Carbon Economy of Sour Orange in Relation to Mycorrhizal Colonization and Phosphorus Status

The effects of plant phosphorus (P) status and the mycorrhizal(M) fungus, Glomus intraradices Schenck & Smith, on thecarbon (C) economy of sour orange (Citrus aurantium L.) weredetermined during and following active M colonization. Therewere four treatments: M seedlings grown at standard-strength(1 mM) P (M1) and nonmycorrhizal (NM) plants grown at one, twoand five times standard-strength P (NM1, NM2 and NM5). Mycorrhizalcolonization, tissue dry mass, P content, root length and leafarea were determined in five harvests from 6 to 15 weeks ofage. Rate of C assimilation (A) was determined at 7, 8 and 12weeks by gas exchange. Partitioning of ¹⁴ C was determined from7 to 15 weeks using a 10-min pulse followed by a 24-h chaseperiod. For a given attribute, M1 plants were compared to thecurve defining the NM response as a function of tissue P concentration.In contrast to the large effects of P nutrition on C economyof sour orange, M effects were generally subtle. Mycorrhizaeincreased the root biomass fraction, the root length/leaf arearatio and the percentage of ¹⁴C recovered from below-groundcomponents. A higher percentage of below-ground ¹⁴ C was inthe respiration and soil fractions in M than NM plants of equivalentP status. Mycorrhizal plants tended to enhance A only for abrief period. Mycorrhizal plants had lower relative growth ratesthan NM plants of equivalent P status, suggesting that the temporarilyenhance A of M plants did not fully compensate for their greaterbelow-ground carbon expenditure. Problems of interpreting thedynamic effects of mycorrhizae on C economy that are independentof P nutrition are discussed.Copyright 1993, 1999 Academic Press Citrus aurantium L., sour orange, carbon economy, ¹⁴carbon, CO₂ assimilation, vesicular-arbuscular mycorrhizae, phosphorus fertilization, phosphorus nutrition     

Growth and root hydraulic conductivity of several citrus rootstocks under salt and polyethylene glycol stresses

The water relations responses to salt of several important citrus rootstocks such as Swingle citrumelo, sour orange, and Milam lemon have not been studied in detail before. Studies were set up to compare growth and root hydraulic properties of these rootstocks to other citrus rootstocks by exposing them to NaCl and polyethylene glycol (PEG) stresses. Seedlings of 7 citrus rootstocks were irrigated for 5 months with nutrient solutions containing NaCl or PEG that had been adjusted to osmotic potentials of -0.10, -0.20 or -0.35 MPa. The 7 rootstocks studied were sour orange (Citrus aurantium), Cleopatra mandarin (Citrus reticulata Blanco), Swingle citrumelo (C. paradisi x P. trifoliata), Carrizo citrange (C. sinensis x P. trifoliata), rough lemon (Citrus jambhiri Lush), Milam lemon (C. jambhiri hybrid), and trifoliate orange (Poncirus trifoliata [L.] Raf.). In both shoot and root growth, Cleopatra mandarin and sour orange were the least sensitive to salt, Milam and trifoliate orange were the most sensitive, and rough lemon, Swingle, and Carrizo were intermediate in sensitivity. Even though the roots were exposed to solutions of equal osmotic potentials, plant growth and root conductivity were reduced more by the PEG treatments than the corresponding NaCl treatments. At -0.10 and -0.20 MPa, shoot and root dry weights were reduced 16 to 55% by NaCl and 24 to 68% by PEG. Shoot root ratio was lowered at the higher concentrations, particularly by PEG. There was a major decrease in root conductivity caused by NaCl at -0.10 MPa (19 to 30% in sour orange and Cleopatra mandarin and 78 to 85% in trifoliate orange and Milam). Conductivity decreased more at -0.20 and -0.35 MPa, but not proportionally as much as at -0.10 MPa. Root weight per unit length increased at the higher salt levels, particularly in trifoliate orange. Water flow rate through root systems followed the same trend as root conductivity; salt affected sour orange and Cleopatra mandarin the least and trifoliate orange and Milam the most. However, reductions in fibrous root length by salt treatment differed. Root lengths of Swingle and Carrizo were least affected by salt while sour orange. Milam, and rough lemon were the most affected. Hence, even though sour orange and Cleopatra mandarin were more tolerant than the other rootstocks in terms of water flow rate or root conductivity, these 2 rootstocks showed a proportionally greater decrease in root length than Carrizo, Swingle, or trifoliate orange.     

