Characterization of Osmotic Restraints on Lettuce Fruit Germination

Germination responses of fruits of lettuce (Lactuca sativa L.cv. Arctic King) to solutions of mannitol or potassium chlorideof different osmotic potentials were examined over a range oftemperatures in both light and dark. The upper temperature limit(‘cut-off’) for germination was progressively loweredby solutions of increasingly negative osmotic potential. Thisobservation explained inhibition of germination by solutionsof low osmotic potential at single experimental temperatures,found in previous investigations. Solutions of the two compoundshaving equal calculated osmotic potentials produced an equalinhibitory effect. No evidence for solute absorption was seen.Solutions of lower osmotic potential were needed to producethe same inhibition of germination in light against total darknessand also at lower temperatures.     

Water Uptake and Protein Synthesis in Germinating Wheat Embryos under the Osmotic Stress of Polyethylene Glycol

The effect of osmotic stress on wheat-seed germination was testedby imbibition in aqueous polyethylene glycol solutions at differentconcentrations. The experiments were designed to allow blockingand the subsequent recovery of germination by 12 h or 24 h pre-imbibitionof seeds in osmoticum, followed by transfer to water. Seedswere alternatively presoaked in water for 12 or 24 h, then transferredto polyethylene-glycol solutions to study the induced blockingof germination. Water content and [³H]leucine incorporationinto embryo tissues (as a measure of in vivo protein synthesis)were determined over a 48-h imbibition period. A close relationshipwas established overall between hydration status and proteinsynthesis rate. Osmotic stress seems to have a strong influenceupon the quantitative synthesis of proteins, suggesting thatthis biochemical activity is associated with the regulationof the germination process. Triticum durum, embryo, osmotic stress, water uptake, protein synthesis     

Advantageous and Detrimental Effects of Osmotic Pre-Sowing Treatment on the Germination Performance of Agrostemma githago Seeds

Dormant and after-ripened seeds of Agrostemma githago (corn-cockle)were pretreated in polyethylene glycol 400 (PEG) solutions attemperatures which would have allowed germination if the seedshad been imbibed in water, viz. 4?C or 20?C for after-ripenedseeds, and 4?C for dormant seeds. Pretreated seeds germinatedfaster than untreated seeds. The maximum decrease of the T₅₀(time to 50% germination) was 66%. Furthermore, pretreated seedswere capable of germination at supra-optimal temperatures whichotherwise had inhibited germination completely (20?C for dormantseeds and 30?C for after-ripened seeds). The percentage germinationat a supra-optimal temperature was considerably higher whenthe seeds had been primed at a temperature at which they developedmore extension power. The advantageous effects of the osmotic pretreatment were lessthan might be expected when the osmoticum had inhibited onlycell elongation. This was largely, if not fully, due to a generaldetrimental effect of osmotic stress and not to a selectiveinhibition of the processes which occur during the pregerminativephase in preparation for growth. Thus, during priming seedscomplete all or almost all processes which occur in water-imbibedseeds prior to radicle emergence. Key words: Agroatemma githago, dormancy, germination, germination performance, osmotic stress, priming     

Effects of Environmental Factors on Germination and Seedling Growth in Quercus floribunda and Cupressus torulosa, Tree Species of Central Himalaya

Quercus floribunda Lindl. (tilonj oak), a late successionalspecies, and Cupressus torulosa D. Don. (surai), an early successionalspecies, were compared in terms of seed germination and seedlinggrowth. In Petri dish germination tests in which light quality,temperature and osmotic water stress were varied, the germinationof both species was reduced by continuous dark or far-red lightand by osmotic water stress. These effects were greater on thegermination of surai than on that of tilonj oak. The growthof seedlings in soil was measured over a twelve-month periodduring which different levels of shading and different wateringregimes were applied. Surai was less affected than tilonj oakby reduced soil moisture, but the effect of deep shade treatmentswas greater on surai than with tilonj oak. At higher soil moisturestress seedlings of surai attained greater height then tilonjoak, but the latter achieved higher dry weight and a higherroot: shoot and lower leaf-weight ratio. Quercus floribunda Lindl. (tilonj oak), Cupressus torulosa D. Don. (surai), seed germination, seedling growth, environmental factors, regeneration     

