Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes

Summary Potato tuber dormancy is usually defined as lasting from tuber initiation until a sprout of 2 mm long has been formed under storage conditions optimal for sprouting. We tried to find out whether there is a period during which buds of seed tubers do not grow and whether different batches of seed take the same time to grow sprouts 2 mm long. We measured changes in number of leaf primordia and length of tuber buds of cvs Diamant and Désirée over two years. After early haulm pulling, buds did not grow for at least 60 days (‘Diamant’) or 95 days (‘Désirée’). Buds in both cultivars and two tuber weights of ‘Diamant’ took about 20 days from the estimated onset of sprouting to grow 2 mm long. We question whether this period is always similar and thus whether the moment sprouts 2 mm long have formed is a good criterion for the end of dormancy.     

Isolation of solanidine from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary The kinetics of enzymatic transformation of total glycoalkaloids (TGA) in haulm and tuber sprouts of potato to solanidine and the kinetics of solanidine isolation from plant material were studied. The optimum reaction conditions for the enzymatic TGA transformation were found for haulm to be: plant material to liquid phase 1:4 w/v, temperature 35°C, pH 5.4; and for tuber sprouts: plant material to liquid phase 1:3 w/v, temperature 37°C, pH 5.4. The. maximum degree of enzymatic transformation of TGA in haulm and tuber sprouts of 65 and 75%, respectively, was achieved after 50h. Carbon tetrachloride was the best solvent for solanidine extraction from the plant materials. The optimum ratio of plant material to carbon tetrachloride for the isolation of solanidine was 1:8 w/v for both extraction cycles, ensuring a yield of solanidine of approximately 55 and 65% from haulm and tuber sprouts, respectively, after 30 min.     

A rapid method for the quantification of steroidal glycoalkaloids by reversed phase HPLC

Summary Methods were developed for clean-up of potato tuber extracts on solid phase extraction CN-cartridges and for analysis of steroidal glycoalkaloids by reversed phase HPLC. The alkaloids α-solanine, α-chaconine, α-solasonine and α-solamargine could be separated on C₈ or C₁₈ reversed phase columns using a mobile phase of acetonitrile/Tris-buffer (3∶2, v/v). The analysis time of tuber extracts containing these alkaloids was less then 4 min, if the pH of the mobile phase was adjusted to 7.4 and run at a flow rate of 0.5 ml/min.     

Relation between growth conditions and dormancy of seed potatoes. 2. Effects of temperature

Summary In two indoor experiments under short day conditions, the effect of temperature during tuber bulking on dormancy of tubers was investigated for cvs Diamant and Désirée. Temperature treatments started after tuber initiation and lasted for 4 weeks, after which the haulm was removed. In Experiment 1, the day/night temperature regimes 18/12, 22/22, 26/18 and 32/12 °C (T18/12 etc.) were compared. In Experiment 2, three day temperatures (18, 24 and 30 °C) were combined with three night temperatures (12, 18 and 24 °C), resulting in nine treatments. The dormancy of cv. Diamant was shortest after very high day temperatures (30–32 °C), but intermediate day temperatures (22–26 °C) had no shortening effect compared to T18/12. Dormancy of cv. Désirée was not shortened, but rather tended to be prolonged by high temperatures (22–32 °C) during growth. High temperatures during growth resulted in more sprouts per tuber after dormancy had ended.     

Action des radiations de lumière rouge sur la survie et la tubérisation de germes de pomme de terre cultivés ‘in vitro’: influence de leur âge physiologique

Résumé De brèves irradiations de lumière rouge appliquées à des germes étiolés, isolés de tubercules de pomme de terre (Solanum tuberosum L.), ont montré des effets variables sur la vitesse de la tubérisation selon la nature des radiations et le moment de leur application après le prélèvement. La survie des germes et la rapidité de tubérisation ‘in vitro’ seraient des phénomènes liés, et placés sous le contr?le probable du phytochrome qui serait présent sous la forme Pfr^* dans les germes. Des traitements lumineux périodiques à basse température sur des tubercules ayant eu un temps suffisant d'incubation permettent un enrichissement de la teneur totale en phytochrome des germes qui en seront issus. Dans tous les cas (germes et tubercules-mères), la sensibilité aux radiations rouges augemente en même temps que le degré d'incubation.

