-dependent heat dissipation in excess photons.     

The photosynthetic properties of rice leaves treated with low temperature and high irradiance

Photosynthetic characteristics in rice (Oryza sativa L.) leaves were examined after treatment with low temperature (15 degrees C) and high irradiance (1,500 micromol quanta m(-2) s(-1)). Decreases in quantum efficiencies in PSII (PhiPSII) and PSI (PhiPSI) and in the rate of CO2 assimilation were observed with a decrease in the maximal quantum efficiency of PSII (F(v)/F(m)) by simultaneous measurements of Chl fluorescence, P700+ absorbance and gas exchange. The decreases in PhiPSII were most highly correlated with those in CO2 assimilation. Although the initial (the activity immediately measured upon extraction) and total (the activity following pre-incubation with CO2 and Mg2+) activities of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) decreased slightly, the maximal activity (the activity following treatment with SO4(2-)) of Rubisco remained almost constant. These results indicate that the decrease in CO2 assimilation rate with the decreasing F(v)/F(m) was not caused by a decrease in Rubisco activity but rather by a decrease in RuBP regeneration capacity which resulted from the decrease in the rate of the linear electron transport. On the other hand, the decrease in PhiPSI was very small and the ratio of PhiPSI to PhiPSII increased. The de-epoxidation state of xanthophyll cycle pigments also increased. Thus, the cyclic electron transport around PSI occurred in photoinhibited leaves.