Effects of Some Growth Regulators on Polyamine Biosynthetic Enzymes in Etiolated Pea Seedlings

This study was designed to examine possible links between polyaminebiosynthesis and effects of growth regulatory compounds. Anauxin (IAA), a cytokinin [benzyladenine; benzylaminopurine (BAP)],an ethylene source (ethephon) and abscisic acid (ABA) were individuallyapplied to terminal buds of excised etiolated or red light (R)-exposedpea epicotyls. Effects were noted on bud fresh weight and onthe two main enzymes of putrescine biosynthesis, arginine decarboxylase(ADC; EC 4.1.1.19 [EC] ) and ornithine decarboxylase (ODC; EC 4.1.1.17 [EC] ).As previously reported [Dai and Galston (1981) Plant Physiol.67: 266], both bud growth and ADC activity are increased byR light. In such buds, ADC is raised further by 1–10 µMBAP or ABA and inhibited by 1–10 µM IAA or ethylene(50 mg/liter or more of ethephon). In all cases, effects ofR-irradiation plus 1 mM growth regulators on ODC activity wasthe inverse of their effects on ADC, indicating independentcontrol of these pathways. These results do not support theview that putrescine biosynthetic activity is correlated withgrowth in etiolated pea seedlings. ¹Supported by a grant from NSF to A.W.G. ²Supported by a grant from the Turkish Government. Permanentaddress: Department of General Botany, University of Istanbul,S?leymaniye, Istanbul, Turkey. ³On sabbatical leave from the Department of Horticulture, HebrewUniversity of Jerusalem, Rehovot, Israel. (Received September 22, 1983; Accepted February 28, 1984)     

Polyamine Biosynthetic Enzymes and the Effect of their Inhibition on the Growth of Some Phytopathogenic Fungi

Studies were conducted on the distribution of two polyaminebiosynthetic enzymes, or-nithine decarboxylase (ODC) and argininedecarboxylase (ADC), and the effect of their inhibitors on growthand polyamine biosynthesis in four phytopathogenic fungi, namely,Helminthosporium maydis, H. carbonum, Fusarium oxysporum f.sp. lycopersici and Ceratocystis ulmi. Three species had highlevel of ODC as compared to ADC activity; in C. ulmi on theother hand, ADC was predominant with very little or no ODC activity.DL--difluoromethylornithine (DFMO) significantly inhibited ODCactivity in all species in vitro with little effect on ADC activity.ADC in all cases was inhibited by DL--difluoromethylarginine(DFMA) but not by DFMO. Mycelial growth of all fungi was inhibitedby 1 to 5 mM concentrations of either DFMO or DFMA within twodays except in H. maydis which remained unaffected even by thehighest concentration (5 mM) of DFMA. In general, the inhibitionwas more pronounced with DFMO as compared to DFMA. Putrescinecompletely reversed the inhibitory effects of DFMO and DFMAin all species. Among the polyamines, spermidine was predominantin all fungi. The cellular concentrations of putrescine andspermidine were considerably lower in the presence of eitherof the inhibitors while spermine levels were higher than thecontrol. ¹Scientific contribution number 1529 from the New HampshireAgricultural Experiment Station. (Received November 25, 1988; Accepted April 11, 1989)     

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     

Effect of shade treatment on biosynthesis of catechins in tea plants

When tea plants were shaded with black lawn cloth for severaldays in the field, the accumulations of (—)-epicatechin,(—)-epicatechin-3-gallate, (—)-epigallocatechinand (—)-epigallocatechin-3-gallate decreased in newlydeveloping tea shoots. Radioactive tracer studies showed thatthe conversions of glucose-U-¹⁴C, shikimic acid-G-¹⁴C and phenylalanine-U-¹⁴Cinto (—)-epicatechin and (—)-epigallocatechin moietieswere depressed by the shade treatment for tea plants but theincorporation of trans-cinnamic acid-3-¹⁴C was not affected.The treatment was found to have no significant effect on theactivities of phospho-2-keto-3-deoxy-heptonate. aldolase (EC.4.1.2.15 [EC] ), 3-dehydroquinate synthase (EC. 4.6.1.3 [EC] ), 3-dehydroquinatedehydratase (EC. 4.2.1.10 [EC] ), shikimate dehydrogenase (EC. 1.1.1.25 [EC] )and trans-cinnamate 4-monooxygenase (EC. 1.14.13.11 [EC] ) in theshoots, whereas the activity of phenylalanine ammonia-lyase(EC. 4.3.1.5 [EC] ) clearly decreased. (Received March 17, 1980; )     