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Summary Short spells (5 min) of red light applied to etiolated potato sprouts after excision (0 time) caused opposite effects on rate of tuberisation after the sprouts had been planted; tuberisation was speeded up by light red (RC) radiation and slowed down by dark red (RS) radiation. If the treatment was postponed to after subjecting the sprouts to darkness, RS effect was reduced whereas that of RC enhanced in relation to the duration of the dark period (Table 1). The effect of RS at 0 time could be explained in terms of the presence of a low level of preformed Pfr (active form of phytochrome) in the etiolated sprouts. The Pfr would disappear gradually in darkness resulting in the loss of efficiency of RS radiation and an increase in the efficiency of RC radiation. The marked effect of RS radiation at 0 time was even more evident if the sprouts were excised from physiologically older tubers (higher incubation temperature). The increase in related physiological responses —persistence and speed of tuberisation in vitro — could be explained by the development during incubation of conditions more favourable to the activity of the photoreceptor in the cells (Table 2). Red light treatment at low temperatures (Table 3) on mature tubers (Table 4) caused an increase in total phytochrome content in etiolated sprouts which would develop later on those tubers in the dark. Light appeared to control tuberisation through its action on an organ which detects the stimulus (tuber) to an organ derived from it (sprout).

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Zusammenfassung Kurze Belichtung von Dunkelkeime mit Rotlicht (5 min) nach dem Ansetzen (Zeit 0) übt eine hemmende Wirkung auf die Knollenbildungsgeschwindigkeit. Die hellroten Strahlen f?rdern und die dunkelroten Strahlen hemmen die Knollenbildung (Abb. 1). Falls das Aussetzen in diese Farblichter verschoben wird, nachdem die Knollen im Dunkeln gehalten wurden, so beobachtet man, dass der Effekt der dunkelroten Strahlen abnimmt, hingegen nimmt die Wirkung der hellroten mit verl?ngerter Dunkelperiode zu (Abb. 1). Die Wirkung von Dunkelrot zur Zeit 0 k?nnte durch das Vorhandensein von einer kleiner Menge der Aktivform des Phytochrom in Dunkelkeimen erkl?rt werden. Im Dunkeln verschwindet die Aktivform des Phytochrom allm?hlich. (Dies zur Folge hat, dass die Wirksamkeit der dunkelroten Strahlen verloren geht, sowie auch der erzielte Effekt der hellroten Strahlen.) Je ?lter die Mutterknolle der geprüften Keime ist (vorgerücktes Inkubationstadium) desto besser ist die Wirkung der dunkelroten Strahlen zur Zeit 0. Die Verbesserung der physiologischen Reaktionen gekoppelt mit —überleben und Knollenbildungsgeschwindigkeit ‘in vitro’ — k?nnte sich erkl?ren durch eine bessere Disposition des Zellmaterials gegenüber dem Lichtempf?nger. Das Phytochrom würde somit bei stark inkubierten Keimen als alterungshemmender Faktor wirken (Tab. 2). Behandlungen mit Rotlicht bei kühlen Temperaturen (Abb. 3) auf reifen Knollen (Abb. 4) erh?hen den Gesamt-Phytochromgehalt in den Keimen, welche sp?ter im Dunkeln aus diesen Knollen gebildet werden. Das Licht würde somit durch das Organ, welches den Stimulus (Knolle) aufnimmt eine Kontrolle auf ein daraus entstehendes Organ (Keim) ausüben.

     

Effect of Cultivar Resistance and Haulm Killing Method on Tuber Infection by <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

A series of field trials combining cultivars with different levels of resistance to Phythophtora infestans and different haulm killing methods was conducted in 1997, 1998 and 1999 to assess the contamination potential of the haulm. In addition, the frequency of tubers with late blight was assessed after harvest and storage, combining effects of pretreatment infection, infection by the haulm at harvest and the development of the disease during storage. Haulm killing was performed by diquat (200, 400, 600 g a.i. ha^-1), half cutting of the haulm in combination with diquat (100, 200, 300 g a.i. ha^-1) or full cutting of the haulm. In those treatments where haulm killing was performed purely chemically the haulm remnants’ contamination potential tended to increase at reduced doses. Full mechanical destruction gave as low a contamination potential as application of the full dose of chemical haulm killer. However, there were no consistent differences between the haulm killing treatments in the frequency of blighted tubers after harvest and storage. This indicates that the input of chemical haulm killers may be reduced. There was a large difference between years in tuber blight after harvest and storage, which confirms that climatic factors are of major importance for tuber infection. The large difference found between the cultivars in the frequency of tuber blight indicates that tuber resistance should be an important part of integrated late blight disease management.     

