Factors Affecting the Formation of In vitro Tubers of Potato (Solanum tuberosum L.)

In vitro (mini) tubers were induced within 6–8 weeks inserially propagated potato shoot cultures by subculturing tomedium containing 2.0 mg 1^–1 benzylaminopurine (BAP) and6 per cent sucrose in 8- and 24-h days. The effect of BAP inpromoting tubering was greater in short than in long days. Inshort days most of the tubers were formed above the agar, inlong days within the agar. Tubering was promoted less effectivelyby the addition of (2-chloroethyl)-trimethylammonium chloride(CCC) to the medium, but CCC reinforced the effect of BAP leadingto earlier tubering above the agar. Tubering eventually tookplace after 4—5 months on medium without hormones, soonerin short than in long days. Periods of short days and low temperaturesgiven to long-day cultures did not accelerate tubering. Abscisicacid had little effect on, and GA2 strongly inhibited, tubering.Tubering was also inhibited by sealing the culture vessels butnot if ethylene-absorbing agents were included. Solanum tuberosum L, potato, tissue culture, tubers, cytokinin, ethylene, daylength, propagation     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: I. RELATIONSHIP BETWEEN TUBER GROWTH RATE AND ENZYME ACTIVITIES OF THE STARCH METABOLISM

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. Cooling (+8°C) of individualtubers decreased their growth rates and increased the growthrates of non-cooled tubers of the same plant. The carbohydrateconcentration in non-cooled and cooled tubers did not differsignificantly, but ¹⁴C-import from labelled photosynthate waslower in cooled than in non-cooled tubers. The markedly lowerconversion rate of ethanol-soluble ¹⁴C to starch in cooled,in comparison to non-cooled tubers, was not associated withsignificant differences in the in vitro activities of starchsynthase, ADPG-pyrophosphorylase and starch phosphorylase understandard assay conditions (+30°C). However, the Q₁₀-valuesof the enzymes differed in vitro in the temperature range between30°C and 8°C, leading to a marked decrease in the activityratio of ADPG-pyrophosphorylase/starch phosphorylase in cooledtubers. In tubers differing in growth rates without manipulation, 14d after tuber initiation significant positive correlations werefound between ¹⁴C-concentration of tuber tissue and the in vitroactivities of starch synthase and ADPG-pyrophosphorylase anda significant negative correlation between ¹⁴C-concentrationand starch phosphorylase. In contrast, in tubers which wereanalysed 5 d after initiation, there were only small differencesbetween tubers in growth rate, ¹⁴C import and the activity ratioADPG-pyrophosphorylase/starch phosphorylase. From various directand indirect evidence it is concluded that the growth rate ofindividual tubers, and thus the sink strength, is at least inpart controlled by the activity of starch synthesizing enzymes. Key words: Potato tuber, cooling, starch synthesizing enzymes     

Effect of Sodium Chloride Stress and Nitrogen Source on Respiration, Growth and Photosynthesis in Lucerne (Medicago sativa L.)

The effects of salinity at different light intensities on freshweight growth and on carbon dioxide influx and efflux were examinedin young plants of lucerne (Medicago sativa L.) that had beengrown in solution culture with nitrogen supplied either as nitrateor by a symbiotic rhizobium. Although the inoculated plantsgrew more slowly than those supplied with nitrate, NaCl at alevel equivalent to an osmotic stress of –0.3 MPa didnot reduce the growth rate of either type of plant under a 12h day-length in a growth chamber. With a day-length of 5 h saltstress (0.0 to –0.6 MPa) did not greatly affect grossphotosynthesis of plants grown on nitrate but respiration ratereached a maximum at –0.3 MPa and declined at larger saltconcentrations. Salt diminished both gross and net photosynthesisin the inoculated plants at a 5 h day-length without stimulatingrespiration. The relationship between photosynthesis and respiration as thephoton flux density was successively decreased was used to inferthe effect of salt on maintenance respiration of the plantssupplied with nitrate. Growth and maintenance components ofrespiration could not clearly be separated in the inoculatedplants suggesting that these were unable to maintain themselvesunder the combined stresses of salt and low light intensity.This view was supported by chemical analysis of the plant material.We conclude that the failure of the inoculated plants to adaptto these conditions could be attributed to the greater demandfor assimilates by the rhizobium. Key words: Medicago sativa, Nitrogen source, Salt stress     