Effect of {alpha}-Naphthalene Acetic Acid on Variations in Free Amino Acid Contents in Developing Fruits of Capsicum annuum L.

Capsicum annuum seeds were pretreated with three concentrationsof -naphthaleneacetic acid (NAA). The fruits of the controland treated plants showed differences in the quantities of freeamino acids during three developmental stages. From a relativelyhigh amount of total free amino acids in the early phase offruit development, there was lowering in the mid-phase and furtherlowering in the terminal phase. There were eight prominent ninhydrin-reactingspots which were identified as tryptophan, glycine, glutamicacid, valine-methionine, -aminobutyric acid, leucine(s), alanine,and aspartic acid and eleven trace spots attributable to tyrosine,serine, lysine, asparagine, cystine, thrconine histidine, phenylalanine,arginine, glutamine, and ornithine. Hormone treatment tendedto decrease the total amino acids in the early- and mid-phasesof fruit development compared with the control fruits. Asparticacid was present in greater quantities in the treatments thanin the controls. In the terminal phase, the treated fruit didnot show any significant change in the total free amino acidcontents. The significance of the NAA-included variation infree amino acids is discussed. Capsicum annuum, amino acids, -naphthaleneacetic acid     

The Dry Storage of Citrus Seeds

The survival of seeds of lemon (Citrus limon L.), lime [C. arantifolia(Christm.) Swing.] and sour orange (C. aurantium L.) was examinedunder a wide range of constant moisture contents and temperatures.Seed longevity was increased by decreasing the moisture contentand temperature of the storage environment. Maximum viabilitywas maintained in the combination of storage conditions includingthe lowest moisture content (5 per cent) and lowest temperature(–20 °C) investigated. The practicality of dry storageof citrus seed for genetic conservation is discussed. Citrus limon L., lemon, Citrus aurantifolia (Christm.), Swing, lime, Citrus aurantium L., sour orange, dry storage, moisture content, temperature, seed viability, seed longevity     

The Partitioning of Photosynthetically Assimilated 14C into Amino Acids in Wheat: 2. Distribution in Amino Acids of Wheat Grain Fractions

Changes in the distribution of ¹⁴C between free and bound aminoacids in wheat grains (Triticum aestivum L. cv. Arkas) at 10and 20 d post-anthesis are described. After ¹⁴CO₂, labellingof the flag leaf, ¹⁴C was initially more rapidly transferredto the grains of 20 d post-anthesis plants than for 10 d post-anthesisplants. However, after a 460 min chase period in the light theamount of ¹⁴C in the grains of the younger and older plantswere similar. In the younger, more rapidly growing grains, agreater proportion of the ¹⁴C was incorporated into structuraltissue and starch. ¹⁴C accumulation in the grains continuedduring the dark in the younger grains but not in the older grains. Although the overall ¹⁴C distribution between the free aminoacid and protein pools of the grain was similar for both treatments,the distribution within the albumin, prolamin and globulin fractionsand between the individual non-bound amino acids differed. Ofthe protein fractions, the albumins were initially the mostheavily labelled but after 460 min chase the prolamins containedmore ¹⁴C. The majority of the ¹⁴C in the albumin and globulinfractions after 280 min chase was in hydrolysable, non-aminoacid compounds. In both tissues, the free amino acid pools lostradioactivity in the dark but the solid residues and proteinscontinued to function as ¹⁴C sinks. Daily fluctuations in the radioactivity in free and bound alanineare consistent with the role of free alanine as a diurnal metabolicnitrogen pool. Wheat, Triticum aestivum¹⁴CO₂, amino acids, proteins, carbon metabolism     

