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.     

The Control of Branch Growth on Potato Tubers: II. THE PATTERN OF SPROUT GROWTH

Following the end of dormancy or after desprouting, many budson a potato tuber start to grow. However, if the storage temperaturefavours rapid growth, a number may remain inhibited. After atime, the smaller sprouts stop growing. This inhibition affectsonly those sprouts below a certain length, which is proportionalto the length of the longest sprout. This critical length isrelatively greater for small tubers than for large ones (i.e.longer sprouts are inhibited); it is also greater for tubersstored under dry conditions than for those under moist conditions.The results are interpreted in terms of a correlative inhibitior,continuously produced under the influence of growing buds andcontinuously destroyed as it moves up into all stems. It issuggested that in the terminal bud of the stem there is a sensitiveregion which controls the growth of the other stem tissues andon which the inhibitor acts. It stems longer than the criticallength the inhibitor is possibly inactivated before it reachesthis sensitive tissue; in shorter stems the inhibitor acts onthe tissue and hence inhibits stem elongation.     

Seasonal changes of the different components of the inhibitor β complex in potato tubers

Seasonal changes of the inhibiting substances in the inhibitor β complex were studied in diethyl ether and methanol extracts of peelings from potato tubers, cv. Majestic, prepared during dormancy and cessation of dormancy. In both extracts the acidic ether soluble substances were investigated. From the methanol extracts also non-ether soluble but butanol soluble substances were studied. At each extraction time experiments were performed to determine the stage of rest in the tubers. Four different inhibitory zones were found with the Avena straight growth test of thin layer chromatograms. One of these was probably an artefact formed during chromatography. The level of all these substances decreased when rest ceased. – Thin layer chromatograms of the butanol fraction of methanol extracts, which should have contained the bound forms of the inhibitors, showed the same inhibitory zones as the ether fractions. This probably resulted from hydrolysis of the bound inhibitors when the extracts were chromatographed in an alkaline solvent system during purification.     

The Influence of Removing Tubers on Dry-matter Production and Net Assimilation Rate of Potato Plants

To study the effect of removing tubers on growth and net assimilationrate (E) of potato, plants were grown in pots partly filledwith soil with the shoot growing through a polythene cover.Tubers developed in the space between the cover and the soilsurface. Removing tubers immediately they began to form had little effecton E at the beginning of the experiment but later greatly reducedit. Shading reduced E more at the beginning of the experimentthan later. Removing tubers decreased total dry weight, butmuch of the material that would have moved to tubers accumulatedin leaves and stems. In intact plants the loss of weight byshading was mainly from the tubers; in plants without tubersit was mainly from stems and leaves. Removing tubers increasedleaves on lateral stems. Increasing the amount of nitrogen supplieddiminished the effect on E of removing tubers, presumably becausethe extra allowed other sinks for carbohydrate to develop. Thegrowth of some buds of the potato plant is so strongly inhibitedthat they cannot grow and act as sinks for excess carbohydratewhen tubers are removed. Such internal inhibition of growthmay sometimes suffice to influence the magnitude of E of normalplants. Removing tubers usually increased sugar and starch contentand protein N content of stems and leaves.     

Tissue-Specific Distribution of Glutamine Synthetase in Potato Tubers

Cytosolic isoforms of the enzyme glutamine synthetase (GS) locatedin the phloem have been implicated in the mobilization of nitrogenfor intracellular transport in higher plants. The potato tuberrepresents an important reservoir of nitrogen and an approachwas made to the characterization of GS in this organ, particularlyat the stages of sprouting and of new tuber formation. By immunoblottingafter SDS-PAGE, and by immunological tissue printing, it waspossible to conclude that a cytosolic GS is present in tubersand sprouts, and that it is mainly expressed in the internalphloem, in a very precise tissue-specific pattern of distribution.These data provide additional clues to the interpretation ofthe functional role of GS in the mobilization of nitrogen andits utilization in growing parts of the plant. The importanceof morphological data and localization studies in complementingmolecular and biochemical work is emphasized. The proposed functionalimportance of the internal phloem inSolanum tuberosum organsis also reinforced. Solanum tuberosum L. cv. Desirée; potato; tubers; plant glutamine synthetase; tissue-specific distribution; phloem; nitrogen mobilization; in situlocalization; tissue printing     

