Isolation and characterization of Azotobacter chroococcum from the roots of Zea mays

Abstract Bacteria showing rapid growth on a nitrogenfree medium and acetylene-reducing activity were isolated from maize roots collected from agricultural soils in Spain. The isolates were Gram-negative motile rods and were identified as Azotobacter chroococcum . Acetylene-reducing activity and microbial counts were determined on root segments from 7- and 30-day-old plants. Rates obtained were in the range of 0.0053–0.848 nmol C₂H₂· g⁻¹· h⁻¹. Root populations were 1.4–6.0 × 10⁴ micro-organisms · g⁻¹. These results showed that there was an association between A. chroococcum strains and roots of maize planted in some Spanish soils.     

Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa). I. Changes during fruit development

The cytokinin content in fruit tissue of the kiwifruit ( Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) was monitored during fruit development to identify which cytokinins were present and if they were linked with specific stages of fruit growth. Cytokinins were isolated and purified by column chromatography and high-performance liquid chromatography and quantified by radioimmunoassay. A novel HPLC step utilising an amine column was successfully introduced as a preparative step in the separation of the O - and 9-glucosides from the free bases and ribosides. The radioimmunoassay results were validated, and the different cytokinins identified, by gas chromatography-mass spectrometry. Cytokinins detected in fruit included the cytokinin free bases, zeatin and isopentenyladenine, their ribosides, nucleotides and both O - and 9-glucosides. Both qualitative and quantitative changes of the cytokinins occurred during fruit development. A decrease in cytokinin concentration occurred after anthesis (from 342 pmol g⁻¹ fresh weight at anthesis to 41 pmol g⁻¹ fresh weight 27 days after anthesis). A large increase in cytokinin concentration and content per fruit occurred as the fruit reached commercial maturity (to 1900 pmol g⁻¹ fresh weight). Individual cytokinins showed quite different patterns. Zeatin, in particular, showed a peak in concentration (13 pmol g⁻¹ fresh weight) 11 days after anthesis that correlated with the beginning of the cell division phase of fruit growth. The accumulation of cytokinin (mostly zeatin riboside or zeatin nucleotide) in mature fruit may be of significance for the postharvest storage of kiwifruit fruit.     

Metabolism of Adenine and Hypoxanthine in a Hormone Autonomous Genetic Tumour Line of Tobacco

Genetic tumour tissues of Nicotiana glauca (Grah.) × N. langsdorffii (Weinm.), which grow on auxin and cytokinin-free medium, were incubated with [14C]-/[3H]-adenine or [3H]-hypoxanthine to investigate cytokinin biosynthesis. Adenine was supplied to tissues of two different ages (2- and 3.5-week-old) for 8, 24 or 30 h. The uptake was over 91.0 % (of "supplied radioactivity") by 2-week-old tissues as compared to around 50.0 % uptake by 3.5-week-old tissues. Incorporation into cytokinins could not be detected. While unmetabolized adenine accounted for only about 24.0 and 13.4 % of "extracted radioactivity" (following 8 and 30 h incubation, respectively) in 2-week-old tissues, relatively higher levels, i.e. 36.0 and 34.5 % (following 8 and 24 h incubation, respectively) were present in 3.5-week-old tissues. The metabolites formed were adenosine and its nucleotides (4.5 - 16.5 % and 37.4 - 60.2 % of the extracted radioactivity, respectively). Hypoxanthine was supplied to 3.5-week-old tissues for 8 and 24 h. While the uptake was low (<28.0 % of supplied radioactivity), the major proportion of extracted radioactivity was due to unmetabolized hypoxanthine (79.8 % and 85.9 % after 8 and 24 h incubation periods, respectively); the minor metabolites were inosine and adenosine (both <0.5 %) and their nucleotides (< 3.5 %). Radioactivity incorporation into cytokinins from hypoxanthine was not detected. Thus in the present investigations precursor incorporation from either adenine or hypoxanthine into cytokinins could not be demonstrated. It is possible that this may be due to slow rate of cytokinin turnover in these tissues.     