Effect of Hormones on Sucrose Uptake and on ATPase Activity of Citrus sinensis L. Osbeck Leaves

Carbohydrate accumulation in young, fully expanded leaves ofCitrus sinensis L. Osbeck is affected by the presence of thefruitlet on the shoot. Previous work gave evidence that gibberellinsmay be involved in this 'fruit effect'. In the present workwe have studied the effect of gibberellic acid (GA₃) on ¹⁴C-sucroseuptake by leaf discs and whether its action could be due toa modulation of the plasma membrane ATPase, which maintainsthe H⁺ gradient that drives H⁺/sucrose co-transport. The effect of GA₃ on ¹⁴C-sucrose uptake depended on the osmolarityof the assay medium. At 300 mOsm a reduction in the uptake ratewas observed. The inhibitory effect of the hormone disappearedafter preincubating the leaf discs with para-chloromercuri-phenylsulphonicacid (PCMPS), a sulphydril binding inhibitor. ATPase activityof isolated plasma membrane vesicles was inhibited by IAA treatments,while GA₃ or ABA did not affect this enzyme, even after a 3h preincubation period. However, in the absence of a surfactantin the assay medium, GA₃, together with turgor pressure, modulatedplasma membrane ATPase activity, possibly through modificationsof membrane permeability. The hormone effect on ¹⁴ C-sucroseuptake may involve action on the sucrose carrier.Copyright 1994,1999 Academic Press Abscisic acid, Citrus sinensis, gibberellic acid, indoleacetic acid, orange, osmotic pressure, plasma membrane ATPase, ¹⁴C-sucrose uptake     

The Effect of Different Levels of N Limitation on Sugars, Amino Acids, Growth and Biomass Partitioning in Broadbean (Vicia faba L.)

Broadbean plants (Vicia faba L.) were submitted to three differentlevels of steady state N limitation. Relative addition ratesof N were 0.06, 0.1 and 0.14d^-1. Plants were harvested at fiveevenly distributed times over a 2d period. Shoot growth correspondedwell with the imposed treatment. Root growth, relative to shootgrowth, was highest at the 0.06d^-1treatment. Diurnal patternsof soluble sugars, amino acids and starch were analysed. Onaverage, soluble sugar levels were highest in the plants ofthe 0.06d^-1treatment whereas average free amino acid levelswere highest in the 0.14d^-1treatment. Shoot growth increasedas the concentration of shoot amino acids increased. No suchcorrelation however could be found between root growth and freesugar levels in the root. Broadbean; Vicia faba L.; exponential addition; N limitation; free sugar; amino acids; diurnal cycle; functional equilibrium; starch     

Accumulation of Free Proline in Citrus Leaves during Cold Hardening of Young Trees in Controlled Temperature Regimes

Free proline increased in leaves of orange (Citrus sinensis [L.] Osb. cv. Valencia) and grapefruit (Citrus paradisi Macfad. cv. Star Ruby) trees on a wide range of citrus rootstocks during cold hardening. Increases in sugars accompanied proline accumulation. During cold hardening, the rate of proline accumulation was greater in old than in young leaves. In leaves of grapefruit trees kept in the dark during cold hardening, neither proline nor sugars increased and the degree of cold hardiness was less than in trees exposed to light. Like sugar accumulations, proline accumulation does not reflect specific degrees of cold hardiness in citrus cultivars.     

The Uptake and Flow of C, N and lons between Roots and Shoots in Ricinus communis L.

