Characterization of AtCHX17, a member of the cation/H+ exchangers, CHX family, from Arabidopsis thaliana suggests a role in K+ homeostasis

The Arabidopsis genome contains many sequences annotated as encoding H(+)-coupled cotransporters. Among those are the members of the cation:proton antiporter-2 (CPA2) family (or CHX family), predicted to encode Na(+),K(+)/H(+) antiporters. AtCHX17, a member of the CPA2 family, was selected for expression studies, and phenotypic analysis of knockout mutants was performed. AtCHX17 expression was only detected in roots. The gene was strongly induced by salt stress, potassium starvation, abscisic acid (ABA) and external acidic pH. Using the beta-glucuronidase reporter gene strategy and in situ RT-PCR experiments, we have found that AtCHX17 was expressed preferentially in epidermal and cortical cells of the mature root zones. Knockout mutants accumulated less K(+) in roots in response to salt stress and potassium starvation compared with the wild type. These data support the hypothesis that AtCHX17 is involved in K(+) acquisition and homeostasis.     

NaCl分根胁迫对羊草幼苗生长及其生理生化特性的影响

在自动控制的遮雨棚中,研究了200 mmol·L-1NaCl胁迫对不同分根处理羊草幼苗生物量、活性氧代谢以及渗透调节物质含量的影响.结果表明:单一胁迫根茎(RHS)、单一胁迫根系(ROS)以及同时胁迫根茎和根系(RHSS)3种处理方式下羊草幼苗各器官干重均低于对照,且大体呈现RHSS>ROS>RHS趋势.在RHS和ROS处理下,羊草叶片和根茎SOD、POD、CAT活性及MDA含量均无显著差异;RHSS处理时根系中SOD、CAT活性相比ROS处理显著降低.3种处理下根茎和根系MDA、可溶性糖、脯氨酸含量均显著高于对照,可溶性糖、脯氨酸含量在RHS和ROS处理间存在显著差异.可见,根茎在羊草响应盐胁迫的生理过程中与根系具有类似的功能;盐胁迫下羊草不同器官同一抗氧化酶对活性氧淬灭具有不同的作用,与POD相比不同器官SOD和CAT作用可能更大;根茎可能参与光合同化物——可溶性糖在羊草地上部和地下部的调节运输,且协同根系增强了羊草对盐胁迫的耐性作用.     

Morphometric analysis of Pinus banksiana Lamb. root anatomy during a 3-month field study

Tree roots are variable in their growth rates, alternating between periods of elongation and dormancy. This variability may have a strong influence on root anatomy. In the present study, field-grown Pinus banksiana Lamb. roots were divided into four distinct anatomical regions (i.e. white without mycorrhizae, white with mycorrhizae, condensed tannin, and cork). Changes in root growth, the proportions of the root system occupied by the various regions, and cortical plasmalemma surface area (CPSA) were determined for 6- to 9-month-old ectomycorrhizal P. banksiana seedlings during a 3-month period (August through October) in northern Ontario. The region in which the greatest change in length occurred was the condensed tannin zone, which was also the dominant contributor to root length (up to 74% of total). The roots of seedlings grown under artificial conditions had the same zones but in different proportions compared to roots in the field. A correlation was noted between increased root growth, low metacutization, and high soil water availability. The CPSA data were assumed to be a factor influencing ion uptake capacity in a positive manner. Interestingly, increases in CPSA were not directly correlated with changes in root length for field-grown seedlings. The primary contributor to CPSA in the field-grown roots was the ectomycorrhizal zone (approximately 80%). In comparison, the bulk (85%) of the CPSA in the chamber-grown roots was found in the white root region. The conditions under which the seedlings were grown strongly influenced the anatomy of their roots. Received: 27 April 1999 / Accepted: 6 December 1999     

