Isolation and identification of a phosphate deficiency-induced C-glycosylflavonoid that stimulates arbuscular mycorrhiza formation in melon roots

Melon (Cucumis melo) roots were inoculated with or without the arbuscular mycorrhizal (AM) fungus Glomus caledonium under low phosphate conditions. High-performance liquid chromatography analysis of the secondary metabolites in butanol extracts from roots revealed that the level of one compound in noninoculated roots showed a significant increase from 30 days postinoculation. No accumulation was observed in mycorrhizal roots and high-phosphate-supplemented roots, indicating that the accumulation of the compound was caused by a phosphate deficiency. The compound was isolated by column chromatography and identified by spectroscopic methods to be a C-glycosylflavone, isovitexin 2'-O-beta-glucoside. The effect of the compound on mycorrhizal colonization in melon roots was examined under low (0.05 mM) and high (2 mM) phosphate conditions. The degree of mycorrhizal colonization in control roots grown under high phosphate conditions (8.8%) was much lower than when grown under low phosphate conditions (22%). The treatment of roots with the compound at concentrations of 20 and 50 microM increased root colonization under both low and high phosphate conditions. In particular, the degrees of mycorrhizal colonization in treated roots grown under high phosphate conditions (25 and 22% at 20 and 50 microM, respectively) were comparable to that in untreated control roots grown under low phosphate conditions (22%). These findings suggest that the phosphate deficiency-induced C-glycosylflavonoid is involved in the regulation of AM fungal colonization in melon roots.     

Iron-Stress Induced Redox Activity in Tomato (Lycopersicum esculentum Mill.) Is Localized on the Plasma Membrane

Tomato plants (Lycopersicum esculentum Mill.) were grown for 21-days in a complete hydroponic nutrient solution including Fe³⁺-ethylenediamine-di(o-hydroxyphenylacetate) and subsequently switched to nutrient solution withholding Fe for 8 days to induce Fe stress. The roots of Fe-stressed plants reduced chelated Fe at rates sevenfold higher than roots of plants grown under Fe-sufficient conditions. The response in intact Fe-deficient roots was localized to root hairs, which developed on secondary roots during the period of Fe stress. Plasma membranes (PM) isolated by aqueous two-phase partitioning from tomato roots grown under Fe stress exhibited a 94% increase in rates of NADH-dependent Fe³⁺-citrate reduction compared to PM isolated from roots of Fe-sufficient plants. Optimal detection of the reductase activity required the presence of detergent indicating structural latency. In contrast, NADPH-dependent Fe³⁺-citrate reduction was not significantly different in root PM isolated from Fe-deficient versus Fe-sufficient plants and proceeded at substantially lower rates than NADH-dependent reduction. Mg²⁺-ATPase activity was increased 22% in PM from roots of Fe-deficient plants compared to PM isolated from roots of Fe-sufficient plants. The results localized the increase in Fe reductase activity in roots grown under Fe stress to the PM.     

Growth and nutrient allocation in Phaseolus vulgaris L. colonized with endomycorrhizae or Rhizobium

Two cultivars of Phaseolus vulgaris L., one responsive to colonization with microsymbionts (Mexico 309) and one less-responsive (Rio Tibagi) were grown in Leonard jars containing sand/vermiculite under greenhouse conditions. Bean plants were either left non-inoculated (controls) or were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or a strain of Rhizobium leguminosarum bv. phaseoli (UMR-1899). Plants from the Mexico 309 cultivar maintained a higher growth rate, supported proportionately more nodules and mycorrhizae, and assimilated relatively more N or P when colonized by Rhizobium or Glomus, respectively, than did plants of the Rio Tibagi cultivar. Estimated specific nodule activity for Mexico 309 beans was more than twice that of Rio Tibagi, whereas the specific phosphorus uptake rate (SPUR) was 35% greater in the non-inoculated roots of Rio Tibagi compared to Mexico 309. Colonization by G. etunicatum more than doubled the SPUR for each cultivar compared to control roots. New acid phosphatase isozymes appeared in VAM-colonized roots of both cultivars compared to controls. Acid and alkaline phosphatase activities were significantly higher in G. etunicatum-colonized Mexico 309 roots, but not in Rio Tibagi mycorrhizae, compared to uninfected roots. Polyphosphate hydrolase activity was elevated in mycorrhizae of both cultivars compared to control roots. These results indicate that the dependence of a host on a specific endophyte increases when there are limitations to the supply of a nutrient that the endophyte can provide. The greater the increase in absorption or utilization capacity following colonization by the microsymbiont, the greater the dependence by the host. More importantly, identification of enzymatic activities that influence these plant-microbe associations opens the possibility that the specific genes that code for these enzymes could be targeted for future manipulation.     