Seedlings of Ricinus communis L. cultivated in quartz sand weresupplied with a nutrient solution containing either 1 mol m^–3NO^–₃ or 1 mol m^–3 NH⁺₄ as the nitrogen source. Duringthe period between 41 and 51 d after sowing, the flows of N,C and inorganic ions between root and shoot were modelled andexpressed on a fresh weight basis. Plant growth was clearlyinhibited in the presence of NH⁺₄. In the xylem sap the majornitrogenous solutes were nitrate (74%) or glutamine (78%) innitrate or ammonium-fed plants, respectively. The pattern ofamino acids was not markedly influenced by nitrogen nutrition;glutamine was the dominant compound in both cases. NH⁺₄ wasnot transported in significant amounts in both treatments. Inthe phloem, nitrogen was transported almost exclusively in organicform, glutamine being the dominant nitrogenous solute, but theN-source affected the amino acids transported. Uptake of nitrogenand carbon per unit fresh weight was only slightly decreasedby ammonium. The partitioning of nitrogen was independent ofthe form of N-nutrition, although the flow of nitrogen and carbonin the phloem was enhanced in ammonium-fed plants. Cation uptakerates were halved in the presence of ammonium and lower quantitiesof K⁺, Na⁺ and Ca²⁺ but not of Mg²⁺ were transported to theshoot. As NH⁺₄ was balanced by a 30-fold increase in chloride in thesolution, chloride uptake was increased 6-fold under ammoniumnutrition. We concluded that ammonium was predominantly assimilated inthe root. Nitrate reduction and assimilation occurred in bothshoot and root. The assimilation of ammonium in roots of ammonium-fedplants was associated with a higher respiration rate. Key words: Ricinus communis, nitrogen nutrition (nitrate/ammonium), phloem, xylem, transport, partitioning, nitrogen, carbon, potassium, sodium, magnesium, calcium, chloride     

纽荷尔脐橙CCS基因的克隆与分析

利用RT-PCR技术从纽荷尔脐橙果实cDNA中分离出辣椒红／辣椒玉红素合成酶（Capsanthin/Capsorubin synthase,CCS）基因（Ccs）全长。该片断长为1619bp,编码503个氨基酸。BLAST比较其氨基酸同源性发现,该序列所推导的氨基酸与已知的甜橙CCS完全一致,与胡萝卜和辣椒的CCS,以及马铃薯新黄质合成酶（neoxanthin synthase,NSY）有70％的同源性。此外,与番茄和柑橘等的番茄红素环化酶也有50%~70%的同源性。半定量RT-PCR分析表明,Ccs在纽荷尔脐橙果实成熟过程中呈先上升后下降的表达趋势,期间9月份的表达量最高。     

The Effects of a Hydrogel Polymer on the Growth of Certain Horticultural Crops under Saline Conditions

The effects of incorporating a hydrogel polymer into sand onthe development of selected horticultural plants grown undersaline conditions has been demonstrated. In separate experiments,the seeds of tomato (Lycopersicon esculentum Mill.), lettuce(Lactuca sativa L.) and cucumber (Cucumis sativus L.) were germinatedin sand/swollen hydrogel polymer mixture (25: 75, v: v) withadded Hoagland nutrient solution. At cotyledon + first trueleaf stage, the plantlets were transplanted into polythene growbagscontaining a range of sand/swollen hydrogel polymer combinations(0: 100, 25: 75, 50: 50, 75: 25 and 100: 0, v: v). Saline solutionscontaining NaCl, CaCl² and MgCl² were prepared as molar solutionsand applied at combined concentrations as follows; Control (Hoagland),2000, 4000, 8000, and 32 000 ppm. Application of the appropriatesolution to the growbags was made twice per week, alternatingwith a comparable watering regime. Harvesting was carried outafter 14 and 28 d. Polymer incorporation encouraged growth ofall species under all saline conditions, the order of effectivenessof the polymer contents being as follows; 75%>50% 25% 100%>0%.At high salinity (32 000 ppm) plants of the test species werereduced in growth but appeared to be tolerant at all levelsof polymer incorporation; in pure sand the level of tolerancein tomato and cucumber was <8000 ppm and in lettuce <4000 ppm. Generally, dry weight, leaf area, succulence, chloroplastpigments (chlorophyll a, chlorophyll b, and carotenoids), photosyntheticactivity, total amino acids, proline, and protein contents wereincreased with polymer incorporation compared with pure sand.This hydrogel polymer appears to be highly effective for useas a soil conditioner in horticulture, to improve crop toleranceand growth in a sand or light gravel substrate under salineconditions. It is intended to confirm the results of these studiesby field trials. Key words: Tomato (Lycopersicon esculentum Mill.), lettuce (Lactuca sativa L.), cucumber (Cucumis sativus L.), salinity, hydrogel, polymer, salt tolerance, growth, free amino acid, free proline, and protein     

