Energy Loss in Tissue 2Sauromatum guttatum (Schott) Analysed by Microcalorimetry

The heat evolved by 1 mm-thick tissue slices of the appendixof the Sauromatum guttatum inflorescence was measured calorimetricallyduring development. From D–5 (5 d before inflorescence-opening,designated as D-day) to D–2 about 8 µW mg^–1fresh wt. was observed, and during D–1 an increase inheat evolution to 14 µW mg^–1 fresh wt. was monitored.The heat was produced through oxidative metabolism, since replacingthe air in the microcalorimeter with nitrogen blocked heatproduction.Addition of salicylic acid to tissue slices of thermogenic organs(appendix, lowest part of the spadix and male flowers) and ofnon-thermogenic organs (female flowers, club-shaped organs andlower part of the spadix) of Sauromatum inflorescences revealedthat the acid boosted heat-production only in the thermogenicorgans. The effect of the acid manifested itself with no appreciablelag time, and it generated non-linearity in the rate of heat-productionby tissue slices of the appendix. In the appendices of the highlythermogenic Arum italicum and of the weakly thermogenic Amorphophallusrivieri, salicylic acid selectively boosted the rate of heat-productionin the appendix of A. italicum. A Q₁₀ of 24 was found between15C to 25 C for 1 mm-thick slices of D–4 appendicesof S guttatum. Addition of digitonin or deoxycholate to pre-D-daytissue slices of the appendix increased the rate of heat-production. Key words: Amorphophallus rivieri, Arum italicum, microcalorimetry, salicylic acid, Sauromatum guttatum     

On the thermogenesis of the Titan arum (Amorphophallus titanum)

