Leaf anatomy and C4 photosynthetic enzymes in three reed ecotypes

Differences in leaf interveinal distances, chloroplasts distribution in bundle sheath cells (BSC) and activities of C₄ photosynthetic enzymes in the leaves of three ecotypes of Phragmites communis Trinius, namely swamp reed (SR), heavy salt meadow reed (HSMR) and dune reed (DR), occurring in the desert region of northwest China were investigated. The two terrestrial ecotypes, DR and HSMR, had denser vascular system, more and longer BSC chloroplasts and higher capacity of CO₂ concentrating mechanism of NAD-ME subtype as compared with the SR ecotype. The enhanced NADP-ME pathway in the HSMR might contribute to its adaptation to the salinity habitat.     

Differential expression of photosynthesis-related genes of reed ecotypes in response to drought and saline habitats

Three ecotypes of reed (Phragmites communis Trinius), swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSMR), growing in desert regions of northwest China were simultaneously investigated in their natural state for gas exchange patterns and the expression of three photosynthesis-related genes, cab (the gene for the light-harvesting chlorophyll a/b binding protein, LHC), psbA (the gene for the reaction centre D1 protein of photosystem 2, PS2), and 16S rDNA (the gene for plastid 16S rRNA). Stomatal conductance (gs) and intercellular CO2 concentration (ci) were markedly lower in the two terrestrial ecotypes (DR and HSMR) as compared to SR, paralleling a similar observed depression in net photosynthetic rate (PN). However, DR with the lowest measured gs and ci still exhibited a higher PN compared to HSMR. These results suggest that both stomatal and non-stomatal factors account for the comparatively low carbon assimilation in the terrestrial ecotypes. An increase in the expression of photosynthesis-related genes was observed in DR compared to SR, whereas the reverse situation was true in HSMR. The expression of photosynthesis-related genes may contribute to reed plants' photosynthetic capacity per leaf area under natural water deficits, but the levels of photosynthesis-related gene expression are not directly correlated with reed plants' general ability for survival and adaptation under water deficient conditions.     

Antioxidant defense system in <Emphasis Type="Italic">Phragmites communis</Emphasis> Trin. ecotypes

The antioxidant defense system in three ecotypes of reed (Phragmites communis Trin.), swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSMR), from northwest China were investigated. The HSMR possessed the highest ratio of ascorbate (ASC)/dehydroascorbate (DHA) and activities of superoxide dismutase (SOD) and catalase among the three reed ecotypes, whereas, the DR exhibited the highest ratio of glutathione/glutathione disulfide and activities of ASC peroxidase (APX) and DHA reductase. Malondialdehyde and hydrogen peroxide contents were highest in HSMR, intermediate in SR, and lowest in DR. In addition, different isoenzymes of glutathion reductase, APX, SOD and DHA were also observed in three reed ecotypes.     

Anatomical and chemical characteristics of foliar vascular bundles in four reed ecotypes adapted to different habitats

