Effect of aluminium on yield and plant chemical concentrations of some temperate legumes

The aluminium (Al) tolerance of 34 temperate legume species (143 genotypes, including 57 from Trifolium repens) was determined in 60 experiments over a 3 year period in a low ionic strength (2.7 × 10^-3 M) solution culture. For each genotype, the relationship between solution Al³⁺ activity (M) and relative yield was determined and the Al³⁺ activity associated with a 50% reduction in yield (Al_RY50) calculated. In addition, plant chemical concentrations were determined in at least one genotype from most species. For white clover, Al_RY50 over all genotypes had an approximately normal distribution with mean of 1.31 M for the tops and 1.51 M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritance. For the other species tested, Al_RY50 ranged from 0.15 to 4.53 M in the tops and from 0.21 to 4.89 M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an Al_RY50 less than 1 M, including all species tested in the genera Melilotus and Medicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an Al_RY50 greater than 2, including all genotypes in the species Lotus pedunculatus. Except for Lotus, there were no consistent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all elements except B in the roots were lower than that of the other species. The Al_RY50 of the species was not related to plant chemical concentrations in the absence of Al. Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemical concentrations for 56–94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K concentrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P concentrations decreased in the tops but increased in the roots. Increasing Al in solution increase plant Al at the average rate of 44 g g^-1 M ^-1 (range 20–87) in the tops and 333 g M ^-1 (range 162–616) in the roots.     

Determination of low boron concentrations in nutrient solution

To study boron (B) deficiency and toxicity in plants in flowing solution culture, it is necessary to establish a wide range of solution B concentrations. The ability of inductively coupled plasma atomic emisson spectrophotometry (ICPAES) to determine solution B concentrations ranging from 0.15 M to 925 M was investigated. The reliablity of B concentration determination in nutrient solutions containing <10 M B is poor. A technique, involving sorption by a B-specific resin (Amberlite-743), was established to concentrate the B present in low B nutrient solutions and to enable reliable measurement using ICPAES following elution from the resin. Acceptable, reproducible recoveries of B from low B solutions, containing known concentrations of B, were obtained using this technique. The technique enables the imposition, monitoring and maintenance of solution B concentrations well below the direct detection limits of ICPAES and colorimetric procedures. ei]L V Kochian     

Effect of bacitracin on flagellar assembly and presumed glycosylation of the flagellins of Methanococcus deltae

Methanococcus deltae is an irregularly-shaped coccoid methanogen which possesses peritrichously arranged flagella. The flagella are composed of 2 flagellins of M _r=27000 and 32000 and possess a carbohydrate component as determined by thymol-sulfuric acid staining of SDS-PAGE. Cell growth was sensitive to bacitracin at levels near 10 g/ml. Growth in the presence of 5g/ml bacitracin resulted in the appearance of presumably hypoglycosylated flagellins as detected by Western immunoblotting. Continual passage of cells from 5 g/ml bacitracin through 10, 25, and 50 g/ml bacitracin resulted in cells capable of growth at 100 g/ml bacitracin. Western immunoblot analysis revealed that cells grown in the highest concentration of bacitracin no longer possessed native flagellins but only the hypoglycosylated forms. Electron microscopy corroborated the absence of normal flagella. These studies suggest that a bacitracin-sensitive dolichol-diphosphate carrier is responsible for attachment of at least a large proportion of the carbonhydrate content of the flagellins, and that a minimum amount of glycosylation is essential for normal flagellum assembly.     