Collection and Germination of Sporocarps of Azolla caroliniana

Azolla caroliniana Willd. with matured mega- and microsporocarpswere harvested from the field, sun dried and sieved to formballs of megasporocarps and massulae. The separated sporocarpswere tested for germination in different media in Petri dishesunder laboratory/greenhouse conditions. Only the swollen, greenmegasporocarps germinated. Nutrient medium was superior to asoil solution. The observed percentage germination was betteron a solid surface than in a liquid medium. Germination didnot occur with dark incubated sporocarps. The addition of phosphorusstimulated sporocarp germination and at a concentration of 30ppm, an 86% increase in germination was noted against the control.Percentage germination varied widely with pH, and optimum germinationwas recorded at a neutral pH. The effect of nitrogen sourceson sporocarp germination indicated that 70 ppm of nitrate, 7.5ppm of ammonium, 15 ppm of nitrite and 15 ppm of urea increasedgermination by 51, 66, 44 and 63%, respectively; further increasesin concentration inhibited germination. Treatment with 100 ppmof either kinetin or gibberellic acid, or a mixture of both,enhanced germination by 67, 55 and 84%, respectively. Azolla caroliniana Willd., sporocarp collection, germination     

Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a criticalinfluence on the germination of halophyte seeds and plant establishment.Salinity affects imbibition, germination and root elongation.However, the way in which NaCl exerts its influence on thesevital processes, whether it is through an osmotic effect ora specific ion toxicity, is still not resolved. Dimorphic seedsof the halophytesAtriplex prostrataandA. patulawere treatedwith various iso-osmotic solutions of NaCl and polyethyleneglycol (PEG). For each treatment, imbibition, germination rate,percent germination, germination recovery and nuclear area ofroot tip cells were compared. Higher concentrations of NaCl(-1.0 MPa) were more inhibitory to imbibition, germination andseedling root elongation than iso-osmotic PEG solutions. Allseeds recovered from a pre-treatment with -2.0 MPa NaCl andPEG solutions, except large seeds ofA. prostratawhich failedto germinate following transfer from -2.0 MPa NaCl. NaCl causeda greater increase in nuclear volume than iso-osmotic PEG solutions.These data suggest that the influence of NaCl is a combinationof an osmotic effect and a specific ion effect.Copyright 1998Annals of Botany Company Atriplex patula,Atriplex prostrata,cytophotometry, osmotic potential, salinity, seed germination.     

Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

Inter-population Variations of Kochia indica During Germination Under Different Stresses

Germination of three populations of Kochia indica Wight fromcontrasting soil types were studied under various levels ofsalinity, alkalinity and osmotic stress with a view to evaluatetheir potential to establish through seeds in saline and alkalineenvironments of various magnitudes. The seeds were germinatedunder controlled conditions in Petri dishes using salinizedsolutions of NaCl, Na₂SO₄, MgCI₂ and CaSO₄ (electrical conductivity,EC, 4–16 ds m^–), sodium carbonate solutions (pH8.5–100), mannitol solutions ( – 2.5 to –100 bar) and de-ionised distilled water (control). Inter-populationdifferences were very marked, showing selective adaptation ofthe populations to a particular stress type. In general, allpopulations exhibited salt tolerance but were rather sensitiveto high osmotic stress. Kochia indica Wight (bui), germination, population, salinity, alkalinity, osmotic stress     

The Effect of Osmotic and Ionic Stress on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

Cells of the euryhaline unicellular green alga Dunaliella tertiolectawere exposed to a range of osmotic potentials imposed by theaddition of NaCl, KCl, sucrose or ethylene glycol to the algalsuspending medium. The alga synthesized glycerol in responseto increased concentrations of NaCl, KCl or sucrose, but notto increased concentrations of ethylene glycol. The overallprocess of photosynthesis was inhibited by all four treatmentsduring the first 100 min, but especially by NaCl and KCl. Theinduction of chlorophyll fluorescence indicated that photosystemIl was inhibited by such treatment although to a lesser extentthan the overall process. The size and half-time of decay ofthe flash-induced field-indicating absorption change at 519nm were decreased by NaCl and KCl but the effect of sucroseand ethylene glycol on the absorption change was much less.Therefore, the photosynthetic processes in intact Dunaliellacells are more markedly inhibited by the combined osmotic andionic stresses due to NaCl and KCl than by osmotic stress alone.In most cases some recovery of the inhibition of photosynthesiswas seen concomitant with the synthesis of intracellular glycerol,suggesting that the alga has the ability to overcome osmoticand ionic stresses. Key words: Dunaliella, Photosynthesis, Osmotic stress     

Mechanism by which ammonium bicarbonate and ammonium sulfate inhibit mycotoxigenic fungi.