We investigated the anatomical and chemical characteristics of the foliar vascular bundles in four ecotypes of common reed (Phragmites communis Trin.) inhabiting the desert region of northwest China: swamp reed (SR), low-salt meadow reed (LSMR), high-salt meadow reed (HSMR), and dune reed (DR). The cell walls of the vascular systems of all four ecotypes exhibited bright autofluorescence. Compared to SR, the three terrestrial ecotypes, LSMR, HSMR and DR, had higher percentages of bundle sheath cell areas, lower percentages of xylem and phloem areas, lower xylem/phloem ratios, and higher frequencies of leaf veins. In addition to differences in the autofluorescence intensity and the morphology of the detached cell walls of the vascular bundle sheath, the three terrestrial ecotypes also exhibited anatomical differences in the outerface tangential walls of the bundle sheath and higher frequencies of pit fields in the walls in comparison to SR. The Fourier transform infrared (FTIR) microspectroscopy spectra of the vascular bundle cell walls differed greatly among the tissues of the different ecotypes as well as within different tissues within each ecotype. Histochemical methods revealed that although pectins were present in all bundle tissue cell walls, large amounts of unesterified pectin were present in the phloem cell walls, especially in the salt reed ecotypes LSMR and HSMR, and large quantities of highly methyl-esterified pectin were present in the xylem and sclerenchyma cell walls of the SR and DR ecotypes. Differences were observed in the lignification and suberization of the xylem and sclerenchyma cell walls of the four ecotypes, but the phloem and bundle sheath cell walls were generally similar. These results suggest that the adaptation of common reed, a hydrophytic species, to saline or drought-prone dunes triggers changes in the anatomical and chemical characteristics of the foliar vascular bundle tissues. These alterations, including higher percentages of bundle sheath areas and lower percentages of xylem and phloem areas and their ratios, changes in the chemical compositions and modifications of the cell walls of different vascular bundle tissues, and differences in the deposition of major cell wall components in the walls of different vascular bundle tissues, could contribute to the high resistance of reeds to extreme habitats such as saline and drought-prone dunes.     

Solute levels and osmoregulatory enzyme activities in reed plants adapted to drought and saline habitats

The pattern of solute accumulation and the activities of key enzymes involved in metabolism of proline and betaine were investigated in three ecotypes of reed from different habitats: swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSR). The two terrestrial reed ecotypes, DR and HSR, exhibited a higher capacity for osmotic adjustment; they accumulated higher contents of K⁺ and Ca²⁺ in the leaves in comparison with SR. DR also had the highest soluble sugar content in its leaves. HSR has higher levels of Na⁺ in its root environment and this was reflected by considerable accumulation of Na⁺ in the HSR rhizome. However, the different zones of its leaf lamina (upper, middle and lower) did not exhibit increased levels of Na⁺, suggesting that HSR has the ability to accumulate Na⁺ in the rhizome to protect the shoots from excessive Na⁺ toxicity. DR and HSR had higher levels of proline and betaine in the leaves than did SR. This difference was consistent with the activities of the various biosynthetic enzymes: betaine aldehyde dehydrogenase (BADH), pyrroline-5-carboxylate reductase (P5CR) and ornithine--aminotransferase (OAT) were enhanced in DR and HSR as compared to SR, whereas proline oxidase (PO) activities were inhibited. These findings suggest that changes in the activities of enzymes involved in osmotregulation might play important roles in the adaptation of reed, a hydrophilic plant, to more extreme dune and saline habitats. The relative contributions of the various proline synthetic pathways are also discussed.     

Regulation of the structure and catalytic properties of plasma membrane H<Superscript>+</Superscript>-ATPase involved in adaptation of two reed ecotypes to their different habitats

The properties and kinetics of ATP and p-nitrophenyl phosphate (PNPP) hydrolysis activities of plasma membrane H⁺-ATPase from the two reed ecot ypes, swamp reed (SR) and dune reed (DR), were investigated. The pH optimum of the plasma membrane H⁺-ATPase in both reed ecotypes was similar but the sensitivity of the enzyme to the reaction medium pH seemed to be higher in DR than that in SR. Compared to SR, the DR exhibited a higher V_max value for ATP hydrolysis whereas the K_m value was almost similar in both reed ecotypes. The PNPP hydrolysis of the plasma membrane H⁺-ATPase was also studied in both reed ecotypes at increasing PNPP concentrations. K_m and V_max for PNPP hydrolysis showed great differences in the two reed ecotypes and in DR the K_m and V_max values were 2- and 10-fold, respectively, higher than those in SR. The ATP hydrolysis activity of the plasma membrane was markedly inhibited by hydroxylamine in both reed ecotypes, and the percentage inhibition of ATP hydrolysis rate seemed higher in DR than that in SR. In addition, the structure or property of the C-terminal end of the plasma membrane H⁺-ATPase were also different in the two reed ecotypes. These data suggest that different isoforms of the plasma membrane H⁺-ATPase might be developed and involved in the adaptation of the plant to the long-term drought-prone habitat.This research was supported by Natural Science Foundation of China (No. 30270238 & No. 30470274) and the National Key Basic Research Special Funds of China (G1999011705).     