黄波罗不同根序的解剖结构及其功能异质性

 细根是树木吸收水分养分的主要器官, 其生长与周转对森林生产力及生态系统物质循环具有重要的影响。为了更好地认识细根的结构特征与功能及其在根序中的分布, 采用石蜡切片方法对黄波罗(Phellodendron amurense) 1～5级根解剖结构(直径、皮层组织、通道细胞数目、维管束发育和菌根侵染等)进行了观察统计。研究表明: 细根直径、维管束直径以及维管束在根中所占的比例随根序增加而增加。1~3级根皮层层数、皮层薄壁细胞直径相近, 但总体呈减少趋势, 部分4级根有少量残留的皮层, 而成熟的5级根已经没有表皮及皮层组织。1~3级根具有通道细胞, 菌丝侵染率均较高; 4、5级根无通道细胞, 也无菌丝侵染。1、2级根是初生根, 无木栓层; 4、5级根是次生根, 具有完整的木栓层; 3级根中既有初生根, 也有次生根, 并逐渐形成木栓层。说明随根序升高, 细根吸收能力减弱, 输导能力增加, 抵御环境胁迫的能力增加, 有利于延长寿命。根据解剖结构、直径和根序的关系, 将黄波罗前3级根中直径小于0.8 mm、未形成连续木栓形成层、具有通道细胞的根定义为细根。     

The Ecological Relation Between Pinus taiwanensis and Fungi in the Process of Ectomycorrhizae Synthesis

The root samples of Pinus taiwanensis from seedlings to large trees of Mt. Huangsban were studied under light microscope(LM) and scanning electron microscope(SEN). It is obvious that ectomycorrhizae from extensively between the pine roots and the fungi. Isolation and pure culture of the samples of sporocarps were carried out, of which six strains were inoculated to the dissinfected seedlings were under laboratory condition. Pisolithus tinctorius was introduced to inoculate the pine seedlings too. Studies on the development of dichotomous mycorrhizae and the early stage of ectomycorrhizae formation were specially emphasized. Three types of the process of hyphae infection and the ontogeny of ectomycorrhizae synthesis, development and subsequent degeneration were described. Some ecological effects of ectomycorrhizae, which increase the growth of pine trees were also mentioned. Finally the authors sugge. st that the success inoculation of Pisolithus tinctorius to the pine trees will offer a new device for the formation and development of the ectomycorrhizae in terms to promote their growth.     

Root-associated bacteria contribute to mineral weathering and to mineral nutrition in trees: a budgeting analysis

The principal nutrient source for forest trees derives from the weathering of soil minerals which results from water circulation and from plant and microbial activity. The main objectives of this work were to quantify the respective effects of plant- and root-associated bacteria on mineral weathering and their consequences on tree seedling growth and nutrition. That is why we carried out two column experiments with a quartz-biotite substrate. The columns were planted with or without pine seedlings and inoculated or not with three ectomycorrhizosphere bacterial strains to quantify biotite weathering and pine growth and to determine how bacteria improve pine growth. We showed that the pine roots significantly increased biotite weathering by a factor of 1.3 for magnesium and 1.7 for potassium. We also demonstrated that the inoculation of Burkholderia glathei PML1(12) significantly increased biotite weathering by a factor of 1.4 for magnesium and 1.5 for potassium in comparison with the pine alone. In addition, we observed a significant positive effect of B. glathei PMB1(7) and PML1(12) on pine growth and on root morphology (number of lateral roots and root hairs). We demonstrated that PML1(12) improved pine growth when the seedlings were supplied with a nutrient solution which did not contain the nutrients present in the biotite. No improvement of pine growth was observed when the seedlings were supplied with all the nutrients necessary for pine growth. We therefore propose that the growth-promoting effect of B. glathei PML1(12) mainly resulted from the improved plant nutrition via increased mineral weathering.     