An efficient adventitious shoot regeneration system for Zhanhua winter jujube (Zizyphus jujuba Mill.) using leaf explants

The direct induction of adventitious shoots from leaf explants obtained from adult plants of Zhanhua winter jujube, an elite variety of Zizyphus jujuba Mill., is reported. The percentage of leaf explants producing shoots and the average number of shoots per explant were significantly improved when 10-day-old leaves were explanted onto Woody Plant Medium and maintained initially in the dark. The plant growth regulator thidiazuron (TDZ) was effective in stimulating shoot regeneration from leaf explants of Zhanhua winter jujube. The highest efficiency of shoot formation was observed with a 20-day culture in the dark on WPM containing 4.54 M TDZ and 2.85 M indoleacetic acid (IAA). The regenerated shoots were transferred to MS medium containing 0.89 M benzyladenine and 5.77 M gibberellic acid for growth. When the shoots were about 2 cm in height, they were transferred to Nitsch medium supplemented with 1.14 M IAA and 2.46 M indolebutyric acid to induce rooting. This system of adventitious shoot production from leaf explants of adult plants could be useful for the genetic engineering and polyploidization of winter jujube.     

Polyamines and proline are affected by cadmium stress in nodules and roots of soybean plants

The effect of moderate (50 M) and high (200 M) doses of Cd were studied in relation to polyamine (Pas) metabolism, proline level and the glutamine synthetase/glutamate synthase system (GS/GOGAT) activity in nodules and roots of soybean plants during 6 days of treatment. The lower Cd concentration increased putrescine (Put) in both nodules and roots, while 200 M Cd increased Spm only in nodules and Put in roots. Spermidine (Spd) decreased in roots under both Cd concentrations. Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) were both involved in Put biosynthesis in roots. In nodules, Put formation could mainly be attributed to ODC activity. Diamine oxidase (DAO) activity was severely reduced by 50 and 200 M Cd either in nodules or roots. The GS/GOGAT system activity was depressed either with 50 or 200 M Cd, but most significantly with the highest metal concentration. Under 200 M Cd, GS activity decayed to 25% or 60% of the control in nodules and roots, respectively, while GOGAT decreased 85% in nodules and 79% in roots by day 4 of treatment. Ammonium increased greatly in nodules (200% over the controls) and roots (100%) under 200 M Cd. Proline concentration increased significantly in nodules and roots under both Cd treatments, more markedly under 200 M Cd. The relationship between Pas and proline accumulation and nitrogen assimilation is discussed.     

Distribution of magnesium in wheat (Triticum aestivum L.) in relation to supply

The aims of this study were to describe the distribution of magnesium (Mg) and its retranslocation within wheat, in order to develop diagnostic procedures for Mg deficiency. Plants were grown in solution culture with both constant supply (0, 5, 10, 20, 40, 80, 160 MMg) and discontinued supply (40 M and 160 M decreased to nil).Magnesium was depleted from old leaves when Mg supply to the roots was halted. However, initial deficiency symptoms occurred on young leaves under constant but inadequate supply, contrasting with previous reports. Magnesium concentrations were also lower in young leaves compared to old leaves. Symptoms of yellowing and necrosis occurred if the leaf tissue contained <1194 gg^–1, irrespective of leaf age. The minimum Mg concentration in whole shoots associated with maximum shoot weight was 932 gg^–1; for the youngest emerged blade (YEB) it was 861 gg^–1. Symptoms were apparent on the young leaf before a reduction in shoot weight was measurable. The concentration of Mg in the YEB and whole shoot were better related to solution Mg concentration than was the Mg concentration in the old leaf.     

SelectingRhizobium phaseoli strains for use with beans (Phaseolus vulgaris L.) in Kenya: Infectiveness and tolerance of acidity and aluminium

Forty strains ofRhizobium phaseoli, isolated from Kenyan soils, were tested for infectiveness on common bean (Phaseolus vulgaris L.). 28 strains were infective and a cultivar × Rhizobium interaction was observed. 48 strains were screened for tolerance of acidity and Al in liquid culture. Assessment of visible turbidity after 14 days indicated 34 strains tolerant of pH 4.5 but none tolerant of pH 3.5. No strain was tolerant of 50 M Al at pH 5.5. Three strains were tolerant of 20 M Al at pH 5.5 and 10 M Al at pH 4.5. Screening on a solid medium identified strains tolerant of 20 and 50 M Al at pH 5.5 and 4.5 which were sensitive to these treatments in liquid culture. Those strains tolerant to 20 M Al at pH 4.5 and 5.5 in liquid culture were correctly identified on the solid medium.     

