Inhibition Of Vegetative Growth Research Articles

The sensitivity of ABI2 to hydrogen peroxide links the abscisic acid-response regulator to redox signalling

ABI1 and ABI2 are two protein serine/threonine phosphatases of type 2C (EC 3.1.3.16) that act as key regulators in the responses of Arabidopsis thaliana (L.) Heynh. to abscisic acid (ABA). They are involved in the control of ABA-mediated seed dormancy, stomatal closure and vegetative growth inhibition. Analysis of the enzymatic properties of ABI2 revealed high sensitivities towards protons and unsaturated fatty acids. Furthermore, the protein phosphatase activity of ABI2 is very sensitive to H2O2, which has recently emerged as a secondary messenger of ABA signalling. Upon H2O2 challenge, ABI2 is rapidly inactivated with an IC50 value of 50 microM in the presence of reduced glutathione. Inhibitor studies with phenylarsine oxide and manipulation of the redox status of ABI2 in vitro indicate that oxidation of critical cysteine residue(s) is responsible for inactivation. The levels of the major cellular thiol compounds cysteine and glutathione in leaves and seedlings of A. thaliana are compatible with a physiological role of H2O2 in regulating ABI2 activity. ABI2 is considered to exert negative regulation on ABA action. Thus, transient inactivation of this protein phosphatase by H2O2 would allow or enhance the ABA-dependent signalling process. In conclusion, ABI2 represents a likely target for redox-regulation of a hormonal signalling pathway in higher plants.

Effects of the Inhibitors of Biosynthesis and Degradation of Catecholamines on Photoperiodic Induction of Flowering in Pharbitis nil

The effects of the inhibitors of biosynthesis and degradation of catecholamines (CA) on photoperiodic induction of flowering were examined in Pharbitis nil , a short-day plant. The inhibitors of CA biosynthesis such as iodotyrosine, methyldopa, methyltyrosine, carbidopa, NSD-1015, and 6-hydroxydopamine inhibited floral initiation when applied before and during a dark period but not after dark treatment, suggesting that these compounds inhibited the production of a flowering hormone in cotyledons. Inhibitors of CA degradation such as SK&F525A, amitriptyline, pargyline, gallic acid, n-butyl gallate, OR-486 and Ro-41-0960 also inhibited flowering, and these inhibitors were effective even when applied after dark treatment, although they did not inhibit floral initiation when applied at 48 h after the end of dark treatment. This result suggested that the inhibitors of CA acted in bud and inhibited the expression of flowering hormone in bud, or the transformation of it into an active substance. The inhibitors used in the present experiment inhibited flowering without the inhibition of vegetative growth. Exogeneous noradrenaline did not induce floral initation under continuous light but partially reversed the inhibitory effect of 6-hydroxydopamine.

Inhibition of reproductive growth of Arabidopsis in airtight vessels

Airtight vessels have various advantages for space experiments. However, Arabidopsis thaliana plants scarcely produced seeds when grown in such vessels. The mechanism by which reproductive growth is inhibited in airtight vessels was studied. The length of the flower stalk was shorter when the plants were grown in airtight vessels. Thus, there was a possibility that the inhibition of reproductive growth was due to the inhibition of vegetative growth. However, even when the plants which has grown under non-airtight conditions and has reached to the flowering stage were transferred to airtight vessels, silique formation was inhibited, suggesting that the airtight environment directly influences reproductive growth. In airtight vessels, anther dehiscence was inhibited, which appears to be the cause of inhibition of silique formation and seed development. Reproductive growth recovered when silica gel was added to the vessels. These results suggest that in airtight vessels, high humidity causes a suppression of anther dehiscence, resulting in the inhibition of reproductive growth. Therefore, the control of humidity by ventilation should be taken into consideration in designing a growth chamber for space experiments.

