Young Sugar Beet Plants Research Articles

Application of a Reverse Genetic System for Beet Necrotic Yellow Vein Virus to Study Rz1 Resistance Response in Sugar Beet.

Beet necrotic yellow vein virus (BNYVV) is causal agent of rhizomania disease, which is the most devastating viral disease in sugar beet production leading to a dramatic reduction in beet yield and sugar content. The virus is transmitted by the ubiquitous distributed soil-borne plasmodiophoromycete Polymyxa betae that infects the root tissue of young sugar beet plants. Rz1 is the major resistance gene widely used in most sugar beet varieties to control BNYVV. The strong selection pressure on the virus population promoted the development of strains that can overcome Rz1 resistance. Resistance-breaking has been associated with mutations in the RNA3-encoded pathogenicity factor P25 at amino acid positions 67–70 (tetrad) as well as with the presence of an additional RNA component (RNA5). However, respective studies investigating the resistance-breaking mechanism by a reverse genetic system are rather scarce. Therefore, we studied Rz1 resistance-breaking in sugar beet using a recently developed infectious clone of BNYVV A-type. A vector free infection system for the inoculation of young sugar beet seedlings was established. This assay allowed a clear separation between a susceptible and a Rz1 resistant genotype by measuring the virus content in lateral roots at 52 dpi. However, mechanical inoculation of sugar beet leaves led to the occurrence of genotype independent local lesions, suggesting that Rz1 mediates a root specific resistance toward BNYVV that is not active in leaves. Mutation analysis demonstrated that different motifs within the P25 tetrad enable increased virus replication in roots of the resistant genotype. The resistance-breaking ability was further confirmed by the visualization of BNYVV in lateral roots and leaves using a fluorescent-labeled complementary DNA clone of RNA2. Apart from that, reassortment experiments evidenced that RNA5 enables Rz1 resistance-breaking independent of the P25 tetrad motif. Finally, we could identify a new resistance-breaking mutation, which was selected by high-throughput sequencing of a clonal virus population after one host passage in a resistant genotype. Our results demonstrate the feasibility of the reverse genetic system for resistance-breaking analysis and illustrates the genome plasticity of BNYVV allowing the virus to adapt rapidly to sugar beet resistance traits.

Protein synthesis is the most sensitive process when potassium is substituted by sodium in the nutrition of sugar beet (Beta vulgaris)

Potassium ions (K+) and sodium ions (Na+) share many physical and chemical similarities. However, their interchangeability in plant nutrition is restricted. Substitution studies showed that K+ can be replaced by Na+ to a large extent in the nutrition of Beta vulgaris L. However, the extent of substitution without negative impacts is not unlimited. The aim of the present study was to identify the process which is most sensitive during the substitution of K+ by Na+ in nutrition of young sugar beet plants. We focused on transpiration, growth, and net protein synthesis. Plants were grown under controlled environmental conditions. With transfer of seedlings into nutrient solution, plants were cultivated in different substitution treatments. For all treatments the sum of K+ and Na+ (applied as chloride) was fixed to 4 mM. The extent of substitution of K+ by Na+ in the nutrient solution was varied from low (0.25% substitution: 3.99 mM K+, 0.01 mM Na+) to almost complete substitution (99.75% substitution: 0.01 mM K+, 3.99 mM Na+). The supply of 3.99 mM K+ in 0.25% substitution treatment guaranteed the absence of K+ deficiency. Transpiration was not affected by the substitution. Growth was inhibited at a substitution level of 99.75%. Net protein synthesis was already affected at a substitution level of 97.50% (0.10 mM K+, 3.90 mM Na+). Hence, net protein synthesis was most sensitive to the substitution and limited the extent of substitution of K+ by Na+ in the nutrition of young sugar beet plants.