Root-Associated Bacteria Contribute to Mineral Weathering and to Mineral Nutrition in Trees: a Budgeting Analysis

The principal nutrient source for forest trees derives from the weathering of soil minerals which results from water circulation and from plant and microbial activity. The main objectives of this work were to quantify the respective effects of plant- and root-associated bacteria on mineral weathering and their consequences on tree seedling growth and nutrition. That is why we carried out two column experiments with a quartz-biotite substrate. The columns were planted with or without pine seedlings and inoculated or not with three ectomycorrhizosphere bacterial strains to quantify biotite weathering and pine growth and to determine how bacteria improve pine growth. We showed that the pine roots significantly increased biotite weathering by a factor of 1.3 for magnesium and 1.7 for potassium. We also demonstrated that the inoculation of Burkholderia glathei PML1(12) significantly increased biotite weathering by a factor of 1.4 for magnesium and 1.5 for potassium in comparison with the pine alone. In addition, we observed a significant positive effect of B. glathei PMB1(7) and PML1(12) on pine growth and on root morphology (number of lateral roots and root hairs). We demonstrated that PML1(12) improved pine growth when the seedlings were supplied with a nutrient solution which did not contain the nutrients present in the biotite. No improvement of pine growth was observed when the seedlings were supplied with all the nutrients necessary for pine growth. We therefore propose that the growth-promoting effect of B. glathei PML1(12) mainly resulted from the improved plant nutrition via increased mineral weathering.     

Development of hormonal regulation of ion transport in embryonic chick red cells

We have found that cation transport in red cells from chick embryos is stimulated by the hormone epinephrine and that this response develops as the embryonic definitive cells mature. Sodium efflux and potassium influx are significantly stimulated (50%) by epinephrine in red cells from embryos incubated ten days or longer, whereas cation fluxes in erythroid cells from 8- or 9-day embryos are stimulated little or not at all. The effect of epinephrine may be mediated by cyclic AMP as adenylate cyclase activity in membranes isolated from embryonic red cells is only slightly stimulated at nine days, but the response increases as the cells mature to a maximum of about 180%. Also the stimulation of cation transport by epinephrine is blocked by propranolol, but not by phentolamine. Although the younger cells respond poorly to epinephrine, cyclic AMP significantly stimulates transport. The enhancement of cation fluxes by epinephrine or cyclic AMP occurs even in the presence of ouabain. Since both K influx and Na efflux are enhanced by these agents, their action is most likely on some form of the “Na-K” pump which is not ouabain sensitive resulting in a significant increase in the maximum velocity of the pump. We suggest the hypothesis that there are two classes of “Na-K” pump in these embryonic cells. One pump is similar to that found in many erythrocytes including mammalian cells in that it selectively pumps potassium in and sodium out, is ouabain-sensitive, and is primarily involved in maintaining intracellular cation concentrations. The second pump is enhanced by epinephrine via cyclic AMP, is not inhibited by ouabain, and may have lower ion selectivity. This hormone sensitive pump activity is lost as the cells mature, a process which is completed when the animal is fully grown and no longer has significant numbers of embryonic cells in its circulation.     

Effect of Plant Growth Promoting Bacillus Strains on Pine and Spruce Seedling Growth and Mycorrhizal Infection

Rifamycin-resistant derivatives of plant growth promotingBacilluspolymyxa strains L6, Pw-2, and S20 were used to evaluate theinteraction of bacterial–mycorrhizal co-inoculation onpine and spruce seedling growth. We were particularly interestedin determining if the mechanism by which bacteria stimulatedseedling growth depended on the presence of ectomycorrhizae.Mycorrhizal inoculum was introduced by adding 2ml of one ofsix forest floor soil types originating from different spruceand pine stands to seedling containers. Mycorrhizal roots developedin 34% of pine and 27% of spruce seedlings treated with forestsoil, but no differences between forest soils were detected.Most mycorrhizae were formed byWilcoxinasp. (E-strain) (98%for spruce and 67% for pine); small numbers ofAmphinema-like,Myceliumradicis atrovirens, Suillus-like,Thelephora-like, andTuber-likemycorrhizae were also found on pine (27% in total).Thelephora-likefungi comprised 2% of spruce mycorrhize. In the absence of bacterialinoculum, spruce seedling biomass was positively correlatedwith the number of mycorrhizal root tips, but this trend wasnot detected in spruce inoculated with bacteria or in pine.Bacterial inoculation did not influence the mycorrhizal statusof seedlings, but all threeBacillusstrains stimulated growthof both conifer species. Root biomass, in particular, was significantlyenhanced by up to 18% compared with uninoculated controls. Mycorrhizalfungi improved the growth of spruce seedlings, but plant growthpromotion byBacilluswas similar for mycorrizal and non-mycorrhizalseedlings of both species. Our results suggest thatBacillusstrainsL6-16R, Pw-2R, and S20-R enhance conifer seedling growth througha mechanism unrelated to mycorrhizal fungi. Hybrid spruce; Picea glaucaxengelmannii ; lodgepole pine; Pinus contortavar.latifoliaEngelm.; inoculation; Bacillus polymyxa; seedling growth promotion; mycorrhizae     

