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     

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     

Influence of Polyamines on the Long Distance Transport of K (86Rb) in Potato Cuttings (Solarium tuberosum cv. Sirtema)-- Comparative Study with some Phytohormones

Plantlets of Solanum tuberosum L. cv. Sirtema were used to studythe regulation of the long-distance transport of potassium.The effects of polyamines and two plant hormones, abscisic acid(ABA) and benzyladenine (BA), on this process were investigated.Foliar sprays of putrescine or BA increased the transport of(K) ⁸⁶Rb to the upper part of the plant. In contrast, spermidinetreatment enhanced the translocation into the growing tuber,as did ABA. These specific effects were partially correlatedto the distribution of endogenous polyamines within the plant.Spermidine was the predominant polyamine in the tuber whileputrescine was as abundant as spermidine in the leaves. Thetotal amount of putrescine, spermidine and spermine decreasedwith the physiological age of the leaves and tubers. Moreover,from heat-girdling experiments, it was shown that the polyamine,¹⁴C-putrescine, supplied to a leaf, was transported via thephloem. It is suggested that polyamines like phytohormones havea regulatory role in long-distance transport. Key words: Hormone-directed-transport, K, phloem, polyamines, potato, ¹⁴C-putrescine transport     

One-Leaf Cuttings as a Model to Study Second Growth in the Potato (Solanum tuberosum) Plant

Second growth is an important physiological disorder of thepotato (Solanum tuberosum L.) plant. A model system to studysecond growth was developed using one-leaf cuttings. Photoperiod,temperature, decapitation and leaf removal treatments were carriedout on the plants from which the cuttings were taken and onthe cuttings themselves. Tuberized, one-leaf cuttings takenfrom moderately-induced plants and exposed to 35 °C afterleaf removal showed 95% second growth within 10 d after treatmentinitiation. Conditions that promoted second growth also reducedstarch and dry-matter content, even in tubers that did not developsecond growth. Cuttings, second growth, potato, Solanum tuberosum L, cv, Bintje, Solanum tuberosum L. cv., Désirée, Solanum tuberosum L. cv., Russet Burbank, tuberization, starch content, dry-matter, heat, photoperiod, decapitation, leaf removal     

Effect of High Temperature on Photosynthesis in Potatoes

The effect of high temperatures on the rate of photosynthesiswas studied in several potato varieties. Temperatures of upto 38 °C did not cause a reduction in the photosynthesisof plants that had been grown at these temperatures for longperiods prior to measurement. Higher temperatures of 40–42°C, or the transfer of plants from daytime temperature regimesof 22 °C to 32 °C, caused a reduction in net photosynthesis.This reduction was found to be essentially mesophyllic in origin.High temperature was found to be associated with a decreasein stomatal resistance, an increase in transpiration, and alarger difference between air and leaf temperatures. Dark respirationrates and compensation points for CO₂ concentration were alsogreater at the high temperatures. It was concluded that thepotato crop can be adopted to grow and have an adequate rateof photosynthesis even at relatively high temperatures. Source-sinkrelationships, which were modified by the later formation oftubers at higher temperatures, did not affect photosynthesisin this study. Varietal differences in resistance to heat stresswere observed, with the clone Cl-884 showing a more efficientcapacity for photosynthesis at temperatures up to 40 °Cthan many commonly grown varieties. High temperature, photosynthesis, potato, Solanum tuberosum L     

A Preliminary Study on the Effects of Nitrogen Supply on the Growth In Vitro of Nine Potato Genotypes (Solanum spp)

