R. M. Reeve

Anatomy and compositional variation within potatoes

Re-examination of the histological development of the potato tuber supports Artschwager’s view that tuber growth is predominantly due to enlargement of the perimedullary zone and is of procambial origin. Pith (medulla) and cortical regions are differentiated from the ground or fundamental meristem derived from the apical meristem of the stolon apex, even before tuberization has been initiated. The procambium gives rise to external phloem, primary xylem, internal phloem and associated parenchyma, and likewise to interfascicular parenchyma. Those parenchyma cells so formed inwardly to the xylem “ring” contribute to the growth of the perimedullary zone. The sequence of tissue origins is diagrammed and discussed from the viewpoint of modern concepts of histogenesis.ResumenLa reexaminación del desarrollo histológico del tubérculo de papa le da creencia al punto de vista de Artschwager que el crecimiento del tubérculo se debe sobretodo al engrandecimiento de la zona perimedular y es de origen procambial. La médula y las regiones corticales se desarrollan por la diferenciación del meristemo fundamental que se deriva del meristema apical del ápice del estolón, aún antes de que empiece la tuberización. El procambio de origen al floema external, xilema primario, floema internal y el parénquima asociado y también al parénquima inter-facicular. Las células parenquimáticas formadas hacia el interior en relación al “anillo” de xilema contribuyen al crecimiento de la zona perimedular. Se da un diagrama de la sucesión ed los orígenes de los tejidos y se discute la sucesión desde el punto de vista de los conceptos modernos de histogénesis.

A review of cellular structure, starch, and texture qualities of processed potatoes

Certain combined characteristics of cellular structure and starch properties provide distinctions between varieties of potatoes and bear strong relation to their culinary qualities. Larger tissue cells and larger average starch granules are associated with mealiness. Smaller cells and starch granules characterize the less mealy and “waxy” varieties. Similarly, the same general relationships hold for the varietal characteristics of high vs. low solids and high vs. low starch contents. Within a variety, proportionately larger numbers of large starch granules are associated with tubers of high specific gravity, and more smaller granules, with low specific gravity. There also is a distinct reduction in percent of small granules during storage of tubers.Differences in starch granule size are accompanied by differences in amylose and amylopectin. Small granules contain less amylose and gel at higher temperatures than do the larger starch granules. Amylose content likewise appears to be a varietal characteristic. These variations in amylose content reflect fundamental differences in the properties of the starch gels formed when different varieties of potatoes are cooked. Likewise, there are similar distinctions between the starches within different tissue zones of individual tubers. Cell size also varies characteristically within different tuber regions.Starch gel properties may be manipulated during processing by such treatments as precooking-heating, chilling, freezing, and thawing. These treatments provide some measure of control of textural quality in the finished product. Additives such as stearates or glycerides complex readily with amylose and also influence gel properties and texture in processed potato products. Sucrose accumulated during tuber storage also may increase gel strength and influence texture.Varietal differences in cell structure and in starch granule size and composition offer opportunities for genetic exploitation. The merits of special processing for texture control vs. development of varieties for specific processed product qualities are briefly discussed.

Anatomy and compositional variation within potatoes II. Phenolics, enzymes and other minor components