Ozone tolerance in snap bean is associated with elevated ascorbic acid in the leaf apoplast

Ascorbic acid (AA) in the leaf apoplast has the potential to limit ozone injury by participating in reactions that detoxify ozone and reactive oxygen intermediates and thus prevent plasma membrane damage. Genotypes of snap bean ( Phaseolus vulgaris L) were compared in controlled environments and in open-top field chambers to assess the relationship between extracellular AA content and ozone tolerance. Vacuum infiltration methods were employed to separate leaf AA into extracellular and intracellular fractions. For plants grown in controlled environments at low ozone concentration (4 nmol mol⁻¹ ozone), leaf apoplast AA was significantly higher in tolerant genotypes (300–400 nmol g⁻¹ FW) compared with sensitive genotypes (approximately 50 nmol g⁻¹ FW), evidence that ozone tolerance is associated with elevated extracellular AA. For the open top chamber study, plants were grown in pots under charcoal-filtered air (CF) conditions and then either maintained under CF conditions (29 nmol mol⁻¹ ozone) or exposed to elevated ozone (67 nmol mol⁻¹ ozone). Following an 8-day treatment period, leaf apoplast AA was in the range of 100–190 nmol g⁻¹ FW for all genotypes, but no relationship was observed between apoplast AA content and ozone tolerance. The contrasting results in the two studies demonstrated a potential limitation in the interpretation of extracellular AA data. Apoplast AA levels presumably reflect the steady-state condition between supply from the cytoplasm and utilization within the cell wall. The capacity to detoxify ozone in the extracellular space may be underestimated under elevated ozone conditions where the dynamics of AA supply and utilization are not adequately represented by a steady-state measurement.     

Movement to bark and metabolism of xylem cytokinins in stems of Lupinus angustifolius

Following uptake of [(3)H]zeatin riboside and [(3)H]dihydrozeatin riboside by girdled lupin (Lupinus angustifolius L.) stems via the transpiration stream, rapid lateral movement of the radioactivity from xylem to bark was observed. Short-term studies with intact stems, and other studies with excised stem tissues, revealed that the ribosides and/or the corresponding nucleotides were the cytokinin forms which actually moved into the bark tissues. Relative to cytokinin metabolism in xylem plus pith, metabolism in bark was both more rapid and more complex. Riboside cleavage and formation of the O-acetylzeatin and O-acetyldihydrozeatin ribosides and nucleotides were almost completely confined to bark tissues. Exogenous (3)H-labelled O-acetylzeatin riboside was converted to zeatin riboside in bark tissue, but the presence of the acetyl group suppressed degradation to adenine metabolites. The sequestration and modification of xylem cytokinins by stem tissues probably contributes significantly to the cytokinin status of the shoot. New cytokinins identified by mass spectrometry in lupin were: O-acetyldihydrozeatin 9-riboside, a metabolite of exogenous dihydrozeatin riboside in stem bark; O-methylzeatin nucleotide and O-methyldihydrozeatin 9-riboside, metabolites of endogenous cytokinins in stem bark; O-methylzeatin nucleotide and O-methylzeatin 9-riboside, metabolites of exogenous zeatin riboside in excised pod walls.     

Survival of κ-carrageenan-encapsulated and unencapsulated Pseudomonas aeruginosa UG2Lr cells in forest soil monitored by polymerase chain reaction and spread plating

Abstract A method was developed for direct extraction, purification and amplification of DNA from forest soil. Eighty-two % of the DNA in Pseudomonas aeruginosa UG2Lr introduced into soil was recovered. The detection limit for the strain was approximately 800 cfu g⁻¹ of dry soil based on the polymerase chain reaction (PCR). Survival of κ-carrageenan-encapsulated and unencapsulated UG2Lr was monitored by antibiotic selective and bioluminescence-based nonselective plating and PCR-amplification of a tnsA fragment. After freeze-thaw treatment of soil samples, the unencapsulated UG2Lr declined from an initial population density of 1 × 10⁹ cfu g⁻¹ of dry soil to below the detection threshold of both selective (14 cfu g⁻¹ of dry soil) and nonselective (1 × 10³ cfu g⁻¹ of dry soil) plating. However, presence of nonculturable UG2Lr cells in the soil was revealed by PCR and resuscitation of the bacteria. Population density of the encapsulated UG2Lr increased from 2.7 × 10⁶ to 2.9 × 10⁸ cfu g⁻¹ of dry soil after a 3-week incubation at 22°C and declined to 6.3 × 10⁶ cfu g⁻¹ of dry soil after the freeze-thaw treatment.     

