The early time course of the inhibition of stem growth of etiolated pea seedlings by fluorescent light

The stem elongation responses of etiolated peas (Pisum sativum L.) to fluorescent light (35–45 mol.m^t-2.s^-1) were recorded using high resolution position transducers. Continuous fluorescent light decreased growth by 70% within 9 min. The growth rate declined to 5% of the control over the next 2 h and remained at this level for 7 h. Pulses of fluorescent light ranging from 8 s to 34 min led to partial suppression of growth and resulted in a complex kinetic response. The distinctive kinetics of blue and red light inhibition were apparent as components of the responses to non-saturating levels of fluorescent light. The rapid suppression of growth by blue light was not affected by concomitant red light. The lag time for the onset of red light inhibition was not affected by concomitant blue, but the rate of inhibition appeared accelerated.     

Light quantity and quality interactions in the control of elongation growth in light-grown Chenopodium rubrum L. seedlings

The spectral control of hypocotyl elongation in light-grown Chenopodium rubrum L. seedlings has been studied. The results showed that although the seedlings responded to changes in the quantity of combined red and far-red radiation, they were also very sensitive to changes in the quantity of blue radiation reaching the plant. Altering the proportion of red: far-red radiation in broad waveband white light caused marked differences in hypocotyl extension. Comparison of the responses of green and chlorophyll-free seedlings indicated no qualitative difference in the response to any of the light sources used, although photosynthetically incompetent plants were more sensitive to all wavelengths. Blue light was found to act primarily of a photoreceptor which is different from phytochrome. It is concluded that hypocotyl extension rate in vegetation shade is photoregulated by the quantity of blue light and the proportion of red: far-red radiation. In neutral shade, such as that caused by stones or overlying soil, hypocotyl extension appears to be regulated primarily by the quantity of light in the blue waveband and secondarily by the quantity of light in the red and far-red wavebands.Abbreviations B blue - FR far-red - k ₁, k ₂ rate constants for photoconverison of Pr to Pfr and Pfr to Pr, respective - k ₁/k ₁ +k ₂= phytochrome photoequilibrium - k ₁ +k ₂= phytochrome cycling rate - Pr=R absorbing form of phytochrome - Pfr=FR absorbing form of phytochrome - P_tot Pr+Pfr - PAR photosynthetically active radiation = 400–700 nm - R red - WL white light     

Light effects on in vitro rooting of pear cultivars of different rhizogenic ability

The effect of varying light regimes on in vitro rooting of microcuttings of two pear (Pyrus communis L.) cultivars was investigated. Cultures of the easy to-root Conference and the difficult-to-root Doyenne d'Hiver were incubated for 21 days with or without indole-3-butyric acid (IBA) in the medium in darkness or under continuous far-red (8 µmol m^–2 s^–1), blue, white or red (15 or 36 µmol m^–2 s^–1) light. Conference rooted without IBA when exposed to red, blue or white light while no rooting was observed under far-red light and in darkness. The high rooting efficiency under red and, by contrast, the inhibition under far-red light and darkness suggest the involvement of the phytochrome system in rhizogenesis. The addition of IBA to the culture medium enhanced root production under all light regimes in both cultivars. Red light, especially at the lower photon fluence rate, had a positive effect by increasing root extension (number × length of roots) and stimulating secondary root formation.Abbreviations IBA Indole-3-butyric acid - R red light - B blue light - FR far-red light - W white light - D darkness - P_fr active (far-red light absorbing) form of phytochrome - P_tot total phytochrome - BA benzyl-adenine     

Lake optics and depth limits for photogenesis and photosynthesis in charophyte meadows

Two series of lakes with increasing attenuation were examined for trends in spectral composition. They became the basis for an evaluation of the light environment at the lower boundary (LB) of Nitella meadows in three other series of lakes. Increased attenuation (K _d PAR) was marked by progressive erosion of the blue window and caused primarily by humic substances. An increase in K _d PAR from 0.06 to 0.81 produced, at the floor of the euphotic zone, a shift in K _d min from 440 to 580 nm. Regressions of boundary depths of Nitella meadows on water clarity produced similar slope coefficients for the three series of lakes. Several trends became evident: 1, PAR irradiance at the LB increases with depth of the LB; 2, red light (E _d 660) declines from richness at shallow LB to near extinction in deep water LB in clear lakes; while 3, blue light (K _d 450) increases to an asymptote. Blue light appears to substitute, although less effectively, for red light irradiance in the growth regulation of charophytes. These data support an hypothesis that spectral quality is involved in the determination of lower boundary depths for benthic macro-algae.     

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

An interaction is demonstrated between the effects of phytochrome and cryptochrome (the specific blue-light photoreceptor) in the inhibition of hypocotyl elongation of light-grown cucumber (Cucumis sativus L.) cv. Ridge Greenline seedlings. At certain fluence rates of blue light the total inhibition response is greater than the sum of the separate responses to each photoreceptor. The threshold for response to blue light is reduced at least 30-fold by additional red-light irradiation. The synergistic effect is demonstrated for two different fluence rates of red light. Synergism is mediated by phytochrome in both the cotyledons and the hypocotyl.Abbreviations and symbols BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - photostationary state of phytochrome - _c calculated      

Does photorespiration protect the photosynthetic apparatus in french bean leaves from photoinhibition during drought stress?