Minor components, including principal phenolics and certain enzymes, are distributed within the potato tuber according to patterns that are significant to many practical problems in the growing, handling, and utilization of potatoes. Chlorogenic acid is much more concentrated in outer than in inner tissue zones; is also highly concentrated in the phloem and phloem parenchyma tissues of both cortex and perimedullary zone. Tyrosine is generally distributed but is more concentrated in the stem end than in the bud end of the tuber and probably is also more concentrated in central than in outer tissues. Results of histochemical tests on distribution of these phenolics agree in general with quantitative analytical results. Phenolases and peroxidase also show characteristic patterns of distribution. Peroxidase affects tissue differentiation and specialization and shows strong histochemical relationship with cell-wall specializations. Phenolases show association with distributions of phenolic substrates and usually are associated with cell contents. Distribution patterns are reviewed for other minor constituents, such as, iron, copper, ascorbic acid, thiamine and solanin.ResumenComponentes menores, incluyendo componentes fenólicos principales y ciertas enzimas, están distribuidos en el tubérculos de papa de un mode que es significante para muchos problemas prácticos en el cultivo, manejo y utilización de papas. El ácido clorogénico está mucho más concentrado en las zonas de tejidos externas que en las internas; también está altamente concentrado en el floema y en el parénquiam del floema tanto en el cortex como en la zona perimedular. Tirosina está generalmente distribuida pero está más concentrada en la parte del tallo del tubérculo que en la parte de la yemas y está probablemente más concentrada en tejidos centrales que en los externos. Los resultados de ensayos histoquímicos sobre la distribución de estas substancias fenólicas están generalmente de acuerdo con los resultados cuantitativos analíticos. Fenolasas y peroxidasa también tienen modos caracteríticos de distribución. La peroxidasa influencia la diferenciación y especialización de tejidos y tiene una fuerte relación con las especializaciones de la pared celular. Las fenolasas están asociadas con la distribución de sustrados fenólicos y estan asociadas generalmente con los contenidos celulares. Se examinan los modos de distribución de otros constituyentes menores, tales como hierro, cobre, ácido ascórbico” thiamina y solanina.

Anatomy and compositional variations within potatoes. III. Gross compositional gradients.

The degree of compositional variations within potato tubers has been related to the development anatomy of the tuber and to exact tissues. The principal component, starch, shows differences in granule size distributions and in composition that appear when the young tuber averages about 1/300 of mature volumetric size. These differences pertain at maturity. When starch differences have been established, growth by cell divisions diminishes and growth by cell enlargement becomes dominant. In the mature tuber the general gradients for specific gravity, percent total solids, and percent total nitrogen decrease from stem end to bud end for cortical, perimedullary and pith tissues. Relationship between specific gravity and total solids is less parallel because differences in cell size and size of minute intercellular spaces also influence tissue density. Relationship between total solids and total nitrogen gradients from cortical tissue to pith were inverse with toal nirogen being higher in those tissues of lower total solids. These variations suggest need for new approaches in basic research on tuber quality improvement.ResumenEl grado de variaciones de la composición entre tubérculos de papa ha sido relacionado al desarrollo anatomico del tubérculo y a tejidos exactos. El componente principal, almidón, muestra diferencias en distribuciones de tamaño de gránulo y en la composición que aparecen cuando el volumen del tubérculo jóven tiene un promedio de 1/300 del volumen cuando maduro. Estas diferencias son pertinentes a la madurez. Cuando la diferencias en almidón hayan sidos establecidas, el crecimiento por division de células disminye y el crecimiento por agrandamiento de las células se hace dominante. En el tubérculo maduro el gradiente general de peso specifico, porcentaje de solidos totales, y el porcentaje de nitrogenos totales decrecn del punto del tallo (stem end) al punto apical (bud end) en los tejidos corticales, perimedulares y medula.La relación entre el peso específico y sólidos tales es menos paralelo porque laos diferencias en el tamaño de las celulas y el tamaño de los diminutos espacios intercelulares también influeyen en la densidad de tejidos. La relación entre gradientes de sólidos tolales y nitrógenos totales desde el tejido cortical a la médula fueron inversos para nitrógenes totales siendo mas altos en los tejidos de menor solidos totales. Estas variaciones indican la nececidad para nuevas metodas y ideas en las investigaciones básicas sobre el mejoramiento de la calidad del tubérculo.