Plant regeneration from callus cultures derived from mature zygotic embryos in white pine (Pinus strobus L.)

Plant regeneration via adventitious shoot organogenesis from callus cultures initiated from mature embryos in white pine (Pinus strobus L.) was achieved in this study. Callus cultures were induced from mature embryos cultured on PS medium supplemented with 2,4-dichlorophenoxyacetic acid, -naphthaleneacetic acid, or indole-3-acetic acid. Adventitious shoot regeneration from callus cultures was induced on medium containing 2 M indole-3-butyric acid (IBA) and 3–12 M N₆-benzylaminopurine, thidiazuron (TDZ), or 6-(,-dimethylallylamino) purine. Sucrose was the most suitable sugar for adventitious shoot organogenesis in white pine. Shoot organogenesis was improved by treatment at 4°C for 6 weeks. The frequency of adventitious shoot formation increased when 0.1 mM putrescine was added to basal medium supplemented with 6 M TDZ and 2 M IBA. Putrescine improved adventitious shoot organogenesis by decreasing lipid peroxidation. These findings provide useful information on adventitious shoot organogenesis and may be valuable to genetic transformation in white pine.     

Interactions betweenpanax quinquefoliumsaponis and vitamin C are observed in vitro

Inasmuch as the oxidation of low-density lipoprotein (Ox-LDL) may play a key role in the initiation and progression of atherosclerosis, it has become increasingly important to identify potential antioxidants. Panax quinquefolium saponins (PQS) are extracted from the stems and leaves of the North American form of ginseng,Panax quinquefolium. Our previous studies have indicated that PQS (0.25-1 mg/ml) can protect against oxidation of LDLin vitro. The purpose of the current work was to investigate the potential interaction of lower concentrations of PQS (1-100 g/ml) with vitamin C on the reduction of LDL oxidation. LDL was isolated from the plasma of healthy human donors by sequential ultracentrifugation. Native LDL (0.05 or 0.2 mg/ml) was incubated with PQS and/or vitamin C for 30 min at 20°C. Oxidative modification was initiated with 2 M or 5 M CuSO₄ at 37°C for 0-24 h. Pretreatment with PQS (100 g/ml) reduced alterations in phospholipids, lipid peroxide levels and relative electrophoretic mobility of Ox-LDL. The presence of vitamin C (1-10 M) significantly enhanced the protective effects of PQS. Pretreatment with PQS (1-100 g/ml) resulted in concentration-dependent inhibition of LDL oxidation and prolongation of lag time as determined from measurements of conjugated lipid hydroperoxide content in Ox-LDL samples. Interestingly, the inhibitory actions of lower amounts of PQS (1 and 10 g/ml) on the formation of conjugated dienes were significantly increased when vitamin C (0.1 or 1 M) was present. In conclusion, our results suggest that PQS not only have direct antioxidant property but at low concentrations, their actions can be enhanced by vitamin C.     

Effects of external phosphorus supply on internal phosphorus concentration and the initiation,growth and exudation of cluster roots in Hakea prostrata R.Br.

The response of internal phosphorus concentration, cluster-root initiation, and growth and carboxylate exudation to different external P supplies was investigated in Hakea prostrata R.Br. using a split-root design. After removal of most of the taproot, equal amounts of laterals were allowed to grow in two separate pots fastened together at the top, so that the separate root halves could be exposed to different conditions. Plants were grown for 10 weeks in this system; one root half was supplied with 1 M P while the other halves were supplied with 0, 1, 25 or 75 M P. Higher concentrations of P supplied to one root half significantly increased the P concentration of those roots and in the shoots. The P concentrations in root halves supplied with 1 M P were invariably low, regardless of the P concentration supplied to the other root half. Cluster root initiation was completely suppressed on root halves supplied with 25 or 75 M P, whereas it continued on the other halves supplied with 1 M P indicating that cluster-root initiation was regulated by local root P concentration. Cluster-root growth (dry mass increment) on root halves supplied with 1 M P was significantly reduced when the other half was either deprived of P or supplied with 25 or 75 M P. Cluster-root growth was favoured by a low shoot P status at a root P supply that was adequate for increased growth of roots and shoots without increased tissue P concentrations. The differences in cluster-root growth on root halves with the same P supply suggest that decreased cluster-root growth was systemically regulated. Carboxylate-exudation rates from cluster roots on root halves supplied with 1 M P were the same, whether the other root half was supplied with 1, 25 or 75 M P, but were approximately 30 times faster when the other half was deprived of P. Estimates of root P-uptake rates suggest a rather limited capacity for down-regulating P uptake when phosphate was readily available.     

