Abscission: Response to Red and Far-Red Light

Craker, L. E., Zhao, S. Y. and Decoteau, D. R. 1987. Abscission:response to red and far-red light.—J. exp. Bot. 38: 883–888. The dose-response and time relationship of red and far-red lightin the inhibition and promotion, respectively, of dark-inducedleaf abscission was quantified using cuttings of coleus (ColeusBlumei Benth.). A continuous photon flux of approximately 15nM m^–2 s^–1 of red light was sufficient to preventleaf abscission. Abscission was promoted by exposure to a photonflux of approximately 10 nM m^–2 s^–1 of far-red lightThe inhibition of abscission by red light could be reversedby treatment with far-red and the promotion of abscission byfar-red light could be reversed by treatment with red lightThe data were consistent with a phytochrome receptor systemlocated in the leaves that controlled the presence of an abscission-inhibitingsubstance in the abscission zones. Key words: Abscission, Coleus Blumei, far-red light red light     

Photoinduction of Spore Germination in a Fern, Mohria caffrorum

Irradiation of spores of the fern Mohria caffrorum Sw. witheither red light (67.4 µW cm^–2) or far-red light(63.2 µW cm^–2) for a period of 24 h induced maximumlevels of germination. Brief irradiations with blue light (127.6µW cm^–2) administered before or after photoinductioncompletely nullified the effects of red or far-red light; however,with prolonged exposure to blue light, germination levels roseto near maximum. The similar effects of red and far-red lightin promoting spore germination makes the involvement of phytochromein this process questionable. Based on energy requirements,the promotive and inhibitory phases of blue light appear toinvolve independent modes of action. Mohria caffrorum, ferns, spore germination, photoinduction, phytochrome     

Morphological and physiological characterization of IAA-less-sensitive and IAA-sensitive phases in rooting of Azukia cuttings

In disbudded epicotyl cuttings taken from light grown 5-dayold Azukia angularis Phaseolus angularis) seedlings, all adventitiousrootlets appeared on the second day of incubation. No root primordiawere observed within the first 24 hr and no increase in thenumber of roots occurred after 48 hr. Puromycin (5.5?10^–5M), p-fluorophenylalanine (1?10^–3M),2-thiouracil (2.3?10^–4M) and 2,6-diaminopurine (2?10^–5M)inhibited rooting when applied to cuttings on the second day,but showed no inhibition when applied on the first day. Unlike these inhibitors, pyrithiamine (7.2?10^–5M) inhibitedrooting when it was applied to cuttings on the first day. A rooting promoting effect was observed with actinomycin D (2.4?10^–6M),2,4-dinitrophenol (3?10^–5M) and p-fluorophenylalanine(1?10^–4M) applied to the cuttings on the first day, whereasindoleacetic acid (1.7?10^–4M) showed its promoting effectmost effectively on the second day. ¹Contribution No. 17 from the Botanical Gardens, Faculty ofScience, University of Tokyo, Tokyo, Japan. (Received June 4, 1969; )     

Bl?tenbildung bei Lemna paucicostata 6746 durch kombinierte Anwendung von Abscisins?ure und GCG

To a certain extent the flowering of Lemna paucicostata 6746is evoked in continuous light by application of abscisic acid(ABA) and CCC. Moreover, the action of the combined substancesappears in two separate concentration ranges. In the range ofABA 2?10^–9 M/CCC 10^–7–10^–6 M floweringis initiated without inhibition of vegetative growth and proceedsonly in the presence of high intensity light and sucrose. Acombination of ABA 2?10^–5 M/CCC 10^–3M simultaneouslycauses a strong inhibition of frond multiplication. Here theeffect can be observed also under low intensity light conditionsand without sucrose in the medium. A range with flower inhibitingactivity lies between the two flower promoting concentrationranges. (Received November 16, 1972; )     

Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod

The response of the germination of seeds of Barbarea vema (Mill.)Aschers, Brassica chinensis L., Brassica juncea (L.) Czern.& Coss., Brassica oleracea L. var. gongylodes L., Camelinasaliva (L.) Crantz, Eruca saliva Mill., Lepidium sativum L.,Nasturtium officinale R. Br., and Rorippa palustris (L.) Besserto white fluorescent light of different photon flux densitiesapplied for different daily durations in a diurnal alternatingtemperature regime of 20 °C/30 °C (16 h/8 h) was quantifiedby linear relations between probit percentage germination andthe logarithm of photon dose, the product of photon flux densityand duration. The low energy reaction, in which increasing dosepromotes germination, was detected in all the seed populationsbut in Barbarea vema and Brassica Juncea the lowest photon doseapplied (10^–5–2 and 10^{–5 7} mol m^–2 d^–1,respectively) was sufficient to saturate the response. Comparisons,where possible, between photoperiods demonstrated reciprocity,i.e. germination was proportional to photon dose irrespectiveof photoperiod, for the low energy reaction in Brassica oleracea(1 min d^–1 to 1 h d^–1), Camelina saliva (1 min d^–1to 8 h d^–1), Eruca saliva (1 min d^–1 to 24 h d^–1),Lepidium sativum (I min d^–1 to 8 h d^–1) and Rorippapalustris (1 min d^–1 to 8 h d^–1), but not in Brassicachinensis and Nasturtium officinale. The high irradiance reaction,in which increasing dose inhibits germination, was detectedin Barbarea vema, Brassica chinensis, Brassica juncea, Brassicaoleracea, and Camelina saliva. The minimum dose at which inhibitionwas detected was lO^–0–3 mol m^–2 d^–1.These results are discussed in the context of devising optimallight regimes for laboratory tests intended to maximize germination The response of germination to photon dose was also quantifiedwith 3 x 10^–4 M GA₂, co-applied (Brassica chinensis, Camelinasaliva, and Lepidium sativum) and with 2 x 10^–2 M potassiumnitrate co-applied (Brassica chinensis). In the latter casepotassium nitrate had no effect in the dark and inhibited germinationin the light, but GA₂, promoted germination substantially inall three species. Variation amongst seeds in the minimum photondose required to stimulate germination was not affected by co-applicationof GA₂, in Brassica chinensis and Camelina saliva, whereas seedsof Lepidium salivum showed a narrower distribution of sensitivitiesto the low energy reaction in the presence of GA₂ Barbarea vema (Mill.) Aschers, Brassica chinensis L., Brassica juncea (L.) Czern. & Coss., Brassica oleracea L. var. gongylodes L., Camelina saliva (L.) Crantz, Eruca saliva Mill., Lepidium satiaum L., Nasturtium officinale R. Br., Rorippa palustris (L.) Besser, Cruciferae, light, gibberellic acid, seed germination, seed dormancy     

Promotion by gibberellin of lettuce seed germiation as a function of presoaking period

Germination of lettuce seeds (Lactuca sativa L. cv. Grand Rapids)was examined in the presence of various doses (10^–5.0–10^–3.0M) of gibberellic acid applied at various times (hour 0–8)of soaking. Germination promotion by gibberellic acid was greateras the dose of gibberellic acid was increased and attenuatedwith the length of the presoaking period. As an exception, ca.95% germination was always evoked by the largest dose (10^–3M) of gibberellic acid given at any time of soaking. The dose-responsecurve obtained for each presoaking period had a distinct sigmoidalprofile. Synergistic and photoreversible promotion by red light of thegibberellin-induced germination was also investigated. Far-redlight pulse given 6 hr after the red pulse was still effectivein removing the red light action. Application of enzyme kineticsto the gibberellin action and also to the synergism betweengibberellin and red light was suggested. ¹National Institute for Basic Biology, Myodaiji, Okazaki 444,Japan. (Received December 18, 1979; )     

Endogenous factors affecting the curved growth of seminal roots of Zea mays L. seedlings grown in liquid culture