Preliminary histological observation on internal blackspot in potatoes

SummaryA variety of histological conditions characterize the internal blackspot that results from bruising of potatoes. Phenolics, principally chlorogenic acid, accumulate in the injured area. Melanin forms on intracellular surfaces of the protoplasts and also inner cell wall surfaces. Cell wall suberization is sporadic in small blackspot sites, but more general in larger ones. Some lignification, increases in hemicelluloses, and change in pectins also may occur. Changes in distribution of intracellular lipids also was observed. Initiation of wound phellogen was observed only in situations where the original periderm had been broken and where crushing of internal cells had occurred. Cell wall suberization, increases in hemicelluloses, and increase in chlorogenic acid are common to both blackspot and physiological necrosis.ResumenUna variedad de condiciones histológicas caracteriza la mancha negra interna que resulta de contusiones sufridas por las papas, Fenoles, principalmente el ácido clorogénico, se acumulan en la parte dañada. Melanina se forma en las superfícies intracelulares de los protoplastos y también en las superfícies de las paredes celulares internas. La suberización de la pared celular ocurre esporadicamente en las manchas negras pequenas, pero es más general en las grandes. Lignificación parcial, incrementos en hemicelulosas, y cambios en pectinas también pueden ocurrir. Además se han observado cambios en la distributión de lipidos intracelulares. La iniciaciń del felógeno en las heridas fué observada solamente en situaciones donde el peridermo original habia sido dañado y donde las células internas habían sido dañadas. La suberización de la pared celular, incremento en hemicelulosas e incremento en ácido clorogénico son comunes tanto a la mancha negra como a la necrosis fisiológica.

Parenchyma cell growth in potato tubers I. Different tuber regions

Enlargement rates of starch-storage parenchyma cells during growth of Kennebec and Russet Burbank potato cultivars were determined for cortical, perimedullary, and pith tissuues of bud ends, midsections, and stem ends of tubers. Average volumetric size of parenchyma cells increased 7 to 18x during growth of Russet Burbank tubers, with the greatest increases occurring in cortical and perimedullary cells of bud ends and midsections, and the least in stem ends and pith tissues. In Kennebec tubers parenchyma cells in both stem end and midsection increased only 5 to 8 x, whereas increases in bud ends ranged from 8 to 20 times.Cell enlargement to tuber enlargement ratios appproached unity early in growth of Russet Burbank tubers. As tubers increased beyond the 45 g size, cell enlargement and tuber enlargement rates were essentially equal. Calculations of cells per unit tissue volume agreed with ratio determinations. The timing of such unity appeared to be delayed in Kennebec tubers, and was not quite as pronounced as in Russet Burbank tubers. This may have been due to differences in growth rates of individual tubers in response to cultural conditions. In general, cells of harvestmature Kennebec tubers were about 60% as large as similar cells of Russet Burbank tubers.

Potato composition: II. Tissue selection and its effects on total sugar, total reducing sugar, glucose, fructose and sucrose contents

Total sugar, reducing sugar, glucose, fructose, and sucrose were determined in three parts (bud-end, stem-end, and core) of tubers of White Rose, Red La Soda, Kennebec, Russet Burbank, Norchip and Lenape. Tubers were sampled at harvest, after storage for 2 and 4 mo at 7 C, and after reconditioning for 3 wk at 20 C after each storage period. The quantity of different sugar fractions varied with cultivar and changed with storage treatments. Only sucrose was uniformly distributed among the different parts of the tuber. Except for fructose and sucrose the relationships among different parts of the tuber for distribution of all other sugar fractions varied significantly with cultivar, and these relationships among parts were not significantly changed by temperature, or duration of storage.ResumenAzúcares totales, azúcares reductores, glucosa, fructosa y sucrosa se determinaron en tres partes (ápice, base y centro) de tubérculos de White Rose, Red La Soda, Kennebec, Russet Burbank, Norchip y Lenape. Los tubérculos fueron muestreados a la cosecha, después de almacenamiento de 2 y 4 meses a 7° C, y después de re-acondicionar por 3 semanas a 20° C después de cada periodo de almacenamiento. La cantidad de las diferentes fracciones de azúcares variaron con el cultivar y cambiaron con los tratamientos de almacenamiento. Solo la sucrosa estuvo distribuída uniformemente entre las diferentes partes del tubérculo. Con la excepción de fructosa y sucrosa las relaciones de distribución entre las diferentes partes del tubérculo de todas las fracciones de azúcares variaron significativamente con el cultivar y esas relaciones entre partes no fueron cambiadas significativamente con la temperatura o con la duraci⤵ del almacenamiento.