The response of citrus plants to the broad mite Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae)

1. Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae) is a common polyphagous mite in tropical and subtropical areas and is considered as an important citrus pest.
2. To understand the response of citrus to P. latus infestation, we have characterized the volatile profile and the molecular defence mechanisms of two citrus genotypes, namely sour orange (Citrus aurantium) and Cleopatra mandarin (Citrus reshni), to P. latus infestation. These two species are important rootstocks for the citrus industry and display differential resistance to Tetranychus urticae Koch (Acari: Tetranychidae), with sour orange showing elevated levels of constitutive and induced resistance associated with the jasmonic acid (JA) pathway compared with Cleopatra mandarin.
3. P. latus infestation activated both the JA- and the salicylic acid-dependent pathways in sour orange but not in Cleopatra mandarin. However, this differential activation resulted in the production of similar volatile blends (a mixture of green leaf volatiles and aromatic compounds).
4. Contrary to T. urticae infestation, sour orange supported larger densities of P. latus than Cleopatra mandarin with similar injury levels.
5. Therefore, sour orange may be more tolerant to P. latus than Cleopatra mandarin.

     

Effect of Nitrate, Ammonium and Some Amino Acids on Growth and Nitrate Reductase Activity in Suspension Cultures of Atropa belladonna

Growth and nitrate reductase activity (NRA) of Atropa belladonnacells were studied in medium supplemented with NaNO₃, NH₄NO₃,and amino acid precursors to tropane alkaloids. Growth and NRAwere stimulated by NH₄⁺ and by proline, by proline plus ornithine,but not by glutamate, in NO₃^–-containing medium. Testedamino acids inhibited neither utilization of inorganic nitrogennor growth. (Received September 30, 1988; Accepted August 28, 1989)     

Phospholipid, galactolipid and free sterol composition of fibrous roots from citrus genotypes differing in chloride exclusion ability

Abstract Fibrous roots of four citrus hybrids and parent rootstocks from which the hybrids were generated, all selected for their different Cl^? exclusion abilities, were assayed for phospholipid, galactolipid and free 4-desmethylsterol content. There was no correlation between a plant's ability to exclude Cl^? and the level of either phospholipid, galactolipid, or total free sterol in the roots of control plants. However, an inverse correlation was established between the ratio of phospholipid to free sterol in control roots and total leaf Cl^? levels of plants treated with 50 mol m^?3 NaCl for 56 d. With the exception of a significant decrease in hybrid 80-05-05, galactolipid levels were unaffected by salt treatment. Phospholipid levels were significantly increased in two parent rootstocks viz. Trifoliate orange (Poncirus trifoliata (L.). Raf.) and Carrizo citrange (Citrus sinensis (L.) Osbeck ×P. trifoliata) and one hybrid (80-02-08) but were otherwise unchanged by salt treatment. Free sterol levels were significantly increased by salt treatment in all of the better Cl^? excluders except Carrizo citrange i.e. in Rangpur lime (Citrus reticulata Blanco var. austera hybrid?), Cleopatra mandarin (Citrus reticulata Blanco) and all hybrids except 80–05–13. In all genotypes examined, salt-treatment resulted in a significant decrease in the ratio of sitosterol to stigmasterol reflecting, primarily, an increase in the stigmasterol level. The two poorer Cl^? excluders (Trifoliate orange and hybrid 80–05–13) both underwent a significant decrease in the ratio of ‘more planar’ to ‘less planar’ sterols. The inverse correlation between the phospholipid to free sterol ratio of control plants and leaf Cl^? level of salt treated plants suggests that this ratio has the potential to be used as a biochemical marker of Cl^? exclusion ability in citrus.     