Dithiothreitol (DTT), an inhibitor of violaxanthin de-epoxidation and zeaxanthin formation in chloroplasts, inhibited blue-light-stimulated stomatal opening in epidermal peels of Vicia faba L. in a concentration-dependent fashion. Complete inhibition was observed at 3 mM DTT. The DTT effect was specific for the stomatal response to blue light, and the red-light-stimulated opening, which depends on photosynthetic reactions in the guard cells, was unaffected. Preirradiation of stomata in epidermal peels with increasing photon fluence rates of red light, prior to an incubation in 10 mol·m^-2·s^-1 of blue light and 100 mol·m^-2·s^-1 red light, resulted in a DTT-sensitive, blue-light-stimulated opening that was proportional to the fluence rate of the red light pre-treatment. Guard cells in epidermal peels and guard-cell protoplasts irradiated with red light showed increases in their zeaxanthin content that depended on the fluence rate of red light, or on the incubation time. The increases in zeaxanthin concentration were inhibited by DTT. The obtained results indicate that zeaxanthin could function as a photoreceptor mediating the stomatal responses to blue light.Abbreviation DTT dithiothreitol This work was supported by grants from the National Science Foundation and the US Department of Energy to E.Z.     

一株高产洛伐他汀红曲霉的筛选与液态发酵条件优化

【背景】洛伐他汀(lovastatin)是红曲霉的次生代谢产物,是重要的临床用降血脂药物。在液态发酵条件下,红曲霉的洛伐他汀产量较低,难以满足工业化生产的要求。【目的】筛选获得一株高产洛伐他汀的红曲霉株,并通过优化液态发酵条件提高洛伐他汀的产量。【方法】从红曲米中筛选获得一株高产洛伐他汀的红曲霉株,依据形态学特征、生理生化特性及18S rRNA基因序列分析对分离菌株进行鉴定;通过响应面法对其产洛伐他汀的液态发酵条件进行优化。【结果】获得一株产洛伐他汀的紫红曲霉(Monascus purpureus M4),该菌在甘油57.80g/L、酵母浸粉5.52 g/L、接种量为6.90%条件下,洛伐他汀产量(173.60 mg/L)较优化前提高了4.8倍。【结论】菌株M4产洛伐他汀最优液态发酵条件的建立,为洛伐他汀的大规模生产及该菌株的工业化应用提供了技术支撑。     

Rearrangement of light harvesting bacteriochlorophyll homologues as a response of green sulfur bacteria to low light intensities

The pigment composition of two species of green-colored BChl c-containing green sulfur bacteria (Chlorobium limicola and C. chlorovibrioides) and two species of brown-colored BChl e-containing ones (C. phaeobacteroides and C. phaeovibrioides) incubated at different light intensities have been studied. All species responded to the reduction of light intensity from 50 to 1 Einstein(E) m^–2 s^–1 by an increase in the specific content of light harvesting pigments, bacteriochlorophylls and carotenoids. At critical light intensities (0.5 to 0.1 E m^–2 s^–1) only brown-colored chlorobia were able to grow, though at low specific rates (0.002 days^–1 mg prot^–1). High variations in the relative content of farnesyl-bacteriochlorophyll homologues were found, in particular BChl e ₁ and BChl e ₄, which were tentatively identified as [M, E] and [I, E] BChl_F e, respectively. The former was almost completely lost upon reduction of light intensity from 50 to 0.1 E m^–2 s^–1, whereas the latter increased from 7.2 to 38.4% and from 13.6 to 42.0% in C. phaeobacteroides and C. phaeovibrioides, respectively. This increase in the content of highly alkylated pigment molecules inside the chlorosomes of brown species is interpreted as a physiological mechanism to improve the efficiency of energy transfer towards the reaction center. This study provides some clues for understanding the physiological basis of the adaptation of brown species to extremely low light intensities.Abbreviations BChl bacteriochlorophyll - [M, E] BChl_F e 8-methyl, 12-ethyl BChl e, esterified with farnesol (F). Analogously: I - isobutyl - Pr propyl - Car carotenoids - Chlb chlorobactene - HPLC high performance liquid chromatography - Isr isorenieratene - LHP light harvesting pigments - PDA photodiode array detector - RC reaction center - RCH relative content of homologues     

Influence of chlorophyll content on phytochrome measurements in turnip cotyledons

Phytochrome determinations at 730/800 nm were performed on de-etiolated turnip (Brassica rapa L.) cotyledons in which chlorophyll (Chl) content had been reduced experimentally to varying degrees by pre-treatment with high temperature (HT), or transfer to 3% ethanol. The magnitude of detectable phytochrome depended on Chl content, showing a linear relationshop in vivo. The results were confirmed by an in vitro experiment where, however, the correlation was exponential. An attempt is made to illustrate phytochrome decay in continuous blue or red light after corretion for Chl interference. To overcome the possible objection that the higher (A) measured in continuous light after HT pre-treatment could be caused by a reduced rate of destruction, apparent re-synthesis following red light was measured after several hours of darkness during which time the HT effect was lost. Under these conditions HT pre-treated samples display a more realistic magnitude of apparent new synthesis and make correlation with a physiological response possible.Abbreviations Chl chlorophyll - HT high temperature - E ethanol - W water - D darkness - FR far red - R red - FW fresh weight     

Cell expansion in the filamentous gametophyte of the fernOnoclea sensibilis L.

