Re-export and metabolism of xylem-delivered ABA in attached maize leaves under different transpirational fluxes and xylem ABA concentrations

By feeding radioactive³H-ABA into attached maize leaves, there-export and metabolism of xylem-delivered ABA and their relationshipswith xylem ABA transpirational fluxes and concentrations wereinvestigated. ABA entering leaves in the transpirational streamwas re-exported out of leaves slowly. Within 24 h the proportionof fed radioactivity that was re-exported was less than 45%.When different concentrations of ³H-ABA (100 nM versus 500 nM)was fed, no difference between the two concentrations was foundin their rates of re-export of the fed radioactivity duringthe first 5 h. After 5 h, very little fed radioactivity wasre-exported in leaves that were fed with 100 nM ³H-ABA, whileleaves that were fed with 500 nM ³H-ABA continued to re-exportsuch that the final proportion remaining in leaves after 24h was less as a result, suggesting a concentration-stimulatedre-export. When ³H-ABA was fed at two different transpirationrates which were induced by different air humidity, a 4-folddifference in transpirational fluxes did not produce any differencein terms of re-exportation of fed radioactivity. The rate ofcatabol-ism of xylem-fed ³H-ABA in the attached leaves was muchfaster than that of re-export. On average fed ³H-ABA had a half-lifeof 2.2 h and only 8% remained unmodified after 24 h of incubation,suggesting that re-exported radioactivity might not be the intactform of ABA at all. Using the parameters obtained from the feeding experiment, wecalculated that in a real soil-drying situation the possiblemaximum amount of xylem-delivered ABA that could accumulatein leaves during a day. It was found that the proportion ofdaily accumulated ABA was only 5% of the leaf ABA in well-wateredplants. In soil-dried plants the maximum amount of daily accumulationby xylem ABA could reach 20% of the leaf ABA at the beginningof soil drying, but it soon declined to about 5% again. Thedeclined contribution was mainly due to a reduced transpirationand an increased total leaf ABA as a result of aggravated leafwater deficit. A tight relationship between leaf conductanceand the accumulation of xylem-delivered ABA was not found. Key words: Abscisic acid, ABA, ABA export, ABA metabolism, xylem-delivered ABA, maize     

Benzyladenine-Directed Transport of Carbon-14 and Phosphorus-32 in Senescing Bean Plants

The distribution of radioactivity from applied sucrose.¹⁴C and³²P to various plant parts were studied in relation to the retardationof leaf senescence by applied benzyladenine (BA) in intact beanplants. In short-time experiments sucrose-¹⁴C was fed to theplants for 48 h through the second trifoliate leaf at weeklyintervals from the third to the eighth week after planting.In long-term experiments sucrose-¹⁴C was fed to all plants for48 h at the third week and changes in distribution examinedat weekly intervals up till the eight week. In both cases, BAapplied to the primary leaves of intact bean plants did notcause a directed mobilization of sucrose-¹⁴C. When the plantswere stripped, leaving the primary leaves and the terminal pod,and fed sucrose-¹⁴C or ³²P through the terminal leaflet of thesecond trifoliate leaf, the BA-treated leaf accumulated relativelymore radioactivity than the opposite water-treated leaf. Itwas concluded that the retardation of senescence by BA in theprimary leaves of intact bean plants does not result directlyfrom the mobilization of metabolites and nutrients from otherplant parts. It is therefore suggested that BA-induced longevityin the primary leaves of the intact plant is accomplished bymetabolic self-sustenance.     

Translocation of organic substances in sunflower I. Downward translocation of 14C-sucrose

A single sunflower leaf was fed ¹⁴C-glucose for 1 min. The plantwas illuminated for 30 min, then the radioactivity in the translocatedsugars was examined. Evidence conclusively showed that sucrosemolecules moved without cleavage during translocation from thefed leaf to the lower stem. Sucrose was the predominant substancetranslocated downwards. The distribution pattern of sugars inthe lower stem differed from that in the upper stem. The conversionrate of glucose into sucrose in the fed leaf was proportionalto the rate of downward translocation. (Received November 20, 1976; )     