Influence of Chloride and Transpiration on Net15NO3-Uptake Rate byCitrus Roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensisL. OsbeckxPoncirus trifoliata Blanco) seedlings were grown incontrolled environment chambers in pots of fine sand. Plantswere irrigated with either non-saline or saline solutions overa 3-week period. After these treatments, plants were transferredto vessels containing a 5 m M¹⁵NO₃K (96% atom excess¹⁵N) solution,and transpiration as well as concentration of¹⁵N and Cl^-in roots,stem and leaves were measured after 24 h. Transpiration and¹⁵NO₃^-uptakerates were inhibited after exposure to NaCl and the concentrationof salt pre-treatment determined the intensity of this inhibitoryeffect. To determine the effect of transpiration on NO₃^-absorption,net¹⁵NO₃^-uptake rate was measured in salt stressed and non-stressedplants exposed to different light intensities or relative humiditiesand also in detached roots. Reduction in NO₃^-uptake was moreclosely related to Cl^-antagonism from salt stress than to reducedtranspiration rate. Copyright 1999 Annals of Botany Company Nitrate, absorption, inhibition transport system, salt, light and humidity.     

Metabolism of Arginine and Ornithine in Suspension-Cultured Cells and Aseptic Roots of Intact Plants of Atropa belladonna

Suspension-cultured cells and aseptically cultured roots ofintact plants of Atropa belladonna L. removed tropane alkaloidprecursors arginine (Arg) and ornithine (Orn) at nearly an equalrate from the feeding medium. A great part of Arg- and Orn-derived¹⁴C-label was found in ethanol-insoluble compounds, mostly inproteins already after 2 h feeding. Ethanol-soluble label inthe roots was found mainly in amino acids (e.g. glutamine, Gln)after 2 h feeding, and after 20 h also in some intermediatesof the urea cycle (e.g. argininosuccinate). In suspension cultures, subculturing of the initiation callusdecreased both the uptake of the basic amino acids tested andtheir binding on to the apoplastic space. After 20 h feedingwith Arg more label was found in organic acids in stationaryphase suspension cultures with repressed alkaloid synthesisthan in roots producing alkaloids. The growth phase and passagenumber also affected into which amino acids the label was incorporated.When the initiation callus was young (the 3rd passage), theintermediates of the urea cycle were actively labelled, butwhen the initiation callus was older (the 8th passage) and thesuspension formed roots, especially Gln was labelled. Only tracesof -N-methylornithine were detected in feeding experiments withOrn and Arg. Considerable arginase activity with a high pH optimumwas observed in cell suspensions and roots of A. belladonna. Key words: Atropa, arginine, ornithine, roots, suspension culture     

Observations on the Mode of Parasitism and Histopathology of Meloidodera floridensis and Verutus volvingentis (Heteroderidae)

Some aspects of the host-parasite relationships of two heteroderid nematodes are described. Meloidodera floridensis induced formation of single uninucleate giant cells in the stelar parenchyma tissue of sand pine (Pinus clausa) roots. Wrinkling and yellowing of the cuticle were associated with maturation of the adult female (cystoid stage). The mode of parasitism of different life stages of Verutus volvingentis on buttonweed (Diodia virginiana) is described. The nematode caused extensive necrosis during penetration and the formation of a large feeding site consisting of nonhypertrophied parenchyma cells with enlarged nuclei and thickened cell walls in the cortex. Walls between cells within the feeding site degenerated, resulting in the formation of a syncytium. Two citrus rootstocks, rough lemon (Citrus lirnon) and trifoliate orange (Poncirus trifoliata), were not hosts of V. volvingentis.     