Possible impact of climate change on the occurrence and the epidemic development of cercospora leaf spot disease (Cercospora beticola sacc.) in sugar beets for Rhineland-Palatinate and the southern part of Hesse

In this study the possible impact of climate change on the occurrence of the Cercospora leaf spot disease (CLS) in sugar beet, triggered by the fungus Cercospora beticola sacc., and its regional differentiation in Southwest Germany was analyzed by means of the forecasting model CERCBET1. The model projects the day of the year (DOY) when 1 %, 50 % and 100 % of the fields in the region are potentially infested by Cercospora Leaf Spot disease (CLS1, CLS50 and CLS100). To run the disease model the data of the REgional climate MOdel REMO were used. The possible impact of climate change on the occurrence was studied comparing three time windows: baseline period ‘B′ (1971–2000), medium-term period ‘K‘ (2021–2050), long-term period ‘L‘ (2071–2100). In addition the ontogenesis of the young sugar beet plants was simulated using a leaf-growth model. The results of CERCBET1 and the leaf-growth model were compared to draw conclusions whether CLS potentially would occur in a different leaf stage. The dates of completion of the 20- and 40-leaf stage (B20 and B40) therefore were examined. The simulation results indicate an earlier CLS occurrence as well as an accelerated leaf growth due to the projected climate change. The disease might occur in earlier growth stages of the sugar beet plants. A possible consequence of the earlier CLS occurrence could be an increasing number of necessary fungicide applications also regarding the prolonged growing season. For period L, especially, projections are difficult to make due to the uncertainties of the archived breeding progress, particularly regarding the breeding for resistance, the development of fungicides and the future socio-economic development.

The IP amplitude of the fluorescence rise OJIP is sensitive to changes in the photosystem I content of leaves: a study on plants exposed to magnesium and sulfate deficiencies, drought stress and salt stress

The hypothesis that changes in the IP amplitude of the fluorescence transient OJIP reflect changes in leaf photosystem I (PSI) content was tested using mineral-deficient sugar beet plants. Young sugar beet plants (Beta vulgaris) were grown hydroponically on nutrient solutions containing either 1 mM or no Mg(2+) and 2.1 µM to 1.88 mM SO(4)(2-) for 4 weeks. During this period two leaf pairs were followed: the already developed second leaf pair and the third leaf pair that was budding at the start of the treatment. The IP amplitude [ΔF(IP) (fluorescence amplitude of the I-to-P-rise) and its relative contribution to the fluorescence rise: ΔV(IP) (amplitude of the relative variable fluorescence of the I-to-P-rise = relative contribution of the I-to-P-rise to the OJIP-rise)] and the amplitude of the transmission change at 820 nm (difference between all plastocyanin and the primary electron donor of photosystems I oxidized and reduced, respectively) relative to the total transmission signal (ΔI(max) /I(tot)) were determined as a function of the treatment time. Correlating the transmission and the two fluorescence parameters yielded approximately linear relationships in both cases. For the least severely affected leaves the parameter ΔV(IP) correlated considerably better with ΔI(max) /I(tot) than ΔF(IP) indicating that it is the ratio PSII:PSI that counts. To show that the relationship also holds for other plants and treatments, data from salt- and drought-stressed plants of barley, chickpea and pea are shown. The relationship between ΔV(IP) and PSI content was confirmed by western blot analysis using an antibody against psaD. The good correlations between ΔI(max) /I(tot) and ΔF(IP) and ΔV(IP) , respectively, suggest that changes in the IP amplitude can be used as semi-quantitative indicators for (relative) changes in the PSI content of the leaf.

10.1007/s11183-008-2006-z

Effect of surplus glucose on physiological and biochemical parameters of leaves of different age was investigated in sugar beet (Beta vulgaris L., subsp. saccharifera) plants in the stages of vegetative growth (SVG). Early and late SVG were differentiated by the ratio between the weights of roots and aboveground organs (0.10 and 0.35, respectively). The excess of Glu was produced by incubation of the disks excised from detached leaves in water or 0.1 M Glu at radiant flux density of 250 μmol/(m2 s) with the light regime pattern described as night/day/night/light (8/16/8/3 h). In all the leaf disks incubated in water and glucose solution, the content of Glu and other soluble carbohydrates considerably increased as compared with their content in the leaves they were taken from. After disk incubation in water and glucose solution, the content of chlorophyll (a + b) rose as compared with its level in respective leaves in early SVG; in late SVG, it declined. In early SVG, the rate of the O2 photosynthetic evolution (Ph) in the ageing leaves under saturating concentration of NaHCO3 after incubation in water and Glu solution declined more considerably than in young leaves. In late SVG, incubation of leaf disks in water and Glu solution weakly affected P n. The rate of O2 dark consumption in the leaf disks of all the types of treatment increased after incubation in water and especially in Glu solution. Activity of soluble carbonic anhydrase (sCA) in the extracts from young leaves in early SVG after their incubation in water and Glu solution was essentially the same, but after the incubation of ageing leaves in Glu solution, it reliably decreased. In late SVG, sCA activity sharply decreased after incubation in water and Glu solution irrespective of the leaf age. In late SVG, activity of Rubisco in the young leaves did not change after their incubation in water but decreased after incubation of the leaves of the three ages in Glu solution. In early SVG, nonphotochemical fluorescence quenching (NPQ) in the young intact leaf was lower than in the ageing leaf, and after leaf incubation in water and Glu solution, it rose. In late SVG, the value of NPQ was greater than in early SVG and, in contrast to the leaves of early SVG, it declined after leaf incubation; in water, this decline was more pronounced than in the Glu solution. In early SVG, efficient quantum yield of photosystem II (PSII) was much greater than in late SVG and it declined in the leaves incubated with Glu. It was concluded that surplus Glu can maintain biosynthetic processes in the young leaves of young sugar beet plants (trophic function). A decline in the level of chlorophyll and the activities of sCA and Rubisco in the course of leaf development and senescence is considered as a symptom of the suppression of biosynthesis of proteins of chlorophyll-protein complexes and the enzymes (Rubisco and sCA).