Monitoring the fate of genetically engineered bacteria sprayed on the phylloplane of bush beans and grass

Abstract The fate of a Bacillus amyloliquefaciens with the recombinant plasmid pSB20 sprayed on the phyllosphere of grass, and of a Tn 5 marked Pseudomonas syringae sprayed on the phyllosphere of bush beans was studied in planted soil microcosms. B. amyloliquefaciens showed a decline from 1.5×10⁸ to 3.1×10² cfu g⁻¹ on the phylloplane of grass in the course of the experiment. B. amyloliquefaciens was easy to follow by selective cultivation due to the complete absence of bacterial background growth. Southern blot hybridization of Hin dIII digested genomic DNA showed plasmid restriction patterns identical with pSB20 indicating high plasmid stability. In total DNA extracts from phyllosphere bacteria the recombinant plasmid was detectable by Southern blot hybridization up to 6×10⁴ cfu g⁻¹ (wet weight). Counts of hybridizing colonies showed that P. syringae established on the phyllosphere of bush beans at between 5×10³ and 4×10⁶ cfu g⁻¹ fresh weight. During senescence of the bean plants the strain was no longer detectable by selective cultivation and subsequent colony hybridization. In contrast, Tn5 marked DNA was detected after PCR amplification over the whole period of the experiment.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Effects of ozone on apoplast/cytoplasm partitioning of ascorbic acid in snap bean

Apoplast/cytoplasm partitioning of ascorbic acid (AA) was examined in four genotypes of snap bean ( Phaseolus vulgaris L.) known to differ in ozone sensitivity. Plants were grown in pots under field conditions using open-top chambers to establish charcoal-filtered (CF) air (36 nmol mol⁻¹ ozone) or elevated ozone (77 nmol mol⁻¹ ozone) treatments. AA in fully expanded leaves of 36-day-old plants was separated into apoplast and cytoplasm fractions by vacuum infiltration methods using glucose 6-phosphate as a marker for cytoplasm contamination. Apoplast ascorbate levels ranged from 30 to 150 nmol g⁻¹ fresh weight. Ozone-sensitive genotypes partitioned 1–2% of total AA into the apoplast under CF conditions and up to 7% following a 7-day ozone exposure. In contrast, an ozone-tolerant genotype partitioned 3–4% of total leaf AA into the leaf apoplast in both CF and ozone-treated plants. The results suggest that genetic background and ozone stress are factors that affect AA levels in the extracellular space. For all genotypes, the fraction of AA in the oxidized form was higher in the apoplast compared to the cytoplasm, indicative of a more oxidizing environment within the cell wall.     

Pathogenesis-related protein b1' in plants and in cell suspension cultures of Nicotiana glutinosa Nicotiana debneyi and an amphidiploid cross (N. glutinosa×N. debneyi)

The expression of PR-protein b₁' in plants and cell suspension cultures of Nicotiana glutinosa L., Nicotiana debneyi Domin, and an amphidiploid cross of these two species, a hybrid, has been investigated. An enzyme linked immunosorbent assay has been employed to determine the concentration of PR-protein b₁' in extracts. The PR-Protein b₁' was constitutively produced in intact plants of the hybrid (around 25 μg g⁻¹ leaf tissue), while only trace amounts of the protein (< 50 ng g⁻¹ leaf tissue) were found in plants of the two parents. In suspension culture, the concentrations of PR-protein b₁' were 8, 0.4 and less than 0.1 mg l⁻¹ medium for the hybrid. N. debneyi and N. glutinosa , respectively. Only trace amounts of the protein were found in extracts from cells. Seven days after infection by tobacco mosaic virus (TMV) the concentration of PR-protein b₁' in leaves of N. glutinosa was 22.5 μg g⁻¹ leaf tissue. In N. debneyi and the hybrid a relatively limited induction of PR-protein b₁' by TMV was observed. The influence of various phenoxyacetic acids on the expression of PR-protein b₁' in the 3 cell cultures has been investigated. Cultures of N. glutinosa responded to treatments with 2,4-D and 2,4,5-T while cultures of N. debneyi and the hybrid were essentially unaffected. In the former case a concentration of 5–10 mg l⁻¹ 2,4,5-T was optimal and cells were most responsive to the treatment 4 days after subcultivation. The concentration of PR-protein b₁' in elicited cell cultures of N. glutinosa was 2 to 4 mg l⁻¹ medium.     