The Titan arum (Araceae) produces the largest bloom of all flowering plants. Its flowering period of two days is divided into a female flowering phase in the first night and a male flowering phase in the second night. Recently, we have documented thermogenesis in the spadix of the Titan arum during the female flowering phase. Here, we document a second thermogenic phase in which the male florets are heated during the male flowering phase. Obviously the two nocturnal thermogenic phases are linked with the two flowering periods. These observations now allow a more detailed understanding of the flowering behavior of the Titan arum.Key words: Amorphophallus titanum, araceae, thermogenesis, infrared thermography, pollinationThe Titan arum (Amorphophallus titanum) is one of the most spectacular flowering plants. It has drawn the attention of botanists and naturalists since its discovery in 1878. However, the species has been rare in cultivation and flowering events in botanical gardens were even rarer. Besides, flowering events observed in the plant''s natural habitat are very few.^1,2 Therefore, the knowledge on A. titanum that depended on exact observations and scientific experiments remained very limited. It was only in the late 90s when a monograph on the species, containing anatomical details and some first experimental hypotheses, has been published.¹The Botanical Gardens of the University of Bonn (Germany) have been cultivating Amorphophallus titanum for more that 70 years and obtained 14 flowerings between 1937 and 2009. These regular flowering events have been the prerequisite to study A. titanum in detail. Consequently the data and hypotheses in the monograph mentioned above were gained mainly from the A. titanum plants in the Botanical Gardens Bonn. As a result of three flowering events in 2006, we have recently documented for the first time, that the inflorescence undergoes thermogenesis in which the central column (spadix) heats up to 36°C. Meanwhile four additional flowering events yielded additional insights into the flowering behavior of A. titanum.The inflorescence of A. titanum consists of a thickened unbranched inflorescence axis bearing hundreds of small female and male florets which are spatially separated (Fig. 1A). The inflorescence axis is extended into an appendix (spadix) and enveloped by a large bract referred to as spathe. The spathe enclosing the florets forms the floral chamber. Since the whole inflorescence functions as a single unit in pollination is often referred to as a bloom or “flower”. A. titanum has two timely separated flowering phases: a female flowering phase during the first evening and night after opening of the spathe and a male flowering phase in the following night.Open in a separate windowFigure 1(A) Flash-light photograph of an Amorphophallus titanum flowering zones showing part of the appendix, the male florets and the female florets. (B) Thermographic image taken during the male flowering phase. The male florets are heated to the maximum temperature of 35.9°C whereas the other parts of the plant have largely ambient air temperature of 26°C.Thermogenesis plays an important role in the pollination ecology of Araceae^3,4 and therefore occurs in many genera.^4–7 Similarly in A. titanum, we have reported the thermogenic spadix during the female flowering phase. Based on our observations of now six inflorescences, the heat production is determined and begins around 20 h, the temperature maximum of 36–38°C being reached around midnight. The duration of heat production differs between individual plants but usually stops between 2 h and 4 h in the morning. The spathe begins to close the next day in the early morning hours or in the forenoon. The opening and closing of the spathe seems to be influenced by the hours of daylight but these might be different in European countries from the plants native habitat in the tropical rainforests of Sumatra. The flowering events in Bonn usually take place in summer, the spathe opens during a daytime when it is still very bright and is fully opened when the daylight is decreasing while it is already dark then in the tropics.Some authors have observed heating of the male florets prior to appendix heating in other Araceae species.^4,5,8,9 In A. titanum however, we could not find an evidence for this, as stated in our previous article. But a question that still remained open is: when exactly the male flowering phase begins and if there might be thermogenic activity during the male flowering phase. To study this, the male florets were made visible by removing a part of the spathe of two flowering A. titanum and observed right after opening of the spathe. The beginning of the male flowering phase is easily to determine since the pollen is shed in well visible string-like structures.The pollen dissemination began in the evening around 17:20 h. Thereupon we filmed the male florets with a thermographic camera (Flexcam, GORATEC) taking an image every five minutes. The male florets were clearly thermogenic reaching a temperature maximum of 35.9°C between 18:40 h and 20:00 h (Fig. 1B). They slowly cooled down to ambient air temperature (ca. 26°C) around midnight. To test whether the temperature in the floral chamber around the male florets increases while they are heated, we recorded the temperature within the spathe of three intact inflorescences with data loggers (Tinytag, Gemini Data Loggers). However, no warming within the chamber in comparison with ambient air temperature could be measured, so the heated florets seem not to affect the temperature within the floral chamber.The flowering behavior of A. titanum is summarised in Figure 2. The carrion-like odor and the thermogenic spadix attract pollinators in the female flowering phase, during the first evening and night of the flowering period. Heating of the male florets occurs when no more odor is produced and hence no olfactorical attraction of the pollinators can take place. As a consequence, there must be only one attraction time period which is more or less restricted to the female flowering phase and to the nighttime where pollinators can be successfully attracted. The pollinators, although not exactly known,¹⁰ hence must be active only in these evening hours and at night. Once attracted, the pollinators stay inside the inflorescence and most likely use it as mating site or as a place to stay during the following day. It has already been hypothesised that Araceae inflorescences forming floral chambers may offer mating sites or places to rest for insects and rather keep their pollinators inside the floral chamber instead of a second attraction phase.^{11, 12} Numerous insects inside a A. titanum inflorescence have indeed been observed in its natural habitat,¹³ although the author did not explain these observations, it provides evidence for our hypothesis that pollinators spend some time inside the inflorescence.Open in a separate windowFigure 2Scheme of the flowering behavior of Amorphophallus titanum over its two-days flowering period. The scheme is idealised but represents observation of seven A. titanum inflorescences that all behave highly similar. Deviations in the time when opening and closing of the spathe begin in individual plants are indicated with a dashed line.The male florets are heated while pollen is released. There is evidence that at least some insects are able to percept IR light and it has been hypothesised that infrared radiation itself could be an attractant for insects, most likely to locate food sources.¹⁵ Floral heat may also be a direct reward for pollinators, helping them increasing their body temperature and thus faster reaching their activity level.^11,14 Both may also apply to A. titanum—the insects that have spent the day within the flower chamber may use the heated surface of the male florets to warm themselves up and by this collect pollen or feed on pollen. Still, a verification of these hypotheses could only come from field observations.To draw a conclusion, the new observations reported here now allow us a good understanding of the flowering behavior of A. titanum. Its two thermogenic phases are clearly linked with the two flowering phases and the plant''s complex interaction with its pollinators.     