Dormancy and Flowering in Anemone coronaria L. as Affected by Photoperiod and Temperature

The effects of day-length and temperature on flowering and dormancyinduction were studied in Anemone coronaria L., with plantsraised either from corms or achenes. An Israeli hybrid sourcewas used (de Caen cv. Hollandia x Israeli wild type). Dormancy onset is characterized by the cessation of foliageleaf production, the appearance of leaf scales protecting theperennating bud, and leaf senescence. Dormancy was induced byhigh temperature and long days but increasing temperatures (from17/12 °C to 32/12 °C) induced earlier dormancy thanprolonging the photoperiod (range 8–16 h). A significant(P = 0.01) interaction was found between these factors, withsmaller photoperiodic effects the higher the temperature. At22/17 °C the critical day-length for dormancy inductionwas between 11 and 12 h. The transition from the vegetative to the reproductive stageappears to be an autonomous process that occurs with developmentin plants raised from either corms or achenes and does not requireenvironmental induction. Photo- and thermoperiodic effects onflowering were indirect, being mediated through their influenceon dormancy induction. Anemone coronaria L., dormancy, flowering, photoperiod, thermoperiod     

Stomatal Functioning of In Vitro and Greenhouse Apple Leaves in Darkness, Mannitol, ABA, and CO2

Leaves from in vitro and greenhouse cultured plants of Malusdomestica (Borkh.) cv. Mark were subjected to 4 h of darkness;4 h of 1 M mannitol induced water stress; 1 h of 10^–4M to 10^–7 M cis-trans abscisic acid (ABA) treatment; 1h of 0.12% atmospheric CO₂. Stomatal closure was determinedby microscopic examination of leaf imprints. In all treatments,less than 5% of the stomata from leaves of in vitro culturedplants were closed. The diameter of open stomata on leaves fromin vitro culture remained at 8 µm. In contrast, an averageof 96% of the stomata on leaves of greenhouse grown plants wereclosed after 4 h in darkness; 56% after 4 h of mannitol inducedwater stress; 90% after 1 h of 10^–4 M ABA treatment; 61%after 1 h in an atmosphere of 0.12% CO₂. Stomata of in vitroapple leaves did not seem to have a closure mechanism, but acquiredone during acclimatization to the greenhouse environment. Thelack of stomatal closure in in vitro plants was the main causeof rapid water loss during transfer to low relative humidity.     

Soya Bean Seed Growth and Maturation In vitro without Pods

Immature Glycine max (L.) Merrill seeds, initially between 50and 450 mg f. wt, were grown and matured successfully in vitro.Excised seeds were floated in a liquid medium containing 5 percent sucrose, minerals and glutamine in flasks incubated at25 °C under 300 to 350 µE m^–2 s^–1 fluorescentlight. During 16 to 21 d in culture, seeds grew to a matured. wt of 100 to 600 mg per seed at an average rate of 5 to 25mg d. wt per seed d^–1 depending on initial size. Growthrates were maximal during the first 8 to 10 d in vitro but declinedwith loss of green colour in the cotyledons. Seed coats rupturedwith rapid cotyledon expansion during the first 2 d in culture.Embryos were tolerant to desiccation and 80 to 90 per cent germinatedif removed from culture before complete loss of green colour.The growth of excised seeds in vitro exceeded the growth ofseeds in detached pods, but when windows were cut in pods topermit direct exposure of seeds to the medium, seed growth wascomparable. Glycine max (L.) Merrill, soya bean, seed culture, seed growth, seed maturation, germination     

Enhancement of Tuberization of Axillary Shoot Buds of Potato (Solarium tuberosum L.) Cultivars Cultured In Vitro

