Ambiol,spermine, and aminoethoxyvinylglycine prevent water stress and protect membranes in Pinus strobus L under drought

The ability of antistress compounds to enhance the drought tolerance of conifer seedlings was tested by feeding plant growth regulators (PGRs) to 1-year-old white pine (Pinus strobus L.), which were then subjected to either a moderate (11 day) or a more severe (16 day) drought. The following PGRs were either fed directly into the xylem or applied as a root drench: the antioxidant Ambiol (2-methyl-4-[dimethylaminomethyl]- 5-hydroxybenzimidazole dihydrochloride), the polyamine, spermine, an anti-ethylene agent, aminoethoxyvinylglycine (AVG), and the inhibitor, abscisic acid (ABA). Leaf water potentials (ƒ_l) declined in untreated seedlings when they were exposed to drought. Preconditioning with PGRs postponed water deficits and prevented membrane leakage under drought. The specific physiological adjustments observed were found to vary, depending on the type of compound. Ambiol, AVG and spermine caused transpirant rates to decline under drought. Although the antitranspirant effects of Ambiol and spermine would explain the increase in water use efficiency under drought, spermine also enhanced photosynthesis. The same compounds promoted osmotic adjustment, which would help to maintain turgor under drought. This was shown by the decline in osmotic potential at full turgor, and at zero turgor, in Ambiol and spermine-treated seedlings. Seedlings treated with Ambiol and ABA could sustain a greater water loss before turgor declined to zero. The possibility that preconditioning may help to maintain leaf physiological functioning under drought by reducing water stress and stress-ethylene production is discussed.     

Early growth invigoration of jack pine seedlings by natural plant growth regulators

 Survival of conifer transplants is often poor on exposed planting sites in the boreal forest. More than one-third of all conifers do not become established. To enhance the competitive ability of jack pine seedlings, seeds were treated with natural plant growth regulators (PGRs; viz., homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine) and growth promotion was studied for 16 days. Homobrassinolide (5 ng l^–1), salicylic acid (100 μg l^–1) and spermine (10 μg l^–1) enhanced elongation growth and elongation rate of whole plant. Homobrassinolide (5 ng l^–1) and salicylic acid (100 μg l^–1) stimulated root elongation by 38% and 10% respectively while spermine (1000 μg l^–1) increased needle growth by 14%. Homobrassinolide stimulated dry weight growth and growth rate. Homobrassinolide recorded over 20% increase in dry matter production, apportioned equally to root and needles, whereas spermine enhanced total dry matter production by almost 10%, mostly by increasing needle weight. Homobrassinolide facilitated nearly 19% increase in growth rate while spermine recorded only a 7% growth promotion. Spermidine inhibited both elongation and dry weight growth at all concentrations. Growth promotion by homobrassinolide, salicylic acid and spermine may be through an acceleration of processes connected to cell elongation, cell division and C allocation and these PGRs showed most promise for the early invigoration and improvement of jack pine seedling growth. Received: 27 August 1997 / Accepted: 8 January 1998     

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N¹-(2-chloro-4-pyridyl)-N²-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10⁻⁵ m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Received September 25, 1997; accepted August 10, 1998     

Growth enhancement and antitranspirant activity following seed treatment with a derivative of 5-hydroxybenzimidazole (Ambiol) in four drought-stressed agricultural species

The biostimulating action of seed treatment with the synthetic antioxidant, Ambiol (2-methyl-4-Edimethylaminomethyl-5-hydroxybenzimidazole dihydrochloride) on subsequent growth and transpiration of seedlings was studied. To study growth and transpiration responses, seeds of four agricultural species, soybean ( Glycine max L.), rapeseed ( Brassica napus L.), winter wheat ( Trilicum aestivum L.) and corn ( Zea mays L.), were soaked in Ambiol for 24 h, using the following concentrations: 0, 0.01, 0.1, 1, 10 and 100 mg 1¹. The subsequent seedlings were subject to simulated soil drought, using computer-automated root misting chambers. The influence of Ambiot on transpiration rate under simulated air drought was studied by growing plants under low humidity in a controlled humidity chamber. Response to Ambiol varied, depending on its concentration, the species used and the environment. Compared to untreated plants, 10 mg 1-⁻¹ Ambiol reduced the mid-day transpiration rate and total daily water usage of soybean by approximately 25%. Under simulated soil drought in the root misting chamber, 10 and 100 mg 1-⁻¹ Ambiol increased growth of rapeseed and soybean by 25–45%, relative to the 0 mg 1-⁻¹ treatment, yielding plants comparable in size to the fully-irrigated controls. However, Ambiol failed to promote growth of two drought-stressed monocotyledons (corn and winter wheat). At 100 mg P. Ambiol inhibited growth of both well-watered wheat and rapeseed, although this inhibition was mitigated by drought.     