Pyrimidine Nucleotide Biosynthesis in Vinca rosea Cells: Changes in the Activity of the de novo and Salvage Pathways during Growth in a Suspension Culture

Marked changes in the activity of the ‘de novo’and ‘salvage’ pathways of pyrimidine biosynthesisduring growth of Vinca rosea cells in a batch suspension culturewere observed. The activity of these pathways was investigated by determiningthe contribution of ¹⁴C of [2-¹⁴Cluracil, 12-¹⁴Cluridine. and[6-¹⁴Clorotate to the cell constituents and by measuring theactivity of the several enzymes of these pathways. During the lag phase of the culture, ‘uracil-’ and‘uridine-salvage’ pathways made the predominantcontribution to nucleotide biosynthesis, but, following theinitiation of cell division, the ‘de novo’ pathwayfor nucleotide biosynthesis operated appreciably. These results suggest that nucleotide synthesis during cellgrowth in a suspension culture can be divided into two stages:a ‘turnover stage’, during the lag phase of cellgrowth, and a ‘true biosynthetic stage’, which isinitiated in the cell division phase.     

Polyamine Biosynthesis during Vegetative and Floral Bud Differentiation in Thin Layer Tobacco Tissue Cultures

Levels of putrescine, spermidine and spermine increase whenvegetative or floral buds form in cultures derived from surfaceexplants of inflorescences of Nicotiana tabacum L. cv. Wisconsin-38.Concomitantly, the activity of arginine decarboxylase (ADC)rises and that of ornithine decarboxylase (ODC) declines. DL--Difluoromethylarginine(DFMA), a specific suicide inhibitor of ADC, inhibits bud initiation,while DL--difluoromethylornithine (DFMO), the analogous suicideinhibitor of ODC, does not. On the other hand, DFMO inhibitsthe subsequent development of newly regenerated floral buds,while DFMA does not. It thus appears that polyamines derivedthrough ADC may be involved in bud initiation, while polyaminesderived through ODC are required for subsequent growth and developmentof such buds. Especially large increases of spermidine are associatedwith floral bud differentiation, indicating a possible specialmorphogenetic role for that polyamine. ¹Present address: Laboratori de Fisiologia Vegetal, Facultadde Farmacia, Universitat de Barcelona, 08028 Barcelona, Spain (Received April 25, 1988; Accepted August 12, 1988)     

Metabolism of (--)-kaurene-3H and (--)-kaurenol-3H during the photoperiodic floral induction in Pharbitis nil

(—)-Kaurene-U-³H was metabolized in seedlings of Pharbitisnil, a short-day plant, to labeled ( — )-kaurenol, ( —)-kaurenal, ( — )-kaurenoic acid, and unidentified polarsubstances, in this sequence. No significant effect of photoperiodicfloral induction upon the metabolism of ( — )-kaurene-U-³Hor ( — )-kaurenol-U-³H was observed, which suggests that( — )-kaurene metabolism is not involved in photoperiodicfloral induction ¹This work was supported in part by grants from the Ministryof Education. (Received September 24, 1970; )     

Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates

During the spring of 1994, we determined the factors responsiblefor the decline of the seasonal diatom bloom in the Gullmarfjord, on the west coast of Sweden. Four species constituted>75% of the biomass—Detonula confervacea, Chaetocerosdiadema, Skeletonema costatum and Thalassiosira nordenskioeldii—reachingconcentrations of 4900, 350, 8200 and 270 cells ml^–1,respectively. Growth of phytoplankton was exponential (growthrate = 0.12 day^–1) from 3 to 21 March, after which a galewith winds >15 m s^–1 caused massive aggregation. Amaximum of 130 p.p.m. (v/v) of marine snow aggregates was observedby in situ video at the peak of the bloom. Critical concentrations(Jackson, Deep-Sea Res., 37, 1197–1211, 1990) were similarto observed showing that coagulation theory could explain thesudden decline of the bloom. The heterotrophic dinoflagellateGyrodinium cf. spirale increased exponentially after the peakof the bloom with maximum (temperature-adjusted) growth rates.After the rapid aggregation and sedimentation of the bloom,they were able to control any further growth of diatoms. Nitrateand silicate were never depleted, but phosphate may have beenlimiting by the end of the study period. We conclude that massaggregation during a gale marked the end of the bloom, and thatintense grazing by heterotrophic dinoflagellates prevented anysubsequent increase of diatoms.     