Factors controlling growth and tuberization of axillary budsin shoots of plantlets of potato (Solarium tuberosum L.) culturedin vitro were investigated. Correlative inhibition restrainedgrowth and tuberization of the axillary buds. Exposure of intactplantlets for various periods (4 to 48 h) to low (2 or 12C)or high (30 C) temperatures as comparedto 18C, did not alleviatecorrelative inhibition. Removal of the apical part of the shoot,the roots or both was generally ineffective Elevating sucroseconcentration from 30 to 80 g dm^–3 promoted tuberizationon axillary buds, and the cytokinin 6-(-dimethylallylamino)purine (2iP), alleviated correlative inhibition and enhancedtuberization in intact plantlets. In the whole plantlet mostof the tubers were formed on the basal nodes, however, oncecorrelative inhibition was eliminated by the dissection of theshoot to single node sections, tubers were formed on every axillarybud. The single most effective factor inducing tuberizationin single node sections was the growth retardant ancymidol,an inhibitor of giberellin biosynthesis. Key words: Potato, Solanum tuberosum L., in vitro tuberization, correlative inhibition     

Analysis of In Vivo Protein Synthesis and Histological Studies of Haustorial Formation in Root Cultures of Witch weed (Striga asiatica L Kuntze)

We recently described an in vitro approach that uses root culturesto study haustorial formation in Striga asiatica. Previous studieshave used haustoria formed on intact radicles of Striga seedlings.In vitro cultured roots formed haustoria that appeared morphologicallysimilar to those formed by Striga radicles, but were 5–10-foldlarger. In this study, we provide biochemical and histologicalevidence to support further the similarity of root culture haustoriato haustoria formed on radicles of seedlings. We examined invivo protein synthesis during haustorial development on rootcultures and radicles by 2-D PAGE. Four proteins increased inabundance in both root cultures and radicles after 6 h of haustorialinduction. All four proteins appeared transiently in root culturesand radicles, being more abundant at 6 h, and less abundantafter 24 h of haustorial induction. Only three of the four haustorial-specificproteins were more abundant in root cultures after 2 h of haustorialinduction; all four had decreased in abundance after 12 h ofhaustorial induction. Using light microscopic analysis we comparedthe ontogeny of root culture haustoria to that of haustoriaon radicles. These studies revealed that root culture haustoriaundergo developmental changes similar to those reported forradicle haustoria such as early expansion of cortical cells,the emergence of haustorial hairs from epidermal cells, andthe development of densely staining cells at the haustorialapex. In addition, these changes occurred within a similar time-frameand sequence in root culture and radicle haustoria. Finally,root culture haustoria were found to be capable of attachingto sorghum host roots. Key words: Striga asiatica L., Kuntze, haustoria, root cultures, proteins, histology, 2D-PAGE     

Effects of High Air and Soil Temperature Stress on Growth and Tuberization in Solanum tuberosum

Potato plants (Solanum tuberosum L.) were grown at differentair and soil temperatures to determine the effects of high-temperaturestress on root, tuber, and shoot growth. Cooling the soil (17–27C) at high air temperatures (30–40 C) relieved noneof the visible symptoms of heat stress on shoot growth; norwas the degree of induction to tuberize in leaves increased,as reflected in tuberization of leaf-bud cuttings. Heating thesoil (27–35 C) at cool (17–27 C) air temperatureshad no apparent detrimental effect on shoot growth or inductionof leaves to tuberize. However, in each case hot soil largelyeliminated tuber development. In one experiment stolons grewup out of the hot soil and formed aerial tubers upon reachingthe cool air. When leaf-bud cuttings from induced plants wereused as a model system, high soil temperatures inhibited tuberdevelopment from the buried leaf buds, in the absence of anyroot growth. Apparently the induction of leaves to tuberizeis affected principally by air rather than soil temperature,but expression of the signal to tuberize can be blocked by highsoil temperature. Solanum tuberosum L., potato, temperature stress, soil temperature, tuberization     

Regeneration of Plants from Protoplasts of Arabidopsis thaliana L. cv. Columbia (C24), Via Direct Embryogenesis

This report describes a protocol for the regeneration of fertileplants from mesophyll protoplasts of Arabidopsis thaliana raceColumbia (C24). Regeneration was rapid and reproducible. Theprotocol is especially novel in that a large proportion of regeneratingprotoplasts regenerated via direct somatic embryogenesis. Protoplastsisolated from in vitro-grown plants entered sustained divisionafter 3–5 d in culture medium and over a period of severaldays 6–22% of protoplasts underwent at least one celldivision. Approximately 2–16% of these protoplasts continuedto divide and after 3 weeks in culture had formed macroscopiccolonies, of which 70–80% were regular embryo-like structures.Four weeksafter release from the alginate culture matrix andtransfer to solid medium in the light, 68–88% of thesestructures had produced well-developed shoots. Shoots couldbe maintained in culture or established in peat blocks. Theregenerated plants were fertile. Key words: Arabidopsis thaliana, protoplast, regeneration, embryogenesis, dicamba     