Development of Photorespiration during Chloroplast Biogenesis in Wheat Leaves

Tobin, A. K., Sumar, N., Patel, M., Moore, A. L. and Stewart,G. R. 1988. Development of photorespiration during chloroplastbiogenesis in wheat leaves.—J. exp. Bot. 39: 833–843. The rate of light-dependent ammonia accumulation in L-methioninesulphoximine (MSO: glutamine synthetase inhibitor)-treated wheat(Triticum aestivum L. cv. Maris Huntsman) primary leaf sectionsincreased with mesophyll cell maturity. Ammonia production inthe more mature sections (beyond 2.0 cm from the basal meristem)was inhibited by elevated CO₂ concentrations and by incubationwith 10 mol m^–3 pyrid-2-yl hydroxymethane sulphonate (HPMS).In contrast, the low levels of ammonia which accumulated inthe immature sections (0 to 2.0 cm from the base) were unaffectedby such treatments. This indicates that the ammonia producedin mature wheat leaf sections is of photorespiratory originand that the capacity of this pathway increases with mesophyllcell and chloroplast development. Rates of CO₂-dependent oxygenevolution by leaf sections (under saturating CO₂) increasedin parallel with ammonia production. Levels of endogenous nitratewere relatively high and increased from 5.15 mol x 10^–13mesophyll cell^–1 in meristematic cells to 6.6 mol x 10^–12mesophyll cell^–1 in mature tissue. There was no significantchange in leaf nitrate level during 30 min light incubationof the wheat leaf sections, indicating that the majority ofthe nitrate was metabolically inactive and stored in the vacuole.Activities of key enzymes of photorespiration (glutamine synthetase,glycollate oxidase), nitrogen metabolism (nitrate reductase,glutamate dehydrogenase, glutamine synthetase) and mitochondrialrespiration (cytochrome oxidase), showed specific and distinctpatterns of development during leaf growth. Chloroplast glutaminesynthetase (GS₂) and peroxisomal glycollate oxidase developedin apparent synchrony with the major increase in activity occurringin regions beyond4.0 cm from the leaf base, i.e. where photorespirationwas developing. Cytosolic glutamine synthetase (GS₁) and nitratereductase (in vivo) activities were identical throughout leafgrowth, reaching maximum rates at 4.0 cm from the base and thenremaining constant. Activities of the mitochondrial enzymesglutamate dehydrogenase (GDH) and cytochrome oxidase were highin meristematic cells and increased in parallel, attaining amaximum towards the leaf tip. This indicated a respiratory,as opposed to a photorespiratory, role for GDH in wheat leafmetabolism. The evidence for controlled, co-ordinated synthesisof pathway enzymes at specific stages of organelle biogenesisis discussed. Key words: Photorespiration, organelle biogenesis     

The Effects of Leaf Age and Senescence on the Distribution of Carbon in Lolium temulentum

Assimilate distribution in leaves of Lolium temulentum was establishedby root absorption of [¹⁴C]sucrose and after exposure to ¹⁴CO₂.Age determined the amount of carbon assimilated, with more labelbeing incorporated during expansion than at maturity. Duringsenescence ¹⁴C assimilation was much lower. Ethanol-solubleextracts from various tissues of root-labelled plants containedmost of the radioactivity chiefly in basic and acidic compounds.The neutral fraction was composed predominantly of sucrose. Sucrose was comparably labelled in leaves from plants fed equalamounts of either [¹⁴C]sucrose, glucose, or fructose and onlytraces of labelled monosaccharides appeared in extracts. Radioactive sucrose was translocated rapidly from mature leaveswhereas, in the expanding leaf, carbon incorporation was directedtowards growth and the greater proportion of label present atligule formation was in ethanol-insoluble material. Induced senescence, of a mature leaf fed during expansion, produceda rapid loss from the pool of insoluble ¹⁴C. This was accompaniedby a reduction in the contents of chlorophyll and soluble proteinand an accumulation of amino acids. The onset of senescencecaused changes in leaf sugar levels which were correlated withincreased rates of respiration.     