Varietal differences in root growth as related to nitrogen uptake by sorghum plants in low-nitrogen environment

Hybrid (Sorghum bicolor (L.) Moench cv CSH 9) and local variety (S. bicolor cv. FSRP) of sorghum were grown in an Alfisol field and in pots of Alfisol in semi-arid tropical India, and the productivity of sorghum in low N condition was studied in relation to N absorption by plant. The grain yield of the hybrid (CSH 9) was higher than that of the local variety (FSRP) irrespective of the rate of N application. The reduction in hybrid grain yield was less than that for the local variety when N was not applied. After booting stage hybrid absorbed more N than the local variety. To estimate the role of roots in N absorption, the characteristics of N absorption were parameterized. Relative growth rate was highly correlated with relative N absorption rate in plant. N absorption was regulated by root activity (specific N absorption rate per unit root mass and length). Specific N absorption rate in roots at physiological maturity was higher in the hybrid than in local variety in low N conditions. Therefore, the smaller reduction of hybrid yield in low-N conditions was ascribed to high-N absorption rate in its roots, and the high ability of roots to absorb N after booting stage.     

Maintenance of growth rate at low temperature in rice and wheat cultivars with a high degree of respiratory homeostasis is associated with a high efficiency of respiratory ATP production

Some plants have the ability to maintain similar respiratory rates (measured at the growth temperature) when grown at different temperatures. This phenomenon is referred to as respiratory homeostasis. Using wheat and rice cultivars with different degrees of respiratory homeostasis (H), we previously demonstrated that high-H cultivars maintained shoot and root growth at low temperature [Kurimoto et al. (2004) Plant Cell Environ., 27: 853]. Here, we assess the relationship between respiratory homeostasis and the efficiency of respiratory ATP production, by measuring the levels of alternative oxidase (AOX) and uncoupling protein (UCP), which have the potential to decrease respiratory ATP production per unit of oxygen consumed. We also measured SHAM- and CN-resistant respiration of intact roots, and the capacity of the cytochrome pathway (CP) and AOX in isolated mitochondria. Irrespective of H, SHAM-resistant respiration of intact roots and CP capacity of isolated root mitochondria were larger when plants were grown at low temperature, and the maximal activity and relative amounts of cytochrome c oxidase showed a similar trend. In contrast, CN-resistant respiration of intact roots and relative amounts of AOX protein in mitochondria isolated from those roots, were lower in high-H plants grown at low temperature. In the roots of low-H cultivars, relative amounts of AOX protein were higher at low growth temperature. Relative amounts of UCP protein showed similar trends to AOX. We conclude that maintenance of growth rate in high-H plants grown at low temperature is associated with both respiratory homeostasis and a high efficiency of respiratory ATP production.     

Selectivity and Kinetics of Ion Uptake by Barley Plants Following Nutrient Deficiency

Barley plants grown without an external supply of phosphorus,sulphur, chlorine or nitrogen subsequently absorbed these nutrients,as phosphate, sulphate, chloride and nitrate, more rapidly thandid nutrient, sufficient control plants under similar conditions.With phosphorus, sulphur and chlorine, increased absorptionwas restricted to the nutrient which had been deficient, orto close chemical analogues of it, the uptake of other anionsbeing unaffected or decreased. The selectivity of enhanced nitrateuptake by nitrogen-deficient plants was not examined. The differencesin the rates of phosphate, sulphate and chloride absorptionby plants of differing nutrient status were due principallyto changes in the maximum transport capacity for these anionsper unit weight of root, although in plants grown without externalchloride there was some evidence that the roots also developedan increased affinity for that ion. Hordeum vulgare, barley, mineral nutrient deficiency, ion absorption, kinetics of ion uptake, phosphate, sulphate, chloride, arsenate, bromide, selenate     

In vivo and in vitro effects of boron on the plasma membrane proton pump of sunflower roots

The effect of boron excess and deficiency on H⁺ efflux from excised roots from sunflower ( Heliarahus annuus L. cv. Enano) seedlings and on plasma membrane H⁺-ATPase (EC 3.6.1.35) in isolated KI-washed microsomes has been investigated. When seedlings were grown in media with toxic levels of H₃BO₃ (5 m M ) or without added boron and exposed to light conditions, an inhibition of the capacity for external acidification by excised roots was observed as compared to roots from seedlings grown with optimal H₃BO₃ concentration (0.25 m M ). Toxic and deficient boron conditions also inhibited the vanadate-sensitive H⁺-ATPase of microsomes isolated from the roots. The mechanism of boron toxicity was investigated in vitro with microsorne vesicles. A strong effect of boron on the vanadate-sensitive, ATP-dependent H⁺ transport was found, but the vanadate-sensitive phospho-bydrolase activity was not affected. These results suggest that boron could exert an effect on the plasma membrane properties, directly or indirectly regulating, proton transport.     