Cultures of nine potato genotypes (seven Solanum tuberosum oneS. sparsipilum and one S. oplocense genotypes) were examinedfor their response to growing on medium containing either 60mol m^–3, 40 mol m^–3 or 20 mol m^–3 nitrogen.Genotypes differed in their response to nitrogen. Reducing thenitrogen regime tended to produce taller plants with longerinternodes, shoots had larger leaves but contained less chlorophyll.No change in fresh weight or number of nodes was observed. Genotypex nitrogen interactions were significant for chlorophyll content,shoot length and internode length. Results suggest that thechanges observed were as a result of changes in the total nitrogenlevel rather than changes in the ammonium : nitrate ratio. Thisstudy suggests that for certain potato genotypes, nitrogen levelsin MS medium are too high for producing desirable microplantsin terms of leaf area and shoot length Key words: Solanum tuberosum, S. sparsipilum, S. oplocense, micropropagation, morphogenesis     

Stomatal Response of some Cultivated and Wild Tuber-bearing Potatoes in Warm Tropics as Influenced by Water Deficits

Leaf resistances of 14 cultivated potato genotypes (Solanumspp) and three tuber-bearing wild Solanum species were comparedwhen plants were grown under water stress at two tropical sitesFactors investigated were diurnal changes in leaf resistance,the effect of plant age, transient drought versus well-wateredconditions of potted and field-grown plants These measurementswere carried out in order to determine the stomatal behaviourof tuber-bearing genotypes and species Significant genotypic differences in leaf resistances were notedwithin the cultivated genotypes All genotypes had higher resistanceswhen water-stressed, but LT-7 appeared to have the lowest leafresistances Genetic differences in stomatal behaviour of tuber-bearingSolanum species were confirmed Abaxial stomatal resistancesof water-stressed plants of the species ranged between 1 74and 13 8 s cm^–1 Stomata of S chacoense were less affectedby drought (three-fold) than S tuberosum (four-fold) The greatesteffect was on S jungasense (five-fold) and on S raphanifoliumThese data show that stomata behaviour among tuber-bearing Solanumspecies is sufficiently different to warrant investigationsof drought-resistance in potato species under dry hot conditions Solanum tuberosum L., Solanum raphanifolium, Solanum chacoense, Solanum jungasense, leaf resistance     

Tuberization in Potato at High Temperatures: Responses to Gibberellin and Growth inhibitors

The responses of potato plants (Solanum tuberosum L., cv. Sebago)to high temperatures (32 day/28 C night or 32/18 °C) andgibberellin are similar, in that they promote haulm growth andsuppress tuber production, whereas low temperatures (22/18 °C)abscisic acid and CCC have the opposite effect, promoting tuberproduction and reducing the growth of the haulms. The inhibitoryeffect of the high temperatures on tuber production, under aphotoperiod of 14 h, was almost completely reversed in theseexperiments by the application of CCC, and partly reversed byABA. Single-leaf cuttings from plants grown at the various temperaturesand chemical treatments responded in the same way as the wholeplant. It is suggested that both haulm growth and tuber initiationare influenced by a common hormonal control, and that temperatureexerts its influence by altering the balance between the levelsof endogenous gibberellins and inhibitors. These substancesapparently act directly on the stolon tip, rather than throughtheir general influence on haulm growth. Solanum tuberosum L., potato, tuberization, temperature response, gibberellin, abscisic acid, 2-chloroethyltrimethylammonium chloride (CCC)     

Effects of High Air and Soil Temperature Stress on Growth and Tuberization in Solanum tuberosum

Potato plants (Solanum tuberosum L.) were grown at differentair and soil temperatures to determine the effects of high-temperaturestress on root, tuber, and shoot growth. Cooling the soil (17–27C) at high air temperatures (30–40 C) relieved noneof the visible symptoms of heat stress on shoot growth; norwas the degree of induction to tuberize in leaves increased,as reflected in tuberization of leaf-bud cuttings. Heating thesoil (27–35 C) at cool (17–27 C) air temperatureshad no apparent detrimental effect on shoot growth or inductionof leaves to tuberize. However, in each case hot soil largelyeliminated tuber development. In one experiment stolons grewup out of the hot soil and formed aerial tubers upon reachingthe cool air. When leaf-bud cuttings from induced plants wereused as a model system, high soil temperatures inhibited tuberdevelopment from the buried leaf buds, in the absence of anyroot growth. Apparently the induction of leaves to tuberizeis affected principally by air rather than soil temperature,but expression of the signal to tuberize can be blocked by highsoil temperature. Solanum tuberosum L., potato, temperature stress, soil temperature, tuberization     