Effect of surplus glucose on physiological and biochemical characteristics of sugar beet leaves in relation to the age of the leaf and the whole plant

Effect of surplus glucose on physiological and biochemical parameters of leaves of different age was investigated in sugar beet (Beta vulgaris L., subsp. saccharifera) plants in the stages of vegetative growth (SVG). Early and late SVG were differentiated by the ratio between the weights of roots and aboveground organs (0.10 and 0.35, respectively). The excess of Glu was produced by incubation of the disks excised from detached leaves in water or 0.1 M Glu at radiant flux density of 250 μmol/(m2 s) with the light regime pattern described as night/day/night/light (8/16/8/3 h). In all the leaf disks incubated in water and glucose solution, the content of Glu and other soluble carbohydrates considerably increased as compared with their content in the leaves they were taken from. After disk incubation in water and glucose solution, the content of chlorophyll (a + b) rose as compared with its level in respective leaves in early SVG; in late SVG, it declined. In early SVG, the rate of the O2 photosynthetic evolution (Ph) in the ageing leaves under saturating concentration of NaHCO3 after incubation in water and Glu solution declined more considerably than in young leaves. In late SVG, incubation of leaf disks in water and Glu solution weakly affected Pn. The rate of O2 dark consumption in the leaf disks of all the types of treatment increased after incubation in water and especially in Glu solution. Activity of soluble carbonic anhydrase (sCA) in the extracts from young leaves in early SVG after their incubation in water and Glu solution was essentially the same, but after the incubation of ageing leaves in Glu solution, it reliably decreased. In late SVG, sCA activity sharply decreased after incubation in water and Glu solution irrespective of the leaf age. In late SVG, activity of Rubisco in the young leaves did not change after their incubation in water but decreased after incubation of the leaves of the three ages in Glu solution. In early SVG, nonphotochemical fluorescence quenching (NPQ) in the young intact leaf was lower than in the ageing leaf, and after leaf incubation in water and Glu solution, it rose. In late SVG, the value of NPQ was greater than in early SVG and, in contrast to the leaves of early SVG, it declined after leaf incubation; in water, this decline was more pronounced than in the Glu solution. In early SVG, efficient quantum yield of photosystem II (PSII) was much greater than in late SVG and it declined in the leaves incubated with Glu. It was concluded that surplus Glu can maintain biosynthetic processes in the young leaves of young sugar beet plants (trophic function). A decline in the level of chlorophyll and the activities of sCA and Rubisco in the course of leaf development and senescence is considered as a symptom of the suppression of biosynthesis of proteins of chlorophyll-protein complexes and the enzymes (Rubisco and sCA).

Growth, photosynthesis, and metabolism of sugar beet at an early stage of exposure to elevated CO2