The Regulation of the Plasma Membrane Redox System and H+-transport in Adaptation of Reed Ecotypes to Their Habitats

The redox system and H⁺-transport activities in the plasma membranes from two ecotypes of reed (Phragmites communis Trin.), named swamp reed (SR) and dune reed (DR) according to their habitats, were investigated. Compared to the SR, the DR possessed the very high rates of NADH oxidation and Fe(CN)₆ ^3– and EDTA-Fe³⁺ reduction when NADH was taken as the electron donor. As NADPH was an electron donor, the rate of NADPH oxidation was also significantly higher in the DR than that in the SR. In addition, the H⁺-transport activity in the plasma membranes was also significantly higher in the DR than in the SR.     

不同生境两种生态型芦苇的抗氧化系统

以分布于甘肃临泽平川乡的两种芦苇生态型——水生芦苇(水芦)和重度盐化草甸芦苇(盐芦)叶片为材料,研究了其抗氧化系统的特征。结果表明,与水芦相比,盐芦中未出现活性氧和MDA(丙二醛)的积累,抗氧化酶SOD(超氧化物歧化酶)、CAT(过氧化氢酶)、POD(过氧化物酶)和APX(抗坏血酸过氧化物酶)的活性显著升高。总抗坏血酸和类胡萝卜素含量在两种生态型芦苇中没有差异,但还原型抗坏血酸和总谷胱甘肽含量在盐芦中显著升高。而且,盐芦的LOX(脂氧合酶)活性比水芦低。这些结果表明,盐芦中有效的抗氧化防御系统对抵抗盐渍胁迫起着重要的作用。此外,盐芦中高活性的Ca^2 -和Mg^2 -ATPase对细胞中过多离子的转运以及避免离子毒害起着重要的作用。     

Leaf anatomy and photosynthetic carbon metabolic characteristics in <Emphasis Type="Italic">Phragmites communis</Emphasis> in different soil water availability

To investigate the variations of anatomical and photosynthetic carbon metabolic characteristics within one species in response to increasing soil water stress, leaf anatomical characteristics, gas exchange and the activity of key enzymes in photosynthesis and photorespiration were compared in different ecotypes of Phragmites communis growing in an oasis-desert transitional zone (ODTZ) from swamp habitat (plot 1–3) via heavy salt meadow (plot 4–7) and light salt meadow habitat (plot 8–9) to dune habitat (plot 10–13) in Northwest China. The results showed that interveinal distance (ID) decreased with increasing water stress except that in plots of dune reed (DR). Vein mean diameter (VMD) in plot 10, 11 and 12 of the DR was significantly larger than that in other ecotypes. Leaf specific porosity (LSP) enhanced from plot 4 to plot 13 from heave salt meadow reed (HSMR) to light salt meadow reed (LSMR) and to DR. Chlorophyll fluorescence in bundle sheath cells were microscopically found in four ecotypes, especially significantly in the DR. Net CO₂ assimilation rate (A _n) dropped rapidly from the swamp reed (SR) to the HSMR and then increased progressively from the LSMR to the DR. Stomatal conductance (g _s) decreased and the water use efficiency (WUE) rose from the wet to the dry ecotypes. Sensitivity of g _s to intercellular CO₂ concentration (C _i) increased, but glycolate oxidase (GO) activity gradually reduced with increasing soil water deficiency. The RuBPCase activity did not reduce in four ecotypes even in DR, but, the PEPCase and NAD-ME activities as well as the ratio of PEPCase/RuBPCase were gradually enhanced with increasing soil water stress. We concluded that anatomical and photosynthetic carbon assimilating characteristics in P. communis were developing to the direction of C₄ metabolism in response to the increasing drought stress in desert areas. The DR enduring severe water stress had more C₄ like photosynthetic features than the HSMR and LSMR as well as SR, according to significantly increased VMD and LSP and higher g _s sensitivity to C _i as well as higher PEPCase activity and lower GO activity in the DR.     