Hydrolysis of glycoalkaloids fromSolanum tuberosum L. haulm by enzymes present in plant material and by enzyme preparation

Summary This paper deals with the kinetics of enzymatic hydrolysis of glycoalkaloids from potato (Solanum tuberosum L.) haulm. The hydrolysis was carried out by the action of the enzymes present in fresh haulm, juice of fresh haulm and in haulm dried at various temperatures. The highest degree of enzymatic hydrolysis of 90% was obtained during fermentation of haulm dried at 40 °C after 30 h incubation time. The enzyme preparation was obtained from the juice of fresh potato haulm by using capillary dialysator HM 16 (AQM 1681, 1.6 m² Hemofan 8 υ). The best degree of enzymatic hydrolysis by enzyme preparation, 68%, was achieved after 20 h time of incubation. The enzyme preparation from juice of fresh haulm was characterized by K_m of 0.70 mM at pH 5.5 and 35 °C.     

Growth and yield studies of potato development in a semi-arid region. 2. Effect of water stress and amounts of nitrogen top dressing on growth of several cultivars

Summary Five potato cultivars were subjected to water deficits as well as to excess water and to corresponding amounts of nitrogen top dressing (N.t.) applied in the irrigation water. The rates of growth in response to water-N. t. were highest for all cultivars whenK _p=1.06 (pan evaporation coefficient) and N.t=173 kg/ha. In the drier treatments (0.87>K _p>0.14 and 127>N.t.>12 kg/ha) and in the wetter treatment (K _p=1.27; N.t.=201 kg/ha), the growth rates decreased. The cultivars differed in their haulm size, especially atK _p=1.0, N.t.=173 kg/ha. At 70 days after planting cv. Cardinal had about half the haulm weight of cv. Désirée. Nevertheless, both cultivars exhibited similar bulking rates. On the other hand, cv. Spunta, which had high bulking rates at the earlier stage of growth, had a marked advantage in yield production in the drier treatments (K _p=0.29−0.14; N.t.=44−12 kg/ha). The maximum leaf area indices (LAI) were obtained atK _p=1.06, N.t.=173 kg/ha and were similar for all cultivars. LAI and leaf area duration (LAD) decreased with increasing water stress. In Cardinal, Désirée, Spunta and cv. Up-to-Date there was a common linear function relating to tuber weigth and to LAD; in cv. Alpha, this function had lower values of tuber weight. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 840-E, 1983 Series.     

Some biogenetic conclusions from changes in the amount and composition of skin wax of apples during their growth and storage

Quantitative and qualitative changes in the chief wax components, isolated from Bulgarian apples (Tetovka variety) were followed up during the period of growth and storage (from August 1st to January 2nd, the following year). After saponification of the soluble in light petroleum wax part, the samples were separated into neutral and acid substances. By means of gas-liquid chromatography of the methyl esters of the isolated acids, the qualitative composition and quantitative content of the individual components in the mixture were established. Using preparative thin-layer chromatography, hydrocarbons, ketones, secondary and primary alcohols were isolated from the neutral part. The individual qualitative and quantitative composition of all these compounds were also estimated by gas-liquid chromatography. On the basis of the results obtained the following biogenetic conclusions were made: 1. The constituents of soluble wax and cutin originate from lipids synthesized in the interior part of the fruit. 2. Paraffin hydrocarbons are formed by fatty acid, especially the C₂₉ hydrocarbon is derived from the C₁₆ acid; 3. Olefines are obtained from respective primary and secondary alcohols, while the diols are derived from primary alcohols; 4. Paraffin hydrocarbons, secondary alcohols and ketones are biogenetically linked and may undergo mutual transformations.     