In this study we examined the mechanism by which ammonium bicarbonate inhibits mycotoxigenic fungi. Elevated extracellular pH, alone, was not responsible for the antifungal activity. Although conidia of Penicillium griseofulvum and Fusarium graminearum had internal pH (pHi) values as high as 8.0 in buffer at an external pH (pHo) of 9.5, their viability was not markedly affected. The pHi values from conidia equilibrated in glycine-NaOH-buffered treatments without ammonium bicarbonate or ammonium sulfate were similar to values obtained from buffered treatments containing the ammonium salts. Thus, inhibition did not appear to be directly related to increased pHi. Ammonium sulfate in buffered media at pH greater than or equal to 8.7 was as inhibitory as ammonium bicarbonate, but was completely ineffective at pH less than or equal to 7.8. The hypothesis that free ammonia caused the fungal inhibition was tested by using ammonium sulfate as a model for ammonium bicarbonate. Viability, expressed as log CFU/ml, and percent germination of P. griseofulvum and F. graminearum decreased dramatically as the free ammonia concentration increased. Germination rate ratios (the germination rate in buffered ammonium sulfate divided by the germination rate in buffer alone) decreased linearly as the free ammonia concentration increased, further establishing NH3 as the toxic agent. Ammonium bicarbonate inhibits fungi because the bicarbonate anion supplies the alkalinity necessary to establish an antifungal concentration of free ammonia.     

Mechanism by which ammonium bicarbonate and ammonium sulfate inhibit mycotoxigenic fungi

In this study we examined the mechanism by which ammonium bicarbonate inhibits mycotoxigenic fungi. Elevated extracellular pH, alone, was not responsible for the antifungal activity. Although conidia of Penicillium griseofulvum and Fusarium graminearum had internal pH (pHi) values as high as 8.0 in buffer at an external pH (pHo) of 9.5, their viability was not markedly affected. The pHi values from conidia equilibrated in glycine-NaOH-buffered treatments without ammonium bicarbonate or ammonium sulfate were similar to values obtained from buffered treatments containing the ammonium salts. Thus, inhibition did not appear to be directly related to increased pHi. Ammonium sulfate in buffered media at pH greater than or equal to 8.7 was as inhibitory as ammonium bicarbonate, but was completely ineffective at pH less than or equal to 7.8. The hypothesis that free ammonia caused the fungal inhibition was tested by using ammonium sulfate as a model for ammonium bicarbonate. Viability, expressed as log CFU/ml, and percent germination of P. griseofulvum and F. graminearum decreased dramatically as the free ammonia concentration increased. Germination rate ratios (the germination rate in buffered ammonium sulfate divided by the germination rate in buffer alone) decreased linearly as the free ammonia concentration increased, further establishing NH3 as the toxic agent. Ammonium bicarbonate inhibits fungi because the bicarbonate anion supplies the alkalinity necessary to establish an antifungal concentration of free ammonia.     

The Effect of Paclobutrazol on Physiological and Biochemical Changes in the Primary Roots of Pea

Primary roots of pea (Pisum sativum L. cv. Taichung No. 11)were treated with 0, 10 and 50 mg dm^–3 paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl)pentan-3-ol]for 1 h at 48 h after germination. Paclobutrazol treatment inhibitedroot extension, promoted swelling (cell expansion was radialrather than longitudinal), and increased cell volume and theactivity of catalase and peroxidase enzymes. Paclobutrazol alsodecreased root respiration and ethylene production. However,under non-stressed conditions, paclobutrazol treatment did notaffect soluble carbohydrate content, water potential, osmoticpotential or water loss. Under osmotic stress with polyethyleneglycol (PEG), paclobutrazol diminished the increase of waterpotential and decreased the rate of water loss caused by theimposed stress, but had no effect on osmotic potential. Catalaseand peroxidase activity were increased in osmotically-stressedroots of treated plants. Key words: Root growth, paclobutrazol, pea, Pisum sativum, water shortage     

The Effect of Soil Water and Aeration on Seed Germination

The time rate of germination and the final germination percentageof Oryzopsis holciformis decreased with increasing water stress.The optimum matric potential for germination was–0.005bar in coarse sand and –0.5 bar in sandy loam soil. Thisdiscrepancy was explained by changes in the rate of water-supplyto the seed, as determined by the area of contact between seedand germination medium, and by the hydraulic conductivity ofthe medium. At high soil moisture potentials germination also decreased.Such a decrease was not found at equivalent osmotic potentials.It seems that this decrease in germination was brought aboutby the thickening of the water films around the seeds, whichinterfered with oxygen diffusion. This assumption was supportedby determinations with Pt electrodes, and by previous work ongermination at lowered oxygen concentrations.     