The Distribution and Identity of Assimilates in Tomato with Special Reference to Stem Reserves

Much of the work on the distribution of ¹⁴C-labelled assimilatesin tomato has been done in winter under low light intensities,and consequently the reported distribution patterns of ¹⁴C maynot be representative of plants growing in high light. Further,there are several somewhat conflicting reports on patterns ofdistribution of ¹⁴C-assimilates in young tomato plants. We soughtto clarify the situation by studying the distribution of ¹⁴C-assimilatesin tomato plants of various ages grown in summer when the lightintensity was high. In addition, the role of the stem as a storageorgan for carbon was assessed by (a) identifying the chemicalfractions in the stem internode below a fed leaf and monitoring¹⁴ C activity in these fractions over a period of 49 d, and(b) measuring concentrations of unlabelled carbohydrates inthe stem over the life of the plant. The patterns of distribution of ¹⁴C-assimilates we found fortomato grown under high light intensity confirmed some of thosedescribed for plants grown under low light, but export of ¹⁴Cby fed leaves was generally higher than reported for much ofthe earlier work. Lower leaves of young plants exported over50% of the ¹⁴C they fixed, although export fell sharply as theplants aged. Initially, the roots and apical tuft were strongsinks for assimilates, but they had declined in importance bythe time plants reached the nine-leaf stage. On the other hand,the stem became progressively more important as a sink for ¹⁴C-assimilates.Older, lower leaves exported more of their ¹⁴C-assimilates tothe upper part of the plant than to the roots, whereas youngleaves near the top of the plant exported more of their assimilatesto the roots. The stem internode immediately below a fed leafhad about twice the ¹⁴C activity of the internode above theleaf. Mature leaves above and below a fed leaf rarely importedmuch ¹⁴C, even when in the correct phyllotactic relationshipto the fed leaf. In the first 3 d after feeding leaf 5 of nine-leaf plants, theorganic and amino acid pools and the neutral fraction of theinternode below the fed leaf had most of the ¹⁴C activity, butby 49 d after feeding, the ethanolic-insoluble, starch and lipidfractions had most of the ¹⁴C activity. Glucose, fructose andsucrose were the main sugars in the stem. Although concentrationsof these sugars and starch declined in the stem as the plantsmatured, there was little evidence to indicate their use infruit production. Stems of plants defoliated at the 44-leafstage had lower concentrations of sugars and starch at maturity,and produced less fruit than the controls. It was concludedthat tomato is sink rather than source limited with respectto carbon assimilates, and that the storage of carbon in thestem for a long period is possibly a residual perennial traitin tomato.Copyright 1994, 1999 Academic Press Lycopersicon esculentum, tomato, assimilate distribution, ¹⁴C, internode storage, sink-source relationships, starch, stem reserves, sugars     

Translocation of organic compounds in sunflower III. Effect of oligomycin, ouabain and phlorizin on translocation of sugars

The apical portions of intact sunflower leaves were infiltratedwith ¹⁴C-glucose, ¹⁴C-fructose or 3-O-methyl-¹⁴C-glucose andthe basal portions were treated with inhibitors. The effects of oligomycin, ouabain and phlorizin on translocationwere studied. Inhibition of translocation from the basal portionof the leaf to the stem was determined by experiments usingoligomycin. In other experiments, each leaf was divided intothree parts. The apical portion was fed with ¹⁴C-glucose andthe basal part treated with oligomycin. The effects of oligomycinon the distribution of ¹⁴C-glucose, ¹⁴C-sucrose, ¹⁴C-fructoseand ¹⁴C-sugar phosphate along the three parts of the leaf wereinvestigated. Inhibition of sucrose synthesis in the leavestreated with oligomycin was observed. Oligomycin inhibited ¹⁴Ctranslocation from the leaf. ¹Present address: Department of Biology, Faculty of Science,Science University of Tokyo, Kagurazaka, Shinjuku-ku, Tokyo,Japan. (Received August 17, 1978; )     

Host-Parasite Relations in Loose Smut of Wheat: II. The Distribution of 14C-Labelled Assimilates