Promotion of Plant Cell Division by an Epidermal Growth Factor

In some specified treatments, an epidermal growth factor (EGF)promoted adventitious root formation in epicotyl cuttings ofVigna angularis. The number of the roots induced in cuttingstreated with 0.1 mg liter^-1 EGF during the first 24 h and with210^-4 M IAA during the second 24 h was 15% greater than thatof the roots in cuttings treated without EGF and with IAA. Analysisof the optimum timing of EGF application was performed by dividingthe first 24 h period into three sequential 8 h periods (0–8h, 8–16 h and 16–24 h). The most effective timeperiods in terms of the root formation were 8–16 h and16–24 h. The 0–8 h period was ineffective with respectto the formation. When carrot suspension cells were culturedfor 15 days at a very low cell density (1,000 cells/3 ml Murashigeand Skoog's medium) with more than 0.1 mg liter^-1 EGF, cellnumbers were 72% higher than those cultured without EGF. Theseresults suggest that EGF promotes cell division of plants. (Received October 5, 1992; Accepted May 24, 1993)     

Measurement of Yield Threshold and Cell Wal Extensibility of Intact Wheat Roots under Different Ionic, Osmotic and Temperature Treatments

Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m^–3 CaCl₂ r, P, Y and were20.7±4.6 µm min^–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min^–1MPa^–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m^–3 KC1 these parametersbecame 12.3±3.5 µm min^–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min^–1MPa^–1. After 24 h osmotic adjustment in 150 mol m^–3mannitol/0.5 mol m^–3 CaCl₂ r= 19.6±4.2 µmmin^–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min^–1 MPa^–01, respectively.After 24 h growth in 350 mol m^–3 mannitol/0.5 mol m^–3CaCl₂ r= 13.3±4.1 µm min^–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min^–1MPa^–1. During osmotic adjustment in 200 mol m^–3mannitol/0.5 mol m^–3 CaCl₂, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min^–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min^–1MPa^–1. Therefore, Y and are influenced by 10 mol m^–3 K⁺ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 2. Interacting Effects of Irradiance, Temperature and Plant Age in Controlled Conditions

A growth analysis was carried out with sweet pepper plants grownin a phytotron. Irradiance conditions were: 0.84 or 3.25 MJm^–2 in 8 h, 1.67 MJ m^–2 in 16 h and 2.51 MJ m^–2in 24 h. Temperatures applied were 25 or 21 °C during thephotoperiod in combination with 25, 21 and 17 or 21, 17 and13 °C respectively during the nyctoperiod. Highest values for leaf area and total dry weight were foundwhen applying 1.67 MJ m^–2 in 16 h, followed by 3.25 MJm^–2 in 8 h, irrespective of the temperature regime. Continuousirradiance ultimately resulted in leaf drop. A reduction inthe day temperature decreased leaf area and total dry weight.At a day temperature of 25 °C the dry weight increased withdecreasing night temperature when applying 3.25 MJ m^–2in 8 h. At a day temperature of 21 °C leaf area and dryweight were reduced when 17 or 13 °C were applied duringa 16 h nyctoperiod. Values for relative growth rate, net assimilation rate, leafarea ratio and leaf weight ratio strongly decreased with advancingplant age. The effects of irradiance treatment on RGR and NARwere analogous to those on total dry weight while the reversepattern was observed for the LAR. A decrease in day temperaturedecreased the RGR. The effects of night temperature exhibitedstrong interactions with day temperature and photoperiod. Theinfluence of temperature on RGR was largely mediated throughchanges in the LAR. The latter parameter was highly correlatedwith the specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature, plant age     