不同生境两种生态型芦苇叶片质膜H~ -ATPase的比较(英文)

利用两相法纯化质膜微囊,研究了分布于西北沙漠地区的两种生态型芦苇(Phragmites communis Trin.)(水生芦苇和重度盐化草甸芦苇,分别简称为水芦和盐芦)叶片质膜H -ATPase的部分性质。结果显示,与水芦相比,盐芦质膜H -ATPase的ATP水解活性升高,Km值由1.27 mmol/L降至0.30 mmol/L,但Vmax没有显著差异。并且该酶活性对温度的敏感性和pH谱型也发生了变化。以对硝基苯磷酸盐为底物,低浓度时盐芦的质膜H -ATPase水解活性高于水芦,高浓度时则没有差异。Km在水芦和盐芦中分别为3.61 mmol/L和1.92 mmol/L,但Vmax在两种生态型中没有差异。钒酸盐抑制实验表明,两种生态型的质膜H -ATPase磷酸-酶区的催化性质不同。胰酶对质膜H -ATPase活性的活化谱型也存在差异,说明该酶C末端的结构或性质发生了变化。此外,与水芦相比,盐芦质膜H -ATPase的质子泵活性及与水解活性的耦联程度也升高了。以上结果说明,当芦苇从水生环境向盐渍环境过渡时,质膜H -ATPase的催化性质发生了变化,这些变化可能是由酶结构的修饰和不同的同工酶谱引起的。H -ATPase催化性质的变化可能是对盐渍生境的适应性反应。     

Comparison of Plasma Membrane H^＋-ATPase Activity in Two Ecotypes of Reed （Phragmites communis） Leaves from Different Habitats

Plasma membrane (PM) vesicles of the leaves of two ecotypes of reed (Phragrnites communis Trin.), swamp reed (SR) and heavy salt meadow reed (HSMR) growing in the desert region of Northwest China, were purified by two-phase partitioning and the properties of their PM H^ -ATPases (EC 3.6.1.35) were compared. The specific activity of this enzyme was greater in HSMR than in SR and the Km lower (1.27mmol/L in SR and 0.30mmol/L in HSMR), and the Vmax of ATP hydrolysis activity showed no significant difference between the two ecotypes. The PM H^ -ATPase was more sensitive to denaturing temperatures in HSMR than in SR, and the pH profile also showed a slight difference, suggesting that the catalytic mechanism of this enzyme was different in HSMR compared with that in SR. The p-nitrophenyl phosphate (PNPP) hydrolysis activity of H^ -ATPase was higher in HSMR than in SR at low concentrations of PNPP, but showed no difference at high PNPP concentration. The Km for PNPP hydrolysis was 3.61mmol/L and 1.92mmol/L in SR and HSMR, respectively. And the Vmax of PNPP hydrolysis showed no significant difference in the two reed ecotypes. An experiment with the inhibitor vanadate showed that the catalytic mechanisms of the phosphatase domain of the ATPase were different in the two ecotypes. The data obtained following trypsin treatment showed a difference in the enzyme activity pattern, suggesting that there existed a possible change in the C-terminus of the ATPase, either in the structure or in the property or both of them. In addition, compared with SR, the ATP-dependent H^ pumping activity of ATPase and the coupling between proton transport and ATP hydrolysis in HSMR were increased. These results indicated that the properties of PM H^ -ATPase were changed in HSMR with compared to those in SR, which might include enzyme modifications and different isoforms expressed. The alterations of the properties of this enzyme might be an adaptive response to the habitat.     