The effect of infection by Ustilago nuda on the distributionof ¹⁴C-assimilates in spring wheat plants at several stagesof growth was examined Only small differences were detectedbetween healthy and infected plants at the early stages, butthere were marked differences between the older plants The amountof assimilate exported by the fed leaf appeared to be dependenton the demand for assimilates in all plants, and was greatestduring a period of rapid growth of host or parasite, such asthe sporulation of the fungus in the infected ear The distributionof exported assimilates from the fed leaf of healthy plantsvaried with the position of the fed leaf, its stage of development,and the age of the plant, the pattern was very similar to thatfound in other plant diseases This pattern was altered by thepresence of the pathogen, which acted as an alternative siteof accumulation Totally different sites received ¹⁴C-labelledassimilates in infected plants, in some cases assimilates weretranslocated over unusually long distances, for example fromthe main shoot flag leaf to infected tiller ears. The differencein distribution correlated well with the differences in growthcaused by the pathogen. In addition, the ratio between the radioactivityin alcohol-insoluble and that in alcohol-soluble compounds wasaffected by the infection, in young infected plants more radioactivitywas present in the insoluble fraction and in older infectedplants in the soluble fraction     

The Anisotropy of the Mesophyll and CO2 Capture Sites in Vicia faba L. Leaves at Low Light Intensities

Experiments are reported on the spatial distributions of isotopiccarbon within the mesophyll of detached leaves of the C₃ plantVicia faba L. fed ¹⁴CO₂ at different light intensities. Eachleaf was isolated in a cuvette and ten artificial stomata providedspatial continuity between the ambient atmosphere (0.03–0.05%v/v CO₂) and the mesophyll from the abaxial leaf side. Paradermalleaf layers exhibited spatial profiles of radioactivity whichvaried with the intensity of incident light in 2 min exposures.At low light, when biochemical kinetics should limit CO₂ uptake,sections through palisade cells contained most radioactivity.As the light intensity was increased to approximately 20% offull sunlight, peak radioactivity was observed in the spongycells near the geometric mid-plane of the mesophyll. The resultsindicate that diffusion of carbon dioxide within the mesophyllregulated the relative photosynthetic activity of the palisadeand spongy cells at incident photosynthetically active lightintensities as little as 110 µE m^–2 s^–1 whenCO₂ entered only through the lower leaf surface. Key words: CO₂ capture sites, Vicia faba L., Artificial stomata     

35S-Methionine Incorporates Differentially into Polypeptides across Leaves of Spinach (Spinacia oleracea)

The distribution of proteins across leaves may have significantimpact on optimal photosynthetic performance of leaves, howeverlittle is known about the distribution of proteins and proteinsynthesis across C₃ leaves. We report here a detailed investigationof ³⁵S-methionine incorporation into polypeptides and the steady-statepolypeptide profiles at different leaf depths across spinachleaves. About 10 highly incorporating polypeptides (three with apparentmolecular masses of 23 kDa, 21 kDa and 17 kDa were especiallydominant) were detected in a few medial leaf sections. Thesehighly incorporating polypeptides were soluble proteins, exceptfor the 17 kDa polypeptide, which was associated with thylakoidmembranes. All of the highly incorporating polypeptides werenuclearly encoded. Light significantly enhanced ³⁵S-methionineincorporation into the highly incorporating polypeptides in"sun" grown leaves, but not in "shade" grown leaves. Microautoradiographyshowed that the highly incorporating polypeptides were associatedmainly with the phloem tissue. A specific identity or functionfor the polypeptides is not known. The concentration of most polypeptides on an areal basis appearedto increase with leaf depth from the adaxial leaf surface, reachinga maximum around 25% of the leaf depth, and then declined graduallytowards the abaxial surface. The periphery of cells exhibitedhigh levels of ³⁵S-methionine incorporation, and microautoradiographyshowed that the label was mainly located in the symplast. Ingeneral, polypeptides exhibited higher rates of ³⁵S-methionineincorporation in the palisade mesophyll than in the spongy mesophy,probably due to cytoplasmic density and light. The data showthat it may be possible to study vascular bundle proteins usingparadermal leaf sections. In addition, we now can investigatehow factors such as light or CO₂ might control protein distributionacross leaves, and further explore the complex interactionsamong photosynthesis, leaf anatomy, and light. ¹The research was supported by grants from the Competitive ResearchGrants Office, U.S. Department of Agriculture (No. 91-37100-6672and No. 93-37100-8855).     

