Observations on the structure and osmotic potentials of parenchyma associated with the internal phloem of potato tubers

The structure and osmotic potentials of parenchyma cells associated with internal phloem of growing, dormant, and sprouting potato tubers (Solanum tuberosum L. cv. Irish Cobbler) were studied. Companion cells, specialized parenchyma cells, and storage parenchyma cells were recognizable by differences in structural characteristics. Companion cells were usually densely cytoplasmic with numerous large mitochondria and plastids with little or no starch. The specialized parenchyma cells which surrounded groups of sieve tubes and companion cells had numerous vacuoles of various size, small mitochondria, plastids with very little or no starch, and protein inclusions. Storage parenchyma cells had amyloplasts with very large starch grains, a large central vacuole with osmiophilic inclusions, and few organelles in a peripheral cytoplasm. The osmotic potentials of specialized parenchyma cells and storage parenchyma cells were similar and did not vary regardless of whether the tubers were growing, dormant, or sprouting.     

Amylase activity in potato tubers

Summary Amylase activity in extracts of sprouted tubers was optimised at final concentrations of soluble starch in the incubation medium of 0.6–2.0 mg cm⁻³. Optimum pH was 6. The exclusion of calcium ions from extraction and incubation media did not result in reduced enzyme activity. This, together with a shift in the absorption maximum of the starch-iodine complex almost identical to that observed with pure β-amylase, indicates the predominance of β-amylase in the extracts. Over a 15-min incubation period the linearity of the response was dependent upon the volume of tuber extract included in the assay medium. Gel filtration of extracts did not influence this response.     

Lipid distribution in potato tubers

Summary To elaborate on off-flavour development in dehydrated potato granules, lipids in subcellular particles and membrane systems of the tuber were investigated. Lipid acyl-hydrolase and lipoxygenase activities were suppressed in tuber homogenates by a buffer isolation medium of pH 7.8 containing nupercaine which minimized the breakdown of phospho- and galactolipids. Phospholipid, glycolipid and neutral lipid constitutents, their fatty acid composition, and unsaturation ratios were reported for amyloplasts, cell wall, microsomes, mitochondria, peroxisomes, and plasmalemma.

---

Zusammenfassung Analysen von Kartoffelknollen wurden durch lipidabbauende Enzyme, Lipidacylhydrolase (LAH) und Lipoxygenase (LOX) behindert. Die LOX-Aktivit?t in handelsüblicherzugten Kartoffeln war hoch (Tabelle 1) und konnte durch gew?hnliche Inhibitoren nicht beeinflusst werden (Tabelle 2). Die LAH-Aktivit?t, die mit Phospholipiden (PL) und Galactolipiden als Substrate hoch war, wurde durch Nupercaine in verschiedenem Ausmass unterdrückt (Tabelle 3), dessen Weglassung w?hrend der Lipidanalyse von Kartoffelmembranen und subzellularen Partikeln hohe Lipidverluste verursachen k?nnte (Tabelle 4). Lipidergebnisse für mikrosomale Pr?parate, Mitochondrien, Peroxisomen, Plasmalemmen und St?rkek?rner (Tabellen 5–9) wurden wiedergegeben: nach Isolation bei pH 7,2, wenn die LOX-Aktivit?t nicht gehemmt war (Verfahren A); in einer Puffersubstanz von pH 7,8 ohne Nupercaine, wenn wohl die Aktivit?t von LOX unterdrückt war, nicht aber jene von LAH (Verfahren B); und bei pH 7,8 mit Nupercaine, wenn die Aktivit?t beider Enzyme unterdrückt war (Verfahren C). In den meisten Analysen zeigte die Lipidzusammensetzung, wenn die Aktivit?t beider Enzyme nicht unterdrückt wurde, eine entsprechende Anreicherung von PL, Sterollipiden und freien Fetts?uren (FFA) und ihrer Abbauprodukte sowie eine Abnahme im Gehalt an Galactolipiden. Kleine Mengen von Lipiden wurden in Form von Lipidpartikeln und verbunden mit Knollenzellw?nden gefunden (Tabelle 10). Die Fetts?urezusammensetzung des Gesamtlipids und einige besondere Lipidbestandteile und ihr Nichts?ttigungsverh?ltnis (UR) wurden nur für Verfahren C berechnet. Wenn dieses Verfahren weggelassen wurde, wie dargestellt mit Hilfe der St?rkelipid-Zusammensetzung, ergab sich nicht nur ein Verlust von Membran-PL und Galactolipiden. Fast die H?lfte der zurückgebliebenen neutralen Lipidfraktion war in Form von FFA in verschiedenen Graden oxydiert (Tabelle 9). Das UR der Gesamtlipide (TL) schwankte zwischen 0,4 und 2,9. Es war niedrig in der Zellwand, h?her im Plasmalemma und am h?chsten innerhalb der Zytoplasmamembranen. Das UR nahm dann bei den Vacuolen mit St?rkek?rnern ab. Die Bedeutung der Ergebnisse für die Bestimmung der Funktion von Lipiden in einem handelsüblichen Verfahren zur Herstellung von Püreepulver wirdt diskutiert.