Influence of aluminum on in vitro formation of Pinus caribaea mycorrhizae

The ability of Pinus caribaea var. hondurensis to form mycorrhizae was determined in vitro with seven species of ectomycorrhizal fungi in the presence of six levels of Al (added as AlCl₃) in a nutrient solution. The time required for mycorrhizal formation, the number of mycorrhizal root tips and the percent mycorrhizae were measured after 15, 30, 60, 90 and 120 days. Cenococcum graniforme was susceptible to Al toxicity at all Al concentrations. Pisolithus tinctorius and Suillus sp. were depressed at lower but stimulated at higher Al concentrations. The inverse was shown for Rhizopogon reaii and Hebeloma cylindrosporum. Tolerance to Al was verified for R. nigrescens and H. crustuliniforme. Pisolithus tinctorius had the largest mycorrhizal capacity, defined as the sum of the values for time, percent and number of mycorrhizae. Ectomycorrhizal fungi appeared to ameliorate Al damage to plant roots even in treatments where no mycorrhizae formed. Inoculation of pine seedlings with Al-tolerant mycorrhizal fungi is likely to improve reforestation efforts in highly-weathered tropical soils.     

Mineral Nutrient Requirements of Pinus silvestris and Picea abies Seedlings

The mineral nutrient requirements of Pinus silvestris L. and Picea abies Karst. were studied according to previously published methods applied to a series of various plant species. The optimum nutrient proportions are similar to those of Vaccinium, with a lower relative potassium requirement than birch and other broad-leaf species. Various ratios between ammonium and nitrate nitrogen were about equally efficient except for a minor growth reduction with pure nitrate, which gave a comparatively low nitrogen content and a high cation/nitrogen ratio. The rate of ammonium uptake was much higher than that of nitrate when both sources were supplied. The required total concentration in the nutrient solution for maximum growth is lower in pine than in spruce, but both fall within the low salt range. Both species, especially pine, are sensitive to high salt concentrations. Although pine and spruce grow on the same type of soils as Vaccinium— leached soils with low base saturation – accumulation of calcium or other cations is not as pronounced as in Vaccinium, especially not in pine. The results are compared with results from similar experiments with a series of other conifers. All the conifers have more flexible cation uptake mechanisms than Vaccinium but the results indicate tendencies to accumulation of anions, nitrate and phosphate. Recommended fertilizer compositions for forest fertilization and nurseries are discussed.     

In Vitro interaction of the truffleTerfezia terfezioides withRobinia pseudoacacia andHelianthemum ovatum

The type of the in vitro root interactions of Terfezia terfezioides with the plants Robinia pseudoacacia and Helianthemum ovatum was investigated including detailed anatomical and ultrastructural characterization. No difference in growth was detected at different phosphate concentrations on agar synthetic medium between the inoculated and control plants during a short-time cultivation. The fungal colonization of the roots increased with higher phosphate level in both plant species, but was always lower in R. pseudoacacia roots. Septate hyphae formed frequently intracellular branched coils in dead cortical cells. In H. ovatum intercellular hyphae were observed forming finger-like structures reminiscent of Hartig-net structures in ectomycorrhizae. A loose hyphal envelope covered the root surface of both colonized and noncolonized roots. The features resembled similar structures described earlier during the mycorrhizae of different Terfezia species. Our detailed anatomical and ultrastructural study shows that the in vitro root interactions of the T. terfezioides cannot be considered unambiguously as mycorrhiza.     