The Oxidative Phosphorylation and ATPase Activity of Arum spadix Mitochondria in Relation to Heat Generation

The respiration of Arum spadix mitochondria is coupled to asub-maximal stoichiometry of ATP synthesis. The P/O ratios associatedwith the oxidation of succinate or malate are decreased by antimycinand increased by m-chlorobenzhydroxamic acid, an inhibitor ofthe alternative oxidase. The mitochondrial ATPase activity of20–40 nmol (mg protein)^–1 min^–1 is independentof the maturity of the spadix and is unlikely to provide themechanism for heat production during the odoriferous stage,which probably results from an increase in the rate of electrontransport via the non-phosphorylating, cyanide-insensitive oxidase.     

AEROBIOLOGY OF SYMPLOCARPUS FOETIDUS: INTERACTIONS BETWEEN THE SPATHE AND SPADIX

The aerobiology of the skunk cabbage, Symplocarpus foetidus (l .) Nutt., is examined as a factor contributing to efficient pollination and temperature regulation around the spadix. Field measurements show that the compass orientation of the asymmetrical opening of the spathe is random, while wind tunnel studies reveal that similar patterns of airflow are generated around the spadix regardless of the orientation of the spathe opening to the direction of airflow. Temperature measurements within a model of the inflorescence reveal that airflow around the spathe effectively maintains heat generated by the spadix, even at airflow speeds of 1.5 m/s. These results are discussed as exaptations of the spathe for pollination and for temperature regulation in sub-freezing weather.     

Respiratory Mechanisms in the Aroid Spadix

The flowers of Skunk-cabbage (Symplocarpus foetidus), like thespadix tissues of other Aroids, have a rapid, carbon monoxideand cyanide (HCN) resistant respiration; oxygen uptake is independentof the oxygen partial pressure over a wide range. Cell fractionswere isolated by differential centrifugation and their oxidativeactivities studied. Oxidation of succinate and citrate by mitochondriacan be inhibited 50 to 60 per cent. by 1 X 10^–3 M. HCN,and antimycin A (AA) causes partial inhibitions. An active mitochondrialcytochrome-c oxidase is present, and it shows a typical sensitivityto cyanide. The mitochondria possess an active reduced diphosphopyridine-nucleotide(DPNH) oxidase system, which is inhibited roughly 80 per cent.by 1 X 10^–3 M. HCN and 1.7 µg./ml. AA. The microsomalDPNH oxidase, which is less sensitive to inhibitors, is lessactive per gramme of tissue than that on the mitochondria. Thefinal supernatant shows little DPNH oxidase. With all fractions,reduced triphosphopyridine nucleotide (TPNH) is oxidized muchmore slowly than DPNH. DPNH-cyto-chrome-c reductase activitywas measured; the mitochondrial system is partially blockedby AA, whereas the microsomal activity is AA-insensitive. Spectro-photometricexamination of a preparation of solubilized mitochondria showedthat cytochromes a, b, and c are present. The results are discussedwith reference to the pathway and localization of hydrogen andelectron transport in the Aroid spadix.     

Respiration Rate and Mitochondrial Oxidase Activity in Arum Spadix

1. Mitochondria prepared from young Arum spadix oxidise succinicand -ketoglutaric acids at about 300µl. O₂/hr./g. wetwt. but as the spadix ages the activity of the mitochondriaincreases more than tenfold. The increase results from a smallrise in the quantity of mitochondrial nitrogen brought downin the centrifuge and a larger rise in oxidase activity permg. mitochondrial nitrogen. 2. The rate of respiration of spadix slices has been measuredunder conditions in which it is not limited by slow diffusionof oxygen. Slices of young spadix respire at about 1,000–2,000µl. O₂/hr/g. but as the inflorescence opens the rate soarsto 20,000µl. O₂/hr/g. and the spadix becomes warm. 3. Cytochrome oxidase was assayed in mitochondria treated withdigitonin. There is at all times enough cytochrome oxidase toaccount for the rates of oxidation of succinate and -ketoglutarate;and enough to account for the relatively slow respiration ofthe young spadix slices but not for the fastest respirationof the mature spadix. 4. The respiration of spadix slices is found, in contradictionto an earlier report, to be sensitive to malonate.     