The effects of CO2 concentration (C a) on growth, photosynthesis, and the activity of enzymes associated with the translocation and assimilation of CO2 were studied in sugar beet (Beta vulgaris L. subsp. saccharifera, cv. Ramonskaya) plants. The plants were grown in controlled-climate chamber to the stage of 3–4 leaves and then used in experiments. Experimental plants were exposed in boxes to doubled C a (700 µl/l, 2C plants), whereas control plants were kept in a chamber with ambient atmosphere (350 µl/l, 1C plants). As compared with 1C plants, in 3 and 8 days, the leaf area of 2C plants increased by 14 and 26%, respectively. The rate of their photosynthesis (P n) measured in 3, 6, and 8 days increased by 85, 47, and 52%, respectively, whereas in normal air, the values of P n in 2C plants were by 12, 19, and 15% lower than in 1C plants. After 8-day growth, the content of soluble carbohydrates in the leaves of 2C plants attained 7.2%, being by 80% greater than in 1C plants; the content of starch did not exceed 3%. The total content of chlorophylls a and b in the leaves of 2C plants was by 14% greater than in 1C plants, but their ratio was essentially the same. The level of protein in 2C plants was by 13.4% lower than in 1C plants. The activity and content of Rubisco in 1C and 2C plants were similar. As compared with 1C plants, in 2C plants the activity of soluble carbonic anhydrase (sCA) was lower by 34% in 3 days and by 18% in 8 days; the activity of carbonic anhydrase of membrane preparations (mCA), was lower by 24 and 77%, respectively. Catalase activity in 2C plants became by 8% lower than in 1C plants only after 8 days. A reduction in the photosynthetic ability of 2C plants in ambient atmosphere, a decrease in activity of sCA and, especially, of mCA observed together with invariable activity and content of Rubisco in the leaf extracts are interpreted as early symptoms of acclimation of young plants of sugar beet to elevated CO2.

The effect of water potential on accumulation of some essential elements in sugarbeet leaves, Beta vulgaris ssp. vulgaris

An investigation has been conducted on the effect of reduced water potential in nutrient solution on the accumulation of some essential macro- and micro nutrients in the aboveground pails of young sugarbeet plants. Plants of 8 different sugarbeet genotypes were exposed for 21 days to a nutrient solution whose water potential of 0.1 MPa was regulated by PEG. Contents of N, P, K Ca, Mg, Fe, Mn, Cu and Zn declined in all genotypes under water deficiency but the intensity of reduction varied among the genotypes. The results indicated that some harmful effects of water deficiency could be attributed to disturbances in plant mineral nutrition, especially the lack of N, P, and Mg, as well as to impaired ratios between the contents of particular elements, especially K/Ca.

EST Sequencing, Annotation and Macroarray Transcriptome Analysis Identify Preferentially Root‐Expressed Genes in Sugar Beet

Abstract: An integrated approach involving EST sequencing, data mining and multiparallel expression profiling by macroarray analysis was established to classify sugar beet gene products with respect to their expression in three different organs. The DNA sequences of 2996 ESTs derived from young sugar beet plants specified 2048 unique gene products with putative functions in primary and secondary metabolism (651), transport processes (136), signal transduction (78) and cellular organization (39). The cDNA clone collection was the basis for the generation of a macroarray. Sensitivity and reproducibility of our macroarray hybridization procedure were estimated first. The detection limit was found to correspond to 10 ‐ 50 copies of single transcripts per cell. Within an interval of two‐fold variation in signal intensities, reproducibility between spots on the same filter was determined to be 98.9 %, between spots on different filters 89.8 %, and reproducibility after hybridization with two probes synthesized from the same poly(A)+RNA sample was 97.6 %. Expression profiles from roots, leaves and inflorescences of field‐grown plant material were generated. Two different samples of each organ were analysed to reduce sampling effects, which accounted on average for 30.3 % of spots with at least two‐fold deviation. Expression values for each organ were determined by a stringent statistical evaluation of eight hybridizations for each clone. Macroarray expression data were confirmed by Northern blot analysis and quantitative RT‐PCR experiments concerning eleven cDNAs. The analysis was then focused on 76 unique cDNAs, for which the amount of detected transcript in roots was at least twice as high as in the other organs tested. Functions of preferentially root‐expressed candidate genes in taproot morphology and physiology are discussed.

Photosynthesis, chlorophyll fluorescence, and water relations in young sugar beet plants as affected by sulfur supply

The effect of different concentrations of sulfur (1 and 3 mM) and interruption of sulfur (S) supply for 25 days on the photosynthesis and leaf water relations in young sugar beet plants (Beta vulgaris L.) was studied in water culture, under greenhouse conditions. Interruption of S‐supply significantly reduced the content of sulfur, chlorophylls a+b and carotenoids, leaf area, density of stomatal and epidermal cells, transpiration rate and leaf water potential, while it increased the free proline content and stomatal diffusion resistance. An increase in S concentration in the nutrient medium from 1 to 3 mM did not significantly affect the tested parameters, except for an increase in leaf S content and a decrease of leaf water potential. Sulfur deficiency caused a pronounced decrease of the rate and quantum yield of photosynthetic oxygen evolution under non‐photorespiratory conditions. This was partly the result of the diminished photochemical efficiency of photosystem II reaction centers. Less efficient excitation of PSII reaction centers is most probably the consequence of higher thermal energy dissipation in the reaction centers of S‐starved plants. These data support that S nutrition is one of the factors regulating plant photosynthesis.