---

Résumé La dégradation enzymatique des lipides par la lipide acyl hydrolase (LAH) et par la lipoxygénase (LOX) génait l’analyse biochimique des tubercules de pomme de terre. L’activité de la LOX était importante dans les pommes de terre cultivées pour la commercialisation (tableau 1) et n’était pas affectée par les inhibiteurs courants (tableau 2). L’activité de la LAH, qui était forte avec les phospholipides (PL) et les galactolipides, était inhibée sur différents substrats par la nuperca?ne (tableau 3); l’absence de cette dernière durant l’analyse de la membrane et des organites intracellulaires du tubercule causait de fortes pertes en lipides (tableau 4). Les résultats obtenus avec les lipides des préparations de microsomes, mitochondries, peroxysomes, plasmalemme et de grains d’ amidon (tableaux 5 à 9) sont exposés; après isolement à pH 7,2 sans inhibition de l’activité de la LOX (procédé A); dans une solution tampon à pH 7,8 sans nuperca?ne alors que l’activité de la LOX est inhibée mais non celle de la LAH (procédé B); et à pH 7,8 avec nuperca?ne et inhibition de l’activité des deux enzymes (procédé C). Dans le cas où l’activité des deux enzymes n’était pas inhibée, la composition en lipides montrait un enrichissement relatif en PL, stérols, acides gras libres (FFA) et en leurs produits de dégradation ainsi qu’une diminution de la teneur en galactolipides. Une petite quantité de lipides était retrouvée sous la forme de particules lipidiques associées aux membranes cellulaires (tableau 10). L’étude de la composition en acides gras des lipides totaux et de quelques constituants lipidiques ainsi que la mesure de leur taux d’insaturation (U.R.) ont été effectuées seulement pour le procédé C. Quand ce procédé n’était pas employé, comme l’illustre la composition en lipides de l’amidon, il y avait non seulement une perte de PL et galactolipides membranaires mais la moitié de la fraction lipidique neutre retenue se trouvait sous la forme de FFA oxydés à différents degrés (tableau 9). L’U.R. des lipides totaux (TL) variait de 0,4 à 2,9; il était bas dans les membranes cellulaires, plus élevé dans le plasmalemme et le plus haut dans les membranes cytoplasmiques. L’U.R. diminuait dans les vacuoles contenant des grains d’amidon. L’intérêt de cette découverte pour la détermination des lipides au cours de la fabrication industrielle de granules de pomme de terre est discuté.

     

Some studies on carbohydrates in potato tubers

Summary Starch and pulp were isolated from three cultivars of potato tubers grown in four localities. The starch content in the pulp was determined by an enzymatic method which is shown to be more accurate than a polarimetric method. On an average, 94% of the starch was isolated and 5% remained in the pulp. The change in low-molecular weight carbohydrates in the potato tubers during storage for 2, 4, 7 and 11 weeks at 9 C was studied. Generally there was an increase of sucrose, glucose, fructose andmyo-inositol during the first 2–4 weeks of storage, followed by a diminishing decrease.     

Phosphorus balance in potato tubers

Summary Tubers of virus-free Norland, Kennebec, Norchip, Russett Burbank, Red Pontiac, Norgold and Early Ohio potato varieties with a common environmental history were freeze-dried, and the major phosphorus-containing fractions determined. The method devised gave very reproducible values for phospholipid, nucleotide phosphorus, phytic acid phosphorus, starch phosphorus and nucleic acid phosphorus. Very little varietal differences were found as long as environmental factors were constant. The greatest variation was in inorganic phosphorus levels. There were no obvious relationships between protein level and any of the phosphorus-containing fractions.