PROMOTING ACTIVITY OF TERPENIC LACTONES IN PHASEOLUS ROOTING AND THEIR REACTIVITY TOWARD CYSTEINE

Sesquiterpenoids which contain exomethylenes conjugated to -lactonecarbonyl-heliangine, helianginol, pyrethrosin and cyclopyrethrosinacetate—promoted the adventitious root formation on hypocotylsof cuttings taken from light-grown (1900 lux) 6-day old Phaseolusmungo seedlings, but their derivatives in which the methylene-lactone systems are reduced-to the saturated lactones—dihydroheliangine,hexahydro-heliangine, dihydrohelianginol, dihydrocyclopyrethrosinacetate and tetrahydrocyclopyrethrosin acetate—showedno effect on the root formation. As far as the present experiment is concerned, every substancewhich showed promoting activity in Phaseolus rooting reactedwith cysteine and formed an adduct, but any of the substancesincapable of promoting root formation did not react with cysteine.The correlation of promoting activity of terpenic lactones inPhaseolus rooting with their reactivity toward SH groups maythus be demonstrated. ¹ Contribution No. 14 from the Botanical Gardens, Faculty ofScience, University of Tokyo, Tokyo.     

Phase Transition Temperatures Determined for Chloroplast Thylakoid Membranes and for Liposomes Prepared from Charged Lipids Extracted from Thylakoid Membranes of Higher Plants

Lipid phase separation temperatures of intact thylakoid membranesfrom a number of chilling sensitive plants were measured usingchlorophyll a as the intrinsic fluorescent probe. The phospho-and sulfolipids were extracted from the thylakoid lamellae ofthese plants and purified by silicic acid column and thin layerchromatographies. These separated lipids were eluted and recombinedto give a total charged anionic thylakoid lipid fraction thatwas used to prepare liposomes containing purified chlorophylla as the fluorescent probe. The phase separation temperaturesof these liposomes were compared to phase separation temperaturesin intact thylakoid membranes isolated from the same plants. The chilling-sensitive plants—corn, pepper, tomato andwater hyacinth — showed phase separation temperaturesranging from 9 to 19°C for both the liposomes and the thylakoidmembranes. In addition, low temperature phase separations wereseen from –21 to –27°C. Mimulus, which is notas chilling sensitive as the former plants, had a phase separationtemperature near 0 to 2.5°C and at –27°C. In general,there was a good agreement between the phase separation temperaturesof intact thylakoids and the purified anionic lipid fractionextracted from these thylakoids. Similar results were obtained using either trans-parinaric acidor chlorophyll a as the fluorescent probe in liposomes madefrom anionic thylakoid lipids or in liposomes prepared frompure dimyristoyl phosphatidyl choline, distearoyl phosphatidylcholine, or mixtures of equal amounts of these phospholipids. ¹ CIW-DPB Publication # 728. ³ Present address: Laboratory of Experimental Physics, Departmentof Biophysics, State University of Utrecht, Princetonplein 5,Utrecht, The Netherlands. (Received January 18, 1981; Accepted July 2, 1981)     

Variation in the Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Development to Flowering Among Eight Maturity Isolines of Soyabean [Glycine max (L.) Merrill]