Effects of increasing saturation vapour pressure deficit on growth and ABA levels in black spruce and jack pine

 Plant responses to saturation vapour pressure deficit (SVPD) were studied by subjecting black spruce [Picea mariana (Mill) B.S.P.] and jack pine seedlings (Pinus banksiana Lamb.) to humid (0.3 – 0.8 kPa) or dry (2.0 – 2.5 kPa SVPD) regimes for 4 weeks using a computer-controlled environmental system to control diurnal variation in SVPD. Dry matter accumulation in needles was not altered by increasing SVPD. However, root growth declined by 60% which increased shoot to root ratio and reduced total seedling dry weight in both black spruce and jack pine. Relative growth rate of jack pine also declined to about half the rate of plants grown under humid conditions. In situ root marking studies showed that the decline in root growth of jack pine under the high SVPD was the result of reduced lateral root initiation, whereas root elongation was unaffected by humidity. A 4-week exposure to dry air increased abscisic acid (ABA) levels in needles, but not roots, of jack pine whereas ABA levels in black spruce were not altered. A short (3-day) exposure failed to increase needle ABA levels in either species. These results suggest that the responses of conifers to dry air were not the result of ABA accumulation. Received: 24 March 1996 / Accepted: 30 May 1996     

Abscisic acid induced electrolyte leakage in woody species with contrasting ecological requirements

To determine the relationship between drought, abscisic acid (ABA) levels, and membrane leakage, these aspects were studied in three woody species with contrasting ecological requirements. Physiological comparisons were made, during a 14-day drought-recovery cycle, on a drought resistant species, jack pine ( Pinus banksiana Lamb.), and two more drought susceptible species, black spruce ( Picea mariana (Mill) B.S.P.) and flooded gum ( Eucalyptus grandis W. Hill ex Maiden). As the xylem pressure potentials (Ψ), declined under drought, both foliar ABA and electrolyte leakage increased significantly. However, ABA increased prior to the increase in leakage, and there was a significant linear correlation between endogenous ABA and leakage in all 3 species. Addition of exogenous ABA to the bathing solutions also significantly increased leakage of both unstressed and (sorbitol) osmotically-stressed leaf segments in response to increasing (log) concentrations of (±) cis-trans ABA [0–10.0 μ M ]. Electrolyte leakage in black spruce and flooded gum was more sensitive to stress-induced ABA than in jack pine. The results suggest that drought increases foliar ABA which initiates membrane leakage, and that sensitivity of membranes to ABA accumulation varies, depending on the ecological requirements of a species.     

Polyamines in Helianthus annuus L. during Germination under Salt Stress

The level of the three main polyamines putrescine, spermidine, and spermine and the biosynthetic enzyme arginine decarboxylase (ADC) decreased in Helianthus annuus L. seedlings subjected to increasing (50, 100, and 150 mm) NaCl concentrations. The pattern of polyamines in control plants increased during the initial 72 h and then reached a plateau. The putrescine level showed an increase of 370% after 72 h of development. The lower salt treatment slightly diminished the overall polyamine content. The highest NaCl concentration (150 mm) induced a strong putrescine diminution (from 381 to 78.9 nmol g⁻¹ FW) at 72 h whereas a small decrease in ADC activity was detected. ODC was detected in neither control nor treated plantlets during the experimental period. The level of spermidine also decreased, but the magnitude of the decay was less pronounced than putrescine. The fact that ODC was not detected and ADC activity followed a pattern similar to that of putrescine led us to suppose that the variation in putrescine content could be attributed entirely to the decrease in ADC activity. α-Difluoromethylarginine and α-difluoromethylornithine (ADC and ODC inhibitor, respectively) did not inhibit but delayed the onset of germination of sunflower seeds, and α-difluoromethylornithine increased the content of spermidine and spermine. The present data suggest that polyamines could be involved in the germination process of H. annuus seeds and in response to salt stress. Received April 14, 1997; accepted July 10, 1997     