Differential response of a sensitive and tolerant sugarbeet line to Cercospora beticola infection and UV‐B radiation

Increased ultraviolet‐B (UV‐B, 280–320 nm) radiation, due to depletion of stratospheric ozone, is an increasing threat to living organisms. Furthermore, increased ground level temperatures as a consequence of global warming may favour development of pathogens, such as Cercospora beticola, that thrive at high temperatures. This study evaluates the effect of combined UV stress and Cercospora leaf‐spot disease on young sugarbeet plants (Beta vulgaris L.). An inoculum consisting of twelve European isolates of C. beticola Sacc. was used in the experiments. One Cercospora‐sensitive and one Cercospora‐tolerant sugarbeet line were analysed from growth regimes where plants were grown either under visible radiation alone or with supplemental UV‐B. Photosynthetic pigments and partial reactions of photosynthesis, including potential yield and quantum yield under illumination, non‐photochemical quenching (qNPQ) and photochemical quenching (qP), were measured to assess plant response. The combination of Cercospora and supplemental UV‐B radiation in the sensitive line resulted in a decreased photosynthetic efficiency, shown by qNPQ and quantum yield under illumination as compared with that for either stress applied alone. The Fv/Fm was unchanged for plants subjected to UV‐B radiation without infection, although the qNPQ decreased. The Cercospora‐tolerant line showed no significant differences under the different treatments. Thus, the line tolerant to Cercospora infection also proved to be tolerant to UV‐B radiation alone and in combination with the infection.

External K requirement of young plants of potato, sugar beet and wheat in flowing solution culture resulting from different internal requirements and uptake efficiency

Potato, wheat and sugar beet were grown in a growth chamber in tanks with flowing solutions containing K-concentrations of 1.5, 5, 15, 50 and 200 μM to find reasons for different K contents of solution needed to reach 90% maximum dry matter accumulation (external K requirement). All species showed variation in dry matter accumulation with varying K levels. To reach 90% maximum dry matter accumulation potato needed 40 μM K, whereas wheat and sugar beet needed 6.4 and 4.4 μM K respectively. These differences in external K requirement could not be explained by differences in their internal K requirement since the internal requirement of potato (7.7% K) was about one and a half times of that of sugar beet (5.4%) but its external requirement was nine times of that of sugar beet. At low K supply potato plants showed a lower influx and a reduced root growth as compared with wheat and sugar beet.

The role of sulphur in detoxication of cadmium in young sugar beet plants

In young sugar beet plants cadmium suppressed the activity of nitrate reductase, glutamine synthetase and glutamate dehydrogenase, whereas sulphur exhibited a protective role towards activity of these enzymes, except of glutamine synthetase. Protein synthesis was suppressed in the absence of S in nutrient medium; the lowest level was at 10-3 M Cd2+. Chloroplast pigment contents were increased by S while Cd2+, even in the lowest concentration, (10−5 M) showed a repressive effect. The highest concentrations of Cd2+ (10−3 M) caused a decrease in dry mass, whereas S induced its increase. Nitrate content was increased in the presence of Cd2+ and decreased by increased concentration of S.

Gas-filled root porosity in response to temporary low oxygen supply in different growth stages