Evaluation of fungal isolates for the inhibition of vegetative growth of Venturis inaequalis

As a part of a broader study on biological control of apple scab, caused by Venturia inaequalis, a collection of 183 microorganisms originating from apple leaf litter was evaluated for their inhibitory effects on the vegetative growth of V. inaequalis. In a first screening, based on dual culture, 31 isolates (17%) showed inhibition. From these isolates, 11 fungi were selected for quantitative evaluation based on the presence of a distinct zone of inhibition. The selected fungi were evaluated again, in a more precise test, which indicated that isolates P164A (Ophiostoma sp.), P66A (Chaetophoma sp.), P26A (Aureobasidium sp.), P59A (Phoma sp.), and P28A (unidentified) inhibited 95.3, 88.9, 85.8, 80.7, and 80.1% of mycelial growth, respectively. Inhibition by the most effective fungus (Ophiostoma sp.) lasted for more than 58 days. A test using culture filtrates, incubated over time, was carried out to determine whether the living fungus was a prerequisite for inhibition. The inhibitory effect of metabolites secreted by the selected fungi was less than 5%. This study revealed the potential of at least five fungi that could be considered in the development of a biological control agent against V. inaequalis. Key words: antifungal inhibition, apple scab, biological control.

Paclobutrazol Reduces Photosynthetic Carbon Dioxide Uptake Rate in Grapevines

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

Effects of selected fungicides on in vitro spore germination and vegetative growth of Ascosphaera aggregata

tive growth of Ascosphaera aggregata, the causative organism of chalkbrood in the alfalfa leafcutter bee, Megachile rotundata. The compounds were incorporated directly into liquid or agar growth medium. EC for inhibition of vegetative growth on an agar surface were estimated as follows: enilconazole, 0.034; Rovral (iprodione), 1.10; Benlate (benomyl), 1.16; and Ascocidin (N-glycosylpolifungin), 135.6 ppm (m/v). DFMO (α-DL-difluoromethyl omithine) stimulated growth resulting in an approximately 50% increased radius at 10 000 ppm compared to the control. Benlate inhibited spore germination; at the highest concentration only, Rovral inhibited germination while Ascocidin and enilconazole exhibited a slight effect. DFMO did not affect spore germination. Ascocidin and Benlate exhibited most effect on germling viability at 48 h followed by Rovral and enilconazole. DFMO had no effect on germling viability. Benlate, Rovral and enilconazole had the most pronounced effect on germ tube growth at 96 h. Ascocidin affected germ tube growth at the higest concentration; DFMO exhibited little to no effect. Comparisons between in vitro results obtained in the present study with previously published in vivo results indicate that in vitro effects on spore germination most closely correlated with efficacy against chalkbrood in vivo, suggesting that compounds with activity against spore germination or germling viability may be the most promising candidates for use against chalkbrood.

The Effects of Sterol Biosynthesis Inhibitors on Cleavage in Allomyces Macrogynus

Two triazoles, cyproconazole and propiconazole, and the imidazole, prochloraz, all commercially available fungicides that inhibit 14a-demethylation during sterol synthesis, were applied to a cholesterolproducing fungus, Allomyces macrogynus, during growth phase. Concentrations of the above inhibitors 1/100-1/500 of the EC50 concentrations needed for inhibition of vegetative growth, caused failure of sporangia to cleave normally and produce uniformly sized, uniflagellate zoospores. Instead, dependent upon the concentration of fungicide used, motile cells were uniflagellate, biflagellate, triflagellate or multiflagellate with the number of nuclei corresponding to the number of flagella. The fungicides were only effective if they were present during the growth phase and impairment of cleavage could not be overcome by adding cholesterol to the discharge medium. Observations were based on light and electron microscope observations. Multinucleate cells with more than one flagellum germinated to produce normal thalli when plated on agar lacking the fungicides. The basis of the interference with cleavage is discussed.

Paclobutrazol Suppresses Shoot Growth and Influences Nut Quality and Yield of Young Pecan Trees

Abstract Paclobutrazol (PBZ) was applied in one or more formulations as a basal trunk drench (0, 19, 38, 76, 152 mg·cm−2 trunk cross-sectional area) or orchard floor application (0, 52, 104, and 208 mg·cm−2 trunk cross-sectional area) to 3- and 10-year-old pecan [Carya illinoensis (Wangenh.)C. Koch] trees. Vegetative growth was highly sensitive to PBZ for at least 3 to 4 years after a single treatment. There were no differences due to formulation for any of the parameters evaluated. Shoot growth and production of in-shell nuts were negatively related in a curvilinear manner to PBZ rate. Nut size increased the first two seasons after treatment, and yield efficiency increased curvilinearly with PBZ rate. Excessive vigor of Iammas shoots coincided with the cessation of vegetative growth inhibition by PBZ. There was a differential cultivar response in nut yield for 3-year-oid ‘Cheyenne’ and ‘Desirable’ trees; however, there was no cultivar differences in 10-year-old trees of ‘Shoshoni’, ‘Desirable’, and ‘Cape Fear’. Use of PBZ appears to allow for the manipulation of tree size of young pecan trees. Chemical names used: β-[(4-chlorophenyl)-ethyl] -α-(1, l-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