Antioxidant Responses of Lentil to Cold and Drought Stress

The effects of cold and drought stress on antioxidant responses and growth parameters in shoots and roots of lentil (Lens culinaris M cv Sultan 1) seedlings were investigated. Ten-day-old hydroponically grown seedlings were subjected to drought and cold (4°C) stress for 5 days. The length and fresh weight of shoots decreased significantly under both stress conditions, contrary to the increase in these growth parameters for roots under the same conditions. The oxidative damage as generation of malondialdehyde and hydrogen peroxide, was markedly higher in shoots under cold. Both stress conditions caused a significant increase in malondialdehyde levels in root tissues. The increase in proline levels was more pronounced under cold stress in shoots and roots. The tested stress conditions had no significant effect on chlorophyll contents. Superoxide dismutase activity was differentially altered in shoot and root tissues under drought and cold stress. The catalase activity was higher in roots under drought stress. On the other hand, ascorbate peroxidase activity increased in root tissues under cold stress. The results indicate that improved tolerance to cold and drought stress in root and shoot tissues of lentil might be correlated to the increased capacity of antioxidative defense system.     

Flooding tolerance of Carex species in relation to field distribution and aerenchyma formation

The flooding tolerance of Carex species was studied in relation to their field distribution and their capacity to form root aerenchyma under controlled conditions. In an alpine meadow, six Carex species were selected which were distributed in a clear zonation correlating with water content of the soil. Carex sempervirens and C. ferruginea were only found on nonflooded soil, the latter species preferring moister conditions. Carex davalliana and C. nigra were both associated with water-saturated soil, whereas C. limosa and C. rostrata preferred partially submerged conditions. Carex davalliana and C. limosa were bound to flooded soils with a relatively high redox potential and horizontally flowing groundwater. Carex rostrata and C. nigra grew in stagnant soil-flooded conditions with low soil redox potentials. The amount of aerenchyma in the roots of all species increased when grown in oxygen-deficient stagnant agar. This increase in root porosity, combined with increased root diameter, presumably improved internal aeration of the roots. Although all species survived experimental soil flooding, partial submergence was lethal to C. sempervirens and, surprisingly, also to the wetland species C. davalliana. Carex ferruginea showed a reduced growth rate during partial submergence. The three other species, all wetland plants, reached highest biomass production under soil-flooded and partially submerged conditions, with slower growth on free-draining soil. It is concluded that aerenchyma is not constitutive in the Carex species under study, and is best developed in Carex species from wetlands. Species with less aerenchyma perform poorly when soil-flooded, but conditions of partial submergence could even affect species with a considerable amount of root aerenchyma.     

硅盐互作下小獐毛植物体内元素分布及生理特性的研究

 以新疆泌盐植物小獐毛(Aeluropus pungens)为材料,研究盐胁迫下小獐毛植物体元素吸收、分泌和过氧化物酶活性的变化以及硅对上述指标的影响。结果表明：在盐分胁迫下,其植物体钠离子浓度升高,钙元素含量降低,其它元素含量变化不明显。叶片硅元素含量随盐胁迫而增加。同时,当盐分浓度由0 mmol·L-1升至120 mmol·L-1浓度时,盐腺对各种离子的分泌作用表现为先加强（60 mmol·L-1）后降低（120 mmol·L-1）的趋势;其叶及根可溶性蛋白变化不明显,但过氧化物酶活性随盐胁迫而升高;可溶性蛋白含量叶片高于根部,而过氧化物酶活性根部高于叶片。同时盐胁迫对小獐毛根部及叶片含水量无明显影响。通过细胞化学定位结果显示, 小獐毛叶表富含硅元素,硅元素在叶表排列沿叶脉方向呈线性分布;在其叶片盐腺上,硅元素分布于帽细胞顶部,在此过氧化物酶（POD）活性也较强。元素分析结果显示,小獐毛体内富积硅元素。在较低的NaCl(60 mmol·L-1)浓度下,施用硅处理可减少叶片钠离子浓度,使地上部对钾、钠元素的相对选择性明显提高。在较高盐浓度（120 mmol·L-1NaCl）下,加硅对叶片钠离子浓度的降低作用效果不明显。在盐胁迫下,加硅未能减少根中钠离子浓度,但可明显增加叶片POD活性。实验结果表明,盐生植物小獐毛可通过维持体内含水量,调节植物体内元素分布以及增加POD活性适应一定程度的盐胁迫。同时低盐条件下施硅处理小獐毛根系培养环境可通过减少盐分向地上部的运输,增加叶片清除自由基的能力从而提高植物抗盐性。     