The Partitioning of Photosynthetically Assimilated 14C into Amino Acids in Wheat 1. Partitioning During Transport to the Grain

When ¹⁴CO₂ was fed to flag leaf laminae at 20 d post-anthesis,the transport organs between the leaf and the grains containedappreciable ¹⁴C in glutamine, glutamate, serine, alanine, threonineand glycine. Smaller amounts of ¹⁴C were present in gamma-aminobutyricacid (GABA), aspartate and cysteine. Other amino acids whichwere labelled in the source leaf were not labelled in the transportorgans. The export of labelled glutamine, serine, glycine andthreonine from the source leaf was favoured in comparison tothe other amino acids mentioned. Threonine accumulated, andwas subsequently metabolised, in the rachis. [¹⁴C]GABA alsoaccumulated in the rachis. In the grains, the relative amountof soluble [¹⁴C]alanine increased with chase time. This wasprobably due to de novo synthesis and reflected the specialrole of alanine in grain nitrogen metabolism. Wheat, Triticum aestivum, ¹⁴CO₂, amino acids, transport, carbon metabolism     

The Strategy of Carbon Utilization in Uniculm Barley: II. THE EFFECT OF CONTINUOUS LIGHT AND CONTINUOUS DARK TREATMENTS

After a photoperiod of 8.25 h during which the youngest fullyexpanded leaf of uniculm barley plants was allowed to assimilate¹⁴CO₂ for 30 min, groups of plants were transfered either tocontinuous light or to continuous dark. Plants were harvestedover a 72 h period to examine the effect of the treatments (comparedwith control plants growing in normal light/dark cycles) onthe transport of ¹⁴C from the exposed leaf, the distributionof ¹⁴C assimilates to the rest of the plant, and the chemicalfate of assimilated ¹⁴C. In continuous light a substantial quantity (22% at 72 h) ofthe ¹⁴C assimilated by the leaf remained in that leaf in theform of starch and neutral sugars compared with only 4% in thecontrol fed leaf. Also the total amount of ¹⁴C respired fromplants maintained in continuous light was significantly less(c. 18% of the total originally fixed by 24 h) than that respiredfrom control plants (c. 36%). The result was that approximatelyequal amounts of ¹⁴C were accumulated in the growing leavesand roots of plants given continuous light or normal light/darkcycles. In continuous dark the fate of ¹⁴C was similar to that of controlplants. This is probably because the two treatments shared acommon light/dark environment for the first 22 h, during whichtime almost complete distribution and utilization of ¹⁴C occurred.     

The Strategy of Carbon Utilization in Uniculm Barley I. THE CHEMICAL FATE OF PHOTOSYNTHETICALLY ASSIMILATED 14C

Following exposure of the youngest mature leaf of uniculm barleyto ¹⁴CO₂, groups of plants were harvested over a 72 h periodto determine the fate of 14C in the photosynthesizing leaf andin growing leaves and roots. Initially, ¹⁴C was mainly presentin sucrose with a little in starch and charged compounds; transportout of the fed leaf was rapid and, by 7 and 24 h, 56 and 93%respectively of the ¹⁴C had been translocated about equallyto growing leaves and roots. Sucrose entering meristems wasquickly metabolized to protein and structural carbohydrate (40and 60% of the ¹⁴C in these organs at 7 and 24 h respectively),while the remainder was converted to short-term storage productsor intermediary metabolites. By the end of the first day c.35% of the 14C originally assimilated had been lost in respiration. The metabolism of the leaf appeared to be organized on a diurnalbasis, for it exported nearly all its carbon within 24 h ofassimilation. In contrast, some of the assimilate imported intogrowing leaves and, to a lesser extent, roots was not immediatelyused for growth but persisted as temporary metabolites and wassubsequently used for growth in the following days.     

Movement of 14C- and 11C-labelled Assimilate in Wheat Leaves: the Effect of IAA

The rate of translocation of naturally-loaded, radiolabelledassimilate has been studied in leaves of wheat treated withIAA. The velocity was measured directly by following the movementof ¹¹C-labelled material along the leaf. The kinetics of translocationwere also estimated by using a two-compartment model to calculatethe rate constant of disappearance of ¹⁴C from the fed area.IAA was applied at three different sites on the leaf and atvarious times up to 24 h before ¹⁴CO₂ feeding. No effects ofIAA were observed on: (1) direction and velocity of transport;(2) loading of assimilate into the phloem; or (3) the site andkinetics of unloading. These results are discussed with referenceto the movement of IAA along the transport path and the useof different tissues as experimental systems.     