---

Zusammenfassung Unsere Arbeit über Kartoffelhybriden mit hohem Proteingehalt erforderte die Kenntnis der Interaktionen zwischen St?rke, Protein, Nukleins?ure und Nukleotiden, was wir in der Literatur nicht finden konnten. Es schien keine hinreichende Zusammenstellung über die wichtigsten phosphorhaltigen Komponenten von Kartoffelknollen zu geben, die unter bekannten Umweltbedingungen angebaut wurden. Eine Fraktionierungsmethode wurde ausgedacht, die es erm?glichte, das Total an Phospholipiden, Nukleotiden, Phytins?ure, St?rke und Nukleins?uren, das in gefriergetrocknetem Knollenpulver vorhanden ist, zu trennen und quantitativ zu bestimmen. Das Verfahren wurde an Knollen von sieben Kartoffelsorten angewendet, die unter streng vergleichbaren Umweltbedingungen angebaut wurden. Die Ergebnisse (Tabelle 1) waren-mit nur kleinen sortenbedingten Unterschieden-gut reproduzierbar und einheitlich, vorausgesetzt die Umweltbedingungen waren vergleichbar. Die Ergebnisse dienen als Vergleichswert, an dem man die Einflüsse von variierenden Ploidiestufen oder variierendem Proteinniveau in der Entwicklung von Hybriden mit hohem Proteingehalt messen kann. Die hohen St?rkegehalte stellten kein Hindernis für die Nukleins?ureausbeute unter unseren Extraktionsbedingungen dar (Tabelle 2).

---

Résumé Notre étude sur les hybrides de pomme de terre, ayant une haute teneur en protéines, exigeait une connaissance des intéractions entre amidon, protéines, acides nucléiques et nucléotides, lesquelles étant introuvables dans la littérature. Aucun inventaire satisfaisant ne semble exister pour la plupart des constituants phosphorés de tubercules de pomme de terre se développant dans des conditions d'environnement connues. Une méthode de fractionnement a donc été con?ue, qui rend possible la séparation et la mesure quantitative des phospholipides, nucléotides, acide phytique, amidon et acides nucléiques totaux présents dans la poudre de tubercules lyophilisés. Le procédé a été appliqué sur sept variétés cultivées dans des conditions d'environnement comparables. Les résultats (tableau I) sont très reproductibles et uniformes, montrant peu de différences entre les variétés, en raison même des conditions de culture. Ils peuvent servir de référence pour qui veut évaluer l'effet des variations du degré de plo?die ou du taux de protéines en vue de l'obtention d'hybrides riches en protéines. Le taux élevé d'amidon ne présentait pas d'obstacle pour l'isolement des acides nucléiques, dans les conditions de notre extraction (tableau 2).

---

This study was carried out while the senior author was a guest, on sabbatical leave, at the Laboratory of Plant Hardiness, Department of Horticultural Science and Landscape Architecture, University of Minnesota, St. Paul, MN 55108.     

Identification of galactinol in potato tubers

Summary An oligosaccharide detected by gas chromatography of trimethylsilyl derivatives of potato extracts has been isolated and identified as galactinol, 1-0-α-D-galactopyranosyl-(1R)-myo-inositol. Galactinol was not detected in freshly harvested tubers, but 0.1% was found in cold-stored tubers. The level of this sugar decreased during reconditioning of cold-stored potatoes. A laboratory cooperatively operated by the Eastern Utilization Research and Development Division. Agricultural Research Service, United States Department of Agriculture; Minnesota Agricultural Experiment Station, North Dakota Agricultural Experiment Station; and the Red River Valley Potato Growers’ Association.     