Further Properties of Adenosine Triphosphatase and {beta}-Glycerophosphatase from Barley Roots

Cell wall preparations from barley roots contain ATP-ase activitythat is stimulated by monovalent cations at alkaline pH values,above that obtained with calcium or magnesium ions. Sodium isthe most effective cation followed by potassium, lithium, andrubidium. Similar activation is obtained with a soluble enzymefraction and with excised root tips. ß-Glycerophosphataseshows no stimulation by calcium and sodium or potassium haveonly a small stimulatory effect. Disc electrophoresis demonstratesthe group character of ATP-ase and ß-glycerophosphataseactivities which consist of multiple forms either specific toone or other substrate or hydrolysing both.     

Vesicular-arbuscular mycorrhizae of epiphytic and terrestrial Piperaceae under field and greenhouse conditions

We examined the roots of 27 epiphytic and terrestrial species of Piperaceae collected in primary and secondary habitats in Monteverde, Costa Rica. Terrestrial roots of only two of the nine Peperomia species, two of eight Piper species, and of Pothomorphe umbellatum contained internal vesicles and/or arbuscules. We did not find internal vesicles and/or arbuscules in 3024 cm of fine roots of epiphytic Piperaceae, even though 15% of these root segments had associated external typical glomalean hyphae. Glomus and Acaulospora spores, and Gigaspora auxiliary cells occurred in both canopy and terrestrial habitats. After inoculation of a low nutrient substrate, the facultatively epiphytic Peperomia costaricensis averaged 23% mycorrhizal root length. Relatively high atmospheric inputs of dissolved inorganic nutrients that alleviate the requirement for mycorrhizae, and heterogeneity of mycorrhiza inocula in the canopy may explain the absence of mycorrhizae from epiphytic Piperaceae. We suggest that the Piperaceae comprises predominantly facultatively mycotrophic species, and that facultative mycotrophism facilitates their radiation to the canopy.     

The Influence of Mineral Nutrition on the Root Development of Trees: III. PLASTICITY OF ROOT GROWTH IN RESPONSE TO CHANGES IN THE NUTRIENT ENVIRONMENT

Lodgepole pine seedlings were grown in solution culture withtheir root systems divided between two contrasting nutrientregimes, viz. a high regime, which provided near optimum conditionsfor growth, and a low regime in which nutrients were limiting.The high nutrient regime stimulated root growth whereas theroots receiving a low level of nutrients grew comparativelyslowly and in certain instances stopped elongating and becamebrown. After differential root growth had been induced certainplants were transferred to a uniform high nutrient environmentand the previously deprived parts of the root system respondedby renewed growth and their growth rate increased in comparisonwith roots which remained in low nutrient conditions. The results show that initial nutritional differences in theenvironment do not lead to dominance in certain roots; the rootsystem remains remarkably plastic.     

The root sap of birch on a podzol

Summary Root sap analyses were made on birch trees growing in a strongly podzolised heath soil. In the early summer the concentration of calcium and phosphorus appears to vary with the quantity of sap produced, and is independent of root environment. Later in the summer, however, this relationship no longer holds; there now being a connection between rooting zone and nutrient concentration. Roots reaching theC horizon absorb greater quantities of bases, whilst the superficial roots show higher concentrations of phosphorus and ammoniacal nitrogen. Throughout the season potassium uptake remains practically independent of both sap yield and rooting zone. In these soils young pine trees do not penetrate to the subsoil, but a comparison of sap analyses from surface roots of pine and birch shows that birch sap is richer in most nutrients. This, together with the ability of the birch to exploit the subsoil, may be a contributory factor to the soil improving properties of a birch crop.     