In Vitro Propagation of the Elephant Yam, Amorphophallus campanulatus var. hortensis Backer (Araceae)

Lateral buds from the corms of field-grown Amorphophallus campanulatusvar. hortensis Backer were cultured on Murashige and Skoog (MS)medium in the presence of various combinations of naphthaleneaceticacid (NAA) and kinetin (KN) and on MS medium lacking hormoneswith and without the addition of coconut water. Callus and plantletdevelopment was optimal at 0.5 µM NAA and 0.05 µMKN. Plantlets transferred to soil after 24–36 weeks ofculture grew normally. Amorphophallus campanulatus, elephant yam, callus, in vitro propagation, micropropagation plantlets, tissue culture     

BEETLE POLLINATION OF DIEFFENBACHIA LONGISPATHA (ARACEAE)

Dieffenbachia is an monoecious understory herb of tropical rain forests that exhibits a complex and specialized relationship with its beetle pollinators. The erect protogynous inflorescence has the spadix divided, with the female flowers in the basal half and male flowers in the upper half. Dieffenbachia longispatha Engler & Krause is pollinated by scarab beetles in the genera Cyclocephala and Erioscelis. The enveloping spathe of the inflorescence opens in the evening, but no flowers are sexually functional until the stigmas become receptive about 24 hr later. Beetles fly to the inflorescence in darkness, suggesting that floral odors play a role as an attractant. Beetles remain in the inflorescence for 24 hr, eating protein-rich staminodia that surround the stigmas. On the evening of the third day the anthers dehisce and beetles become covered with pollen as they crawl up the spadix in the process of leaving. Beetles fly an average of 80 m between inflorescences, usually to the nearest female inflorescence, although distances of 400–1,000 m have been observed. Minimal estimate of genetic neighborhood sizes are large for D. longispatha (750 to 8,900 plants) and neighborhood areas encompass 41,000 to 67,000 m². Experiments demonstrate that the species is self-compatible and that fruit production is pollinator limited.     

Infrared thermography ofArum lily inflorescences

The infrared radiation emitted from the surface of inflorescences of 12 aroid species was monitored with an infrared camera, capable of 0.1°C resolution, and the data were converted to temperature values by means of temperature reference standards. Images representing surface temperatures were obtained forAmorphophallus bulbifer Blume,A. campanulatus Blume,A. forbesii Engl. et Gehrm.,A. rivieri Dur.,Philodendron selloum Koch,Monstera deliciosa Liebm.,Dracunculus vulgaris Schott,Arum italicum Mill.,A. dioscoridis Sibth.,A. creticum Boiss et Heldr.,Caladium sp., andRemusatia vivipara Schott. These images were different among species with respect to temperature, duration of detectable heat development, and organ type (male and female flowers, spathe and appendix) found to be thermogenic. All these species, however, exhibited three common characteristics: 1) production of heat by the male flowers; 2) pollen-shedding immediately after heat production had ceased; and 3) when male flowers were some distance away from female flowers along the spadix, heat was not detected in female flowers. Heat emission was associated with the alternative, cyanide-insensitive pathway that was fully operative.     

Salicylic Acid Levels in Thermogenic and Non-Thermogenic Plants

The natural trigger for heat production in the thermogenic inflorescencesof Sauromatum guttatum Schott (voodoo lily) was recently identifiedas salicylic acid (SA), which induced heat production at levelsas low as 13 ng g f. wt^–1. Since then the levels of SAwere determined in other thermogenic and non-thermogenic plantspecies. In thermogenic inflorescences of five aroid species,and in male cones of at least four thermogenic cycads SA levelsduring heat production exceeded 1 µg g f. wt^–1.SA was not detected in the thermogenic flowers of a water lily,Victoria regia Lindl. (Nymphaeaceae), and Bactris major Jacq.(Palmae). Levels of salicylic acid varied substantially in thefloral parts of seven non-thermogenic species and in the leavesof 27 non-thermogenic species. Amorphophallus campanulatus Blume ex Decne, Arum italicum Mill., Arum dioscoridis Sibth. & Son., Philodendron selloum Koch, Monstera deliciosa Liebm., Encephalartosferox Bertol. f., Encephalartos hildebrandtii A. Br. & Bouché, Encephalartos gratus Prain, Dioon edule Lindl. cv. edule, Dioon edule Lindl. cv angustifolium, Sauromatum guttatum Schott, voodoo lily, Victoria regia Lindl., Bactris major Jack, salicylic acid, thermogenicity, heat production     