The Translocation of 14C-Photoassimilate from Normal and Mutant Leaves to the Pods of Pisum sativum L.

In experiments using radioactive carbon dioxide (¹⁴CO₂) a comparisonwas made of the ¹⁴C-photoassimilate translocation potentialsof two normal leaved (genotype AfAfTlTl) and two mutant formsof Pisum sativum (pea). A ¹⁴CO₂ administration method is describedthat permitted ¹⁴C-translocation studies to be conducted underfield conditions. One of the mutants available produced tendrils in place of leaves(afafTlTl). The other mutant studied was without tendrils buthad a much branched petiole with numerous relatively minuteleaflets (afaftltl). These mutants and the normal-leaved cultivarswith which they were compared were not isogenic lines. Lengthybackcrossing would be required before full assessment couldbe made of the possible agronomic value of such mutations. An interim evaluation of these mutants was based on ¹⁴C-distributionassays that were conducted 48 h after feeding ¹⁴CO₂, to specifiedleaves. The indication was that in translocation terms the leafand pod had a well defined respective source and sink relationshipthat was independent of leaf morphology. In each case the podswhich constituted the major ¹⁴C sinks depended on which leafhad been fed ¹⁴CO₂. With regard to sink specific activity asdefined by the quantity of ¹⁴C incorporated per unit dry weightof pod, the mutants were not significantly different from normal. The implication of these findings was that fundamental changesin pea leaf morphology could be made genetically without a markedeffect on the photoassimilate export potential of the leaf.     

C3 and CAM Photosynthetic Characteristics of the Submerged Aquatic Macrophyte Littorella uniflora: Regulation of Leaf Internal CO2 Supply in Response to Variation in Rooting Substrate Inorganic Carbon Concentration

The relationships between CO₂ concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO₂ supply around the roots. Free CO₂ in sediment-interstitial-waterranged from 1–01 mol m^–3 (Esthwaite), 0.79 mol m^–3(peat), 0.32 mol m^–3 (silt) and 0–17 mol m^–3(sand), with plants maintained under PAR of 40 µmol m^–2s^–1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO₂ had larger leaf fresh weight (0–69 g) andtotal surface area (223 cm² g^–1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm²g^–1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO₂ concentration[CO₂], was highest in the sand-grown plants (2–69 molm^–3, corresponding to 6.5% CO₂ in air) and lowest inthe Esthwaite plants (1–08 mol m^–3). Expressionof CAM in transplants was also greatest in the low CO₂ regime,with H⁺ (measured as dawn-dusk titratable acidity) of 50µmolg^– fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO₂]₁ and would makea major contribution to daytime CO₂ fixation in vivo. A range of leaf sections (0–2, 1–0, 5–0 and17–0 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO₂ evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO₂ and 1–0mol m^–3 exogenous CO₂ was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O₂ g^–1 fr. wt. h^–1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO₂ g^–1 fr. wt. h^–1) with a K_0.5 of 80 mmol m^–3.In terms of light response, saturation of photosynthesis intissue slices occurred at 850–1000 µmol m^–2s^–1 although light compensation points (6–11 µmolm^–2s^–1) and chlorophyll a: b ratios (1.3) were low.While CO₂ and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO₂ supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO₂ concentrating mechanisms interact inintact plants to maintain saturating CO₂ levels within leaflacunae, although the responses of the various components ofCO₂ supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO₂ concentration, crassulacean acid metabolism, root inorganic carbon supply, CO₂ concentrating mechanism     

Biological activities of rishitin, an antifungal compound isolated from diseased potato tubers, and its derivatives