Rapid Osmotic Adjustment in Detached Wheat Leaves

Osmotic adjustment is induced in detached wheat leaves by rapiddrying to a relative water content below 0·65, followedby re-saturation. Quantitatively, the response to this treatmentis comparable to the maximum of adjustment obtained with pottedplants at the same developmental stage. Low temperatures duringdrying and re-saturation of the leaves reduce the adjustmentresponse. We conclude that drought stress serves as a triggeronly, while the metabolic events lowering the osmotic potentialare favoured by high or intermediate water contents. Triticum durum L., durum wheat, rapid dehydration, osmotic adjustment, pressure-volume curves     

Inter-population Variations of Kochia indica During Germination Under Different Stresses

Germination of three populations of Kochia indica Wight fromcontrasting soil types were studied under various levels ofsalinity, alkalinity and osmotic stress with a view to evaluatetheir potential to establish through seeds in saline and alkalineenvironments of various magnitudes. The seeds were germinatedunder controlled conditions in Petri dishes using salinizedsolutions of NaCl, Na₂SO₄, MgCl₂ and CaSO₄ (electrical conductivity,EC, 4–16 dsm¹), sodium carbonate solutions (pH 8.5ndash;10.0), mannitol solutions ( —2.5 to —10.0 bar) andde-ionised distilled water (control). Inter-population differenceswere very marked, showing selective adaptation of the populationsto a particular stress type. In general, all populations exhibitedsalt tolerance but were rather sensitive to high osmotic stress. Kochia indicaWight (bui), germination, populatio, salinity, alkalinity, osmotic stress     

Tomato Seed Germination. Osmotic Pretreatment and Far Red Inhibition

At 25 °C germination of tomato (Lycopersicon lycopersicum)seeds is inhibited by continuous and intermittent far red illumination.It is also inhibited by a single 30 min far red irradiationgiven 8 h from the start of imbibition. The incubation of seedsin a mannitol solution inhibitory for germination has no effecton the final germination percentage after seeds are subsequentlytransferred to water. A 30 min far red irradiation at the timeof transfer results in partial inhibition of germination. Thisinhibition can be released by the continuation of osmotic incubationfor several days before the transfer to water. At the end ofa 7 d dark period of osmotic incubation, inhibition of subsequentgermination in water can be realized only by continuous farred illumination. Seeds osmotically pretreated for 7 d and afterwardsdried-back show a mean time to 50% germination significantlylower than that of untreated seeds. Moreover, besides singleand intermittent, even continuous far red light has no inhibitoryeffect on the germination of these seeds. It is concluded that,in addition to the already known germination advantages, osmoticpresowing treatment also induces the ability of seeds to germinateunder unfavourable light conditi.     

INTERACTION OF GIBBERELLIN A3, AND INORGANIC PHOSPHATE IN TOBACCO SEED GERMINATION

1. Investigation was made on the influence of inorganic phosphateupon the germination of positively photoblastic tobacco seed(Nicotiana tabacum L. var. uirginica (AGDH.) COM. "Bright Yellow")induced by GA₃, GA₃M, kinetin, red light, and ammonium saltsof various organic acids.
2. Inorganic phosphate increases theGAs-induced germination, andinhibits the germination causedby ammonium citrate, while itdoes not influence the germinationbrought about by GA₃M, kinetin,and red light.
3. The optimumpH for the GA₃-induced germination lies in the acidicpH range,indicating that the undissociated form of GA₃ is operative.The stimulatory effect of phosphate is, however, not ascribedmerely to the pH control in the mediurr. Phosphate exerts somespecific influence for which the presence of the free carboxylgroup of GAs is required.
4. The observed contrasting effectsof phosphate on the GA₃-inducedgermination (i.e., acceleration),on the one hand, and on theammonium citrate-induced germination(i.e., inhibition), onthe other, were explained by assumingthat the phosphate effectsultimately consist in acceleratingthe uptake of the carboxylicacid into the seeds.
5. GA₃M alsohas an activity of inducing the germination of tobaccoseedwithout light.