Rectification of the Olfactory Cyclic Nucleotide-Gated Channel by Intracellular Polyamines

Polyamine-induced inward rectification of cyclic nucleotide-gated channels was studied in inside-out patches from rat olfactory neurons. The polyamines, spermine, spermidine and putrescine, induced an `instantaneous' voltage-dependent inhibition with K <sub>d</sub> values at 0 mV of 39, 121 μm and 2.7 mm, respectively. Hill coefficients for inhibition were significantly < 1, suggesting an allosteric inhibitory mechanism. The Woodhull model for voltage-dependent block predicted that all 3 polyamines bound to a site 1/3 of the electrical distance through the membrane from the internal side. Instantaneous inhibition was relieved at positive potentials, implying significant polyamine permeation. Spermine also induced exponential current relaxations to a `steady-state' impermeant level. This inhibition was also mediated by a binding site 1/3 of the electrical distance through the pore, but with a K _d of 2.6 mm. Spermine inhibition was explained by postulating two spermine binding sites at a similar depth. Occupation of the first site occurs rapidly and with high affinity, but once a spermine molecule has bound, it inhibits spermine occupation of the second binding site via electrostatic repulsion. This repulsion is overcome at higher membrane potentials, but results in a lower apparent binding affinity for the second spermine molecule. The on-rate constant for the second spermine binding saturated at a low rate (∼200 sec⁻¹ at +120 mV), providing further evidence for an allosteric mechanism. Polyamine-induced inward rectification was significant at physiological concentrations. Received: 17 February 1999/Revised: 27 April 1999     

Growth promotion of bean (Phaseolus vulgaris L.) by a polyamine-producing isolate of Streptomyces griseoluteus

Of seventy-five actinomycetes isolated from a bean rhizosphere in the United Arab Emirates, an isolate of Streptomyces griseoluteus (WT) was found to be capable of producing relatively high levels of putrescine on decarboxylase agar medium and to produce putrescine, spermidine and spermine in liquid decarboxylase medium. In the glasshouse, the application of the WT strain to soil amended with arginine (as a precursor for putrescine) significantly (P < 0.05) promoted the growth of bean plants and increased the fresh and dry weights and lengths of roots and shoots, compared with control plants. Infestation of soil with the WT strain resulted in a significant (P < 0.05) increase in the levels of putrescine, spermidine and spermine, certain endogenous plant growth regulators (PGRs) (indole-acetic acid, and gibberellic acid), chlorophylls (a, b) and carotenoids with a concomitant reduction in the level of abscisic acid in bean plants, compared with control plants. A polyamine non-producing mutant strain (PNPM) obtained from the wild-type isolate (WT), however, failed to promote plant growth. There were no significant (P > 0.05) differences between the levels of polyamines, endogenous PGRs, chlorophylls (a, b), and carotenoids between plants that were not exposed to either of the strain (control) and those grown in soil with the PNPM strain. Both WT and PNPM strains were incapable of producing in vitro detectable levels of PGRs, indole-acetic acid, indole-pyruvic acid, gibberellic acid, isopentenyl adenine and zeatin in the culture filtrates. This study is the first to demonstrate the potential of a polyamine-producing actinomycete to promote plant growth. In addition, it is also the first published report of the production of polyamines by streptomycete actinomycetes.     

Ethylene evolution and ABA and polyamine contents in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> during UV-B stress

Changes in plant growth, membrane integrity, ethylene evolution, ABA content, and the content of free polyamines were examined in 14-day-old Arabidopsis thaliana (L.) Heynh., strain Columbia (Col-0) plants after a single UV-B irradiation with low (3 kJ/m²), moderate (6–9 kJ/m²), high (18 kJ/m²), and lethal (27 kJ/m²) doses. The UV-B treatment caused dose-dependent suppression of plant growth. One hour after irradiation, the membrane damage was evident from the increased leakage of electrolytes. The low-dose and moderate-dose irradiation caused a transient increase in evolution of ethylene and in the content of putrescine (spermidine and spermine precursor) with the peaks of these parameters attained at 5 and 24 h, respectively. The high-and lethaldose irradiation induced a smaller rise in ethylene evolution, with a slight trend to its decrease, especially, after the exposure to the lethal dose. The high and lethal doses of UV-B suppressed putrescine accumulation, depleted spermidine and spermine pools, and caused severe injuries and plant death. During the first day after irradiation, the ABA content increased in proportion to the irradiation dose. On the second day, the accumulation of ABA was observed in plants irradiated with moderate doses. The accumulation was arrested after a high-dose irradiation and was diminished by 45% after a lethal dose treatment. The results provide evidence for the involvement of ethylene, ABA, and polyamines in plant responses induced by UV-B irradiation.     