Bioluminescence of sound-scattering layers in the Gulf of Maine

Submersible-based investigations of bioluminescence were conductedin sound-scattering layers (SSLs) in the Gulf of Maine, usingintensified video and dual-beam acoustic methods. Stimulatedbioluminescence in the SSLs was high (3–41 µW sr^–1m^–3 while spontaneous bioluminescence was not detected.The average intensity of individual bioluminescent sources inthe SSLs was 30–200 times greater than the intensity oflight emitters outside the SSLs. The two brightest sources ofbioluminescence were identified as the euphausiid, Meganyctiphanesnorvegica and the cydippid ctenophore, Euplokamis sp. Meganyctiphanesnorvegica formed a SSL within 50 m of the bottom during theday and migrated to the uppermost 30 m of the water column atnight, forming a near-surface SSL. Euplokamis sp., which producedexceptionally intense and long-lasting bioluminescent secretions,occurred within the near-bottom SSL in concentrations up to7 m^–3. Our findings indicate that traditional methodsof identifying the primary light emitters in a region, basedon light measurements from net- or pump-captured organisms,may have underestimated the significant in situ bioluminescencepotential of euphausiids and gelatinous zooplankton. ³ Present address: NOAA/NURP/R-OR2, Silver Spring, MD 20910,USA     

Size-fractionated phytoplankton carboxylase activities in the Indian sector of the Southern Ocean

During the ANTARES 3 cruise in the Indian sector of the SouthernOcean in October–November 1995, the surface waters ofKerguelen Islands plume, and the surface and deeper waters (30–60m) along a transect on 62°E from 48°36'S to the iceedge (58°50'S), were sampled. The phytoplankton communitywas size-fractionated (2 µm) and cell numbers, chlorophyllbiomass and carbon assimilation, through Rubisco and ß-carboxylaseactivities, were characterized. The highest contribution of<2 µm cells to total biomass and total Rubisco activitywas reported in the waters of the Permanent Open Ocean Zone(POOZ) located between 52°S and 55°S along 62°E.In this zone, the picophytoplankton contributed from 26 to 50%of the total chlorophyll (a + b + c) with an average of 0.09± 0.02 µg Chl l^–1 for <2 µm cells.Picophytoplankton also contributed 36 to 64% of the total Rubiscoactivity, with an average of 0.80 ± 0.30 mg C mg Chla^–1 h^–1 for <2 µm cells. The picophytoplanktoncells had a higher ß-carboxylase activity than largercells >2 µm. The mixotrophic capacity of these smallcells is proposed. From sampling stations of the Kerguelen plume,a relationship was observed between the Rubisco activity perpicophytoplankton cell and apparent cell size, which variedwith the sampled water masses. Moreover, a depth-dependent photoperiodicityof Rubisco activity per cell for <2 µm phytoplanktonwas observed during the day/night cycle in the POOZ. In thenear ice zone, a physiological change in picophytoplankton cellsfavouring phosphoenolpyruvate carboxykinase (PEPCK) activitywas reported. A species succession, or an adaptation to unfavourableenvironmental conditions such as low temperature and/or availableirradiance levels, may have provoked this change. The high contributionof picophytoplankton to the total biomass, and its high CO₂fixation capacity via autotrophy and mixotrophy, emphasize thestrong regeneration of organic materials in the euphotic layerin the Southern Ocean.     