Alicyclic acid metabolism in plants 3. Fate of 14C-shikimate and 14C-quinate in mung bean plants

Young mung bean plants (Phaseolus mungo) were exposed to ¹⁴C-shikimateor ¹⁴C-quinate in the light. After 8 or 23.5 hr of incubationat 25°C, radioactivities in free and bound amino acids,organic acids, soluble and insoluble carbohydrates, ether-solublefraction and lignin were determined. Shikimic and quinic acidswere separated by the combined use of paper-chromatography andcolumn chromatography. Specific activity of formed quinate orshikimate was only slightly lower than that of fed shikimateor quinate. Specific activities of phenylalanine, tyrosine andbound tryptophan were high as compared with those of non-aromaticamino acids. Discussion is focused upon the interconversionbetween shikimate and quinate, and their roles in the biosynthesisof aromatic amino acids. (Received November 15, 1968; )     

Long-Term Phosphate Starvation and Respiratory Metabolism in Suspension-Cultured Catharanthus roseus Cells

In order to clarify the metabolic adaptation of respiratorypathways in plants to limited levels of P_i, the effects of long-termstarvation of P_i on the activities of various enzymes relatedto respiratory metabolism were examined in suspension-culturedCatharanthus roseus cells. When the activities were expressedas units per g fresh weight, only those of phosphoenolpyruvate-hydrolyzing(PEP-hydrolyzing) enzyme (which may possibly be equivalent tothe acid phosphatase activity derived from vacuoles) and PEPcarboxylase were higher in the Pⁱ-starved cells than in controlcells. Activities of other enzymes in the Pⁱ-starved cells werelower than or similar to those of the control cells. Time-coursestudies indicated that PEP-hydrolyzing activity was inducibleby starvation of Pⁱ. However, in contrast to the results reportedby Duff et al. [(1989a) Plant Physiol. 90: 1275.], fluctuationsin the activity of PP¹:fructose-6-phosphate 1-phosphotransferaseduring starvation of Pⁱ were similar to those in levels of phosphofructokinaseand 6-phosphogluconate dehydrogenase. These data suggest thatthe concept of the phosphate starvation-inducible ‘bypasses’,which are engineered via the coarse control (i.e., induction)of specified enzymes and were proposed initially by Duff etal. in Brassica nigra cells, is not directly applicable to Catharanthusroseus cells in suspension. Tracer experiments using [U-¹⁴C]glutamineindicated that a significant proportion of respiratory substratescould be supplied from the enlarged pool of amino acids duringstarvation of Pⁱ. These assumptions are supported by the observedfluctuations in levels of free amino acids and of protein inP¹-fed and P¹-deficient Catharanthus roseus cells. ¹Part 41 in the series ‘Metabolic Regulation in PlantCell Cultrue’ ²Present Address: Morinaga Mild Industry, 5-1-83, Higashihara,Zamma-shi, Kanagawa, 228 Japan     

Morphological and Physiological Responses of Echinoderm Larvae to Nutritive Signals

SYNOPSIS. Echinoid larvae have been found previously to developshorter arms as phytoplankton concentrations increase. In thepresent study, the skeletal dimensions of larvae of the seaurchins Lytechinus pictus and Strongylocentrotus purpuratuswere measured after exposure to dissolved organic compoundsin seawater. The presence of glucose or individual amino acids(at 1 or 2 µM), a mixture of 16 different amino acids(100 nM each), or algal exudate resulted in larvae with shorterarms (by 12 to 88%), relative to larvae in seawater with noadditions. Larvae exposed to mixtures of amino acids also hadchanges in the constituents of their internal free amino acidpools (as determined by HPLC). For another echinoid, Dendrasterexcentricus, amino acid transport (T, from 500 nM) by individuallarvae (n = 47) scaled to arm length (L) as follows: T = 2.06L^0.81(0.81 ± 0.26,95% confidence intervals). Mass (M) andmetabolic rate (MR) did not scale in the same manner (as transport)to arm length for larvae of the echinoid Centrostephanus coronatus(MR = 148L^1.51; M = 1.7L^2.01). These characteristics may scaleto arm length independently from transport rate under certainconditions. Larvae of echinoderms respond morphologically to"signals" in their environment that may indicate the availabilityof dissolved and paniculate nutrients. This in turn will haveconsequences for their ability to take up and metabolize thesenutrients. The response may be mediated by surface receptorsfor dissolved organic compounds, or by changes in the sizesof intracellular substrate pools.