Growth and production of heterotrophic nanoflagellates in a meso-eutrophic lake

The growth of heterotrophic nanoflagellates (HNF) in mesotrophicLake Constance was measured in situ during a 13 month period.Experiments were conducted with 10 µm pre-filtered lakewater incubated in diffusion chambers at 3 m water depth atthe sampling location for 24 h. Growth rates were calculatedfrom changes in cell numbers occurring during the period ofincubation. Growth rates of all dominant taxa showed pronouncedseasonal variation (–0.13 to 1.76 day^–1 and weregenerally highest in summer at high water temperatures. In situgrowth rates were well below maximum growth rates known forthe respective and similar species from laboratory experiments.While water temperature was a key parameter positively relatedto the growth of all HNF species, the effect of various potentialfood items was taxon specific and less clear. Bacterial abundancewas equally important as temperature for growth in the smallbactenvorous Spumella sp., but was insignificant for growthrates of the larger omnivorous Kathablepharis sp. In Spuniellasp., 84% of the observed seasonal variation of its growth ratecould be explained by temperature and bacterial food supply.Based on these results, a multiple linear regression equationwith temperature and bacterial concentration as dependent variableswas calculated for the growth rate of Spumella. Taxon-specificproduction rates were derived from growth rates and averagebiomass of these two species, and compared to total HNF productionestimated from previously measured community growth rates andbiomass in Lake Constance. Production peaks of Spumella sp.and Kathablepharis sp. alternated seasonally. Total HINF productionranged from –0.01 to 10 mg C m^–3 day^–1. Theaverage seasonal production varied between 1.4 and 33 mg C m^–3day^–1 over 6 consecutive years. These small protozoa thuscontribute a substantial amount to total zooplankton productionin Lake Constance.     

Methanol Accumulation in Maturing Seeds

During in vitro growth and maturation of soybean seeds, cessationof embryo growth and dry weight accumulation occurred in thepresence of abundant C and N nutrients. Axis followed by cotyledontissues changed from green to yellow, and post-harvest germinationpotential declined if cultured after yellowing of axis tissues.A tissue specific accumulat;on of methanol occurred during thein vitro culture of immature seeds (i.e. initially 50 to 70mg fresh weight) to maturity in liquid medium. Methanol accumulatedto 3.0 g m^–3 or 50 µg seed^–1 in the medium,while methanol decreased from 37 to about 3.0 µg g^–1fresh weight in cotyledons. By contrast, axis tissues increased20-fold in methanol concentration to 90 µg g^–1 during20 d in culture. Ethanol was present only in trace amounts inaxis tissues and medium. Addition of exogenous methanol vapourto in situ grown seeds during precocious maturation decreasedsubsequent seedling vigour and germination with increasing levelsof exposure. Methanol accumulation in axis tissues during thegermination phase was not correlated with high temperature andtissue water content treatments which simulated pre-harvestdeterioration of seeds. However, the accumulation of methanolduring in vitro seed development and maturation in liquid culturemay contribute to reduced post-harvest germination performance. Key words: Soybean, Glycine max, seed maturation, in vitro, methanol     

Interrelation Between Growth Rate of Individual Potato (Solanum tuberosum L.) Tubers and Their Cell Number

In potato plants fast and slow growing tubers develop on thesame plant. A hypothetical causality between tuber growth rateand tuber cell number was investigated by determining the tubercell number with the aid of an automatic counting procedure.Our data show a close correlation between tuber size and cellnumber over the whole range of tuber volumes considered (3–28cm³). If the influence of tuber size on cell number is eliminatedby means of a partial correlation analysis, the cell numberof the entire tuber is not significantly correlated with itsgrowth rate. An exclusive consideration of the smaller cells(10–30 µm) in the apical tuber region, where thecell division rate in potato tubers is highest, reveals a loosebut significant partial correlation to tuber growth rate (r= 0.383, P < 0.05). The growth rate of the slow growing tubers of any potato plantmay be enhanced by removing the fast growing tubers. In thefirst few days this enhanced growth rate is not due to a stimulationof cell division rate, but rather due to cell expansion. Potato, Solanum tuberosum L., tuber growth rate, tuber cell number     

The Effects of Modifying Sucrose Concentration on the Development of Maize Kernels Grown in vitro