NaCl胁迫下黄瓜幼苗体内K+、Na+和Cl-分布及吸收特性的研究

采用营养液水培法,研究了不同浓度NaCl胁迫对黄瓜幼苗不同器官K 、Na 和Cl-含量的影响。结果表明,NaCl胁迫下黄瓜植株体内K 含量下降,Na 和Cl-含量升高,变化幅度随NaCl浓度的增加而增大;NaCl处理4 d后,各器官中K 含量下降幅度剧增,叶片中Na 和Cl-含量快速升高;3种离子在器官间呈区域化分布,Na 主要积累在根和茎部,K 和Cl-主要积累在茎部,而且K 的含量下降幅度由根向叶递减。在低浓度NaCl胁迫或高浓度NaCl短期胁迫下,黄瓜植株对K 的吸收选择性以及向地上部运输的选择性提高,离子区域化分布的能力增强,有利于避免离子代谢紊乱,减轻NaCl胁迫的伤害。可见,离子在器官水平的区域化分布是黄瓜植株耐盐性的重要机理之一。     

Functional aspects of root architecture and mycorrhizal inoculation with respect to nutrient uptake capacity

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.     

Comparative proteome analyses of phosphorus responses in maize (Zea mays L.) roots of wild-type and a low-P-tolerant mutant reveal root characteristics associated with phosphorus efficiency

SUMMARY: Low phosphorus (P) availability is a major limitation for plant growth. To better understand the molecular mechanism of P efficiency in maize, comparative proteome analyses were performed on the roots of the low-P-tolerant mutant 99038 and wild-type Qi-319 grown under P-sufficient (+P) or P-deficient (-P) conditions. Over 10% of proteins detected on two-dimensional electrophoresis (2-DE) gels showed expression that was altered twofold or more between the genotypes under +P or -P conditions. We identified 73 (+P) and 95 (-P) differentially expressed proteins in response to phosphate (Pi) starvation. These proteins were involved in a large number of cellular and metabolic processes, with an obvious functional skew toward carbon metabolism and regulation of cell proliferation. Further analysis of proteome data, physiological measurements and cell morphological observations showed that, compared to the wild-type, the low-P-tolerant mutant could accumulate and secrete more citrate under Pi starvation, which facilitates solubilization of soil Pi and enhances Pi absorption. The proportion of sucrose in the total soluble sugars of the low-P-tolerant mutant was significantly higher, and cell proliferation in root meristem was accelerated. This resulted in better developed roots and more advantageous root morphology for Pi uptake. These results indicate that differences in citrate secretion, sugar metabolism and root-cell proliferation are the main reasons for higher tolerance to low-P conditions in the mutant compared to the wild-type. Thus, the mutant displayed specialized P-efficient root systems with a higher capacity for mobilization of external Pi and increased cell division in the root meristem under Pi starvation.     

Effect of salinity on soluble protein,free amino acids and nicotine contents inNicotiana rustica L.

Nicotiana rustica plants were grown under two grades of salinity conditions, 50 mM and 100 mM NaCl. High levels of NaCl added to the nutritive solution produced a progressive absorption of Na in detriment of K, thereby causing an ionic disequilibrium, particularly in leaves. The weight and longitudinal growth of plants grown under salinity conditions were lower than control plants, while their protein content was higher. Deficit of K induced by salinity increased the levels of free amino acids, especially of aspartic acid, glutamic acid and proline. On the other hand, the levels of nicotine in leaves of treated plants were lower than controls. In contrast, treatment of the plants with 100 mM NaCl induced in general an increase of nicotine in the roots. These results indicate that there was an unclear effect of salinity either on synthesis or on translocation of nicotine from roots to leves.     