Influence of woodlot floor topography on microbial decomposer distribution

The distribution of microbial populations that decomposed sugar, cellulose and lignin-related substrates was examined in a beech Fagus grandifolia Ehrh. and maple Acer saccharum Marsh. dominated woodlot developed on glacial till. The topography of the woodlot, characterized by rises, depressions and more extensive level areas about 1 m in diameter with a 0.5 m vertical maximum, produced a mosaic of decomposer habitats designated as high, level and low sites.
In general, populations of sugar, cellulose and lignin decomposing organisms (based on ten estimates made from April to October) were two to four times higher in litter and soil samples from low sites than those from high sites. Sugar decomposing bacteria in litter were most abundant at all topographic sites. 135 × 10⁶ g⁻¹ dry litter at high sites, 396 × 10⁶ g⁻¹ at level sites and 456 × 10⁶ g⁻¹ at low sites; lignolytic fungi were least abundant, 391 × 10² g⁻¹ dry litter at high sites. 700 × 10⁶ g⁻¹ at level sites and 954 × 10² g⁻¹ at low sites. Numbers of microbial decomposers in the topographic sites were correlated with organic matter content. Distribution of fungal genera did not appear to be related to topographic site. Most populations examined showed two numerical peaks, one in late May or June and one in late September or October. It is suspected that these peaks were influenced by the coincident timing of favourable physical conditions and priming by soluble nutrients leached from litter.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria × ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

Carbon, nitrogen and caloric content of eggs, larvae, and juveniles of the walleye pollock, Theragra chalcogramma

Measurements of dry weight (wt), carbon (C), nitrogen (N) and calories were made on walleye pollock eggs (0.24 mg, 35.3% C, 8.3% N, and 4.6 kcal g⁻¹ dry wt), larvae (0.16 g, 42.9% C, 11.1% N and 5.1 kcal g⁻¹ dry wt) and juveniles (22.4 g, 47.2% C, 9.0% N and 5.6 kcal g⁻¹ dry wt). For juvenile fish (9–360 g wet wt) the measured values were related to dry weight and Fulton's condition factor index (CFI) by regression models. The CFI was a better predictor of body composition than dry weight. As CFI improved from a minimum starvation level of 0.42 to a maximum of 1.16, body caloric content, percentage C, and the C/N ratio increased (kcal g⁻¹ dry wt = 4.4 CFI + 1.7, percentage carbon = 49.7 CFI^0.5, C/N ratio = 5.0 CFI + 0.9), while percentage N and percentage ash decreased (percentage N =−3.5 CFI + 12.1; percentage ash = 9.1 CFI^−1.4). The results of this study suggest that seasonal C, N and caloric content of young pollock can be estimated from measurements of Fulton's condition factor index.     

Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.     

Production of amylase by the intestinal microflora in cultured freshwater fish

The amylase-producing ability of the intestinal microflora in cultured specimens of ayu, carp, channel catfish, Japanese eel and tilapia was determined. Mean viable counts of aerobes and anaerobes ranged from 1·1×10⁶ to 3·7×10⁸ cfu g⁻¹ and from 1·3×10³ to 1·6×10⁸ cfu g⁻¹, respectively. Aeromonas spp. and Bacteroidaceae were predominant in four to five fish species. Of 206 strains examined, 65 (31·6%) produced ≥0·01 U amylase ml⁻¹. The percentage of producers differed among families and genera of bacteria and fish species. While 56% of the anaerobes produced amylase, only 20% of the aerobes did. More than 50% of Aeromonas , Bacteroidaceae and Clostridium strains produced amylase efficiently while Acinetobacter , coryneforms, Enterobacteriaceae, Moraxella , Plesiomonas and Streptococcus strains did not. High amylase production (≥0·05 U ml⁻¹) was found in 12 strains, 11 from Aeromonas and one Pseudomonas . The percentage of high amylase producers in Japanese eel was lower than the other four fish (2–30%). These results strongly suggest that the amylase produced by the intestinal microflora play an important role in the digestion of starch in freshwater fish to some extent.     

Methanogenesis and methanotrophy within a Sphagnum peatland

Abstract: Methane production and consumption activities were examined in a Massachusetts peatland. Peat from depths of 5–35 cm incubated under anaerobic conditions, produced an average of 2 nmol CH₄ g⁻¹ h⁻¹ with highest rates for peat fractions between 25–30 cm depth. Extracted microbial nucleic acids showed the strongest relative hybridization with a 16S rRNA oligonucleotide probe specific for Archaea with samples from the 25–30 cm depth. In aerobic laboratory incubations, the peat consumed methane with a maximum velocity of 67 nmol CH₄ g⁻¹ h⁻¹ and a K _s of 1.6 μM. Methane consumption activity was concentrated 4–9 cm below the peat surface, which corresponds to the aerobic, partially decomposed region in this peatland. Phospholipid fatty acid analysis of peat fractions demonstrated an abundance of methanotrophic bacteria within the region of methane consumption activity. Increases in temperature up to 30°C produced an increase in methane consumption rates for shallow samples, but not for samples taken from depths greater than 9 cm. Nitrogen fixation experiments were carried out using ¹⁵N₂ uptake in order to avoid problems associated with inhibition of methanotrophy. These experiments demonstrated that methane in peat samples did not stimulate nitrogen fixation activity, nor could activity be correlated with the presence of methanotrophic bacteria in peat fractions.     