Glucose-6-phosphate dehydrogenase plays a central role in modulating reduced glutathione levels in reed callus under salt stress

In the present study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in regulating the levels of reduced form of glutathione (GSH) to the tolerance of calli from two reed ecotypes, Phragmites communis Trin. dune reed (DR) and swamp reed (SR), in a long-term salt stress. G6PDH activity was higher in SR callus than that of DR callus under 50–150 mM NaCl treatments. In contrast, at higher NaCl concentrations (300–600 mM), G6PDH activity was lower in SR callus. A similar profile was observed in GSH contents, glutathione reductase (GR) and glutathione peroxidase (GPX) activities in both salt-stressed calli. After G6PDH activity and expression were reduced in glycerol treatments, GSH contents and GR and GPX activity decreased strongly in both calli. Simultaneously, NaCl-induced hydrogen peroxide (H₂O₂) accumulation was also abolished. Exogenous application of H₂O₂ increased G6PDH, GR, and GPX activities and GSH contents in the control conditions and glycerol treatment. Diphenylene iodonium (DPI), a plasma membrane (PM) NADPH oxidase inhibitor, which counteracted NaCl-induced H₂O₂ accumulation, decreased these enzymes activities and GSH contents. Furthermore, exogenous application of H₂O₂ abolished the N-acetyl-l-cysteine (NAC)-induced decrease in G6PDH activity, and DPI suppressed the effect of buthionine sulfoximine (BSO) on induction of G6PDH activity. Western-blot analyses showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI in DR callus. Taken together, G6PDH activity involved in GSH maintenance and H₂O₂ accumulation under salt stress. And H₂O₂ regulated G6PDH, GR, and GPX activities to maintain GSH levels. In the process, G6PDH plays a central role.     

不同生境两种生态型芦苇叶片质膜H+-ATPase的比较

利用两相法化纯化质膜微囊,研究了分布西北沙地区的两种生态型芦苇(Phragmites communis trih.)水生芦苇和重度盐化草甸芦苇,分别简称为水芒和盐芦)叶片质膜H - ATPase的部分性质.结果显示,与水芦相比,盐芦质膜H -ATPase的ATP水解活性升高,Km值由1.27mmol\l降至Vmax没有显著差异.并且该酶活性对温度的敏感必玫PH谱型也发生了变化.以对硝基苯磷酸盐为底物,低浓度时盐芦的的质膜H -ATPase水解活性有差异.钡酸盐抑制实验表明,两种生态的质膜H -ATPase磷酸-酶区的催化性质不同.胰酶对质膜H -ATPase活性的活化谱型也存在差异,说明该酶C末端的结构或性质发生了变化.此外,与水芦相比,盐芦质膜H -ATPase的质子泵活性的耦联程度也升高了.以上结果明,当芦苇从水生环境向盐渍环境过渡时,质膜H -ATPase的催化性质发生了变化,这些变化可能是由酶结构的修饰和不同的同工酬酶谱引起的.H -ATPase催化性质的变化可能是对盐渍生境的适应性反应.     

Photosynthetic Electron Transport,Photophosphorylation, and Antioxidants in Two Ecotypes of Reed (Phragmites Communis Trin.) from Different Habitats

We compared chloroplast photochemical properties and activities of some chloroplast-localised enzymes in two ecotypes of Phragmites communis, swamp reed (SR, C₃-like) and dune reed (DR, C₄-like) plants growing in the desert region of north-west China. Electron transport rates of whole electron transport chain and photosystem (PS) 2 were remarkably lower in DR chloroplasts. However, the electron transport rate for PS1 in DR chloroplasts was more than 90 % of the activity similar in the SR chloroplasts. Activities of Mg²⁺-ATPase and cyclic and non-cyclic photophosphorylations were higher in DR chloroplasts than in the SR ones. The activities of chloroplast superoxide dismutase (SOD) and ascorbate peroxidase (APX), both localised at or near the PS1 complex and serving to scavenge active oxygen around PS1, and the content of ascorbic acid, a special substrate of APX in chloroplast, were all higher in DR chloroplasts. Hence reed, a hydrophytic plant, when subjected to intense selection pressure in dune habitat, elevates its cyclic electron flow around PS1. In consequence, it provides extra ATP required by C₄ photosynthesis. Combined high activities of active oxygen scavenging components in DR chloroplasts might improve protection of photosynthetic apparatus, especially PS1, from the damage of reactive oxygen species. This offers new explanation of photosynthetic performance of plant adaptation to long-term natural drought habitat, which is different from those, subjected to the short-term stress treatment or even to the artificial field drought.     