Rishitin, a norsesquiterpene alcohol, found in infected, resistantpotato-tuber tissue completely inhibited zoospore germinationand germtube elongation of Phytophthora infestans (MONT.) DEBARY at 10^–3M. There was little difference in sensitivityto rishitin among races of Phytophthora infestans. IAA-inducedelongation of Avcna coleoptile sections and GA₃-induced elongationof wheat leaf sections were also inhibited by rishitin. Theinhibition of IAA-induced elongation of Avena coleoptiles wasrelieved to some extent by increasing IAA concentration. However,little relief of the inhibition of GA₃-induced elongation ofwheat leaf sections was obtained by increasing GA₃ concentration.No plant injury was observed at this concentration of rishitin(10^–3M). Examination of a series of rishitin derivatives indicated thatthe hydroxyl group at C-3 is indispensable for antifungal activity.This activity was intensified by saturating the double bondbetween the rings of rishitin and/or that of the isopropenylgroup at C-7, though activity decreased when oxygenated functionalgroups were introduced into the side chain. Aromatization of the A ring did not lower biological activities.The antifungal activities of most rishitin derivatives almostparalleled their activities as plant growth retardants. However,some compounds without antifungal activity were active as growthretardants. ¹Studies on the phytoalexins (5). (Received August 14, 1968; )     

Stomatal response to abscisic acid fed into the xylem of intact Helianthus annuus (L.) plants

The effect of abscisic acid on stomatal apertures of sunflower(Helianthus annuus (L.)) was investigated with a new methodfor feeding solutions into an attached leaf of an intact plant.Xylem sap was sampled with a Passioura-type pressure chamber.Then it was modified in its composition and fed back into amature leaf of the plant from which it had been collected beforethe experiment. Simultaneously, unmodified xylem sap was fedinto a control leaf at the same internode. The use of the Passioura-typepressure chamber during feeding, prevented embolisms and ensuredminimum dilution of the feeding solution. The effect of feedingwas measured by two gas exchange systems, located at the treatmentand at the control leaf. During the feeding experiments up to84% of the water volume transpired by the leaf was substitutedby the supplied feeding sap. When feeding xylem sap, to which2.5 mmol m^–3 ABA (physiological range) was added, leafconductance decreased to a similar value as in drought experiments.A log-linear relationship between the fed ABA-concentrationand leaf conductance was observed. Low stomatal con-ductancewas dependent on a continuous supply of ABA to the leaf. Whentotal ABA-influx into the leaf was large, either due to long-termfeeding of low concentrations or short-term feeding of highconcentrations (i) recovery after feeding started later and(ii) the rate of recovery was decreased. Therefore, stomatalresponses after short-term and long-term ABA-feeding were dependenton the loading of ABA into the leaf and not only on ABA-concentrations.The effectiveness of fed ABA was also dependent on the lightintensity at the fed leaf. Key words: Abscisic acid, feeding method, stomata, gas exchange, Helianthus annuus     

Factors Influencing Alanine Aminotransferase Activity in Leaves of Lolium temulentumL.: II. EFFECTS OF GROWTH REGULATORS AND PROTEIN BIOSYNTHESIS INHIBITORS

Effects of kinetin (K), gibberellin A₃ (GA₃), and 2-(chloroethyl)-trimethylammoniumchloride (CCC) on levels of alanine aminotransferase (GPT) andrates of protein synthesis were studied with both intact plantsand isolated leaf segments of Lolium temulentum L. In intactplants CCC stimulated and CA₃ reduced GPT activity, the effectsbsing much greater in 8.h than in 16-h photoporiods. CCC showedmaximum stimulatory effects at 10^–2 M and K at 5 x 10⁵M. No effect of GA₃ could be demonstrated with concentrationsup to 10^–4M. Both K and CCC retarded GPT decline in leafsections, the latter without associated effects upon pigmentbreakdown. Cycloheximide was highly effective in reducing proteinsynthesis in leaf sections. A close correlation between rateof protein synthesis and GPT activity was found over an inhibitorconcentration range from 10^–6 to 10^–4 M. The resultsare discussed in terms of possible methods of in vivo regulationof GPT activity.     

Transport of 14C-IAA in Cucurbita maxima: A Comparative Study of Rapid, Non-Polar Movement and Slow, Polar Auxin Transport

The transport of ¹⁴C-IAA has been studied in Cucurbita maxima.IAA fed to the leaf of an intact plant moves rapidly in a non-polarfashion in the phloem. Collection and analysis of exudate fromsevered sieve tubes showed that there was no metabolic conversionor complexing of IAA for several hours. Polar movement of ¹⁴C-IAA in isolated internode segments occursat rates an order of magnitude slower than movement in the phloem.The importance of discrete and isolated channels of hormonetransport, that vary in direction and rates, is briefly discussed.