Tuberization in Potato at High Temperatures: interaction between Shoot and Root Temperatures

Tuber formation in intact potato plants (Solanum tuberosum L.cv. Sebago) was reduced by high shoot or root temperatures andstrongly inhibited when both were high. When both the shootand root temperatures were high, disbudding strongly promotedtuberization. There was a smaller increase with warm roots andcool shoots, but no response with warm shoots and cool roots.When both the shoots and roots were cool, disbudding reducedtuberization. Exogenous GA₃, effectively substituted for thebuds at high temperatures, completely preventing tuberization.In apical cuttings, removal of the terminal bud, but not theroots, reduced the inhibitory effects of high temperatures ontuberization. The experiment indicates that tuber productionmay be controlled by at least three factors: a promoter, whichis not assimilate, produced by the buds at cool temperatures;an inhibitor, derived from the buds, but dependent on warm roottemperatures for its formation; and a second inhibitor derivedfrom the mature leaves and produced in response to warm shoottemperatures. Solanum tuberosumL, potato, tuberization, temperature, disbudding, gibberellic acid     

Effect of Temperature on Carbohydrate Metabolism in Potato Plants

The effect of temperature on partitioning of newly fixed ¹⁴Cbetween the various carbohydrate fractions was studied in differentplant organs of three potato varieties. Incorporation of ¹⁴Cinto starch in the tubers was reduced at high temperatures,but the amount of labelled sucrose increased. In all varietiesthe incorporation of ¹⁴C into the cell wall components in theapex of the plant and in the stem, as well as its incorporationinto starch in the stem, was increased at high temperatures.The variety Norchip, which was found to be less sensitive tohigh temperature as indicated by carbon translocation to thetubers, was found to be less affected also in terms of ¹⁴C incorporationinto starch in the tubers. We suggest that high temperatureaffects carbon metabolism in the various plant organs and theresulting changes are associated with the change in the partitioningof assimilates between these organs.     

Pinitol occurrence in soybean plants as affected by temperature and plant growth regulators

Unsuitable temperatures are frequently encountered by soybean(Glycine max L. Merr.) plants grown in the field. Certain polyolshave been reported to protect plants from high temperature orfrost damage. Controlled environment studies were conductedto investigate the effect of stressful temperature regimes onthe content of pinitol (3-O-methyl-D-chiro-inositol) in soybeanplants. Hydroponically-grown soybean plants were subjected tohigh (35/30 C) or low (15/10 C) day/night temperature stresses,and pinitol content in different plant parts was determinedusing high performance liquid chromatography (HPLC). A syntheticplant growth regulator, PGR-IV, was foliarly applied to theplants to evaluate its effect on pinitol content in differentplant components. Uniformly-labelled ¹⁴C-glucose was fed intothe leaves via the transpiration stream, and the effects ofhigh temperature and EXP-S1089, another synthetic plant growthregulator, on the incorporation of ¹⁴C-glucose into pinitolwas evaluated using HPLC separation and scintillation spectrometry.High-temperature stress significantly increased plant pinitolcontent and the incorporation of ¹⁴C-glucose into pinitol, butdecreased the content of sucrose, glucose and fructose. Underlow-temperature stress, there was hardly any change in pinitolcontent, but a drastic increase in soluble sugars. PGR-IV enhancedpinitol translocation from leaves to stems and roots, whileEXP-S1089 increased pinitol/sucrose ratio. Accumulation of pinitolmay be an adjustment mechanism of the plant to reduce high-temperaturedamage, but not low-temperature injuries. Key words: Pinitol, soybean, temperature, plant growth regulator     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 1. Leaf Appearance, Expansion Growth, Life Spans of Leaves and Stem Branching

Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlledglasshouse to collect data on the rate of leaf apearance, leafexpansion, apical lateral branching and active life spans ofleaves The treatments consisted of three rates of nitrogen supply,i e the NI treatment with 2 5 g N per pot and the N2 and N3treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d^–1(one leaf per 28 °C d) and was negligibly affected by nitrogensupply The rate of leaf expansion was related to leaf numberand nitrogen supply The areas of mature leaves increased withleaf number on the main stem to reach a maximum for leaf numbers12–14, and declined for higher leaf numbers Leaves onapical lateral branches declined in mature area with increasein leaf number The expansion rate of leaves was the dominantfactor that determined the mature leaf area, irrespective ofleaf number and nitrogen treatment The smallest leaves wereobserved at the lowest rate of nitrogen supply Nitrogen promotedapical branching and hence the total number of leaves that appearedon a plant The proportion of total leaf area contributed byleaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearanceand yellowing of the leaf, showed a similar relation to leafnumber as mature leaf area, at least in qualitative terms Leavesof the N3 treatment showed systematically longer life spansthan leaves of the NI and N2 treatment in the order of 3 weeksThe number of main stem leaves was not affected by nitrogensupply Potato, Solanum tuberosum L, leaf development, leaf extension, plant structure, nitrogen nutrition     

Variation in 14C Partitioning in the Tips of Growing Stolons of Potato (Solanum tuberosum L.)

¹⁴C partitioning was examined in growing stolons of field-grownpotato (Solanum tuberosum L.) cv. Maris Piper. Considerablevariation was evident on single plants and on a fresh weightbasis many stolon tips, which showed no signs of sub-apicalswelling, had higher specific activities (cpm g^–1 f. wt)of ¹⁴C in both ethanol soluble and insoluble forms than larger,visibly tuberized stolons. Furthermore, many tips of low freshweight had a higher insoluble to soluble ¹⁴C ratio than visiblytuberized stolons suggesting greater efficiency of conversionof soluble ¹⁴C to insoluble ¹⁴C in the smaller stolons. Theresults suggest that the onset of visible ‘tuberization’,namely the sub-apical swelling of the stolon, is preceded byincreased soluble carbon accumulation at the stolon tip togetherwith an increase in the conversion of soluble to insoluble formsof carbon. Tuberization, ¹⁴C, stolon tip     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: I. RELATIONSHIP BETWEEN TUBER GROWTH RATE AND ENZYME ACTIVITIES OF THE STARCH METABOLISM

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. Cooling (+8°C) of individualtubers decreased their growth rates and increased the growthrates of non-cooled tubers of the same plant. The carbohydrateconcentration in non-cooled and cooled tubers did not differsignificantly, but ¹⁴C-import from labelled photosynthate waslower in cooled than in non-cooled tubers. The markedly lowerconversion rate of ethanol-soluble ¹⁴C to starch in cooled,in comparison to non-cooled tubers, was not associated withsignificant differences in the in vitro activities of starchsynthase, ADPG-pyrophosphorylase and starch phosphorylase understandard assay conditions (+30°C). However, the Q₁₀-valuesof the enzymes differed in vitro in the temperature range between30°C and 8°C, leading to a marked decrease in the activityratio of ADPG-pyrophosphorylase/starch phosphorylase in cooledtubers. In tubers differing in growth rates without manipulation, 14d after tuber initiation significant positive correlations werefound between ¹⁴C-concentration of tuber tissue and the in vitroactivities of starch synthase and ADPG-pyrophosphorylase anda significant negative correlation between ¹⁴C-concentrationand starch phosphorylase. In contrast, in tubers which wereanalysed 5 d after initiation, there were only small differencesbetween tubers in growth rate, ¹⁴C import and the activity ratioADPG-pyrophosphorylase/starch phosphorylase. From various directand indirect evidence it is concluded that the growth rate ofindividual tubers, and thus the sink strength, is at least inpart controlled by the activity of starch synthesizing enzymes. Key words: Potato tuber, cooling, starch synthesizing enzymes     