Indole butyric acid induces regeneration of phenotypically normal apricot (Prunus armeniaca L.) plants from immature embryos

A prerequisite for most transformation systems is an efficient and reliable method to regenerate phenotypically normal plants. Immature embryos or cotyledons were cultured at three developmental stages (stage 1, 2 and 3, PF=3, 30–60, and 100, respectively) from two unrelated apricot genotypes, Zard and NJA82. Explants were cultured on MS media supplemented with either BA or TDZ at four concentrations (0, 0.5, 5.0 or 20 M) and 2,4-D at 0 or 1 M. Stage 1 embryos cultured on MS medium without growth regulators formed embryoid-like structures. Shoot primordia induction was greatest with stage 2 cotyledons on media containing 5–20 M TDZ and 1 M 2,4-D, although shoot morphology was abnormal, especially with the highest level of TDZ. In another factorial experiment, stage 2 cotyledons were cultured on media containing TDZ (0, 5, 7.5, 10, 15 or 20 M) in combination with either no auxin, 1 M 2,4-D, 1 M IBA, or 5 MIBA. Regeneration percentages of 80% or more were observed on media containing 1–5 M IBA and 5–10 M TDZ. The medium containing 5 M IBA and no TDZ exhibited the highest frequency of phenotypically normal plantlet regeneration.Abbreviations BA 6-benzylaminopurine - IBA indole-3-butyric acid - 2,4-D 2,4 dichlorophenoxyacetic acid - 2iP 2-isopentenyladenine - MS Murashige and Skoog basal medium - NAA 1-naphthaleneacetic acid - PF percent fill [(embryo length/seed length) × 100] - TDZ thidiazuron [N-phenyl-N(1,2,3,-thidiazol-5-yl)-urea] - WPM McCown's woody plant medium     

Angiogenesis and myogenesis as two facets of inflammatory post-ischemic tissue regeneration

Recently Hippophae rhamnoides has been reported to render chromatin compaction and significantly inhibit radiation induced DNA strand breaks. To investigate the mechanism of action of RH-3, a preparation of Hippophae rhamnoides, in this connection, present study was undertaken. Chromatin compaction induced by RH-3 (100 g/ml or more) was maximum at alkaline pH but was completely negated by acidic pH (< 6) or presence of free radical scavengers like glycerol, DMSO etc. In a concentration dependent manner, RH-3 inhibited the intercalation of ethidium ions from Et Br into calf thymus DNA and also increased the precipitation of DNA-protein cross-links (DPC) in thymocytes. Chromatin compaction caused by RH-3 treatment did not permit the separation of proteins from DNA even after treatment with 2 M NaCl solution. SDS-PAGE profiles also revealed that RH-3 in a dose dependent manner compacted the chromatin organization, induced DPC and inhibited the extraction of both histone and non-histone matrix proteins from chromatin maximally at 80 g/ml. More than 80 g/ml of RH-3, though extracted low molecular weight histones but did not separate non-histone proteins. The RH-3 mediated DPCs were resistant even to 1% SDS, 4 M NaCl and 3.8 M hydroxyl amine hydrochloride but were prone to both urea (8 M) and guanidine hydrochloride (6 M) indicating covalent bonding between DNA and proteins (serine/threonine). RH-3 in a concentration dependent manner induced superoxide anions and the phenomenon was dependent upon nature of medium, presence of metal ions and pH. RH-3 at concentrations up to 100 g/ml in presence of 50 M copper sulfate inflicted significant damage to extraneously added 2-deoxyribose molecules and maximum TBARS were formed at a concentration of 100 g/ml. Higher concentrations of RH-3 more than 100 g/ml quenched free radicals and inhibited 2-deoxyribose degradation. RH-3 also induced strand breaks in plasmid DNA at concentrations lower than 100 g/ml but completely inhibited at concentrations higher than 250 g/ml, indicating bimodal function. Strand breaks induced by lower concentrations of RH-3 (up to 100 g/ml) were inhibited by antioxidants like GSH, DFR etc. RH-3, in a concentration dependent mode also inhibited the relaxation of supercoiled plasmid DNA (PBR322) by topoisomerase I.Present study indicated that RH-3 caused compaction of reversible (< 100 g/ml) and irreversible (> 100 g/ml) nature which was related to the magnitude of DNA-protein cross-links formed. Maintenance of chromatin organization, induction of hypoxia, hydrogen atom donation, free radical scavenging and blocking of cell cycle at G2-M phase by interfering with topoisomerase I activity seem to contribute towards the radioprotective efficacy of RH-3.     