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     

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     

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 Gibberellin-like Substances and Growth Inhibitors in Developing Strawberry Leaves

Gibberellin-like substances and inhibitors present in extractsof runner buds, and unfolding and mature leaves of strawberryhave been fractionated and compared. The runner-bud water-solubleresidue was more strongly inhibitory than that from unfoldingand mature leaves. The crude acid fraction from unfolding andmature leaves contained appreciable amounts of an inhibitor,probably abscisic acid, which was not detected in the buds.The unfolding leaves had a higher concentration of acidic gibberellin-likesubstances than either buds or mature leaves; they also containeda number of neutral gibberellin-like substances. Mature leaveshad a low concentration of gibberellin-like substances, allof which were acidic. A number of these were highly non-polartypes, not found in the buds or unfolding leaves.     

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     

Rhizomorph Behaviour in Armillaria mellea (Vahl) Quel: II. Logistics of Infection

The growth of rhizomorphs of Armillaria mellea from small woodyinocula through tubes of soil was characterized by a progressivedecline in weekly growth increments. Initial growth rate wasrelated to the size of the inoculum food-base; the subsequentdecline is attributed partly to depletion of nutrient reservesin the inoculum through fungal respiration and growth, and partlyto competition for nutrients between the main growing apex ofthe rhizomorph and its subordinate branch apices. The vigourof infection of potato tubers by rhizomorphs from such smallwoody inocula increased with size of the inoculum, and decreasedwith increasing distance between inoculum and tuber. When inoculumpotential of A. mellea was low, the fungus was generally overtakenin the tuber tissues by soft-rotting bacteria, which preventedits further advance.     

Initial Anatomical Changes Associated with Tuber Formation on Single-node Potato (Solanum tuberosum L.) Cuttings: A Re-evaluation

Cell division and cell expansion during early stages of tuberdevelopment were studied using developing axillary buds on single-leafcuttings from potato (Solanum tuberosum L.). Cuttings takenfrom plants induced to form tubers, by short day (SD) treatment,were compared with cuttings from non-induced (long day, LD)plants. In the apical zone of the buds, cell division occurredfrom the first day after cutting, in both LD and SD cuttings.The planes of these divisions were transverse, associated withelongation of the buds. At day 5, a new orientation of celldivision was observed in the subapical zone of SD cuttings only.These divisions were longitudinal, associated with radial growth.Cell expansion occurred in both SD and LD cuttings, and wasnot uniquely related to the onset of tuber formation. Copyright1999 Annals of Botany Company Solanum tuberosum L., potato, tuber formation, cell division, cell expansion.     

Fungal Assciations: I. Synergistic Relation between Rhizoctonia solani Kuhn and Fusarium solani Snyder and Hansen in causing a Potato Tuber Rot

Rhizoctonia solani, Fusarium solani, and Phoma foveata werechosen for the study of disease caused by these fungi in differentcombinations in potato tubers. An initial Rhizoctonia infection,when followed by a Fusarium infection, gave an extensive rottingwith external pimple-like formations in some cases. This typeof rotting could not be brought about by individual infectionswith either of the two fungi, or jointly by them when Fusariumwas inoculated first. Microscopic observations of infected matureand young potato tubers showed that Rhizoctonia grew intracellularlywhen infected alone, whereas it grew inter- as well as intra-cellularlyin the successive double infection. Fusarium formed more haustorium-likestructures when inoculated alone that when it followed Rhizoctonia.The length of these structures in the double infection was greaterin mature than in young tubers. Atmospheric humidity affectedthe amount of rotting, the shape and colour of the rot, andthe morphology of the fungus in the tissue.     