The development of gas-filled root porosity in response to temporary low oxygen supply was tested for a range of edible and ornamental crops: rice, maize, wheat, sugar beet, tomato, cucumber, sweet pepper, carnation, gerbera and rose. In a first experiment, the roots of tomato, maize and gerbera had a higher gas-filled root porosity, Ep (% v/v), when grown permanently in a non-aerated instead of aerated solution. The Ep of roots increased during two weeks when half the root system of a young plant was transferred to a non-aerated solution; in older plants this response was not seen. Carnation had a negligible gas-filled porosity in all treatments. In a second experiment, a comparison was made between high (20 kPa) and low (about 2 kPa) O2 partial pressure in a recirculating nutrient solution. Half of the root system was transferred to low O2 at various growth stages. In most species older plants did not increase Ep on exposure to low O2. For tomato, sweet pepper and rose, Ep was normally in the range 3–8% (v/v). Young plants of cucumber, wheat and sugar beet also had an Ep in that range, but in older plants values ranged from 1 to 3%. Transverse root sections examined by light microscopy showed, on average, 60% more intercellular spaces in the root cortex than the measurements of gas-filled porosity, probably because some gaps and spaces in the cortex were not gas-filled. This effect was most pronounced in tomato. A negative pressure in the cortex may be needed for gaps to be gas-filled. An exodermis may increase the effectiveness of gas spaces in the cortex by closing the gas channels and, by offering some resistance to water uptake, allowing a negative pressure head in the cortex which keeps gaps gas-filled. A redox dye method was developed to study the length of root which is effectively supplied with oxygen, as a function of Ep. Results indicated that for every percent Ep the root can remain aerated over at least 1 cm in a non-aerated medium under the conditions of the test.

A new approach to quantify the utilization of non-exchangeable soil potassium by plants

To predict the contribution of soil K fractions of different mobility to K supply of plants, the kinetics of K release from soil was related to the kinetics of K uptake of young sugar beet and wheat plants. For this purpose K release rates from soil were measured by continuously percolating samples of a luvisol with 0.01 M CaCl2 solution and effective diffusion coefficients, De, were determined. Two soil K fractions of different mobility were obtained. De values of the more mobile ‘exchangeable K’ and the less mobile ‘non-exchangeable’ K fraction were found to be 58.9 × 10−9 and 8.2 × 10−9 cm2 s−1, respectively. In a pot experiment, sugar beet and wheat plants were grown, for 15 days and both root growth and K uptake were measured. K uptake kinetics of both crops was determined in a separate experiment using flowing solution culture. To integrate these data quantitatively, the simulation model of Claassen et al. (1986) was applied. Results show that calculated total K uptake agreed closely with real K uptake of the plants. On this basis, 64 and 79% of the K taken up by wheat and sugar beet plants was derived from the rapidly released ‘exchangeable’ and 21–36% from the less mobile ‘non-exchangeable’ soil K fraction.

A genetic analysis of the number of cells, length of cell, and gibberellic acid sensitivity in sugar beet and their relation to bolting mechanism

Three series of full-sib progenies and parental inbred lines or populations were used to study the inheritance of the number of cells and length of cell along the hypocotyl length, and the response to gibberellic acid in young plants of sugar beet. Variance components were determined by using a factorial cross design. There were no significant estimates of non-additive genetic variation for either cellular characters. Both additive and non-additive genetic variance were responsible for the variability of stem length after GA3 treatment. It is concluded that additive type genes predominantly control the number of cells in all series. The length of cell had significant additive variances in most cases, but it was indeed markedly influenced by environmental factors. Number of cells (cell division rate) and GA3 sensitivity in young plants even before vernalization were related to bolting tendency. Bolting-susceptible genotypes generally expressed higher stem length in the response to added GA3 as compared to the bolting-resistant genotypes. However, some genotypes bolted easily in the field but reacted weakly to the GA3 treatment and vise versa. Genotypes that were susceptible to bolting and/or sensitive to GA3 had a specific range (intermediate) of cell number. There were, however, some genotypes containing an intermediate number of cells which demonstrated low bolting. These responded faintly to gibberellin treatment. The results suggest that several physiological requirements have to be fulfilled before bolting can occur, and that other plant characters interfere with the bolting phenomenon.

Fast-Growing, Aerobic, Heterotrophic Bacteria from the Rhizosphere of Young Sugar Beet Plants

Fast-growing, aerobic, heterotrophic bacteria from the root surface of young sugar beet plants were inventoried. Isolation of the most abundant bacteria from the root surface of each of 1,100 plants between the second and tenth leaf stage yielded 5,600 isolates. These plants originated from different fields in Belgium and Spain. All isolates were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cellular proteins. Comparison of protein fingerprints allowed us to inventory the bacteria of individual plants of different fields or leaf stages and to analyze the composition and variability of the rhizobacterial population of young sugar beet plants. Each field harbored a specific population of bacteria which showed a highly hierarchic structure. A small number of bacteria occurring frequently at high densities dominated in each field. The major bacteria were identified as Pseudomonas fluorescens, Xanthomonas maltophilia, Pseudomonas paucimobilis, and Phyllobacterium sp. The former three species showed a high genetic variability as they were represented by different protein fingerprint types on the same or different fields or leaf stages. Twinspan analysis and relative abundance plots showed that the structure and composition of the bacterial populations varied strongly over time. Pseudomonads were typically early colonizers which were later replaced by X. maltophilia or Phyllobacterium sp.