Periods of Shoot Chilling Sensitivity in Soybean Flower Development, and Compensation in Yield after Chilling

Soybeans [Glycine max (L.) Merr. cv. Ransom] grown at a constant 25 °C were placed in a 12-h inductive photoperiod at two weeks of age. Subgroups were shoot-chilled for one week at a constant 10 °C during each of the first four weeks of floral induction. Controls were photoinduced but not chilled. Chilling during the first week of photoinduction inhibited production of floral primordia, but did not increase the abscission rate of flowers and pods. Chilling during the second week did not affect primordium production or abscission rate, but did cause a significant increase in numbers of fused and malformed pods. Chilling during the third week caused loss of 77 per cent of early flowers and pods by abscission, while fourth week chilling caused less severe losses by abscission. Inhibition of vegetative growth may have been responsible for primordium loss in first-week plants, while disturbances in the development of flowers were responsible for the losses in the other chilling weeks. Although chilling during the first and third photoinduction weeks caused a significant reduction in early pod numbers, plants harvested at 16 weeks of age showed no significant loss in seed yield. Low abscission rates late in pod filling and increased weight of individual seeds compensated for early losses of pods. These compensatory responses to a chilling-induced loss of pods are similar to those reported for mechanically depodded soybeans.

The effects of flooding on water relations and growth ofTheobroma cacaovar.catongoseedlings

SummarySoil flooding induced stomatal closure and lowered the transpiration rate of Theobroma cacao var. catongo seedlings within 2 h. The early stomatal closure was not associated with leaf dehydration. Subsequent responses to flooding included inhibition of leaf formation and expansion, reduction in dry weight increment and in relative growth rates of leaves, stems and roots (with root growth reduced most), height growth and stem diameter growth. In addition, flooding was followed by leaf epinasty, extensive decay of roots, and formation of hypertrophied lenticels and adventitious roots on submerged stems. The effects of flooding differed quantitatively on dry weight increment and on the relative growth rates of leaves, stems and roots. Flooding the soil in a controlled-environment chamber inhibited seedling growth more than flooding in a greenhouse. The greatly lowered root:shoot ratio of flooded seedlings indicated that drought tolerance of seedlings will be reduced after the flood waters recede because the absorption of water by the small root systems will be too low to meet transpiration requirements. Inhibition of vegetative growth by flooding will probably reduce the yield of T. cacao by prolonging the time to first flowering and by suppressing vegetative growth.

Inhibitors of Fruiting-body Formation and Challenge Time Experiments in Myxococcus xanthus

Purines, amino acids and their analogues, polypeptide and other antibiotics, and a range of other chemicals were screened by a spot-testing technique for inhibition of vegetative growth, or of fruiting-body formation, in the bacterium Myxococcus xanthus. Selected fruiting inhibitors were tested by challenge time-transfer experiments. In general, delayed addition of inhibitors up to the time of late aggregation prevented subsequent completion of fruiting. Conversely, cells held in the presence of a fruiting inhibitor for extended periods did not rapidly lose the ability to fruit subsequently on removal of the inhibitor.

THE PHYSIOLOGICAL ASSOCIATION BETWEEN APHIS CRACCIVORA KOCH AND VIGNA SESQUIPEDALIS FRUW.

In a greenhouse experiment, adult apterae of Aphis craccivora were either confined to the second trifoliate leaf of 19‐day‐old plants of Vigna sesquipedalis or allowed to move freely after infestation. When the aphids were confined the dry wt of the plant after 14 days infestation was 62% of the controls; when they were free to move, it was 29·5% of controls. When the second trifoliate leaf was infested, the rate of photosynthesis per unit leaf area decreased to 3·6% of its initial rate on day 10, when it was moribund. Over 10 days, the total photosynthesis of the infested leaf was 56% of the control but this was reduced to 32% if the longer life of the control (more than 20 days) was taken into account. Photosynthesis was not stimulated at any time. Respiration of the infested second trifoliate was little influenced by infestation until it became prematurely moribund. Infestation of the young third trifoliate was accompanied by a slower expansion of the second trifoliate and by increased photosynthesis by that leaf during the first 6 days: the photosynthetic rate per unit area of the second trifoliate was 1·18 and 1·34 times that of the control on days 3 and 6 respectively, but declined to 0·85 on day 10. Infestation reduced the quantity of photosynthate available for movement from the second trifoliate to normal sinks from over 80% to less than 1% of the amount produced. When the third trifoliate was infested and the second was given 14CO2, the aphids were able to divert over 20% of translocated assimilate from its normal destination. The inhibition of vegetative growth is discussed in relation to these physiological changes.