Levels of endogenous polyamines and NaCl-inhibited growth of rice seedlings

The role of endogenous polyamines in the control of NaCl-inhibited growth of rice seedlings was investigated. Putrescine, spermidine and spermine were all present in shoots and roots of rice seedlings. NaCl treatment did not affect spermine levels in shoots and roots. Spermidine levels in shoots and roots were increased with increasing concentrations of applied NaCl. NaCl at a concentration of 50 mM, which caused only slight growth inhibition, drastically lowered the level of putrescine in shoots and roots. Addition of precursors of putrescine biosynthesis (L-arginine and L-ornithine) resulted in an increase in putrescine levels in NaCl-treated shoots and roots, but did not allow recovery of the growth inhibition of rice seedlings induced by NaCl. Pretreatment of rice seeds with putrescine caused an increase in putrescine level in shoots, but could not alleviate the inhibition effect of NaCl on seedling growth. The current results suggest that endogenous polyamines may not play a significant role in the control of NaCl-inhibited growth of rice seedlings.Abbreviations PUT putrescine - SPD spermidine - SPM spermine     

Participation of polyamines in the flowering of the short-day plant Pharbitis nil

The effect of the exogenous application of polyamines on the flowering induction of the short-day plant Pharbtis nil was investigated. Putrescine, spermidine and spermine applied on the cotyledons of 4-day seedlings had no significant effect on the flowering of this plant under conditions of full induction caused by a 16-hour-long inductive night. Under the conditions of partial induction caused by a 13-hour-long subinductive night, polyamines inhibit or stimulate flowering, depending on the time of application. Also, inhibitors of the biosynthesis of polyamines influenced the flowering process. Analysis of endogenous polyamines revealed significant fluctuations in their content in cotyledons during an inductive night, as well as under continuous light conditions. Particularly large changes occurred in spermidine and spermine levels. The putrescine level in induced seedlings was lower than in non-induced ones. However, induced seedlings contained a higher level of spermine and spermidine. The highest spermidine and spermine levels were observed at the 8th h of the night, although the total concentration of spermine during photoinduction was always 2–3 times lower than that of spermidine. A break in the inductive night, leading to a complete inhibition of flowering, had caused significant changes in the polyamine level by the end of the night. The results suggest that the flowering induction of Pharbitis nil took place at a low putrescine level and increased spermidine and spermine levels.     

Spermine facilitates recovery from drought but does not confer drought tolerance in transgenic rice plants expressing <Emphasis Type="Italic">Datura stramonium</Emphasis><Emphasis Type="Italic">S</Emphasis>-adenosylmethionine decarboxylase

Polyamines are known to play important roles in plant stress tolerance but it has been difficult to determine precise functions for each type of polyamine and their interrelationships. To dissect the roles of putrescine from the higher polyamines spermidine and spermine, we generated transgenic rice plants constitutively expressing a heterologous S-adenosylmethionine decarboxylase (SAMDC) gene from Datura stramonium so that spermidine and spermine levels could be investigated while maintaining a constant putrescine pool. Whereas transgenic plants expressing arginine decarboxylase (ADC) produced higher levels of putrescine, spermidine and spermine, and were protected from drought stress, transgenic plants expressing SAMDC produced normal levels of putrescine and showed drought symptoms typical of wild type plants under stress, but the transgenic plants showed a much more robust recovery on return to normal conditions (90% full recovery compared to 25% partial recovery for wild type plants). At the molecular level, both wild type and transgenic plants showed transient reductions in the levels of endogenous ADC1 and SAMDC mRNA, but only wild type plants showed a spike in putrescine levels under stress. In transgenic plants, there was no spike in putrescine but a smooth increase in spermine levels at the expense of spermidine. These results confirm and extend the threshold model for polyamine activity in drought stress, and attribute individual roles to putrescine, spermidine and spermine.     