In soyabean [Glycine max (L.) Merrill] the period between sowingand flowering is comprised of three successive developmentalphases—pre-inductive, inductive and post-inductive—inwhich the rate of development is affected, respectively, bytemperature only, by photoperiod and temperature, and then againby temperature only. A reciprocal-transfer experiment (carriedout at a mean temperature of 25°C) in which cohorts of plantswere transferred successively between short and long photoperiodsand vice-versa showed that eight combinations of three pairsof maturity alleles (E₁/e₁, E₂ /e₂, E₃ /e₃) had their greatesteffect on the duration of the inductive phase in long days.This phase was increased with the increasing photoperiod sensitivityinduced by the different gene combinations, and ranged fromabout 27 to 54 d according to genotype. In a short day regime(11·5 h d^-1), less than the critical photoperiod, theduration of the inductive phase was brief—requiring about11 photoperiodic cycles in the less photoperiod-sensitive genotypesand only about seven cycles in the more sensitive ones. Thematurity genes also affected the duration of the two photoperiod-insensitivephases; these durations were positively correlated with thephotoperiod-sensitivity potential of the gene combinations.The largest effect was on the pre-inductive phase which variedfrom 3 to 11 d, while the post-inductive phase varied from about13 to 18 d. As a consequence of these non-photoperiodic effectsof the maturity genes, even in the most inductive regimes (daylengthsless than the critical photoperiod) the time taken to flowerby the less photoperiod-sensitive combinations of maturity geneswas somewhat less than in the more sensitive combinations—rangingfrom about 28 to 34 d. The genetic and practical implicationsof these findings are discussed.Copyright 1994, 1999 AcademicPress Glycine max (L.) Merrill, soyabean, maturity genes, isolines, flowering, photoperiod     

Effect of nitrate on nitrogen-fixation by the blue-green alga Anabaena cylindrica

The effect of nitrate on nitrogen-fixation in the blue-greenalga Anabaena cylindrica Lemm (Fogg strain) was investigated.At concentrations up to 2x10^–2 M, nitrate neither inhibitedthe activity of nitrogenase nor repressed its formation. Atthe late logarithmic phase, more than 50% of cell nitrogen wasprovided by nitrogen-fixation when the cells were grown in thepresence of nitrate. Ammonia at a concentration of 1x10^–3M completely repressed the formation of nitrogenase, but hadno effect on its activity. Nitrogen-fixing activity in the algavaried to a considerable extent during growth on N₂ and themaximum activity was attained at the middle logarithmic phase.However, atmospheric nitrogen did not directly affect the inductionof nitrogenase. The formation of nitrogenase in A. cylindricaappears to be controlled by the intracellular level of a certainnitrogenous metabolite. ¹ This work was supported by grant No. 38814 from the Ministryof Education. (Received January 26, 1972; )     

Dimethipin (2,3-Dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide) Effects on Soybean Seedling Growth and Metabolism

Three-day-old dark-grown soybean [Glycine max (L.) Merr.] seedlingswere transferred to 2 mM CaSO₄ or 10^–5 M dimethipin in2 nM CaSO₄ and root-fed via liquid culture. Plants were placedin continuous darkness or in continuous white light (200 µE.m^–2?s^–11,PAR) at 25?C. Dimethipin inhibited root and shoot elongationin dark-grown plants after 24 h and 48 h, respectively. In thelight, root elongation was inhibited also after 24 h, but hypocotylelongation was not significantly affected. Extractable phenylalanineammonia-lyase (PAL) activity per axis in dimethipin-treateddark-grown axes was not generally affected but, in the lightdimethipin caused a significant decrease in PAL activity (24to 96 h). Total soluble hydroxyphenolics in axes were not affectedby dimethipin in light- or dark-grown plants. Anthocyanin andchlorophyll levels were lowered in hypocotyls of dimethipin-treatedplants after 48 to 96 h. Soluble protein in hypocotyls of light-or dark-grown seedlings was not substantially affected by dimethipin.Nitrate reductase (NR) activity (per organ) was generally notaffected by dimethipin in light-grown cotyledons, but in theroots of these seedlings, NR activity was significantly decreased.Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide,LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide,BAPA) indicated little effect on enzyme activities per organin roots and hypocotyls. These data suggest that dimethipinat low concentrations can cause significant growth inhibitionin soybean seedlings grown in either light or darkness and thatfurthermore, extractable activities of some enzymes associatedwith nitrogen metabolism and secondary metabolism are alteredby this chemical. Light also plays a role in the activity ofthis chemical. (Received November 29, 1983; Accepted January 25, 1984)     