Phenolic Growth Inhibitors Isolated from Dormant Buds of Sugar Maple (Acer saccharum Marsh)

Phenolic growth-inhibiting substances were isolated from dormantbuds of sugar maple (Acer saccharurn Marsh) by paper chromatographyof their aqueous methanolic extracts. Inhibition was determinedin germination bioassays using lettuce (Lactuca sativa var.Grand Rapids) seeds. An inhibition of some 20% was attributedto four major phenolics identified as ferulic, vanillic, p-coumaric,and caffeic acids. Quercetm was also present and caused a weakstimulation of growth. Fractionation of the extract with acidic, neutral, and basicgroups indicated that more phenolic compounds were in the acidicgroup than in the neutral, while none were in the basic group. On a seasonal basis, autumn buds had a higher phenolic contentthan winter and spring buds. The results presented are not inconsistentwith the view that growth-inhibitory phenolic compounds couldcontribute to dormancy in sugar maple buds.     

Studies on the biochemical basis of physiological processes in the potato tuber

Summary The breakdown of starch in potato tubers which starts when buds begin to grow, stops if the sprouts are removed. The sprout controls the utilization and translocation of food reserves from the tuber. Movement of reserves can occur over the whole cross section of the tuber and is not restricted to the vascular shell. The presence of a growing sprout does not affect the permeability of the tuber tissue to sugar or amino acid.Previous part: Edelman and Singh (1968).     

Studies on Endogenous Bacteria in Potato Tubers Infected by Phytophthora erythroseptica Pethybr

Infection of potato tubers by the soft-rotting fungi Phytophthoraerythroseptica and Pythium debaryanum resulted in multiplicationof endogenous tuber bacteria. This effect was not evident afterinfection by dryrotting fungi. Some of the bacteria isolatedproduced pectolytic and hemicellulolytic enzymes in vitro andwere themselves capable under certain conditions of degradingtuber tissue.     

Effect of Mastoparan on Phospholipase A2 Activity in Potato Tubers Treated with Fungal Elicitor

Participation of phospholipase (PL) A₂ in signal trans-ductionhas been reported to elicitate a resistance reaction in potatocells by inoculation of an incompatible race of Phytophthorainfestans, the late blight fungus, or by treatment with fungalelicitor hyphal wall components (HWC). Mastoparan, a genericG protein activator, has been shown to activate PLA in a G protein-dependentmanner in animal cells. We analyzed the effects of mastoparanand the inactive analog Mas-17 on PLA₂ activity in potato tubers.In healthy potato tubers, the activation of PLA₂ by mastoparanwas detected in the soluble fraction, but not micro-somal fraction.However, in potato tubers treated with HWC, PLA₂ activity wasstimulated by mastoparan in both soluble and microsomal fractions.Pretreatment of the microsomal fraction with neomycin, a PLCinhibitor, and staurosporine, a protein kinase inhibitor, inhibitedthe mastoparan-induced activation of PLA₂. This suggested thatthe PLA₂ activation in potato tubers by mastoparan was mediatedby the PLC pathway and protein phospho-rylation. We also examinedthe accumulation of potato phytoalexin rishitin. Mastoparanstimulated rishitin accumulation induced by HWC, but did notinduce the accumulation. This indicated that mastoparan mightactivate the signal transduction pathway in the resistance reactionsinduced in potato tubers. (Received March 12, 1998; Accepted August 6, 1998)     

A phosphatidyl choline exchange protein isolated from germinated castor bean endosperms

A phospholipid exchange protein (PLEP) functioning between theendoplasmic reticulum and the mitochondrion was purified fromthe cytosolic fraction of germinated castor bean endosperms.In the protein fraction eluted from Sephadex G-100 column, theexchange rate reached 7.3µg phospholipids exchanged/mgprotein/15 min, which was 60-fold that of pota to tuber PLEP.The lipid transfer by this protein was specific for phosphatidylcholine and the transfer rate from microsomes to mitochondriawas as high as that from mitochondria to microsomes. Castorbean PLEP transferred phospholipid from castor bean microsomesto mitochondria from other sources such as potato tubers, cauliflowerinflorescences, pumpkin hypocotyls and rat livers, and to liposomes,but not to Avena etioplasts. In addition, it transferred phospholipidfrom potato microsomes to potato mitochondria. (Received November 17, 1978; )     

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