Fluctuation in free and conjugated polyamines in Scots pine seedlings after changes in temperature and daylength

Free, soluble and insoluble conjugated polyamines from the needles, roots and stem of five month old Scots pine (Pinus sylvestris L.) seedlings inoculated with Suillus variegatus (Fr.) O. Kuntze and seedlings without inoculation were analysed during decrease in daylength and temperature. Temporary changes in free, soluble and insoluble conjugated polyamine pools caused by a decrease in daylength or temperature were observed. Inoculation of pine seedlings affected significantly the polyamine levels of five month old pine seedlings. The roots of inoculated seedlings contained significantly higher levels of free and soluble conjugated purtrescine and free, soluble conjugated and insoluble conjugated spermidine than the roots of noninoculated seedlings. The needles of inoculated seedlings contained significatly higher concentrations of free putrescine and soluble conjugated spermidine but lower amount of free spermine than the needles of noninoculated seedlings. The stems of inoculated seedlings contained higher concentrations of free putrescine but lower amounts of insoluble conjugated spermine. Changes in polyamine levels in noninoculated seedlings were observed after shortening of the daylength, whereas in inoculated ones changes were induced mainly by the decrease in temperature. The possible role of polyamines in the initial stage of cold hardening process is discussed.     

Involvement of Abscisic Acid in Mesocotyl Growth in Etiolated Seedlings of a Foxtail Millet Dwarf Mutant

Etiolated seedlings of foxtail millet (Setaria italica Beauv.) dwarf mutant CH84113 were treated with various concentrations of abscisic acid (ABA), mefluidide, mannitol, or polyethylene glycol (PEG) 6000. It was found that these chemicals, at suitable concentrations, could increase mesocotyl length significantly, whereas these chemicals at higher concentrations had an inhibitory effect. Endogenous levels of ABA in mesocotyl were measured by enzyme-linked immunosorbent assay. It was found that endogenous ABA increased progressively in a chemical (ABA, mefluidide, mannitol, or PEG 6000) concentration-dependent manner, indicating that the effects of these chemicals on mesocotyl growth may be mediated by increased endogenous ABA levels. On the other hand, S-3307, an inhibitor of the oxidative reactions in gibberellin (GA) biosynthesis, inhibited the elongation of mesocotyl significantly. When ABA and GA₃ were applied simultaneously, the effect on mesocotyl growth was additive. These results imply that ABA and GA may control different processes in the regulation of mesocotyl growth. Received October 27, 1997; accepted May 11, 1998     

Effects of abscisic acid on the contents of polyamines and proline in common bean plants under salt stress

The effects of ABA treatment on the contents of polyamines (PAs) and proline (Pro) in the glycophyte Phaseolus vulgaris L. during plant adaptation to salt stress were studied. Two-week-old common bean seedlings grown in the phytotron chamber on the Jonson nutrient medium were subjected to salinity for 6 days by one-time NaCl addition to medium up to final concentrations of 50 and 100 mM. During first three days of salinity, the root system was daily treated with ABA (1, 5, 10, or 50 μM) for 30 min. Salt stress (100 mM NaCl) elevated the level of endogenous ABA, increased the content of Pro 14-fold, reduced sharply the content of free PAs (putrescine, spermidine, spermine, and cadaverine), and the accumulation of 1,3-diaminopropan, a product of oxidation of high-molecular PAs. Common bean plant treatment with 1 μM ABA weakened the adverse effects of salt stress (100 mM NaCl), which was manifested in the maintenance of plant growth, stimulation of chlorophyll (a and b) and carotenoid accumulation, a stabilization of water and Na⁺ balance. Seedling treatment with ABA suppressed NaCl-induced Pro and intracellular ABA accumulation and restored the levels of putrescine and spermidine. The content of spermine in the leaves of plants subjected to salt stress and treated with ABA was approximately threefold higher than in control plants, whereas the content of cadaverine increased under similar conditions more than fivefold. Simultaneously, the contents of 1,3-diaminopropan and malondialdehyde as well as activity of superoxide dismutase were reduced, which indicates a weakening of oxidative stress, one of the possible causes of defensive ABA effects against salt stress. In addition, the suppression by exogenous ABA of Pro accumulation and stimulation of PA content under salt stress confirm indirectly our hypothesis that ABA is involved in the coordinated regulation of two biosynthetic pathways, Pro and PA formation, which use a common precursor, glutamate, and play an important protective role during stress in plants.     