Endogenous ethylene requirement for adventitious root induction and growth in tomato cotyledons and lavandin microcuttings in vitro

The role of ethylene in the formation of adventitious roots in vitro was studied in tomato (Lycopersicon esculentum Mill. cv. UC 105) cotyledons and lavandin (Lavandula officinalis Chaix × Lavandula latifolia microshoots. Both systems were able to form roots on hormone-free medium evolving low amounts of ethylene. The addition of 20–50 M indole-3-acetic acid (IAA) inhibited root formation in tomato cotyledons while increasing ethylene production. Naphthaleneacetic acid (NAA, 3 M) stimulated root number in lavandin explants and induced a transient rise in ethylene evolution. Enhanced ethylene levels via the endogenous precursors 1-aminocyclopropane-1-carboxylic acid (ACC, 25–50 M) drastically impaired root regeneration and growth in tomato. In lavandin, 10 M ACC stimulated ethylene production and significantly inhibited the rooting percentage and root growth. Conversely, ACC enhanced the root number in the presence of NAA only. Severe inhibition of rooting was also caused by ethylene reduction via biosynthetic inhibitors, aminoethoxyvinylglycine (AVG, 5–10 M) in tomato, and salicylic acid (SA, 100 M) in lavandin. A strict requirement of endogenous ethylene for adventitious root induction and growth is thus suggested.Abbreviations LS Linsmaier and Skoog medium - BA N⁶-benzyladenine - NAA 1-naphthaleneacetic acid - IAA Indole-3-acetic acid - AVG Aminoethoxyvinylglycine - SA Salicylic acid - ACC 1-aminocyclopropane-1-carboxylic acid     

Responses of nitrogen-fixing and nitrate-supplied alfalfa (Medicago sativa L.) to iron chelates in an alkaline hydroponic medium

Ferric ethylenediamine di-(o-hydroxyphenylacetate) (FeEDDHA) and ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) were evaluated as Fe sources for hydroponic growth of alfalfa (Medicago sativa L., cv. Mesilla), either dependent on N₂ fixation or supplied with NO₃. The hydroponic medium was maintained at pH 7.5 by addition of CaCO₃. Nitrogen-fixing cultures were inoculated with Rhizobium meliloti 102 F51 and grown in medium without added nitrogen. After five to seven weeks of growth under greenhouse conditions, plants were harvested. Nitrogen fixation was measured by the acetylene reduction method.When FeEDDHA was supplied, growth of alfalfa, whether dependent on N₂ fixation or supplied with NO₃, was severely limited at concentrations typically used in hydroponic medium (10 or 20 M). Maximum yield of NO₃-supplied alfalfa was obtained at 100 M while maximum yield of N₂-fixing alfalfa was obtained in the range of 33 to 200 M FeEDDHA. Nodule fresh weights and N₂ fixation rates increased with FeEDDHA concentration up to 33 M and remained essentially constant up to 200 M. With FeHEDTA, maximum yields of both NO₃-grown and N₂-fixing alfalfa were obtained at 10 M. Growth of NO₃-supplied plants was inhibited at 200 M FeHEDTA while growth of N₂-fixing plants was inhibited at 100 M FeHEDTA. The numbers of nodules per plant increased between 3.3 and 10 M FeHEDTA; however, inhibition of nodule formation occurred at a concentration of 33 M or higher. Nodule weights per plant and N₂ fixation rates were depressed at 3.3 M as well as at 100 M FeHEDTA. The results suggest that alfalfa dependent on N₂ fixation is more sensitive to limited Fe availability than alfalfa supplied with NO₃.     