Cell wall thickness during growth of domestic and foreign potato cultivars

During growth of Russet Burbank tubers from less than 100 to over 250 g, thickness of parenchyma cell walls nearly doubled (1.9X) to slightly over 1 μ. Although affecting cell size at harvest maturity, different levels of N fertilizer and soil moisture had little influence on wall thickness. Wall thickness in Kennebec and Norchip increased to 0.9μ (1.7X), and in White Rose to slightly under 0.8 (1.2X). During the same growth, cell size nearly doubled in Russet Burbank. Cells of Kennebec, Norchip and White Rose averaged smaller than those of Russet Burbank at harvest maturity.Wall thickness and cell size showed similar relationships in foreign cultivars. Wall thickness in European varieties Bintje and Pimpernel was comparable to that of White Rose. Thickness in Atjimba closely approached that of Russet Burbank, and in Kamarz was similar to that of Norchip. Among South American cultivars, Doré had unusually thick walls (1.36μ), whereas those in Fruitella and Papa Bianca were between those of Norchip and White Rose. Bintje was comparable to domestic cultivars in tuber size, but all other foreign cultivars studied had medium to small tubers. Doré had unusually large cells for a small tuber.Differences in wall thickness may be due to differences in amounts of cell wall material, to differences in hydration properties of pectic components, or to combinations of both. Independently of wall thickness, the many primary pit fields in parenchyma walls may be a limiting factor in wall strength. The very thin pit membranes consist mainly of cellulosic microfibrils formed early in cell growth.

Potato composition: I. Tissue selection and its effects on solids content and amylose/amylopectin ratios

Solids content and amylose/amylopectin ratios were determined in different parts of tubers of White Rose, Red La Soda, Kennebec, Russet Burbank, Norchip and Lenape at harvest, after storage at 7 C for 2 and 4 mo, and after reconditioning at 20 C for 3 wk following each storage period. In all cultivars, solids content was greatest in stem-end, lower in bud-end and lowest in core tissue. The relationships for distribution of solids among the different parts of the tubers was not changed by storage treatments in any of the cultivars. Amylose/amylopectin ratios were similar in all parts of the tuber. Both the solids content and amylose/amylopectin ratio were changed by storage, but not uniformly in all cultivars.ResumenEl contenido de sólidos y las proporciones de amilosa/amilopectina fueron determinados en diferentes partes de tubérculos de White Rose, Red La Soda, Kennebec, Russet Burbank, Norchip y Lenape a la cosecha, después de almacenamiento a 7°C por 2 y 4 meses, y después de reacondicionamiento a 20° C por 3 semanas después de cada periodo de almacenamiento. En todos los cultivares el contenido de soolidos fue mayor en la base, menor en el apice y mucho menor en el centro. Las relaciones de distributión de sólidos entre las diferentes partes del tubérculo no fué cambiada por el almacenamiento aninguno de los cultivares. Las proporciones de amilosa/amilopectina fueron similares en todas las partes del tuberculo. El contenido de sólidos y la proportión amilosa/amilopectina fueron cambiados por el almacenamiento, pero no uniformemente todos los cultivares.

Cell size in Russet Burbank potato tubers with various levels of nitrogen and soil moisture tensions

Russet Burbank potatoes were grown at levels of added nitrogen of 0, 135, and 270 kg/ha and soil moisture tensions (SMT) of 0.5 and 1.0 atm. With all combinations, there was a consistent gradient of larger to smaller starch-storage parenchyma cells from stem end to bud end of mature tubers.Stem and bud ends of tubers grown at a SMT of 0.5 atm with N had smaller cortical and pith (innermost medullary or water-core) cells than did ends of tubers grown without N. Perimedullary tissues of bud ends of tubers receiving N likewise contained smaller cells than did corresponding tissues of tubers grown without N. No pronounced differences in cell size were found in tissues from the midsections.In bud-end tissue of tubers grown at a SMT of 1.0 atm, there were no consistent differences in cell size with respect to N levels. However, pith, perimedullary, and cortical tissues of the midsections and stem ends of tubers receiving N had smaller cells than did corresponding tissues from tubers without N. The different patterns of cell size in tubers grown at different SMT indicate that the effects of N may be influenced by soil moisure.