Tensile properties of potato tubers

Mechanical properties of Kennebec and Russet Burbank potato tubers were computed from Force-elongation data on specimens cut from the tuber and tested in tension. Specimens cut from three locations in fresh and stored tubers were tested at varying strain rates at 70 F (21 C) and at 42 F (6 C). Results were analyzed for significant differences. Tests were conducted in 1964 and 1966. In spite of some differences in tuber condition and test and analysis methods, there was good agreement of results between the years. Mean values of properties for all tests were: tensile strength, 98 psi; strain at failure, 0.193 in./in.; and failure modulus (stiffness), 727 psi. Properties varied greatly with location in the tuber. The pith, in the center, is stronger and stiffer than the perimedullary zone surrounding it, and the skin-cortex exhibits different properties than either of these two. Storage affected properties at the skin and in the center much more than in the perimedullary zone. As strain rate increased, tensile strength and stiffness generally increased, and strain at failure decreased. Stiffness generally increased when temperature decreased. Effect of variety was mixed. One of the greatest problems in designing and using potato handling and processing equipment is damage to the potatoes. This lowers their market value and increases their susceptibility to disease and deterioration in storage. Various investigators, by dropping or hitting tubers experimentally or by following them through normal hanlling operations, have determined the external causes of damage to whole tubers and conditions that promote it. These experiments have yielded much needed information, but they tell little about the properties of th tubers that make them so susceptible to injury. Finney (2) and Timbers (7) have attempted to determine some of the mechanical properties of potato tubers and report them in engineering terms. This type of approach is necessary for an understanding of the behavior of potatoes in handling and processing operations. The purpose of this study is to determine mechanical properties of potato tuber tissue and report them in terms that will be usable by people who do further work in this area. Because at least some cracks in potatoes are caused by failure in tension, and because no record of tests on potato tissue in tension was found, these tests were conducted on specimens of potato tuber in tension.     

Detection ofErwinia carotovora var.atroseptica in potato tubers with immunofluorescence following induction of decay

Summary The simplest method of inducing tubers to decay in order to detect contamination by the blackleg organism,Erwinia carotovora var.atroseptica, was to wound them and place them in a mist chamber for four days. Incubating the decayed tubers in air for a further two days improved detection of the blackleg organism by immunofluorescence, which was a more sensitive test than the double diffusion method.     

Comparison of the protein in axillary bud tubers and underground stolon tubers in potato

To determine if axillary leaf bud tubers can be used to study tuber protein synthesis in potato we have compared the proteins in axillary bud tubers with those in underground stolon tubers in the variety Superior. By SDS polyacrylamide gel electrophoresis and by electrophoresis in nondenaturing polyacrylamide gels at pH 8.6, the proteins in axillary bud tubers appear to be the same as those in underground stolon tubers. The proteins also appear to be immunologically identical based on Ouchterlony double immunodiffusion test and immunoelectrophoresis.     

Variation in specific gravity of potato tubers

Specific gravity of tubers from the Irish Cobbler, Kennebec, Norgold Russet, Norland, Red Pontiac, Russet Burbank, Snowflake, and Viking varieties grown at 2 locations over 3 years were determined by the brine solution method. The usual differences in specific gravity were noted between varieties and locations. There was a narrow range in specific gravity of individual tubers within lots of Norland and Russet Burbank, and a wide range within lots of Kennebec and Snowflake, with the remaining varieties intermediate. Low variation of tubers within a variety as measured by standard deviation did not indicate low or high specific gravity. Varieties with low variation tended to remain low from one year to the next.     

Subcellular localisation of calcium in potato tubers

Summary Deposits, believed to contain calcium, were located in different cells of the potato tuber after using an antimonate procedure. In the starch-storage parenchyma of the medulla and cortex antimonate deposits were abundant within vacuoles, on the tonoplast, and to a lesser extent in cell walls. Phloem tissues contained a high concentration of deposits, mainly within companion cells and phloem parenchyma, consistent sites of deposition being mitochondria, plastids and tonoplasts. Deposits were abundant within vacuoles of cells of the xylem parenchyma. Within vessel elements deposits were limited to the surface of secondary wall thickenings. Antimonate deposits associated with the middle lamella of xylem parenchyma were rarely found. The results are discussed in relation to previous findings for potato tubers and for higher plant cells in general.     

Ultrastructure of potato tubers infected with potato virus X

The ultrastructure of Katahdin tubers infected with potato virus X (PVX) is compared with PVX-free tubers by electron microscopy. Electron-dense globules surrounding the inner periphery of the tonoplast were observed in PVX-infected tubers, while PVX-free tubers did not show such bodies. Other organelles were comparable in PVX-infected and PVX-free tubers