Identification and Plant Interaction of a Phyllobacterium sp., a Predominant Rhizobacterium of Young Sugar Beet Plants

The second most abundant bacterium on the root surface of young sugar beet plants was identified as a Phyllobacterium sp. (Rhizobiaceae) based on a comparison of the results of 39 conventional identification tests, 167 API tests, 30 antibiotic susceptibility tests, and sodium dodecyl sulfate-polyacrylamide gel electrophoretic fingerprints of total cellular proteins with type strains of Phyllobacterium myrsinacearum and Phyllobacterium rubiacearum. It was found on 198 of 1,100 investigated plants between the 2nd and 10th leaf stage on three different fields in Belgium and one field in Spain. Densities ranged from 2 x 10 to 2 x 10 CFU/g of root. Five isolates exerted a broad-spectrum in vitro antifungal activity. DNA-DNA hybridizations showed that Phyllobacterium sp. does not contain DNA sequences that are homologous with the attachment genes chvA, chvB, the transferred-DNA (T-DNA) hormone genes iaaH and ipt from Agrobacterium tumefaciens, iaaM from A. tumefaciens and Pseudomonas savastanoi, or the nitrogenase genes nifHDK from Klebsiella pneumoniae. Phyllobacterium sp. produces indolylacetic acid in in vitro cultures and induces auxinlike effects when cocultivated with callus tissue of tobacco. When Phyllobacterium sp. was transformed with a Ti plasmid derivative, it gained the capacity to induce tumors on Kalanchoe daigremontiana. The potential role of Phyllobacterium sp. in this newly recognized niche is discussed.

Further Studies on Growth and Osmoregulation of Sugar Beet Leaves under Low Salinity Conditions

In previous work, Nunes and Dias (1980) demonstrated that low sodium concentrations in the root medium of intact or decapitated young sugar beet plants grown under controlled conditions modified leaf water relations and increased leaf area and dry weight. The present study confirms these findings and presents further results concerning the effect of salt on the concentrations of the main osmotic substrates and on the structural and chemical fractions of the cell dry weight. Increases of water and turgor potentials (0.25 MPa and 0.4 MPa, respectively) and a small decrease in osmotic potential (0.16 MPa) were found in the leaves of salt treated plants. In these plants, osmotic potentials estimated from the concentration of ions and organic solutes in the leaf sap agree with those measured showing that the observed increase in sodium concentration may account for the small decrease in the osmotic potential. No changes were detected in the concentration of orthophosphate or malic acid but total acidity of the leaf sap from salt treated plants was significantly lower. It was found that all the main components of cell dry matter (total protein, soluble sugars, pigments and crude cell wall) contributed to the dry weight increase in the salt treated plants. Among the polysaccharide fractions of the cell wall, pectins increased significantly relative to hemicellulose and cellulose.

Einsatz der hochleistungsflüssigkeitschromatographie zur bestimmung der uridine-5′-diphosphoglucose:phenol-β- D-glucosyltransferase-aktivität in vitro mit partiell gereinigtem enzym aus pflanzen von beta vulgaris ssp. Rapacea var. altissima döll

Employment of high-performance liquid chromatography for the determination of uridine-5′-diphosphoglucose:phenol-β- D-glucosyltransferase activity in vitro by use of partially purified enzyme from plants of Beta vulgaris ssp. rapacea var. altissima Döll Activity of uridine-5′-diphosphoglucose (UDPG):phenol-β- D-glucosyltransferase (E.C. 2.4.1.35) in protein extracts from leaves of young plants of sugar beet ( Beta vulgaris ssp. rapacea var. altissima Döll) is detected by a cell-free system with UDPG as glucose donor and the methylester of p-hydroxybenzoic acid as substrate. The analysis of products formed is carried out by high-performance liquid chromatography combined with UV-detection. Integration of peak areas yields an relative measure of the rate of glucoside formation. This measure is used immediately for comparative studies and determination of Michaelis constant ( K M ) values. The method described here is suitable for analysing enzyme reactions in vitro without employment of radioactive substrates.