STUDIES ON HOMOSERINE DEHYDROGENASE IN PEA SEEDLINGS

Partially purified homoserine dehydrogenase was prepared frompea seedlings. The optimum pH for this enzyme is approximately 5.4. The K_mvaluesfor ASA and TPNH are 4.6xl0^–4Af and 7.7xl0^–5M, respectively.This enzyme can also utilize DPNH but less effectively thanTPNH. In contrast with yeast homoserine dehydrogenase whichis insensitive to — SH reagents, the pea enzyme is inhibitedalmost completely by 10^–4MPCMB and 10^–5MHgCl₂, theinhibition being removed by 10^–2M thioglycolate. Homoserinedehydrogenase was found not only in decotylized seedlings, butalso in cotyledons. The significance of this enzyme in homoserine biosynthesis ingerminating pea seeds has been discussed. (Received February 20, 1961; )     

Ammonium Triggers Uptake of NO-3 by Chenopodium rubrum Suspension Culture Cells and Remobilization of their Vacuolar Nitrate Pool

Photoautotrophic cell suspension cultures of Chenopodium rubrumrequire high concentrations of nitrate and ammonium. Duringthe growth phase total NH₄⁺ and the greater portion of NH₃^–were consumed. During the stationary phase nitrate uptake continuedbut at a substantially smaller rate than during the growth phase.During growth the bulk of the absorbed N was incorporated intoprotein, the amount of which was then maintained constant untilsenescence. NH₃^– was accumulated upon transition betweenthe growth and the stationary phase. NH₃^–, like the freeamino acids, was deposited in the vacuole but, unlike thesecompounds, could not be remobilized upon transfer of the cellsinto N-free medium. Readdition of NH₄⁺ to the medium, however,resulted in a mobilization of the vacuolar NH₃^–-pool.Reutilization of both vacuolar N-storage pools must have beenaccomplished by recycling from the vacuole to the cytoplasmbecause N-metabolizing enzymes could not be detected in isolatedvacuoles. Transfer of the cells of the stationary phase intomedium containing NH₃^– and NH₄⁺ resulted in an inductionof nitrate uptake by the cells, but only after a lag phase of4–5 days. It is conceivable that NH₄⁺ induces NH₃^–-translocatingsystems in the plasmalemma and in the tonoplast. (Received December 19, 1988; Accepted March 2, 1989)     

N-Ethylmaleimide Blocks the H+ Pump in the Plasma Membrane of Chara corallina Internodal Cells

The sulfhydryl (SH) modifying reagent N-ethylmaleimide (NEM)was applied to the internodal cells of Chara corallina to studythe role of SH residues in the activity of the plasma membraneH⁺ pump. NEM (1 µM) caused a marked depolarizing shiftof the resting potential by 6410mV (n=7) together with depressionof the conductance peak at around —200 mV, indicatinga marked depression of the H⁺ pump activity. This effect ofNEM was partly reversible, the membrane repolarized and theconductance peak was restored after extracellular washing. TheH⁺ pump inhibitor, dicyclohexylcarbodiimide (DCCD), caused noadditive membrane depolarization and/or depression of the H⁺pump conductance, in the presence of NEM. This suggests thatNEM blocks the H⁺ pump and that SH residues play a pivotal rolein maintaining the H⁺ pump activity in Chara corallina. (Received April 10, 1993; Accepted July 29, 1993)     

The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/10⁶ and 156 parts/10⁶in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m^–2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from2–3 x 10^–2 through 6 x 10^–2 to 8–9 x10^–2 m² g^–1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (A_K, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m^–2 through c. 0.3 at7.3 W m^–2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m^–2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = –0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root^–1 h^–1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot^–1 h^–1). The implicationsof this relationship are discussed.     