Regional distribution and pH sensitivity ofAzospirillum associated with wheat roots in Eastern Australia

In a survey ofAzospirillum spp. on the roots and associated soil of wheat grown in eastern Australia, azospirilla were isolated from approximately 40% of samples from areas of soil pH between 5.0 and 6.6. However, azospirilla isolates were rare in soil between pH 4.5 and 5.0 and absent below pH 4.5. Of 25 independent isolates, 17 wereA. brasiliense and eight wereA. lipoferum. No selection forA. brasiliense Nir^– strains by wheat roots was observed. Only one of six endorhizosphere isolates wereA. brasiliense Nir^–, compared with three of nine from unsterilized roots plus associated soil, and three of eight from soil. With a medium buffered with 0.05 M malate and 0.05 M phosphate, it was found that allAzospirillum isolates had a lower minimum pH for growth when supplied with fixed nitrogen than when grown under nitrogen-fixing conditions. Strains isolated from soils had a minimum pH for growth that was less than the pH of the soil from which they were isolated. However, a significant proportion of strains isolated from roots had a minimum pH for growth that was higher than the pH of the associated soil suggesting that the wheat roots provided an ecological niche protecting against soil acidity.     

The Absorption of Ions by Excised Root Systems: I. APPARATUS AND PRELIMINARY EXPERIMENTS

1. An apparatus is described by means of which the absorptionofions from a complete nutrient solution of constant compositionby excised root systems of plants, grown under known nutrientdeficiencies, may be measured in standard conditions of aerationand temperature. Results of some prelimi nary experiments aredescribed.
2. It was found that the roots readily absorbed theelement inwhich they were deficient, but tended to lose thoseelementswhich were already present in normal amounts.
3. Therewas almost invariably a loss in fresh weight of the rootsafterthe absorption period and also a loss in dry weight. Thislossappears to be complex and is partly attributable to lossofrespiratory material.
4. The addition of 2 per cent. sucroseto the solution from whichthe root systems of phosphorus-deficientbarley plants wereabsorbing increased the nitrogen and phosphoruscontents ofthe roots and maintained the potassium content,while in absenceof sucrose only the phosphorus content increased,but this increasewas significantly less than in the presenceof sucrose.
5. It was shown that roots excised from plants growingin soilwere capable of absorbing phosphorus or nitrogen—elementsin which they were apparently deficient.
6. The interpretationof data obtained from excised roots is discussed,and it isconcluded that excised roots from plants grown incomplete nutrientare not likely to behave in the same way,as regards absorption,as corresponding roots of intact plants,but that roots grownunder conditions of deficiency will behaverather similarlywhether excised or intact. This fact providesa potential methodfor diagnosing and evaluating nutrient deficiencies.
7. The low-saltcondition of roots postulated by Hoagland and Broyeris notnecessarily the primary requisite for rapid absorptionof aparticular ion. It is rather that the roots should be deficientin that ion. The roots could be high in other salts.

     

Endogenous auxins and branching of wheat roots gaining nutrients from isolated compartments

The auxin content in roots of hydroponically grown wheat (Triticum durum Desf.) plants was affected by imbalanced distribution of nutrients when the root medium fed to plants from isolated compartments. One day after the transfer of seedlings on the nutrient medium with uneven ion distribution, the IAA content in roots contacting concentrated nutrient solution became significantly higher than in roots bathed with a dilute solution. The IAA content reached the peak on the second day and remained steadily high later on. The lateral root primordia developed in these roots were more numerous; the largest difference in this parameter was observed in 1–2 days after the increase in root content of auxin. One day later, numerous lateral roots appeared on the parent roots contacting the concentrated nutrient solution. Thus, the increase in concentration of the nutrient solution bathing a part of root system raised the IAA content in the affected roots prior to the enhanced root branching. This hormonal response of plants might play an important role in changes of root growth rate and root branching, thereby improving plant nutrition.     

Absorption of manganese by rice under flooded and unflooded conditions

Summary Manganese absorption by rice plants under flooded and unflooded conditions, in an upland and a lowland soil was studied. Both under flooded and unflooded conditions the rate of manganese absorption was high during 3rd to 4th week and again during 9th to 10th week.Rice grown under flooded conditions, in lowland soil absorbed more manganese and showed higher dry matter accumulation than under unflooded conditions. However manganese absorption and dry matter accumulation in rice grown under flooded conditions in upland soil were lower than under unflooded conditions.Rice grown under flooded conditions may give lower yields than rice grown under unflooded conditions due to some factor or combination of factors one of which may possibly be a high soluble iron content which interferes with the absorption of manganese.