Inhibition of Bacillus subtilis growth and sporulation by threonine.

A 1-mg/ml amount of threonine (8.4 mM) inhibited growth and sporulation of Bacillus subtilis 168. Inhibition of sporulation was efficiently reversed by valine and less efficiently by pyruvate, arginine, glutamine, and isoleucine. Inhibition of vegetative growth was reversed by asparate and glutamate as well as by valine, arginine, or glutamine. Cells in minimal growth medium were inhibited only transiently by very high concentrations of threonine, whereas inhibition of sporulation was permanent. Addition of threonine prevented the normal increase in alkaline phosphatase and reduced the production of extracellular protease by about 50%, suggesting that threonine blocked the sporulation process relatively early. 2-Ketobutyrate was able to mimic the effect of threonine on sporulation. Sporulation in a strain selected for resistance to azaleucine was partially resistant. Seventy-five percent of the mutants selected for the ability to grow vegetatively in the presence of high threonine concentrations were found to be simultaneously isoleucine auxotrophs. In at least one of these mutants, the threonine resistance phenotpye could not be dissociated from the isoleucine requirement by transformation. This mutation was closely linked to a known ilvA mutation (recombination index, 0.16). This strain also had reduced intracellular threonine deaminase activity. These results suggest that threonine inhibits B. subtilis by causing valine starvation.

Inhibition of vegetative growth and fruiting body formation in Myxococcus xanthus

Inhibition of vegetative growth and fruiting body formation in Myxococcus xanthus

Inhibition of vegetative growth and fruiting body formation inMyxococcus xanthus

Inhibition of vegetative growth and fruiting body formation in<i>Myxococcus xanthus</i>

Change of growth correlations in the shoot meristem as the cause of age dependence of flowering in Chenopodium rubrum

Summary Three, six and nine days old seedlings of the short-day plant Chenopodium rubrum show marked differences in the number of inductive cycles they need to evoke floral differentiation. The older the plants, the more inductive cycles and the longer the time required for flowering. We have compared the changes in the anatomical structure of the shoot apex and in the growth of leaf and bud primordia in the age groups mentioned. The speed of floral differentiation does not correlate with the zonal pattern of the shoot apex before induction. Floral differentiation is, however, influenced by the amount of meristematic tissue and the number of leaves initiated. Photoperiodic treatment causes an immediate inhibition of leaf growth in all age groups and, soon after, a release from apical dominance in the apex. Consequently, branching of the shoot apex occurs and the growth of leaf primordia is inhibited. Finally, formation of new leaves in the peripheral zone ceases and differentiation of the terminal flower takes place. If the number of inductive cycles is insufficient, restored leaf organogenesis and a correlated inhibition of bud primordia resume, and a reversal to the vegetative state sets in. The manner of initiation of the lateral organs — leaves and buds — is similar in plants of various age. There are, however, quantitative differences in the number and growth of the lateral organs at the onset of photoperiodic induction as well as during induction and during postinductive changes. These differences in growth cause differences in the number of inductive short-day cycles required for inhibition of vegetative growth and the changes leading to flowering. In younger plants having less well-developed vegetative growth, a single photoperiodic cycle is sufficient to induce flower formation. In older plants a single cycle results in an initial change of the growth correlations between leaf and bud primorida, i.e. in branching, while further floral differentiation requires repeated photoperiodic cycles. Thus, with Chenopodium rubrum the importance of the suppression of leaf growth during the transition from the vegetative to the reproductive state may be demonstrated.

Outgrowth and vegetative growth inhibition of Bacillus subtilis spores after transient exposure to polymyxin B

Polymyxin B combined with the resting spores of Bacillus subtilis and inhibited outgrowth and vegetative growth after germination. The antibiotic was released from the resting spores and its inhibitory action was reversed by the addition of di- and trivalent metallic cations.