Somatic embryogenesis and plantlet regeneration from cell suspension cultures of palmarosa grass (Cymbopogon martinii)

A cell suspension culture was established from nodal callus ofCymbopogon martinii (Roxb.) Wats in a liquid medium containing Murashige and Skoog (1962) basal salts, vitamins, 100 mg 1^–1 myo-inositol and 20 g l^–1 of sucrose (MS) that was supplemented with 13.6 M 2,4-dichlorophenoxyacetic acid and 1.15 M kinetin. An initial inoculum density of 2 x 10⁴ cells ml^–1exhibited optimum cell growth. Calli were obtained 12–15 days after the suspension was plated onto semisolid medium of a similar composition. When calli were transferred to semisolid regeneration medium containing MS + 6.7 M N ⁶-benzyl-adenine + 1.15 M kinetin, somatic embryogenesis and plantlet regeneration occurred after 10–25 days. There was no significant decrease in the regeneration potential of the calli even when the cultures were initiated from 47-week-old cell suspensions. Chromosome counts of cells in suspensions, calli and somatic embryos derived from cultures of different ages revealed the presence of diploids, tetraploids and octaploids. However, the 33 regenerated plants tested were all diploid, indicating that only diploid cells were capable of regeneration in vitro.Abbreviations MS Murashige and Skoog (1962) basal salts with vitamins (100 mg1^–1 myo-inositol, 20 g1^–1 sucrose) - 2,4-D 2,4-dichlorophenoxyacetic acid - BA N ⁶-benzyl-adenine - Kn kinetin - MSC MS + 13.6 M 2,4-D + 1.15 M Kn - MSR MS +6.7 M BA + 1.15 M Kn     

Plantlet regeneration from callus initiated from flower buds in the wild species Allium senescens var. minor

Callus regeneration was observed from flower buds of Allium senescens var. minor inoculated in BDS, MS or B5 medium supplemented with 4.4 M benzyladenine alone or in combination with 4.5 M 2,4-dichlorophenoxy-acetic acid (2,4-d), with 2,4-d and kinetin (4.5 M/4.6 M) or with 5.3 M naphthaleneacetic acid. Ovules enlarged initially but the embryogenic tissue degenerated as callus development progressed from the nectar regions of the petals. Shoot buds and leaf primordia developed from the meristematic protuberances that originated from the surface of the callus. BDS medium with 4.5 M 2,4-d and 13.3 M BA was most suitable for shoot multiplication. The regenerated shoots were rooted in respective liquid medium without any growth regulators and successfully transferred to soil with 90% survival rate.Abbreviations BA N⁶-benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - NAA -naphthaleneacetic acid     

Amplification of phleomycin induced death and DNA breakdown by caffeine in Escherichia coli