Intact Zea mays L. kernels attached to cob tissue develop tomaturity when grown in vitro. This experiment was designed todetermine if it is possible to prolong kernel growth by refreshingthe culture medium. Blocks of maize kernels were grown in vitroon media containing several concentrations of sucrose. Kernels,at all concentrations of sucrose, developed to maturity at 30–35d post-pollination, indicating that it is not possible to extendthe kernel growth phase by supplying a carbohydrate source.Kernels grown on media containing 80 g 1^–1 or higher sucroseconcentration had a significantly greater percentage of kernelsthat developed to maturity, and had greater weight and starchcontent per seed. Zea mays, kernel culture, seed development, starch     

Callus Culture of Sainfoin (Onobrychis viciifolia) and Plant Regeneration through Somatic Embryogenesis

Callus of sainfoin (Onobrychis viciifolia Scop.) was initiatedfrom stem and root explants which were obtained from seedlingsgrowing in vitro, on Linsmaier Skoog (LS) medium supplementedwith 1 mg l^–1 2, 4-D and 1 mg l^–1 BA or only 1 mgl^–1 BA, and the Vacin and Went medium without hormones.Somatic embryos were formed on LS medium containing 1 m l^–1BA. Embryos developed into complete plants on filter paper saturatedwith hormone-free LS medium. Onobrychis viciifolia, somatic embryogenesis, callus culture, plant regeneration     

Direct Organogenesis from Petiole and Thin Cell Layer Explants in Sugar Beet Cultured In Vitro

Detrez, C., Tetu, T., Sangwan, R. S. and Sangwan-Norreel, B.S., 1988. Direct organogenesis from petiole and thin cell layerexplants in sugar beet cultured in vitro.—J. exp. Bot.39: 917–926. Plant regeneration was obtained by direct bud formation frompetiole as well as from thin cell layer explants taken fromsugar beet (Beta vulgaris L.) plants grown in vitro. The budswere mainly induced in the blade-petiole transition zone ofthe explants. High frequency bud regeneration was observed inpetiole and thin layer explants of 10 different breeding linesof sugar beet tested. Organogenesis resulted when petiole explantsexcised from 8-d-old seedlings grown on half-strength Murashigeand Skoog medium (MS) containing 3.0 mg dm^–3 naphthaleneacetic acid (NAA), 3.0 mg dm^–3 6-benzylaminopurine (BAP)and 1.0 mg dm^–3 2, 3, 5, triiodobenzoic acid (TIBA) werecultured on MS with 3.0 mg dm^–3 NAA and 3.0 mg dm^–3BAP. Thin cell layer strips isolated from shoot apices culturedon MS medium supplemented with 0–9 mg dm^–3 BAP or1.0 mg dm^–3 indolebutyric acid (IBA) formed adventitiousbuds on MS medium containing 0–5 mg dm^–3 NAA + 5.0mg dm^–3 BAP. Histological studies confirmed the sub-epidermalorigin of shoots. Key words: Beta vulgaris, direct organogenesis, in vitro culture, petiole, regeneration, thin cell layer     

Effects of nitrogen nutrition on salt-stressed Nicotiana tabacum var. Samsun in vitro plantlets

Tobacco shoots were grown in vitro for 35 d, in MS culture mediummodified to include various sources (nitrate-N, ammonium-N ora mixture) and levels (0–120 mM) of N, and in the presenceof 0–180 mM NaCI or iso-osmotic concentrations of mannitol.Growth of control plantlets was significantly inhibited whenNH₄⁺-N was the sole N source, and at high (120 mM) NO^–₃-N supply. Under conditions of salt stress (90 and 180 mM NaCI)growth was repressed, with roots being more severely affectedthan shoots. Salinity also inhibited root emergence in vitro.The only alleviation of the salt stress by nitrate nutritionobserved in this study was on shoot growth parameters of plantletsgrown on 60 mM NO^–₃-N and 90 mM NaCI. Although both weresignificantly inhibited by NaCI, nitrate reduc-tase activitywas more severely affected than nitrate uptake. When mannitolreplaced NaCI in the culture medium, similar Inhibition of growth,nutrient uptake and enzyme activity were recorded. These observations,together with the relatively low recorded values for Na⁺ andCI^– uptake, indicate that under in vitro salt stress conditionsthe negative effects of NaCI are primarily osmotic. Key words: Growth, nitrogen metabolism, osmotic stress, salinity