Nitric oxide functions as a signal in salt resistance in the calluses from two ecotypes of reed

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed [DR] and swamp reed [SR]), which show different sensitivity to salinity, were used to study plant adaptations to salt stress. Under 200 mm NaCl treatment, the sodium (Na) percentage decreased, but the calcium percentage and the potassium (K) to Na ratio increased in the DR callus, whereas an opposite changing pattern was observed in the SR callus. Application of sodium nitroprusside (SNP), as a nitric oxide (NO) donor, revealed that NO affected element ratios in both DR and SR calluses in a concentration-dependent manner. N(omega)-nitro-l-arginine (an NO synthase inhibitor) and 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde (a specific NO scavenger) counteracted NO effect by increasing the Na percentage, decreasing the calcium percentage and the K to Na ratio. The increased activity of plasma membrane (PM) H(+)-ATPase caused by NaCl treatment in the DR callus was reversed by treatment with N(omega)-nitro-l-arginine and 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde. Western-blot analysis demonstrated that NO stimulated the expression of PM H(+)-ATPase in both DR and SR calluses. These results indicate that NO serves as a signal in inducing salt resistance by increasing the K to Na ratio, which is dependent on the increased PM H(+)-ATPase activity.     

Pyrosequencing Reveals Bacterial Diversity in the Rhizosphere of Three Phragmites australis Ecotypes

Here we present the use of high-throughput DNA pyrosequencing to assess bacterial diversity in the rhizosphere of three Phragmites australis ecotypes from the Hexi Corridor, China. In total, 43404 sequences were obtained for the three ecotypes, representing 31 phyla and a small amount of unclassified bacteria. The predominant bacterial groups in the rhizosphere of P. australis were Proteobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Planctomycetes. The bacterial community structure varied with the different degrees of wetland degradation, which were exhibited by the three P. australis ecotypes in the study area. At the phylum level, the Caldiserica, Chlamydiae, Deferribacteres, Lentisphaerae, and candidate division WS3 were only detected in the swamp reed (SR) sample. Then, δ-proteobacteria, Acidobacteria, Cyanobacteria and Fusobacteria decreased, the Actinobacteria increased with the degree of degradation from SR through salt meadow reed (SMR) to dune reed (DR). The functional bacterial genera also varied with wetland degradation. The sulfur and sulfate-reducing, nitrifying and nitrogen-fixing bacteria were more abundant in the rhizosphere of the SR sample. Methane-oxidizing bacteria were abundant in the SR and DR samples but less so in the SMR. In our study, pyrosequencing of different P. australis ecotypes provided insight into the structural variation of the rhizosphere bacterial community. This study gave a database for the use of bacteria in the protection and ecological restoration of wetland.     

Analyses of Soluble Protein,Total and Free Amino Acids in Leaves of Different Ecotypes of Phragmites communis Growing in the Hexi Corridor