Summary Caffeine enhanced the degradation of DNA to acid soluble fragments in cultures of Escherichia coli exposed to Phleomycin (2 g/ml). Enhancement was particularly striking with stationary phase cultures, which normally exhibit negligible DNA breakdown when treated with 2 g/ml of Phleomycin. There is little DNA breakdown or death in UVR strains treated with phleomycin (2 g/ml) during exponential growth but when caffeine was present as well as Phleomycin, the kinetics of DNA breakdown and the amounts of DNA degraded were identical in all cultures tested including those of UVR, EXR, B/r type and B strains and equal to the maximum rate observed (with an EXR strain) in the absence of caffeine (ca. 1.7 % per min). High concentrations of Phleomycin (10 g/ml) had the same effect as the caffeine+Phleomycin (2 g/ml) combination and produced a uniform pattern of DNA breakdown in all strains tested. Caffeine did not seem to increase permeability of the bacterial coat. Given to the cells before exposure to Phleomycin it was ineffective in enhancing DNA breakdown. On the other hand, exposure of the bacteria to Phleomycin for a period of 40 min at 37° followed by caffeine was as effective as adding the two drugs together.Caffeine increased the efficiency of Phleomycin as an antibiotic for both growing and stationary phase cultures of e. coli B. It is suggested that caffeine aids the cooperative denaturation of DNA initiated by the attachment of Phleomycin molecules to thymine bases. This would allow single strand-specific endonucleases to attack the DNA and initiate DNA breakdown and cell death.This paper is dedicated to charlotte Auerbach on the occasion of her official retirement.     

Effects of boron deficiency in cell suspension cultures of Populus alba L.

Cell suspension cultures of Populus alba L. (original cells) require at least 10 M boron for appropriate growth. Using original cells we established a cell line, T-5B, which can grow in a medium containing low levels of boron (5 M). The level of boron localized in the cell walls of T-5B cells was one-half that found in the cell walls of original cells maintained in medium containing 100 M boron, and the level of the rhamnogalacturonan II dimer, cross-linked by a borate ester, also decreased in the former. The sugar composition of whole cell walls of the T-5B cell line was similar that of the original cells, however pectic polysaccharides composed of arabinose or galacturonic acid were easily extracted from T-5B cell walls with 50 mM trans-1,2-cyclohexanediamine-N,N,N,N-tetraacetic acid. Our results suggest that boron deficiency causes a weakening of the interaction among pectic polysaccharides due to a decrease in boron-rhamnogalacturonanII cross-linkage.     

Efficient plant regeneration protocol through callus for Saussurea obvallata (DC.) Edgew. (Asteraceae): effect of explant type, age and plant growth regulators

A callus induction and in vitro plantlet regeneration system for the endangered state flower of Uttaranchal (Saussurea obvallata) was optimized by studying the influence of explant type (root, hypocotyl, cotyledon and leaf), age and different concentrations of plant growth regulators. Explants from 10 to 15-day-old seedlings showed maximum callus induction. Callus formation and shoot differentiation was initiated on Murashige-Skoog (MS) medium containing 6-benzyladenine (BA) and -naphthalene acetic acid (NAA) in all explant types. The best results were obtained using leaf explants: 100% callusing was achieved in MS medium supplemented with 2.5 M BA and 1.0 M NAA, and 100% differentiation along with a multiplication rate of 12 shoots per explant with a combination of 5.0 M BA and 1.0 M NAA. However, the results reflected the existence of high inter-explant variability in response to growth regulators. In vitro rooting of shoots was achieved at an efficiency of 100% in one-half strength MS medium supplemented with 2.5 M indole-3-butyric acid. Application of this protocol has potential for mass multiplication of the target species in a limited time period.     

In vitro susceptibility ofTrichophyton rubrum isolates to griseofulvin and tioconazole. Induction and isolation of a resistant mutant to both antimycotic drugs

The in vitro susceptibility of three clinicalTrichophyton rubrum isolates to griseofulvin and tioconazole, determined by the minimal inhibitory concentration (MIC), was 2 and 0.5 to 1.0g/ml, respectively. One mutant (gril) obtained after mutagenic treatment of one of these isolates was selected and showed simultaneous resistance to griseofulvin (MIC > 2000g/ml) and tioconazole (MIC=1.0g/ml). The clinical importance and the possibility of a multidrug resistance (MDR)-type mechanism being involved in this event is discussed.