Influence of Polyamines on Growth of Hairy Root Cultures of Witloof Chicory (Cichorium intybus L. cv. Lucknow Local) and Formation of Coumarins

The effect of polyamines (putrescine, spermidine, and spermine) was examined for growth and production of two coumarins, esculetin and esculin, in the hairy roots of chicory (Cichorium intybus L. cv. Lucknow local). Of the polyamines administered, 1.5 mm putrescine alone resulted in a 2.3-fold higher increase in the growth of hairy roots as well as in the production of esculetin and esculin, which was 3.37 times more than that of the control on day 21. The endogenous level of conjugated putrescine was more than fivefold that of free putrescine levels in untreated samples. The production of esculetin and esculin in hairy root cultures strictly correlated with growth in all of the treatments. Putrescine at 1.5 mm resulted in a greater length of primary root (18.29 ± 1.37 cm) compared with the control (10.96 ± 0.82 cm) and more secondary and tertiary roots. This study also provides insight into the morphogenetic changes that occur in roots in response to the external supply of polyamines. Received July 20, 1998; accepted January 19, 1999     

Polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine (Pinus virginiana Mill.) plantlets

Polyamines have been demonstrated to play an important role in adventitious root formation and development in plants. Here, we present a detailed analysis of influence of exogenously added polyamines on adventitious root development and its relationship to cold tolerance in Virginia pine (Pinus virginia Mill.). Our results demonstrated that polyamines putrescine (Put), spermidine (Spd), and spermine (Spm) at 0.001 mM improve rooting frequency and promote root elongation. Put, Spd, and Spm at 0.01–1 mM decrease rooting frequency and reduce root elongation root elongation. Measurements of diamine oxidase (DAO, EC 1.4.3.6) and polyamine oxidase (PAO, EC 1.4.3.4) activities showed that higher DAO and PAO enzyme activities were obtained when high concentrations of polyamines were applied and when plantlets were treated for 5–7 week at 4°C and 16°C. Survival rate of plantlets increased with the treatment of polyamines at low temperature. Polyamines increased mitotic index of cells in root tips of regenerated plantlet cultured on medium containing 0.001 μM Put, Spd, or Spm, but did not increase mitotic index in tissues of needle tips of the same plantlets. These results demonstrated that polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine plantlets.     

Exogenous spermidine alters in different way membrane permeability and lipid peroxidation in water stressed barley leaves

In order to see whether polyamines will modify membrane functioning in the water stressed plants, barley (Hordeum vulgare) seedlings were treated with spermidine (Spd) prior to dehydration and then the stress-evoked changes in membrane permeability (i.e. in electrolyte leakage from leaves) and lipid peroxidation (indicated by modifications of the malondialdehyde (MDA) level, and of the lipoxygenase (LOX) activity) were followed. The Spd treatement lowered injury index in plants subjected to water deficit, although it slightly increased the stress-promoted LOX activity and increased the MDA level in the studied leaves. Presented results confirm that spermidine stabilizes plant membranes under water stress conditions. However, this effect does not seem to be associated with the Spd-induced modifications in the lipid peroxidation activities.     

A Possible Role for Polyamines in the Repression of Growth of Bradyrhizobium japonicum Bacteroids in Soybean Nodules

Soybean plants (Glycine max L. Merr. cv. Tamahomare) accumulatesufficient putrescine and spermidine in their nodules to inhibitthe growth of bacteroids of Bradyrhizobium japonicum strain138NR. Gas-chromatographic analysis showed that the mature nodulesfrom 35-d-old plants contained approximately 1.5 µmoleseach of putrescine and spermidine per g fresh weight. Water-soluble(free) putrescine and spermidine were present at concentrationsof 0.39 and 0.13 µmoles per g fresh weight, respectively.Cadaverine and spermine were not detected in the nodules. Ina yeast-extract mannitol broth at a pH above 7.0, putrescine,cadaverine, spermidine, and spermine at more than 0.5, 0.2,0.05, and 0.05 mM, respectively, inhibited the growth of thebacteroids. The effect of the polyamines was bactericidal athigher concentrations. More than 95% of bacteroids were notable to form colonies on agar plates that contained 0.5 mM spermidineat pH 7.0. The high sensitivity to polyamines was a unique characteristicof the bacteroidform cells of this strain. The bacteroids losttheir sensitivity to the polyamines within 24 hours after theirisolation from nodules. The cultured cells of this strain multipliedin the presence of 2 mM spermidine or spermine. (Received January 28, 1993; Accepted June 14, 1993)