七株外生菌根真菌与三种松苗菌根的形成能力

松树外生菌根菌资源丰富,但实际应用的种类不多。为筛选出与松苗形成菌根能力较强的菌种,采用播种接菌和芽苗截根移栽接菌两种方法,对7株外生菌根真菌与马尾松、湿地松和黑松3种松苗的菌根合成进行了研究。结果表明：形成的菌根以二叉分枝状为主,棒状菌根相对较少,多叉状菌根以马尾松较多。PC2形成的菌根表面菌丝厚且紧密,504、EG、Pt,形成的菌根表面菌丝紧密程度中等,而505、ZJ和HX形成的菌根其表面菌丝则比较稀疏;Pt1、Pt2、EG形成的菌根外延菌丝较长,而505、HX形成的菌根外延菌丝极短。截根接菌时的感染率和感染指数要高于播种接菌。504形成菌根的能力最强,在3种松苗上的菌根感染率都达100％,感染指数最高可达90,最低也达70;Pt2和EG与马尾松和黑松形成菌根的能力较强;而505和HX仅与马尾松形成菌根的能力较强;Pt1形成菌根的能力较差,在3种松苗上菌根感染率和感染指数都较低。在3种松苗中,马尾松的菌根化状况最好,其次为黑松,湿地松的菌根化状况较差。     

The effect of drought on mycorrhizal production and very fine root system development of Norway spruce under natural and experimental conditions

Mycorrhizal growth rates were measured monthly, using a new method, in two neighouring plots of a natural spruce stand. One of the plots was irrigated while the other suffered from drought during the late summer and autumn months. Drought did not completely stop mycorrhizal growth. It caused a higher rate of root dormancy and a reduced elongation rate of the parent roots but an increased development of new mucorrhizal last order laterals. Thus, the branching density of the very fine root system was increased, even though fewer growing mycorrhizae were found in the non-irrigated plot during the dry period. Similar results were observed in a water-stress experiment with pot-cultures. After rewetting, elongation rate was stimulated and the number of growing mycorrhizae increased rapidly on the non-irrigated plot. Possible relationships between dry weight, distribution and branching density of growing fine root systems are presented.     

The supply of nutrient ions by diffusion to plant roots in soil

Summary A single-root technique is used to measure the rate of supply of potassium by diffusion to 1-cm portions of cylindrical roots of onion and leek plants growing in soils containing different levels of exchangeable potassium. The relation between uptake and characteristics of the plant and soil is interpreted on the basis of a diffusion supply model. Uptake is accounted for in terms of the geometry of the absorbing root surface, the physiologically controlled absorbing power of the root, and the diffusion through the soil. The different uptakes of potassium by roots of comparable absorbing power from different soils can be predicted with some success from calculations using the root dimensions and either diffusion coefficients of potassium in soil, derived from flux to a cation exchange resin paper, or the form of the potassium scorption isotherm relating the concentration of labile ions to those in the soil solution. It is calculated that diffusion through the soil has reduced potassium uptake by the roots to between 87 and 39 per cent of that expected for roots of the same absorbing power in a stirred culture solution at the same initial soil solution concentration.     

SEASONAL VARIATIONS IN THE PROPORTIONS OF SUBERIZED AND UNSUBERIZED ROOTS OF TREES IN RELATION TO THE ABSORPTION OF WATER

Growing root tips usually constituted less than 1 per cent and mycorrhizal roots less than 6 per cent of the total root surface under a 34-year-old pine stand. Growing root tips usually constituted less than 1 per cent of the total root surface under a yellow poplar stand, although one sample taken in May contained 9 per cent of unsuberized roots. The water permeability of various types of roots was measured under a pressure gradient of 31 cm of mercury. It differed widely among individual roots, ranging from an average of 6.6. mm³/cm²/hr for suberized pine roots 1.33 mm in diameter, to 36.6 mm³ for suberized pine roots 3 mm in diameter, and 178 mm³/ cm²/hr for unsuberized roots grown in water culture. Water intake through a group of unsuberized roots grown in soil averaged 37.4 mm³/cm²/hr. The permeability of yellow poplar roots varied even more, ranging from essentially zero to 30,000 mm³/cm²/hr. It is concluded that the major part of water absorption in pine occurs through suberized roots, some through mycorrhizal roots, and relatively little through growing root tips. Likewise, in yellow-poplar most of the water probably enters through suberized roots. Further study is needed of the role of suberized roots in water and salt absorption.