Seminal roots of Zea mays L. show curved growth, i.e. waving,meandering and spiral growth, when water cultured. Root curvaturewas accelerated by exogenously applied indole-3-acetic acidat 10^–9 M and gibberellic acid at 10^–6M; this curvaturedisappeared when 10^–7 M p-chlorophenoxyisobutyric acidwas added. Roots curved more when the tops of seedlings wereexposed to light than when the tops of seedlings were covered.These results suggest that auxin may induce root curvature. (Received February 29, 1980; )     

Frond and flower production in Lemna gibba G 3 in presence of respiratory inhibitors

Effects of respiratory inhibitors on frond and flower productionin light culture of a long-day duckweed, Lemna gibba G 3, wereinvestigated. The inhibitors examined could be divided into3 groups based on their specific actions: (A) 2,4-Dinitrophenol(10^–6M), arsenate (10^–4M), malonate (10^–2M),o-phenanthroline (10^–6M), ,'-dipyridyl (10^–5M) andazide (10^–6M) inhibited flower production by suppressingthe rate of flower production without affecting the inductionperiod. Frond production, however, was promoted by these reagents.Effective time of application came one day after the end ofthe induction period. (B) Iodoacetate (10^–6M) and fluoride(10^–4M) inhibited both flower production and, less significantly,frond production. Reduced rate of flower production was responsiblefor the inhibition of flowering. Effective time of applicationpreceded by one day that of A group inhibitors. (C) Salicylaldoxime(10^–6M), diethyldithiocarbamate (10^–6M) and 8-hydroxyquinoline(10^–7M) enhanced flower production by reducing the lengthof the induction period, and simultaneously slightly inhibitedfrond production. Effective time of application was the latterhalf of the induction period. The implications of these findingsare discussed with special reference to the component processesinvolved in photoperiodic induction of flowering in duckweed. (Received March 27, 1969; )     

Removal of the sugar inhibition of flowering in Lemna gibba G3 by catecholamines

DL-Epinephrine (10^–8–10^–7 M), DL-norepinephrine(10⁶ M) and DL-isoproterenol (10^–8–10^–6 M)alleviated floral inhibition due to 1% of sucrose, in Lemnagibba G3. The induction period extended by sucrose was curtailedby epinephrine, frond multiplication enhanced by the sugar beingleft unaltered. The pattern of action of catecholamines appearedto be very similar to that of cAMP. DL-Epinephrine, however,was ineffective in the presence of 10^–7 M DL-propranololwhich affected neither flower nor frond production by itself.Quabain and nicotinic acid also nullified the epinephrine actionon duckweed flowering. These and other relevant findings supportthe hypothesis that the cAMP-adenyl cyclase system participatesin the processes of flower induction in this long-day plant. (Received August 21, 1973; )     

Effects of indoleacetic, p-chlorophenoxyisobutyric and 2,4,6-trichlorophenoxyacetic acids on three phases of rooting in Azukia cuttings

In adventitious root formation of disbudded epicotyl cuttingstaken from light-grown, 5-day-old Azukia angularis seedlings,indoleacetic acid (IAA), 1 x 10^–4 M, applied during thefirst day showed no effect, but enhanced the effect of IAA,1 x 10^–4 M, applied during the second day. Treatment duringthe second day promoted rooting by about 70%, and a combinationof treatments for the first and second days promoted rootingsome 200%. p-Chlorophenoxyisobutyric acid (PCIB), 3 x 10^–4M, and2,4,6-trichlorophenoxyacetic acid (2,4,6-T), 2 x 10^–44M, applied the first day also enhanced the effect of IAA, 2x 10^–4 M, applied the second day. When applied the second day, PCIB, 2 x 10^–4M, increasedthe number of root primordia or clusters of small cells, butnot die number of protruded roots. Formation of the cell clusterwas inhibited by 2,4,6-T, 3 x 10^–4M, applied the secondday. Rooting processes in Azukia cuttings seem to include at leastthree phases: the first phase is induced not only by IAA butalso by PCIB or 2,4,6-T, the second phase is induced by IAAor PCIB and the diird phase depends specifically on IAA. (Received October 28, 1970; )     