Feeding of Sagitta enflata and vertical distribution of chaetognaths in relation to low oxygen concentrations

Zooplankton samples were collected in Mejillones Bay, northernChile (23°00'15'S, 70°26'43'W ). Sampling was conductedat 4 h intervals, for 24 h during three seasons, austral spring(October 2000), summer ( January 2001) and winter (August 2001)at three different strata (0–25, 25–50 and 50–100m). Five species of chaetognaths were collected. Sagitta enflatawas the most abundant species, representing up to 65% of allchaetognaths in total numbers, followed by Sagitta bierii, makingup 34% of the total abundance of chaetognaths. S. enflata wasdistributed mainly above the Oxygen Minimum Zone, while S. bieriiremained below this zone. Feeding rates were relatively constantwithin the upper layer (0–25 m depth), for each samplingdate, averaging 1.2 prey S. enflata day^–1, and decreasingwith depth. Gut content analyses demonstrated that predationwas principally focused on small copepods (<1500 µm),with greatest feeding activity occurring at night. The dailypredation impact on the total standing stock of small copepodsvaried seasonally between 6% in spring and 0.4% in winter. Thispercentage may represent a negligible impact on the entire copepodcommunity, but it is relevant at the species or genus level,since S. enflata removed more than 20% of the standing stockof Centropages brachiatus and Corycaeus sp. Thus, during someperiods of the year, chaetognaths may strongly influence theabundance and size distribution of copepods in coastal upwellingecosystems.     

Some Effects of Indol-3-ylacetic Acid on the Rates of Initiation and Development of Flower Buds of Chrysanthemum morifolium

Frequent applications of a solution containing 50 p.p.m. IAAto the upper leaves of Chrysanthemum plants reduced the numbersof open and opening flowers and delayed harvesting. The ratesof initiation and development of flower buds were studied bydissection in relation to the concentrations of indol-3-yl-aceticacid (IAA) (20–200 p.p.m.) applied to the tops of theplants. Inereasing the concentrations of IAA resulted in a progressivedelay in bud initiation (P<0•001), but had little effecton their subsequent rates of development. The results differedfrom those previously obtained with copper deficient plantsin that the latter deficiency affected both initiation and developmentof the buds.     

Comparison of east and west chlorophyll a standing stock and oceanic habitat along the Transition Domain of the North Pacific

Chlorophyll (Chl) a was measured every 10 m from 0 to 150 min the Transition Domain (TD), located between 37 and 45°N,and from 160°E to 160°W, in May and June (Leg 1) andin June and July (Leg 2), 1993–96. Total Chl a standingstocks integrated from 0 to 150 m were mostly within the rangeof 20 and 50 mg m^–2. High standing stocks (>50 mg m^–2)were generally observed westof 180°, with the exceptionof the sporadic high values at the easternmost station. Thetotal Chl a standing stock tended to be higher in the westernTD (160°E–172°30'E) than in the central (175°E–175°W)and eastern (170°W–160°W) TD on Leg 1, but thesame result was not observed on Leg 2. It was likely that largephytoplankton (2–10 and >10 µm fractions) contributedto the high total Chl a standing stock. We suggest that thehigh total Chl a standing stock on Leg 1, in late spring andearly summer, reflects the contribution of the spring bloomin the subarctic region of the northwestern Pacific Ocean. Thedistribution of total Chl a standing stock on Leg 2 was scarcelyaffected by the spring phytoplankton bloom, suggesting thattotal Chl a standing stock is basically nearly uniform in theTD in spring and summer. Moreover, year-to-year variation inthe total Chl a standing stock was observed in the western TDon Leg 1, suggesting that phytoplankton productivity and/orthe timing of the main period of the bloom exhibits interannualvariations.     

Vertical distribution of pelagic chaetognaths and feeding of Sagitta enflata in the Central Equatorial Pacific

The vertical distribution and feeding of pelagic chaetognathsat 5°S, 160°W in the Central Equatorial Pacific wereinvestigated using a series of 0–500 m vertical haulswith a VMPS net over a 24 h period between 6 and 7 October 1990.The total number of individuals per haul was between 370 and688. Fourteen species in four genera were found at this station.The most abundant species was Sagitta enflata which comprised32.4–61.1% of the individuals collected from the 0–500m layer. Mesopelagic species made up 9.3–15.1% of thetotal number of individuals. Sagitta enflata and Pterosagittadraco were found in the upper part of the thermocline both byday and at night. The fraction of the population containingfood items (FCF) of S.enflata in the 0–50 m layer variedbetween 4.8 and 12.5% (mean 10.8%) and feeding activity washighest between sunrise and noon. The percentages of Copepoda,Foraminifera, crustacean larvae, Chaetognatha, Pteropoda, Ostracoda,fish and unidentified material in the gut of S.enflata were51.9,6.7,3.8,2.9,1.9,1.9 and 30.9%, respectively. Sagitta enflataconsumed food organisms which were mainly between 0.5 and 1.0mm in length. The daily feeding rate of S.enflata was 1.81 preyper individual, which was equivalent to 8.06 mg C m^–2day^–1. This corresponded to     