An artificial neural network approach to prediction of the colorimetric values of the stripped cotton fabrics

This paper presents an artificial neural network (ANN) modeling by Levenberg-Marquardt (LM) algorithm for predicting the colorimetric values of the stripped cotton fabrics dyed using commercial reactive dyes. Achieving the expected efficiency in the application of stripping process is a very important aspect for the success of the reproduction. In the study, the predictions of L* and ΔE colorimetric values of stripped cotton samples for different stripping applications by artificial neural network are reported. We set up different network structures with different number of nodes in the hidden layer, the number of inputs and MSE of results as stopping criteria in order to get the best fitting model. According to the result of the best neural network models predicting L* and ΔE, we achieved 97 % of R for both of them. We are able to predict the L* value of the stripped samples using some working parameters as inputs with only 1.2 % error. We think that our results are very promising and the predictions of L* and ΔE values of stripped samples before applying any process are possible using the ANN model set up in the study, especially for L*.     

High value triterpenic compounds from the outer barks of several Eucalyptus species cultivated in Brazil and in Portugal

The chemical composition of the lipophilic extracts of the inner and outer bark fractions of Eucalyptus grandis and Eucalyptus urograndis (E. grandis × Eucalyptus urophylla) cultivated in Brazil and Eucalyptus maidenii, cultivated in Portugal was studied by gas chromatography-mass spectrometry. The extracts were shown to be mainly composed of triterpenic compounds (along with mono and sesquiterpenes in E. maidenii) followed smaller amounts of fatty acids, fatty alcohols, and aromatic compounds.Triterpenic acids (mainly ursolic, betulinic and oleanolic acids), are particularly abundant in outer barks representing 5.2 g/kg, 5.7 g/kg and 9.3 g/kg in E. urograndis, E. grandis and E. maidenii outer barks, respectively. Although these compounds were found in considerably smaller amounts than those previously reported for Eucalyptus globulus, the total amounts of bark generated every year in South American pulp mills using E. urograndis and E. grandis, as well as the growth potential of E. maidenii plantations, the bark residues from these species are obvious candidates for the extraction of valuable triterpenic compounds.     

Potato and Human Exploration of Space: Some Observations from NASA-Sponsored Controlled Environment Studies

Future space exploration by humans will require reliable supplies of food, oxygen and clean water to sustain the expeditions. Potato is one of several crops being studied for such a “life support” role. Tests sponsored by the US National Aeronautics and Space Administration (NASA) confirmed the well-known short day tendencies for tuberisation, but also revealed that some cvs. (e.g., Norland, Denali and Russet Burbank) could tuberise well under continuous high light. Horticultural tests showed that plants grew well and tuberised readily using a nutrient film technique (NFT). CO₂ enrichment studies with potato showed typical C₃ responses in photosynthesis and yield, with maximum rates occurring near 1000 μmol mol⁻¹. The highest tuber yields from these controlled environment studies reached 19.7 kg FM m⁻² or equivalent to nearly 200 t ha⁻¹. This equated to a productivity of 38 g m⁻² DM m⁻² day⁻¹. Stand evapotranspiration (ET) rates ranged from 3.4 to 5.2 l m⁻² day⁻¹ throughout growth, while maximum ET rates for canopies could approach 10 l m⁻² day⁻¹. Harvest indices (tuber DM/total DM) typically ranged from 0.7 to 0.8, indicating that waste (inedible) biomass from potato would be less than that from many other crops. An experiment was conducted in 1995 on NASA’s Space Shuttle using excised potato leaves to study tuber formation at axillary buds during spaceflight. The results showed that tubers formed equally well in space as in the ground controls, indicating that reduced gravity should not be an impediment to tuberisation.     

Fatty Acids, Sterols, Phenols and Antioxidant Activity of Phoenix theophrasti Fruits Growing in Crete, Greece

In the present study we report the chemical composition of the Cretan Phoenix theophrasti Gr. fruits, in comparison with dates, from its close relative Phoenix dactylifera L. for their nutritional value and their potential exploitation as a source of bioactive components such as phytosterols, lipids and polyphenols. The non polar dichloromethane (CH₂Cl₂) extract of the fruits was analysed by several techniques (TLC, CC, GC and GC-MS) and was found to consist mainly from fatty acids, hydrocarbons and phytosterols. Palmitic acid was the most abundant fatty acid, 12.49% of total saponifiables, while β-sitosterol was the most prevalent phytosterol, 29.46% of total unsaponifiable lipid fraction. The polar methanolic extract was examined for its total phenolic content, by the Folin–Ciocalteu assay, as well as for its antioxidant activity through DPPH assay, in comparison with previous studies on the fruits of several Phoenix dactylifera varieties. This fraction was found to possess strong antioxidant activity despite its lower content of phenolic compounds in comparison with previously studied Phoenix dactylifera specimens.     

Characterization of a Potential Nutraceutical Ingredient: Pomegranate (Punica granatum L.) Seed Oil Unsaponifiable Fraction

The chemical fingerprinting of the unsaponifiable fraction of different Punica granatum seed oils was performed in order to evaluate their potential as a functional food ingredient. Qualitative and quantitative determinations of tocopherol, aliphatic alcohol (including policosanol), squalene, phytosterols and triterpene contents were performed by GC-MS. A high yield (3.1–4.2%) of unsaponifiable matter was obtained and consistent levels of squalene (up to 800 mg/kg) and policosanol (118–185 mg/kg) were noticed. β-sitosterol (up to 8069 mg/kg) and cycloartenol (5916–7766 mg/kg) were predominant in phytosterol and triterpene fractions, while β- and δ-tocopherol were the most abundant vitamin E forms. Some minor variations were noticed between samples. From the results obtained, it can be suggested that the seed oil of P. granatum can be considered an interesting alimentary source of substances of nutraceutical value involved in the modulation of cholesterol metabolism.     

Improving production and health of seed potato stocks in Italy

Summary When nodal explants from sprouts grown from virus-free tubers of ten cultivars were propagated on half-strength Murashige and Skoog medium, cvs Arsy, Nicola, Kennebec and Spunta grew best. Rooted plantlets, 5–8 cm tall, were transplanted from culture vessels into pots containing soil, vermiculite and sand. They were weaned by growing in a glasshouse for about three weeks. Over 90% of the plantlets survived and these were then planted in the field and protected against aphids by a double screen (a large tunnel covering four adjacent small tunnels) and chemical treatments. Prebasic seed tubers thus obtained were virus-free and production ranged from 49.9 t.ha⁻¹ (‘Monalisa’) to 27.1 t.ha⁻¹ (‘Majestic’). A survey showed that ‘elite’ (near virus-free) seed could be produced from prebasic seed by early planting and early haulm killing regardless of location, but late planting on the plains and normal planting dates on the mountains resulted in 1 to 5% virus infection levels acceptable only for certified seed.     

Residues of free and bound maleic hydrazide in potato tubers

Summary The method of Vadukul (1991) for determining maleic hydrazide (MH) was modified and gave recoveries of free MH of 89%±4%. The values recorded on individual tubers ranged from 2–14 mg kg⁻¹. Maleic hydrazide was evenly distributed throughout the tuber (peel, outer and inner flesh) but concentration increased slightly as tuber size increased. The concentration of free MH decreased from 7 to 3 mg kg⁻¹ over the storage period of 5 1/2 months. Acid hydrolysis released substantial amounts of MH particularly from older potatoes (13 mg kg⁻¹) compared with 6 mg kg⁻¹ from new potatoes, implying that free MH is gradually converted to a bound form with time after treatment. No evidence was found for the presence of a β-glucoside of MH.     

Impact of Agronomic Strategies (Seed Tuber Pre-sprouting,Cultivar Choice) to Control Late Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) on Tuber Growth and Yield in Organic Potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Crops

In order to optimize potato crop management in organic farming systems, knowledge of crop growth processes in relation to limitations and reductions by nitrogen (N) and disease is necessary. This paper examines the effect of different prevention measures (seed tuber pre-sprouting, choice of cultivars: resistance to Phytophthora infestans; earliness of tuber initiation) against disease-related constraints on yields, depending on the N-mediated growing conditions of organic potato crops. Under conditions of a relatively high N supply, accelerating the early development and tuber initiation of potato crops by seed tuber pre-sprouting (yield increase of c. 18–23%) or the selective choice of cultivars with an earlier tuber initiation (yield increase of c. 0–21%) are the most effective strategies in combating late blight. They bring forward the crop development c. 7–10 days, escaping the negative impact of the fungus on tuber growth. Under conditions of a relatively low N supply, these strategies do not affect final tuber yield. The reason for the differences of the effect depending on N supply of the crops is, that the lower the N supply, the shorter the period of time over which tuber growth takes place, independent of whether P. infestans becomes severe or not. Tuber growth of organic crops low in N has mostly ceased by the time late blight becomes potentially important for limiting yield, with the consequence that preventative measures against P. infestans are meaningless. Surprisingly, the level of cultivar haulm resistance to late blight did not affect tuber yields in years with an early and strong late blight development. Probably, the positive effect of a longer resistance to the fungus (c. 1 week) was counterbalanced by a later tuber initiation (also c. 1 week). In years with a moderate late blight incidence, less susceptible cultivars were able to produce higher tuber yields on fields with a lower N availability (c. 17–20%), probably due to higher N use efficiency and a better match of N mineralization and N uptake. Under conditions of a relatively high N supply, the tested cultivars with a higher haulm resistance to late blight were not able to improve tuber yields.     

Einfluss von Lagerung und Sorte auf die Verteilung der Glykoalkaloide in der Kartoffelknolle

Zusammenfassung Fünf Speisekartoffelsorten wurden w?hrend einer sechsmonatigen Lagerung fünfmal auf α-Solanin und α-Chaconin untersucht. Es wurden vier Gewebebereiche der Knolle getrennt überprüft. Der Gesamtglykoalkaloidgehalt betrug im Augenbereich 164, in der restlichen Schale 101 und in der Gef?ssbündelzone mit ?usserem Speichergewebe 8mg/100g. Trockensubstanz. Im restlichen Innenk?rper waren nur noch Spuren (0.164mg/100g TS) nachzuweisen. Zwischen den Sorten und diesen Gewebepartien traten statistisch gesicherte Wechselwirkungen auf, die im wesentlichen von einer Sorte verursacht wurden. W?hrend der Lagerung sind die Alkaloidgehalte leicht, aber statistisch nicht gesichert gesunken. α-Solanin und α-Chaconin kamen generell im Verh?ltnis von etwa 1∶1.5vor; die Korrelation zwischen beiden Formen ist sehr eng (r=0.865). Bezogen auf die gesamte Knolle lagen die Gesamtglykoalkaloide je nach Sorte zwischen 2.4 und 8mg/100g Frischsubstanz und damit im gesundheitlich unbedenklichen Bereich.

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Summary Five table potato cultivars (Erna, Granola, Gusto, Ulse, Margit) from the same source were examined for their content of α-solanine and α-chaconine during a sixmonths storage period. For the testing and subsequent analysis the tubers were dissected into four kinds of tissues: eye-zone, peel, vascular bundle region, medulla. The total glycoalkaloid content (TGA) in the total tuber mass varied between 2.4 and 8mg per 100g fresh matter depending on cultivar (Fig. 1). Despite significant differences between cultivars (Table 1), all potato cultivars remained within the safe range during the entire storage period. Remarkable differences in TGA per 100g dry matter could be noted in the tuber parts. For the eye-zones a TGA of 164mg was found; the peel region showed 101mg and the vascular bundle zone 8mg. The medulla of the tubers contained only traces of TGA (0.164mg/100g dry matter, Fig. 2). The statistical analysis only revealed significant interactions between cultivars and tuber parts (Table 1), mainly caused by the cultivar Gusto which showed higher contents of α-solanine and α-chaconine in its vascular bundle regions (Figs 3–5). The ratio between amounts of α-solanine and α-chaconine was approximately 1∶1.5, and after eliminating effects of cultivar, storage and tuber parts, the correlation coefficient between amounts was 0.865. This close correlation can be used for breeding. The non-significant, slightly negative effect of the six-months storage period on alkaloid content was noteworthy. It is assumed that only after long storage periods or through inappropriate storage (sprouting of tubers) a significantly higher glycoalkaloid content may be expected.

     

Effect of leaf age on photosynthesis,carbon transport and carbon allocation in potato plants

Summary Photosynthetic characteristics, carbon allocation and partitioning of newly-fixed¹⁴C among the various carbohydrate fractions were studied in leaves of potato plants (Solanum tuberosum L. cv. Désirée) of different ages. The higher photosynthetic rate of young leaves was associated with higher levels of starch and reducing sugars. After 24 hours, in young leaves the fixed¹⁴C had been partitioned mainly to the residue and starch fractions, while in older leaves there was an increase in partitioning to sucrose and reducing sugars. The activities of the various sink organs were found to be dependent upon their distance from the source leaf. Tuber activity, however, was affected similarly by all fully expanded leaves. Although young fully expanded leaves are thought to be the major source of assimilates for tuber growth, it seems that a vast potential for contributing to plant productivity and tuber yield lies also in the older leaves, which translocate most of their photoassimilates to the tubers.     

Métabolisme des lipides dans le tubercule de pomme de terre (Solanum tuberosum L.). 1. Evolution des lipides au cours de la conservation des tubercules

Résumé Le métabolisme des lipides des tubercules de pomme de terre au cours de leur conservation à différentes températures ou sous des atmosphères de composition variée, a été étudié, et les modifications induites pour un traitement à la ‘rindite’ mélange synergique connu pour lever le repos végétatif, ont été examinées. Une augmentation appréciable de la teneur en acides gras totaux dans la pulpe a été enregistrée à 0,4,10 et 18°C, dans les premiers mois de conservation. Une chute de la teneur en acides gras totaux de la pulpe a été notée au cours de l'entreposage dans les atmosphères enrichies en CO₂ (20%) ou en O₂ (37%). La ‘rindite’ provoque une synthèse accrue de lipides, surtout dans la période de croissance active des germes.

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Summary The potato tuber is low in lipids, which form only 0.1% of the fresh weight of the tissue. Of the tuber lipids, 60–80% are unsaturated fatty acids, linoleic acid predominating (Tables 1 and 2). It has been observed that there is an appreciable increase in the total fatty acid content of the tuber flesh during storage at 10°C and 18°C. This increase occurs mainly during the phase of rapid sprout growth, thus fairly long after the tubers have broken dormancy. The increase continues in the case of tubers stored at 10°C, up to the stage of incubation or tuberisation of the sprouts. The opposite occurs in tubers stored at 18°C; total fatty acids decrease during this period. This is probably due to a physiological imbalance of the cells arising from a heavy loss of water by the tubers (Fig. 3). With regard to tubers stored at low temperature (0°C and 4°C), it has been noted that the total fatty acid content increases (accompanied by an increase in the degree of unsaturation of the lipids). This increase is followed by a marked fall during the final months of storage. This could be accounted for either by a disturbance of cellular function at low temperature or by a progressive degradation of the lipids by lipases (Fig. 3). Study of tuber storage in different atmospheres gave interesting results. The mixture enriched with oxygen (37%) partially inhibits sprout extension and apical dominance; air containing 20% CO₂ totally inhibits sprouting and leads to the death of the tuber. On the other hand, air containing 6% CO₂ accelerates sprouting, leads to earlier tuberisation of the stolons and increases the number of tubers formed per sprout. Such a result could be of interest in practical agronomy (Fig. 4). It was observed that, with the onset of sprouting, there is an increase in total fatty acids in the flesh of tubers stored in air enriched with CO₂ (6%). This is followed by a decrease. In the case of air containing 20% CO₂, even if the total fatty acid content remains more or less static for a period, a sharp fall follows. On the other hand, the flesh of tubers stored in air and in an atmosphere low in oxygen shows an appreciable increase in total fatty acid content; whereas in air enriched with oxygen (O₂:37%) there is a fall (Fig. 5). ‘Rindite’, a compound which breaks dormancy, has a marked effect on the formation of fatty acids in the tuber parenchyma. It leads to a progressive synthesis of lipids. particularly during the period of active sprout growth. This increase in the total fatty acid content affects particularly the unsaturated fatty acids and also palmitic acid. This increase in lipid synthesis could be due to a general increase in carbon metabolism by the ‘rindite’ (Fig. 7 and 8).

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Zusammenfassung Die Kartoffelknolle ist ein an Lipiden armes pflanzliches Organ, stellen diese Verbindungen doch nur ungef?hr 0,1% der Frischsubstanz dar. Die wesentlichen Lipide der Knolle sind reich an unges?ttigten Fetts?uren (60–80%), wobei die Linols?ure vorherrscht (Tabellen 1 und 2). Man hat festgestellt, dass im Verlauf der Lagerung bei 10°C und 18°C eine nennenswerte Erh?hung im Gesamtgehalt an Fetts?uren im Knollenfleisch erzeugt wird. Diese Erh?hung findet vor allem w?hrend der raschen Wachstumsphase der Keime statt, also ziemlich lange Zeit nach Ende der Keimruhe der Knollen. Diese Erh?hung setzt sich fort bei den bei 10°C gehaltenen Knollen bis zum Stadium der Inkubation oder der beginnenden Knollenbildung. Dagegen ist bei den bei 18°C aufbewahrten Knollen eine Verminderung der Gesamtmenge der Fetts?uren w?hrend dieser Periode festzustellen; diese Tatsache ist wahrscheinlich auf ein physiologisches Ungleichgewicht der Zellen zurückzuführen, das von einem starken Wasserverlust der Knollen herrührt (Abb. 3). Was die Knollen betrifft, die bei niedriger Temperatur aufbewahrt wurden (0°C und 4°C). so hat man ein Ansteigen des Gesamtgehaltes an Fetts?uren bemerkt (begleitet von einer Abnahme des Grades der S?ttigung der Lipide). Dieser Steigerung folgt ein starker Abfall w?hrend des letzten Monates der Lagerung. Für diese Tatsache kann eine Erkl?rung gefunden werden, sei es in der Unregelm?ssigkeit des Funktionierens der Zellen bei tiefen Temperaturen, sei es in einer wachsenden Degradation der Lipide durch die Lipasen (Abb. 3). Das Studium der Lagerung von Kartoffelknollen unter verschiedenen Atmosph?ren hat interessante Ergebnisse gebracht. Das mit Sauerstoff angereicherte Gemisch (37%) hemmte teilweise das L?ngenwachstum der Keime und die apikale Dominanz; die mit 20% CO₂ belastete Luft verhindert die Keimung vollst?ndig und führt zum Tod der Knolle. Dagegen beschleunigt die mit 6% CO₂ belastete Luft die Keimung, f?rdert die frühere Knollenbildung der Stolonen und erzeugt pro Trieb eine gr?ssere Anzahl von Tochterknollen. Ein solches Ergebnis k?nnte für die landwirtschaftlich Praxis von Interesse sein. Man hat zu Beginn der Keimung ein Ansteigen des Gesamtgehaltes an Fetts?uren im Fleisch von Knollen, die in mit 6% CO₂ angereicherter Luft gelagert wurden, festgestellt. Auf diesen Zuwachs folgt eine Abnahme. Wenn die Luft mit 20% CO₂ angereichert war, ging der Gesamtgehalt an Fetts?uren, wenn er w?hrend einer gewissen Zeit auch beinahe gleich blieb, nachher doch deutlich zurück. Dagegen stieg in nennenswerter Weise der Gesamtgehalt an Fetts?uren im Fleisch von Knollen, die bei normaler Luftzusammensetzung und in sauerstoffarmer Atmosph?re gelagert wurden; in mit Sauerstoff angereicherter Luft (O₂:37%) f?llt der Gehalt an diesen S?uren stark (Abb. 5). Die Wirkung der ‘Rindite’, einem Mittel zur Brechung der Keimruhe, auf die Weiterentwick lung der Fetts?uren des Parenchyms der Kartoffelknolle ist sehr deutlich. Sie bewirkt eine wachsende Synthese von Lipiden, besonders in der aktiven Wachstumsperiode der Keime. Dieses Ansteigen des Gesamtgehaltes an Fetts?uren betrifft besonders die unges?ttigten Fetts?uren und auch die Palmitins?ure. Diese Zunahme der Lipid-Synthese k?nnte auf eine allgemeine, durch ‘Rindite’ hervorgerufene Beschleunigung des Kohlenstoff-Stoffwechsels zurückgeführt werden (Abb. 7 und 8).