Dependência do crescimento das plantas ao regime de umidade do solo

A produção de uma planta resulta do desenvolvimento integrado de inúmeros processos fisiológicos que, por sua vez, apresentam considerável individualidade nas interrelações com o meio ambiente. Neste trabalho foi observado o crescimento de plantas de batata (Solanum tuberosum L.), em condições de campo, quando submetidas a três regimes de umidade do solo, individualizados em três estádios fenológicos. O desenvolvimento vegetativo foi avaliado através de estimativas semanais da área foliar. Os resultados mostraram que ao final do primeiro estágio (cerca de 25 dias após a emergência das plantas) o desenvolvimento vegetativo nos tratamentos irrigados quando o potencial matricial da água do solo atingia -0,5 bar, superou, em cerca de 34%, àquele verificado nas plantas submetidas a déficits híbridos moderados (-1,0 bar) e, em aproximadamente 80%, aquelas sujeitas a déficits mais severos (-5,0 bares). Entretanto, a limitação do crescimento no primei 6 ro caso, foi parcialmente recuperada após o restabelecimento de condições mais adequadas de umidade no solo, no estádio intermediário. O mesmo não foi verificado onde ocorreram déficits hídricos mais severos no estádio inicial, quando o crescimento foi quase irreversivelmente reduzido. A intensa desidratação imposta após o completo desenvolvimento vegetativo apressou a senescência das plantas em relação aos tratamentos melhores supridos com água.

Suppression of long-day flowering by nitrogenous compounds in &lt;italic&gt;Lemna perpusilla&lt;/italic&gt; 6746

The long-day flowering of Lemna perpusilla 6746 on an SH inhibitor-containing medium was inhibited by the application of ammonium ion to the medium. Ammonium ion not only suppressed long-day flowering, but relieved the inhibition of vegetative growth caused by the inhibitors. Nitrite, casamino acids, glutamine and asparagine had a similar effect, suggesting that the inhibition of long-day flowering by ammonium ion is not a direct effect of the ion. Most amino acids, with the exception of glutamate and aspartate, also prevented long-day flowering, but their effects on vegetative growth varied. No qualitative differences in amino acid composition were observed among plants cultured on media containing nitrate, nitrite or NH44NO3as the sole nitrogen source. However, the amounts of free and total amino acids werehigher in plants fed with nitrite or NH4NO3 than in those fed with nitrate. This suggests that the inhibition of long-day flowering by ammonium and nitrite can be ascribed to increased nitrogen metabolism. Though decreased activity by SH inhibitors of nitrate reductase (SH enzyme) is assumed to result in long-day flowering by lowering the nitrogen metabolism, lowering the nitrogen level in M medium did not bring about floral initiation in the absence of SH inhibitors.

Changes of growth and RNA synthesis in shoot apical meristems of Chenopodium rubrum as a consequence of photoperiodic induction

Summary In Chenopodium rubrum requiring three inductive cycles for flowering, incorporation of uridine-5- 3 H into the central zone of the shoot apex was studied by means of radioautography, RNA content was estimated using cytophotometry and the size of the nucleoli was also measured. In addition morphological changes occurring in the apex were investigated. When plants were induced by three short days, RNA content and growth activity of the meristem were reduced during induction in comparison with plants growing in continuous light. Activation of RNA synthesis, increase in RNA content and in size of the nucleoli were found following three inductive cycles. The first morphological changes linked with the transition to the reproductive state occurred one day later. When the plants were transferred to continuous light after one inductive cycle (insufficient to induce flowering), a similar activation of RNA synthesis, increase in RNA content and in size of the nucleoli occurred and was followed by incipient morphological differentiation resembling that observed after three photoperiodic cycles. However, after a few days a reduction occurred in all parameters investigated. Reproductive differentiation ceased and vegetative growth was resumed. A comparison between non-induced control plants grown either in continuous light or in 16 h dark periods interrupted by 31/2 h light showed that the latter light conditions also lead to an activation of the meristem, even though it is less intensive than after induction and occurs with a certain delay. From these results it is infered that the activation of RNA synthesis is the first stage in growth activation and represents one of the first events of floral differentiation. These changes already occur on the basis of the first inductive cycle and need not be followed by floral differentiation proper. For the completion of the transition to the reproductive state an inhibition of vegetative growth is probably also necessary. Such an inhibition takes place during induction lasting for a longer time.