The Effect of Pollination and Ethylene on the Colour Change of the Banner Spot of Lupinus albifrons (Bentham) Flowers

In Lupinus albifrons flowers the banner spot of the standardis initially coloured white or pale yellow. Two to three daysafter reaching the stage of full flower opening, this bannerspot develops a pinkish blush and is deep magenta after a further24 h. The development of this pigmentation is accelerated byexposure to ethylene in a concentration- and time-dependentmanner. Flowers with a pinkish banner spot produced the greatestamounts of ethylene and production was much lower in flowerswhich had either completed the colour change or in which thebanner spot colour remained unchanged. Treatments such as stigmaremoval or pollination increased the rate of ethylene production.Dissection of the flowers showed that while the banner spotis changing colour there is no change in the rate of productionof ethylene from the standard, i.e. from the banner spot orsurrounding tissue. The major sites of production at this timeare the keel and pistil. Isolated flowers withered within 2 d of removal from the plantand therefore did not show any change in the colour of the bannerspot unless exposed to ethylene. The increase in banner spotpigment was about fourfold when isolated floweres were exposedto ethylene (0·24 µl 1^–1): however, the increasewas less than twofold when isolated standards were exposed toethylene (0·27 µl I^–1). Application of silverthiosulphate (STS) to intact isolated flowers, as a 1 h pulseprior to ethylene exposure, partially prevented the pigmentaccumulation, whilst a continuous supply of STS reduced theethylene-induced colour change by approx. 50% Low concentrationsof cycloheximide (CHI) (0·01 mg ml^–1) reduced theaccumulation of pigment in the banner spot of ethylene-treatedflowers, and higher concentrations (1·0 mg ml^–1)completely prevented the ethylene-induced colour change. Ethylene, flower senescence, Lupinus albifrons, pollination     

Borate absorption in excised sugarcane leaves

Borate absorption in sugarcane consists of a rapid and reversibleinflux into the mesophyll cells of the leaf which is completedwithin 20 rains. (Phase I), followed by a slower and irreversibleaccumulatory phase (II). Phase II uptake represents the summationof 3 absorption mechanisms, each dependent upon the externalconcentration. Highly specific mechanisms 1 and 2 transportborate across the initial barrier into the cells, reaction 3carries the borate across the vacuolar membrane. Calcium isshown to be essential for maximum rates of borate absorption.All 3 reactions are inhibited by OH^– through a combinationof competitive inhibition and irreversible disruption of cellularfunction or structure. Temperature changes over the range of10–40 profoundly affect V_maz and K_m1, but have no effecton K_m2 and K_m3. Reactions 1 and 2 are unaffected by 50 mtl Cl^–,SO^–– or H2PO4^–, whereas each of these anionscompetes with H2BO3^– for site 3. Specific metabolic inhibitorswere used to delineate a linkage of mechanisms 1 and 2 to respiratoryelectron transport. Mechanism 3 is coupled to oxidative phosphorylation. ¹Published with the approval of the Director of the Hawaii AgriculturalExperiment Station as Technical Paper No. 954.     

Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux

Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 50–65 mm P.atlanticum removed53% of phytoplankton standing stock in the 0–10 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 0–50 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.4–1.6 x 10⁶ pellets m^–210 h^–1 or 305–1035 mg C m^–2 10 h^–1 and1.4 x 10⁵ pellets m^–2 10 h^–1 or 87.4 mg C m^–210 h^–1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}60–70%after 45 h. We believe that given the sinking rate of 70 m day^–1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer.