The Effects of Pectic Enzymes and Phosphatidases on Potato Tuber Tissue

Extracts from rots of potato tubers caused by Erwinia atrosepticaand Corticium praticola were fractionated by precipitation withammonium sulphate and by gel filtration. For the various fractionsof the E. atroseptica extracts there was a close relation betweenthe activity of pectate franj-eliminase and capacity to increasethe permeability of protoplasts as assessed by loss of electrolytes.There was no such relation with phosphatidase acting on lecithin. For certain fractions of C. praticola extracts there was a similarclose relation between increase in permeability and activityof a polygalacturonase but for other fractions with low polygalacturonaseactivity there was a better relation with phosphatidase thoughall fractions that caused increase in permeability did havesome polygalacturonase activity. Phosphatidases which probablyplay no part in the killing of cells in E. atroseptica rotsmay, therefore, have some role in the killing of cells in C.praticola rots though they are likely to be less important thanpectic enzymes. Extracts from E. atroseptica rots caused marked increases inuptake of oxygen by tuber discs. Dialysis decreased and heatingeliminated this increase and had corresponding effects on permeability.However, after fractionation with ammonium sulphate, fractionswith high trans-eliminase activity had little effect on oxygenuptake whereas fractions with low trans-eliminase had littleeffect on permeability and greatly increased oxygen uptake. Similar results were obtained with C. praticola rot extracts.In contrast, nigericin and Triton X-100 both increased permeabilityand caused large increases in oxygen uptake The significance of these results is discussed especially inrelation to the killing of protoplasts by extracts from bothtypes of rot.     

Studies in the Physiology of Parasitism: XXI. The Production and Properties of Pectic Enzymes secreted by Fusarium moniliforme Sheldon

Fusarium moniliforme secreted macerating enzymes in liquid mediaonly when these contained certain natural extracts, pectic substances,or galacturonic acid. Apple extract was unsuitable for enzymesecretion and also inhibited enzyme secretion in synthetic mediaotherwise suitable. Protopectinase activity of solutions was highest in the pH range8·0–9·0, was rapidly lost at temperaturesabove 50–60° C., and was reduced by concentrationsof phosphate higher than 0·02 M. The enzyme was partiallypurified by precipitation in 60 per cent. acetone at pH 6·0. Protopectinase solutions also contained an enzyme which reducedthe viscosity of solutions of various pectic substances. Theproperties of this enzyme were, in general, similar to thoseof protopectinase. When activity of enzyme solutions was measured by the liberationof reducing groups, pectate solutions were more rapidly degradedthan were solutions of a high methoxyl pectin, particularlyin the early stages of the reaction. Paper chromatography ofthe products formed showed that pectate and pectin were degradedin different ways. Although the pathogen readily secreted protopectinase in potatoextract, potato tubers were not readily parasitized. In contrast,Fusarium avenaceum which readily attacked tubers, secreted littleprotopectinase in potato extract.     

Translocation of Assimilates Within and Between Potato Stems

Three aspects of translocation in potato were examined: (i)translocation within stems (ii) translocation between individualstems of a plant (iii) translocation between tubers followinginjection of ¹⁴C sucrose into a single daughter tuber. Assimilatesexported from single leaves of evenly illuminated potato stemsremained confined to the same side of the stem as the sourceleaf in a pattern consistent with the internal arrangement ofvascular bundles in the stem, and tubers borne on stolons verticallybelow the source leaf contained higher concentrations of ¹⁴Cthan those on the opposite side. Consequently ¹⁴C import intothe tubers bore little relationship to tuber growth rates. However,alteration of source/sink relations by pruning stems to a singlesouce leaf resulted in an even distribution of ¹⁴C throughoutthe vascular bundles of the stem and ¹⁴C import into the tubersbore a stronger relationship to tuber growth rates than to thephyllotactic relationship of the tubers with the source leaf. Labelling one stem of a potato plant resulted in little or nomovement of ¹⁴C into tubers on other unlabelled stems. However,removal of the unlabelled stems at ground level induced a significantmovement of ¹⁴C from the labelled stem to the tubers on unlabelledstems, this movement occurring via the mother tuber. Shadingthe unlabelled stems had less effect than stem removal. ¹⁴C sucrose injected into single daughter tubers was translocatedto other tubers on the same stem and also to tubers on a secondstem at the opposite end of the mother tuber. The sucrose wasconverted to starch in these tubers. The results favour the view that each potato stem functionsas an independent unit with potential for assimilate redistributionwithin a stem but with little or no carbon exchange occurringbetween stems, unless under severely altered source/sink patterns. Assimilates, ¹⁴C, autoradiography, potato (Solanum tuberosum L.), tuber growth     

An Analysis of the Mussell and Morre Quantitative Bioassay for Polygalacturonases using Pectate trans-eliminase from Erwinia atroseptica

The Mussell and Morré method for estimating the activityof chain-splitting pectic enzymes was tested with sections ofparenchyma from cucumber fruit and potato tubers. It provedto be a very sensitive test for the pectate trans-eliminaseof Erwinia atroseptica, between 10 and 100 times as sensitiveas a viscometric method based on degradation of polypectate.Loss of fresh weight was readily detected within a few minutesafter immersion in enzyme solution and continued until the sectionof tissue had lost coherence. For some time after immersion,loss of weight was mainly due not to loss of cells from thesurface of the section but to loss of water and solutes, presumablybecause of the effect of the trans-eliminase in decreasing thepermeability of the protoplasts. In the later stages loss ofcells became more important. Potato sections lost weight atabout half the rate of cucumber sections but the rate of increaseof absorbance at 235 nm of the ambient solution was about athird higher for potato than for cucumber. Potato sections lostelectrolytes much more rapidly than did cucumber sections. Thesedifferences probably reflect, at least in part, the much higherwater content of cucumber sections. The advantages of the Mussell and Morré method are itssensitivity and the fact that the natural substrates of chain-splittingenzymes can be used for assessing activity.     

Characterization of Monoclonal Antibodies Specific for Erwinia carotovora subsp. atroseptica and Comparison of Serological Methods for Its Sensitive Detection on Potato Tubers

Seven monoclonal antibodies (MAbs) to Erwinia carotovora subsp. atroseptica have been produced. One, called 4G4, reacted with high specificity for serogroup I of E. carotovora subsp. atroseptica, the most common serogroup on potato tubers in different serological assays. Eighty-six strains belonging to different E. carotovora subsp. atroseptica serogroups were assayed. Some strains of serogroup XXII also reacted positively. No cross-reactions were observed against other species of plant pathogenic bacteria or 162 saprophytic bacteria from potato tubers. Only one strain of E. chrysanthemi from potato cross-reacted. A comparison of several serological techniques to detect E. carotovora subsp. atroseptica on potato tubers was performed with MAb 4G4 or polyclonal antibodies. The organism was extracted directly from potato peels of artificially inoculated tubers by soaking or selective enrichment under anaerobiosis in a medium with polypectate. MAb 4G4 was able to detect specifically 240 E. carotovora subsp. atroseptica cells per ml by indirect immunofluorescence and immunofluorescence colony staining and after soaking by ELISA-DAS (double-antibody sandwich enzyme-linked immunosorbent assay) after enrichment. The same amount of cells was detected by using immunolectrotransfer with polyclonal antibodies, and E. carotovora subsp. atroseptica and subsp. carotovora were distinguished by the latter technique. ELISA-DAS using MAb 4G4 with an enrichment step also efficiently detected E. carotovora subsp. atroseptica in naturally infected tubers and plants.     

LABORATORY STUDIES ON DAMAGE TO POTATO TUBERS BY SLUGS

The ability of eight species of slugs to damage intact potatotubers c .v. Maris Piper was investigated. Four species, previouslyimplicated as pests of field crops, caused primary damage totubers. Interactions between three of the species Milax budapestensis(Hazay), Arion hortensis (Fèrussac) and Deroceras reticulatum(Müller) were studied using potato tubers of five cultivars.Single species groups caused most damage to tubers and interactionbetween species reduced damage irrespective of cultivar. Theresults are discussed in relation to past work. ^*Present address: 59 Valley Park Drive, Clanfield, Hants. PO80PL. (Received 19 August 1986;     

Physiological Basis for a Cycloheximide-induced Soft Rot of Potatoes by Pseudomonas fluorescens