The difference of total and free amino acids and protein extracted from the leaves of four different reed ecotypes growing in Hexi corridor of Gansu Province were investigated. In all of the different reed ecotypes, the content of Asp, Glu, Gly, Leu and Ala in total amino acids were high, while the contents of Ala, Phe, Met and Thr, Pro in total amino acids varied among different reed ecotypes. Albeit Ala, Glu, Asp, Gly and Ser were the chief composition of free amino acids in leaves of all reed ecotypes, but temarkble difference was found in the content of each free amino acid from different reed ecotypes. The content of free Pro in leaves of salt meadow and salt meadow-sand dune transitional zone reed were 3.5 and 1.6 times respectively as much as in leaves of swamp reed. Swamp reed had 11 soluble proteins whereas other three reed ecotypes show that each has 13 soluble proteins. Three “salt adaptation proteins” (66 kD, 40.3 kD, 16.5 kD) were found in leaves of three reed ecotypes with varying degree of salt stress, however, the contents of 3 “salt adaptation protens” showed a negative correlation with the degree of salt stress. There was a large amount of “special protein” (11.7 kD) in leaves of sand dune reeds. These results suggest that the difference in cytogene expression takes a priority basis of adaptation of reed plants to different habitats, while a closer relationship of reeds tolerance to salt or drought stress with Pro accumulation in cells is seen than with the of accumulation stress adaptation protein.     

Comparative study on calli from two reed ecotypes under heat stress

The different physiological responses to heat stress in calli from two ecotypes of common reed (Phragmites communis Trin.) plants (dune reed (DR) and swamp reed (SR)) were studied. The relative water content, the relative growth rate, cell viability, membrane permeability (MP), H₂O₂ content, MDA content, proline level, and the activities of enzymes, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and lipoxygenase (LOX) were assayed. Results showed that under heat stress, DR callus could maintain the higher relative growth rate and cell viability than SR callus, while H₂O₂ content, MDA content, and MP in SR callus increased more than in DR callus. The activities of antioxidant enzymes, such as SOD, CAT, POD, APX, and GR in two calli were enhanced by high temperature. However, antioxidant enzymes in DR callus showed the higher thermal stability than those in SR callus. LOX activity increased more in SR callus than in DR callus under heat stress. High temperature markedly elevated proline content in DR callus whereas had no effect on that in SR callus. Taken together, DR callus is more thermotolerant than SR callus, which might be due to the higher activity of antioxidant enzymes and proline level compared with SR callus under heat stress.     

Seasonal changes of polyamines in habitat adaptation of different ecotypes of reed plants

The leaves of four reed ecotypes (Phragmites communis Trinius) growing in the desert regions of northwest China were investigated for levels of polyamines and activity of arginine decarboxylase (ADC; EC 4.1.1.19) during the growing season of 5 months. The polyamines in the leaves of all reed ecotypes consisted of putrescine, spermidine and spermine. The polyamine levels of the leaves were lower in the swamp reed than in the terrestrial reed ecotypes. Leaf polyamine levels decreased in all ecotypes over the course of the season. Compared to the swamp reed, the terrestrial reed ecotypes maintained higher ADC activity and a predominance of spermine, resulting in a lower ratio of putrescine to spermidine and spermine. It seems that the adaptation of reed plants to drought and saline habitats may be correlated with putrescine synthesis via the ADC pathway, and with a successful conversion of putrescine to spermidine and spermine.     

DNA Damage and Repair of Two Ecotypes of Phragmites communis Subjected to Water Stress

In order to thoroughly understand the mechanism of drought resistance in plants at DNA level, the DNA damage of two ecotypes of reeds ( Phragmites communis T.) stressed by PEG 6000 was analyzed by means of fluorescence analysis of DNA unwinding (FADU). The results showed that the residual double strand DNA percentages (dsDNA%) in dune reed (DR) were significantly higher than those in swamp reed (SR) treated with either 20% or 30% PEG 6000. This meant that the DNA of DR was less damaged in comparison with SR. Similarly, DR resisted DNA damage more strongly than SR as reactive oxygen species (ROS) increased by adding ROS producers diethyldithio carbamate (DDC), H2O2 and Fe2+ of different concentrations. Meanwhile, treating PEG stressed SR with ROS scavengers such as dimethyl sulphoxide (DMSO) and ascorbic acid (Vc) resulted in the reduction of DNA damage, suggesting that ROS could cause DNA damage. In addition, the DNA repair for water-stressed reeds indicated that DR repaired DNA damage much faster and more completely. This might be the first indication that drought stress led to DNA damage in plants and that drought resistance of plants was closely related to DNA damage and repair.