An analysis of relative elemental growth rate, epidermal cell size and xyloglucan endotransglycosylase activity through the growing zone of ageing maize leaves

The effect of development on leaf elongation rate (LER) andthe distribution of relative elemental growth rate (REGR), epidermalcell length, and xyloglucan endotransglycosylase (XET) activitythrough the growing zone of the third leaf of maize was investigated.As the leaf aged and leaf elongation slowed, the length of thegrowing zone (initially 35 mm) and the maximal REGR (initially0.09 mm mm^–1 h^–1) declined. The decline in REGRwas not uniform through the growth profile. Leaf ageing sawa maintenance of REGR towards the base of the leaf. Epidermalcell size was not constant at a given position in the growingzone, but was seen to increase as the leaf aged. There was apeak of XET activity close to the base of the growing zone.The peak of XET activity preceded the zone of maximum REGR.XET activity declined as leaves aged and their elongation rateslowed. When leaf elongation was complete a distinct peak ofXET activity remained close to the base of the leaf. Key words: Leaf elongation rate (LER), relative elemental growth rate (REGR), xyloglucan endotransglycosylase (XET)     

Regulation of K+ Influx in Barley: Evidence for a Direct Control of Influx by K+ Concentration of Root Cells

Siddiqi, M. Y. and Glass, A. D. M. 1987. Regulation of K⁺ influxin barley: Evidence for a direct control of influx by K⁺ concentrationof root cells.—J. exp. Bot. 38: 935–947. The kinetics of K⁺ (⁸⁶Rb⁺) influx into intact roots of barley(Hordeum vulgare L. cv. Fergus) seedlings having different combinationsof root and shoot [K⁺], different growth rates and differentroot:shoot weight ratios were studied. K⁺ influx was stronglycorrelated with root [K⁺]; shoot [K⁺], growth rates, and root:shoot ratios appeared to have little effect on K⁺ influx. Adetailed study showed that both V_max and K_m for K⁺ influx wereaffected by root [K⁺] but not by shoot [K⁺]. We have suggestedthat factors such as growth rates and root: shoot ratio mayaffect K⁺ influx indirectly primarily via their influence onroot factors such as root [K⁺]. We have reiterated that othertypes of kinetic control, e.g. increased or decreased synthesisof ‘carrier systems’, may operate in addition todirect (allosteric?) control of K⁺ influx by root [K⁺]. Thenegative feedback signal from root [K⁺] appeared to be the primeeffector in the regulation of K⁺ influx. Key words: Barley, K⁺ influx     

14C-Translocation in Kalanchoe pinnata at two Different Stages of Development

Mayoral, M. L. and Medina, E. 1985. ¹⁴C-translocation in Kalanchoepinnata at two different stages of development.—J. exp.Bot. 36: 1405–1413 Translocation of ¹⁴C-compounds from mature leaves was measuredin plants of Kalanchoe pinnata to determine the interactionbetween plant age and CAM phase when CO² is taken up. Matureleaves of 4 and 12 month old plants were fed with ¹⁴CO² eitherduring CAM phase 1 (midnight) or at the beginning of CAM phase4 (early afternoon). Export of ¹⁴C activity from source leaves,and distribution of ¹⁴C activity in soluble and insoluble compoundswas measured both in source leaves and sink organs. In 4 monthold plants 4 d were needed to export 76% of total ¹⁴C activityincorporated during CAM phase 1, while leaves labelled at thebeginning of CAM phase 4 exported 44% of total ¹⁴C activityafter 4 h, and 80% after 24 h. In both cases the major fractionof total radioactivity translocated was found in the roots inthe form of neutral sugars. Differences in translocation patternsare due to distribution of ¹⁴C in the source leaves, 96 % of¹⁴C taken up during CAM phase 1 is found in the insoluble fractionat the end of the subsequent phase 3, while 93 % of total radioactivitytaken up at the beginning of phase 4 is found in the solublefraction at the end of this phase. In 12 month old plants labelledduring phase 1 very little translocation could be detected atthe end of phase 3, while only 20% of total radioactivity wastranslocated from leaves labelled during phase 4 and measured4 h later. ¹⁴C activity in the older leaves had a similar distributionin soluble and insoluble fractions as the one determined inthe younger plants. Ability to translocate carbon compoundsfrom source leaves during phase 3 was shown by loading matureleaves at dawn with ¹⁴C-sucrose. Here again, mature leaves ofyounger plants showed faster translocation of radioactivitythan those of older plants Key words: Kalanchoe, crassulacean acid metabolism, translocation, sink, source relationships