¹Present address: Department of Vegetable Crops, Universityof California, Davis, California, U.S.A. (Received March 12, 1962; )     

Priming and accelerated ageing affect L-isoaspartyl methyltransferase activity in tomato (Lycopersicon esculentum Mill.) seed

Damage and degradation of cellular proteins is observed duringage-induced seed deterioration. L-Isoaspartyl protein methyltransferase(EC 2.1.1.77 [EC] ) is an enzyme hypothesized to play a role in limitingand repairing age-induced damage to proteins. Tomato (Lycopersiconesculentum Mill. ‘New Yorker’) seeds were assayedfor changes in L-isoaspartyl methyl-transferase activity duringaccelerated ageing and after osmotic priming. Accelerated ageingof seeds for 1–4 d at 45C and 100% relative humidityreduced germination from 94% to 71%, increased the mean timeof germination (MTG) from 2.4 to 5.8 d, and was accompaniedby a correlative decrease in L-isoaspartyl methyltransferaseactivity (r²=0.90). Aged and untreated seeds were primed for7 d at 20C in darkness using aerated solutions of 3% KNO₃ orpolyethylene glycol 8000 (PEG) with equivalent osmotic potential(–1.25 MPa). Priming with KNO₃ decreased the MTG, butdid not improve germination percentage for untreated seeds.Priming did not affect L-isoaspartyl methyltransferase activityin untreated seeds, but restored activity in aged seeds primedin KNO₃ to levels near that of untreated seeds. Priming withPEG did not effectively improve the MTG or increase L-isoaspartylmethyltransferase activity. During germination, L-isoaspartylmethyltransferase activity remained constant for 48 h post-imbibitionand then declined, suggesting that the enzyme was developmentallyregulated and inactivated or degraded as radicle emergence occurred. Key words: L-Isoaspartyl methyltransferase, protein repair, seed priming, accelerated ageing, Lycopersicon esculentum     

The 7B-1 mutant in tomato shows blue-light-specific resistance to osmotic stress and abscisic acid

Germination of wild-type (WT) tomato ( Lycopersicon esculentum Mill.) seed is inhibited by mannitol (100-140 mM) in light, but not in darkness, suggesting that light amplifies the responsiveness of the seed to osmotic stress (M. Fellner, V.K. Sawhney (2001) Theor Appl Genet 102:215-221). Here we report that white light (W) and especially blue light (B) strongly enhance the mannitol-induced inhibition of seed germination, and that the effect of red light (R) is weak or nil. The inhibitory effect of mannitol could be completely overcome by fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, indicating that mannitol inhibits seed germination via ABA accumulation in seeds. The inhibition of WT seed germination by exogenous ABA was also amplified by W or B, but not by R. In a recessive, ABA-overproducing, 7B-1 mutant of tomato, seed germination and hypocotyl growth were resistant to inhibition by mannitol or exogenous ABA, both in W or B. Experiments with fluridone suggested that inhibition of hypocotyl growth by W or B is also partially via ABA accumulation. De-etiolation in the mutant was especially less in B compared to the WT, and there was no difference in hypocotyl growth between the two genotypes in R. Our data suggest that B amplifies the responsiveness of tomato seeds and hypocotyls to mannitol and ABA, and that W- or B-specific resistance of the 7B-1 mutant to osmotic stress or ABA is a consequence of a defect in B perception or signal transduction.     

Effect of osmotic shock on auxin-induced cell extension, cell wall changes and acidification in Avena coleoptile segments

The effect of plasma membrane alteration caused by osmotic shockof different strengths on the auxin-induced responses of Avenacoleoptile cells was observed. Osmotic shock brought about by0.5–0.7 M mannitol solution for 10 or 30 min, followedby phosphate-buffer (1 mM, pH 6.0) treatment for 10 min at 4?Ccaused no significant inhibition of auxin-induced cell extension.The osmotic shock did not affect auxin-induced cell wall looseningrepresented by stress-relaxation time and a decrease in thenoncellulosic glucose level of the cell wall. The shock causedonly a temporary inhibition of transmembrane potential and noinhibition of oxygen consumption. However, it inhibited auxin-stimulatedH⁺ secretion which was reversed by 0.1 mM CaCl₂. We concludedthat the Osmotic shock may partly modify the plasma membranerelated to the hydrogen ion pump which interacts with auxin,but this modification which is reflected little by the transmembranepotential and cellular metabolism, is not closely related toauxin-induced cell wall loosening and thus cell extension inAvena coleoptiles. ³ Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan (Received February 17, 1978; )