The Role of the Red/Far-Red Ratio in the Response of Tropical Tree Seedlings to Shade

The West African species Khaya senegalensis and Terminalia ivorensiswere grown in a controlled environment, varying the photon fluxdensity in the range 18–610 µmol m^–2 s^–1and the red/far-red ratio over an appropriate range to simulatethe shade of a tree canopy versus unattenuated daylight. Theshade tolerant seedlings of Khaya were relatively insensitiveto the red/far-red ratio. The light demanding Terminalia wasconsiderably affected: when the ratio was low the specific leafarea was increased and the leaves produced were very much largerin area. Thus, the Leaf Area Ratio was enhanced and the plantsdisplayed an increase in Relative Growth Rate. Khaya, Terminalia, tropical trees, shade, red/far-red ratio     

The Effect of Cycloheximide on Absorption of Ions by Bean (Phaseolus vulgaris L) Roots

10^–7 M cycloheximide inhibited bean (Phaseolus vulgaris)root elongation by about 20 per cent but it inhibited absorptionof rubidium, sodium, and phosphate ions to a much greater extent(34–71 per cent). Tips of intact plant roots grown inthe inhibitor showed more inhibition in ion uptake than adjacentproximal portions of the same roots and this is taken to indicatethat 10^–7 M cycloheximide does not exert its effect onion uptake by any uncoupling action. Sodium uptake from 0.5 or 10 mM NaCl solutions by root tipswas inhibited by 10^–7 M cycloheximide to twice the extentthat it was in the elongating region of the root. Assuming thatthe inhibitor affects the plasmalemma more than the tonoplast,Epstein's model of parallel operation of system 1 and system2 at the plasmalemma is supported.     

Haustoria of Cuscuta japonica, a Holoparasitic Flowering Plant, Are Induced by the Cooperative Effects of Far-Red Light and Tactile Stimuli

When seedlings of Cuscuta japonica were grown with Vigna radiata(the host plant) in a flower pot for 6 d under white light andthen irradiated with far-red or blue light (ca. 6 µmolphotons m^–2 s^–1), the seedlings parasitized V. radiata.However, no parasitism of the seedlings was observed under redor white light or in darkness. The parasitic behavior of seedlingsof C. japonica was observed even if an acrylic rod was usedas a substitute for the host plant. Upon incubation under far-redlight, the seedling twined tightly around the rod and developedhaustoria towards it. Haustoria also developed when apical andsubapical regions of seedlings were held between two glass platesthat were about 0.7 mm apart and were irradiated with far-redlight. However, no haustoria were induced by either the holdor irradiation alone. These results indicate that parasitismof Cuscuta japonica is controlled by the cooperative effectsof two physical signals, far-red light and appropriate tactilepressure. Our findings suggest that parasitism by the genusCuscuta involves a novel strategy. (Received April 10, 1996; Accepted August 21, 1996)     

Regulation of Free Calcium Concentration in the Pitchers of the Carnivorous Plant Sarracenia purpurea: A Model for Calcium in the Higher Plant Apoplast?

The pitcher of the carnivorous plant Sarracenia purpurea L.contains an entrapped body of liquid within which its prey isdigested. Free calcium in the pitcher is derived from eitherthe pitcher walls or from prey falling into the pitcher; inthe absence of exogenous (prey-derived) calcium it will dependon the active and passive calcium regulatory properties of thepitcher walls and may to some extent therefore mimic calciumin the apoplast of plant cells. Using a calcium-specific electrode,the free calcium concentration of the pitchers of Sarraceniaplants was investigated and the effect of adding a variety ofconcentrations of calcium in water determined. The mean pitcherfree calcium concentration in vivo was 2.3 x 10^–5 M±2.5x 10^–5 M; when pitchers were washed and filled with watercontaining lower calcium concentrations, the concentration inthe pitcher water rose to 1–5 x 10^–5 M. When highercalcium concentrations (up to 1 x 10^–4 M) were added,the pitcher calcium concentration declined to 1–7 x 10^–5M. Concentrations of calcium above 1 x 10^–4 M were alsoreduced, but to a lesser extent. Metabolic inhibition of activeion transport, while inhibiting pitcher acidification, did notinhibit regulation of pitcher free calcium, suggested that itoccurs as a result of calcium exchange sites in the pitcherwalls. The data are discussed in relation to the physiologyof Sarracenia pitchers and to the usefulness of the pitcheras a model for free calcium in the higher plant apoplast. Sarracenia purpurea L., carnivorous plant, pitcher, free calcium, plant apoplast     