Cycloheximide renders discs of potato tissue (Solanum tuberosum,cultivar Kennebec) susceptible to soft rot by a non-pathogenicisolate of Pseudomonas fluorescens. Pectate lyases (E.C. 4.2.99.3 [EC] )are the dominant extracellular macerating agents produced bythe test organism. Potato discs aged 24 h become resistant tomaceration by purified lyase preparations. Cycloheximide blocksthe development of resistance by inhibiting suberization. Thesite of inhibition is thought to be the cycloheximide-sensitivesynthesis of phenylalanine ammonia-lyase (E.C. 4.3.1.5 [EC] ) in potatodiscs. This enzyme is necessary for production of phenolic precursorsof suberin. Comparison of tissue from a number of potato cultivarscorrelates the synthesis of phenylalanine ammonia-lyase withresistance of discs to attack by the Pseudomonad. Resistance of potato tissue to pectate lyase is also affectedby intrinsic reactions not involving suberization. Resistanceincreases in fresh unsuberized discs when tubers are transferredfrom cold storage to room temperature before use. Resistancedecreases rapidly when tubers are transferred back to the cold.The intrinsic resistance appears to increase in the surfacelayer of cells in ageing discs. It is estimated that intrinsicreactions and suberization contribute equally to resistanceof aged discs to pectate lyase maceration.     

The Transport of Sugar, Water, and Ions into Developing Potato Tubers

Diurnal variations in the pattern of movement of sugars, water,and ions into developing tubers of the potato (Solanum tuberosumL.) were investigated. It was demonstrated using a recordingbalance that large increases in the fresh weight of tubers occurduring a dark period of reduced transpiration. Movement of assimilated¹⁴C did not reflect similar large changes and much of the weightchange observed is considered to be fluctuations in tuber watercontent. This water was shown to be moving predominantly throughthe xylem of the stolon by introducing labelled ions, ³²P and⁸⁹Sr into the plants. ³²P, which moves in both xylem and phloem,was transported to the tuber at a constant rate whereas ⁸⁹Sr,which behaves like calcium and is relatively immobile in thephloem, only moved into the tuber during the dark period. As well as the over-all long-term diurnal fluctuations severalsmaller rapid changes were recorded in the rate of water movement.Switching from darkness to light caused a transient increasefollowed by a rapid decrease in tuber weight. Switching fromlight to darkness caused a rapid increase in tuber weight. Insome experiments small oscillations in tuber weight were recorded.The possibility of these oscillations being directly relatedto cyclic changes in transpiration is considered. The resultsare discussed in relation to solute movement within plants.     

Identification of Free Cytokinins and the Changes in Endogenous Levels during Tuber Development of Sweet Potato (Ipomoea batatas Lam.)

Trans-zeatin, trans-zeatin riboside and N⁶-(²-isopentenyl)adenosine(i⁶Ado) were found to be the major cytokinins by high performanceliquid chromatographic separation and gas chromatography-massspectrometric analysis in the small tubers of sweet potato (Ipomoeabatatas Lam. cv. Minamiyutaka) with a diameter of about 5 mm.During tuber development cytokinin levels were high in tubershaving a diameter below 12 mm, minimal in tubers with a diameterof 22.5 mm, and then gradually increased as the tuber developed. The role of cytokinins in tuber development of the sweet potatois discussed. (Received May 20, 1982; Accepted August 10, 1983)     

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     

Effects of Temperature and Photoperiod on Assimilate Partitioning in Potato Plants

The effects of temperature and photoperiod on d. wt partitioningand ¹⁴C translocation were studied in three potato varieties.High temperatures and long days enhanced plant growth in termsof plant height and number of leaves, and also affected d. wtpartitioning between the plant organs. However, no temperatureeffect was noted on total plant d. wt, nor on the export of¹⁴C from the source leaf. Translocation of ¹⁴C to the vegetativeorgans (leaves and stems) was greater at higher temperatures,while translocation to the tubers was less under these conditions.We suggest that, under the temperature regimes studied, themain effect of high temperature is on assimilate partitioningand not on total plant productivity. Differences in responseto high temperatures were observed among varieties, with Norchipshowing the least and Up-to-Date showing the most sensitivity. High temperature, partitioning of assimilates, ¹⁴C-translocation, potato, Solanum tuberosum var. Desirèe, Solanum tuberosum var. Norchip, Solanum tuberosum var. Up-to-Date     

Long-term Metabolism of [14C]Sugars in Stored Potatoes

[¹⁴C]Sucrose, [¹⁴C]glucose and [¹⁴C]fructose were introducedinto potato tubers held at 10 °C and the redistributionof label chased over a 65 d period in storage. Respiratory losseswere identical in all treatments, as was the partitioning of¹⁴C between soluble and insoluble forms. Sucrose was the predominantlabelled sugar in the tubers after 20 h, regardless of the original[¹⁴C]sugar introduced, and was loaded and distributed throughoutthe tubers by the internal phloem system. After 20 h the proportionsof labelled sugars bore no relationship to those of the unlabelledendogenous sugars. However, with time the percentage of ¹⁴Cin sucrose fell while that in glucose increased and by 65 dthe proportions of the labelled sugars more closely resembledthe endogenous pools. Fructose represented a consistently lowproportion of both the labelled and unlabelled sugars. By 21d a considerable proportion of the soluble ¹⁴C had been convertedto starch (approx. 25% of the total tuber 14C), this value remainingrelatively constant for the remainder of the storage period.Sprouts which formed on the tubers contained up to 6% of thetotal tuber ¹⁴C but less than 0.2% of the tuber dry matter.It is suggested that the bulk of the translocated [¹⁴C]sucroseentered the symplast and exchanged slowly with the bulk of thesugars in the storage cell vacuoles. [¹⁴C]sugars, phloem loading, starch, potato tuber, Solunum tuberosum, cold storage     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Studies on factors in sweet potato root which induce spore germination of Ceratocystis fimbriata

Spore germination of Ceratocystis fimbriata was studied in termsof host-parasite specificity. The sweet potato, coffee and cacaostrains of Ceratocystis fimbriata germinated well in a fractionof sweet potato root water extract which had been passed througha column of cation exchange resin. The results showed that germinationof these strains was independent of exogenous cations. On theother hand, the prune, oak, taro and almond strains requiredfor germination both the absorbed and unabsorbed fractions ofsweet potato root water extract which were separated from eachother with a cation exchange resin column. Divalent cationssuch as Ca²⁺ Mg²⁺, Mn²⁺ and Zn²⁺ were identified as the activeprinciples in the absorbed fraction and Ca²⁺ showed the highestinductive activity for spore germination in the presence ofthe unabsorbed fraction. The active principle(s) in the unabsorbedfraction has not yet been identified. There was no relationshipbetween the Ca²⁺ and Mg²⁺ contents of the spores and the requirementof exogenous Ca²⁺ for germination. Ca²⁺ appeared to functionas a trigger of spore germination, not as a normal nutrient.These results suggest that the divalent cations such as Ca²⁺and Mg²⁺ in sweet potato contribute to the establishment ofhost-parasite specificity of this system. (Received August 10, 1977; )     

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     

Effects of Gamma-Irradiation on the Activity of Tonoplast H+-ATPase from Potato Tubers (Solanum tuberosum L.)

Tonoplast vesicles were prepared from potato tubers (Solariumtuberosum L.) on a step gradient (0% and 6%, w/w) of dextranT-70 to clarify the mechanism by which the tonoplast H⁺-ATPaseis inactivated by gamma-irradiation. H⁺-ATPase activity andH⁺ -pumping were examined after irradiation of tubers (in vivoirradiation) and of isolated tonoplast vesicles (in vitro irradiation)at doses up to 1.0 kGy. Both in vivo irradiation and in vitroirradiation resulted in significant decreases in ATPase andH⁺-pumping activities. The ATPase and H⁺-pumping activities12 h after irradiation were much lower than those 2 h afterirradiation. Solubilized H⁺-ATPase was inactivated, in a dose-dependentmanner, by irradiation (enzyme irradiation) to a greater extentthan was observed after in vitro irradiation or in vivo irradiation.The activity of ATPase 12 h after enzyme irradiation was almostthe same as it was 2 h after enzyme irradiation. The free fattyacid content of vacuolar membranes was increased by in vivoirradiation and by in vitro irradiation with an accompanyingdecrease in tonoplast H⁺-ATPase activity. Lipids from irradiatedtonoplasts had a considerable inhibitory effect on the activityof solubilized H⁺-ATPase. This result suggests that the directinactivation of H⁺-ATPase in potato tonoplast by gamma-irradiationis augmented by the effects of deterioration of membrane lipidsthat is induced by the irradiation. (Received December 21, 1994; Accepted May 16, 1994)     

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     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: II. RELATIONSHIP BETWEEN GROWTH RATE, CARBOHYDRATE CONCENTRATION AND 14C-PARTITIONING WITHIN TUBERS

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. The growth rates of individualtubers were closely reflected by their ¹⁴C-content 20 h after¹⁴CO₂ had been applied to the aerial parts of the shoot for4 h. The ¹⁴C-content of the tuber (sink strength) was significantlycorrelated to the ¹⁴C-concentration of the tuber tissue (¹⁴Cg^–1 fr. wt.=sink activity). The sink activity, which differedbetween individual tubers by up to a factor of 10, was alsoclosely related to the conversion rates of ¹⁴C into the starchand the remainder as well as to the ¹⁴C-content in the ethanolsoluble fraction. This indicates the simultaneous use of photosynthatefor growth and storage in the growing tubers. No preferenceof photosynthate utilization for either of these processes couldbe detected in relation to the sink activity of the tubers.Tubers with high sink activity imported ¹⁴C-labelled photosynthateat higher rates although their tissue contained higher concentrationsof reducing sugars and sucrose than the tissue of tubers withlow sink activity. Despite the close relationship between sinkactivity and the rate of starch synthesis (¹⁴C-conversion intostarch), no significant correlation was found between sink activityand the actual starch concentration of the tissue. The applicationof zeatin riboside directly onto individual tubers increasedtheir growth rates in comparison to non-treated tubers of thesame plant. The results indicate the importance of both growthand storage processes for the regulation of sink activity inyoung potato tubers. Key words: Potato tuber, ¹⁴C-photosynthate partitioning, zeatin riboside application     

Structure of potato tubers formed during spaceflight

Potato (Solanum tuberosum L. cv. Norland) explants, consistingof a leaf, axillary bud, and small stem segment, were used asa model system to study the influence of spaceflight on theformation of sessile tubers from axillary buds. The explantswere flown on the space shuttle Columbia (STS-73, 20 Octoberto 5 November 1995) in the ASTROCULTURE^TM flight package, whichprovided a controlled environment for plant growth. Light andscanning electron microscopy were used to compare the preciselyordered tissues of tubers formed on Earth with those formedduring spaceflight. The structure of tubers produced duringspaceflight was similar to that of tubers produced in a controlexperiment. The size and shape of tubers, the geometry of tubertissues, and the distribution of starch grains and proteinaceouscrystals were comparable In tubers formed in both environments.The shape, surface texture, and size range of starch grainsfrom both environments were similar, but a greater percentageof smaller starch grains formed in spaceflight than on Earth.Since explant leaves must be of given developmental age beforetubers form, instructions regarding the regular shape and orderedtissue geometry of tubers may have been provided in the presenceof gravity. Regardless of when the signalling occurred, gravitywas not required to produce a tuber of typical structure. Key words: Spaceflight, development, potato tuber, microgravity     

The Permeability to Oxygen of the Periderm of the Potato Tuber

The permeability to oxygen of the periderm of the potato tuberhas been measured during its development and storage. When expressedas ml O₂, diffusing through 1 cm² periderm in 1 sec under anO₂, pressure of 1 atm, the values for freshly harvested tubersranged from a maximum of 2.4 x 10^–4 in immature tubers,to less than 0.7 x 10^–4 in tubers harvested mature someweeks after the death of the foliage. In every case, after storagefor up to 10 weeks at 10^° C, the permeabilities, as expressedabove, were less than 0.7 x 10^–4 (minimum values, c. 0.5x 10^–4 It was shown that the oxygen deficit under theperiderm was unlikely to exceed 0.03 atm during development,and the oxygen status of the developing tuber should thus beadequate for the low oxygen-affinity oxidase system (if present)to function.