Effects of exogenous cytokinins on root formation in pea cuttings

Benzylaminopurine (BAP) or zeatin continuously supplied through the rooting solution to cuttings of pea ( Pisum sativum L. cv. Weibull's Marma), inhibited root formation down to a concentration of 3.10⁻⁹ M . The inhibitory effect of BAP in the concentration range 10⁻⁸–10⁻⁷ M was readily reversible if the cuttings were transferred to solutions without cytokinin after treatment for 1–4 days. A slight increase in the number of roots formed was obtained after treatment with low cytokinin concentrations for 1–2 days. Evidence from microscopic studies of primordia formation indicates that BAP inhibits differentiation of primordia at an early stage in their development. Growth of already formed primordia, or root elongation, was considerably less sensitive to the inhibitory effect of BAP. The results indirectly support the hypothesis that endogenous cytokinins prevent root formation in stems of intact plants and may be of importance for the regulation of rooting in cuttings.     

Detection and quantification of Desulforhabdus amnigenus in anaerobic granular sludge by dot blot hybridization and PCR amplification

A species-specific 16S rRNA oligonucleotide probe (ASRB1) was developed for the detection of Desulforhabdus amnigenus in anaerobic granular sludge. The presence of nucleic acids from cells of D. amnigenus in granular sludge was determined using ASRB1 as a specific primer for polymerase chain reaction (PCR) amplification or as a probe for dot blot hybridizations. The detection threshold and the reproducibility of these two methods were determined with sludge amended with 10⁴–10¹⁰ D. amnigenus cells per gram of volatile suspended solids (VSS). For D. amnigenus cells with a ribosomal RNA content of 15 fg cell⁻¹, the lowest number of target cells detected by hybridization was 1 × 10⁸ cells g⁻¹ VSS. With the PCR amplification method the lowest number of target cells which could be detected was 1 × 10⁷ g⁻¹ VSS. This corresponds to a threshold level for hybridization of 0·1–0·001‰ of the total bacterial sludge population, while the threshold level obtained with the PCR approach amounted to 0·01–0·0001‰. The rRNA content of D. amnigenus was found to be affected by the growth rate and the growth phase, and it ranged from 19 fg cell⁻¹ in slow-growing cultures to 90 fg cell⁻¹ in fast-growing cultures. Therefore, the detection threshold of the dot blot hybridization method for fast-growing cells is lower than for slow-growing cells.     

Quantification of pathogenic micro-organisms in the sludge from treated hospital wastewater

The sludge from hospital waste treatment facilities is a potential source of infectious organisms. The average numbers of micro-organisms in the sludge of hospital wastewater in Taiwan were as follows: total count 8·1 × 10⁷ cfu g⁻¹ (dry weight of sludge), and 1·4 × 10⁶, 3·6 × 10⁵, 1·6 × 10⁵, 2·2 × 10⁵ and 5·5 × 10⁴ cfu g⁻¹ (dry weight of sludge) for total coliforms, faecal coliforms, faecal streptococci, Pseudomonas aeruginosa and Salmonella spp., respectively . Salmonella spp. were detected in 37% (10 of 27) of the sludges from hospital wastewaters. Therefore, the treatment of such sludge to reduce pathogenic micro-organisms should be considered.     

Cytokinin concentration in relation to mineral nutrition and benzyladenine treatment in Plantago major ssp. pleiosperma

Cytokinins in shoot and root tissue were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) grown on a concentrated and on a dilute nutrient solution. Cytokinins of plants transferred from the concentrated to the dilute solution were compared with plants treated similarly but with 10⁻⁸ M benzyladenine (BA) added to the dilute solution. Cytokinin concentrations were also measured in plants that had been grown throughout on one of the two nutrient solutions. A restricted supply of minerals was correlated with low cytokinin concentrations. Transfer from a concentrated nutrient solution to a dilute solution depressed the cytokinin concentration by 50% within two days of transfer. This decline did not appear if similar plants were supplied with 10⁻⁸ M BA in the dilute solution. The glucosides were the only major cytokinins enhanced by mineral shortage. This effect of low mineral supply was retarded but not entirely prevented by exogenous BA. The increased synthesis of glucosides in the BA-treated plants was accompanied by lowered concentrations of free bases and their ribosides and of nucleotides. The sum of cytokinins in BA-treated plants was thus similar to that in plants grown at the high mineral level. The results are discussed in relation to a possible role of cytokinins in regulating growth responses to changes in mineral nutrition.