The Photocontrol of Spore Germination in the Fern Ceratopteris richardii

This paper describes how different wavelengths of light regulatespore germination in the fern Ceratopteris richardii. This speciesdoes not exhibit any dark germination. Maximum photosensitivityof the spores is reached 7 to 10 d after imbibition. An increasein the red light fluence above the threshold fluence of 10¹⁶quanta.m^–2 leads to a corresponding increase in germination.In sequential irradiation experiments, farred light can reversethis red light-mediated germination to the level observed withthe far-red light control. Blue light fluences above 10²⁰ quanta.m^–2can also block the germination response to red light. Moreover,this antagonistic effect of blue light is not reversed by subsequentirradiation with red light. It is therefore concluded that phytochromeand a distinct blue light photoreceptor control C. richardiispore germination. These interpretations are entirely consistentwith the published literature on other fern genera. (Received November 28, 1986; Accepted April 6, 1987)     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

A possible mechanism for sugar inhibition of duckweed flowering

Sugar (ca. 1%) reduced the floral index in Lemna gibba G3 byca. 50%, and supplemental addition of cyclic AMP (ca. 10^–5M)removed nearly all of this sugar action. Inhibition by sugarof duckweed flowering may be explained in terms of cataboliterepression. (Received October 9, 1971; )     

Function of cAMP as a Mat-Forming Factor in the Cyanobacterium Spirulina platensis

A dense suspension of Spirulina platensis trichomes aggregatedrapidly and formed a diskshaped algal mat when cAMP was added.Cyclic AMP significantly stimulated algal mat formation at concentrationsas low as 10^–7 M. Stimulation of the mat formation wasmost rapid at about 10^–5M cAMP, but higher concentrationswere not increasingly effective. Other nucleotides such as cGMP,ATP and AMP showed no stimulatory effect on algal mat formation.CCCP, an inhibitor of ATP synthesis, was found to suppress thecAMP-stimulated algal mat formation. Cyclic AMP also stimulatedrespiration and gliding movement of this cyanobacterium. (Received September 2, 1991; Accepted October 15, 1991)     

Replacement by ionophores of the photoperiodic light requirement in Lemna gibba G3

Light requirement during the phytochrome-mediated L1-phase ofLemna gibba G3 can be replaced by 10 µg/liter of valinomycinor gramicidin, supporting the idea (5) that a promoted K⁺-iontransport across membranes would be involved in the photoperiodiclight action on the L1-phase. (Received June 6, 1977; )     

Effect of Spermidine and Methylglyoxal-bis (Guanyl-hydrazone) (MGBG) on In Vitro Pollen Germination and Tube Growth in Catharanthus roseus

Incorporation of polyamine-spermidine into the nutrient mediumat 10^–6 and 10^–5 M concentrations stimulates pollen-tubegrowth in vitro in Catharanthus roseus L. G. Don. MGBG, an inhibitorof spermidine biosynthesis, at 0.5 x 10^–3 and 1 x 10^–3M concentrations reduced the percentage of germination as wellas tube growth and at a concentration of 1.5 x 10^–3 Mgermination was totally inhibited. Pollen grains incubated inthe medium containing 1.5 x 10^–3 M MGBG, when transferredto a fresh medium with 10^–5 M spermidine, resulted in80% germination recovery, along with considerable tube growth.Experiments with actinomycin-D indicate that stimulation ofpollen-tube growth by spermidine may involve de novo synthesisof protein. Catharanthus roseus, pollen germination, tube growth, spermidine, MGBG, inhibition, actinomycin-D