Potato Seed-tuber Age Affects Mobilization of Carbohydrate Reserves During Plant Establishment

During the early stages of growth, developing sprouts rely heavilyupon tuber carbohydrate reserves. Strong sprouts are producedfrom young potato (Solaman tuberosum L.) seed-tubers, whereastubers of advanced physiological age produce sprouts with reducedvigour. Single-eye seedcores from 7- and 19-month-old seed-tuberswere sprouted in order to study the effect of tuber age on carbohydratereserve mobilization. Following 24 d of growth, the same amountof total shoot dry matter was produced from both ages of seedcores.However, d. wt of individual shoots from older seedcores was93 % lower than that from younger cores, reflecting a significantloss in apical dominance with age. Furthermore, core d. wt lossper unit gain in plant d. wt was greater from 19-month-old seedcores,indicating an age-related decrease in the efficiency of reservemobilization over the growth interval. During sprouting, ratesof starch hydrolysis and subsequent increases in total solublecarbohydrates were similar for both tuber ages. Reducing sugars(mg g d. wt^–1) accumulated faster in older than in youngercores; non-reducing sugars (mainly sucrose) decreased 53% inolder seedcores over the 24 d growth interval. Non-reducingsugar content (mg g d. wt^–1, mg core^–1) of youngercores remained constant. The results suggest that older coresare either less efficient at converting glucose to sucrose (themain translocatable carbohydrate in potatoes) or have higherrates of sucrose hydrolysis (e.g. increased invertase activity)compared with younger tuber tissues during sprouting Potatoes (Solanum tuberosum L.), seed-tuber age, carbohydrate mobilization, plant growth potential     

Nucleotide ratios and quantitative RNA changes in potato plants elicited by photoperiod and temperature

The nucleotide composition of potato plants, Solanum tuberosumL., grown under four environmental regimes was studied. Althoughthere were marked quantitative differences in RNA followingthe temperature and photoperiod treatments as previously observed,nucleotide composition of all types of RNA did not change appreciably. ¹ Scientific Journal Series Article Number 7642 of the MinnesotaAgricultural Experiment Station. (Received August 23, 1971; )     

Effects of the Temperature of the Rooting Zone on the Growth and Development of Roots of Potato (Solanum tuberosum)

In solution culture the effect of optimal (20 °C) and supra-optimal(30 °C) root-zone temperatures on root growth and root morphologyof six potato clones (Solanum tuberosum L spp) was studied Growthwas compared with sweet potato (Ipomoea batatas L) and cassava(Manihot esculenta Crantz) Significant genotypical differencesin the responses of potato roots to supra-optimal temperatureswere observed, indicating the potential for selecting heat tolerantpotato clones In both heat tolerant and heat sensitive clones,the size of the root system was reduced by supra-optimal root-zonetemperature This was principally a result of decreased numberand length of lateral roots The first symptom of heat damagewas a reduction in the rate of cell division, followed by cessationof root elongation Bending of the apical root-zone togetherwith the formation of root hairs on the inner (concave) andlateral roots on the outer (convex) side were other symptoms,these coincided with the loss of starch granules in the root-cap Potato, genotypical differences, root morphology, root growth, temperature, Solanum tuberosum L     

Tuberization in Potato at High Temperatures: Interaction between Temperature and Irradiance

Potato plants (Solanum tuberosum L., cv. Sebago) responded similarlyto high temperatures and low irradiance by diverting dry matterto the shoots rather than the tubers, and changes were notedin a range of morphological characteristics. It is proposedthat the effect of both high temperature and low irradianceis brought about by the increased production of a growth substance,possibly gibberellin, which inhibits tuber formation, and thattuber yield is determined by the balance between temperatureand irradiance. Solanum tuberosum L., potato, tuberization, temperature, irradiance, gibberellin