Filamentous gametophytes of the fernO. sensibilis were exposed to paired combinations of light of different qualities, hormones and cations in the attempt to elucidate the underlying processes that regulate cell expansion. Simultaneous treatments with high-pH buffers or the auxin antagonistp-chlorophenoxyisobutyric acid abolished blue-light-mediated expansion but did not influence growth in red light. In contrast, the red-light response was preferentially altered by the ethylene absorbant KMnO₄ or the Ca²⁺ chelator ethyleneglycol-bis(-aminoethyl ether) N,N-tetraacetic acid. The Ca²⁺ ionophore A23187 caused a significant reduction in cell expansion under both blue and red irradiation. A marked promotion of expansion was mediated by high concentrations of indole-3-acetic acid, but this effect was dependent on the presence of low-pH buffers. The ethylene-generating agent 2-chloroethylphosphonic acid decreased the magnitudes of both photoresponses; this inhibition was further enhanced by high Ca²⁺ concentrations. These findings and those with other plants are interpreted in terms of two independent control mechanisms for cell expansion: 1) a blue light photoreceptor-auxin-hydrogen ion system, and 2) a phytochrome-ethylene-calcium ion system.Abbreviations APW-X artificial pond water (the associated number designates pH) - CEPA 2-chloroethylphosphonic acid - EGTA ethyleneglycol-bis(-aminoethyl ether)N,N-tetraacetic acid - IAA indole-3-acetic acid - PCIB p-chlorophenoxyisobutyric acid     

Action spectra for changes in the “high irradiance reaction” in hypocotyls of Sinapis alba L.

Detailed action spectra are presented for the inhibition of hypocotyl extension in dark-grown Sinapis alba L. seedlings by continuous (24 h) narrow waveband monochromatic light between 336 nm and 783 nm. The results show four distinct wavebands of major inhibitory action; these are centred in the ultra-violet (_max=367 nm), blue (_max=446 nm), red (_max=653 nm) and far-red (_max=712 nm) wavebands. Previous irradiation of the plants with red light (which also decreases Ptot) causes decreased inhibitory action by all wavelengths except those responsible for the red light inhibitory response. Pre-irradiation did not alter the wavelength of the action maxima. It is concluded that ultra-violet and blue light act mainly on a photoreceptor which is different from phytochrome.Abbreviations B blue - D dark - FR far-red - HIR high irradiance reaction - HW half power bandwith - Pr R absorbing form of phytochrome - Pfr FR absorbing form of phytochrome - Ptot total phytochrome=Pr+Pfr - R red - UV ultra violet     

Effect of light and gibberellic acid on cell division in the first foliage leaf of durum wheat (Triticum durum Desf.)

The present paper is part of a research program which aims at a quantitative analysis of the effects of light and gibberellic acid (GA₃) on growth of the first foliage leaf in durum wheat (Triticum durum Desf.). Since leaf growth is the combined result of the increase in cell number (cell division) and cell enlargement, the influence of light and GA₃ treatment on cell division in the basal meristem of the first leaf in two cultivars, Cappelli and Creso, was investigated. Creso is a short-strawed cultivar carrying the Gai 1 gene which influences both plant height and insensitivity to applied GA₃. Cell division, as measured by mitotic index, was similar in darkness, continuous red light and dichromatic irradiation (far-red plus red), while lower mitotic rates were observed under continuous far-red light: this indicates that the response of cell division is modulated by a high-irradiance reaction of phytochrome in both cultivars. The two cultivars showed different responses to blue light. In Cappelli, blue light and dichromatic irradiation (blue plus red) gave lower mitotic indices than the dark control, indicating the action of a specific blue-light-absorbing photoreceptor, whereas in Creso the response kinetics to all light regimes which included blue light were more complex. On the basis also of the results obtained with GA₃ application in Cappelli, it appears that (i) the hormonal treatment is able to change the pattern of mitotic index only in the presence of the action of a blue-light receptor and (ii) the different responses of the two cultivars could be the result of different endogenous hormonal levels. The importance of the observations in relation to the data for first-leaf longitudinal growth reported in a previous paper (Baroncelli et al. 1984, Planta 160, 298–304) is discussed.Abbreviations BL blue light - D darkness - FR far-red light - GA gibberellin - GA₃ gibberellic acid - m.i. mitotic index - Norflurazon 4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-totyl-3(2H)) pyridazinone - R red light - WL white light - phytochrome photoequilibrium     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Formation of water-solubleMonascus red pigments by biological and semi-synthetic processes

Summary New water-soluble red pigments were produced byMonascus sp. in a chemically defined fermentation medium containing glutamate as nitrogen source. They were isolated and characterized as glutamate derivatives of the well-known orangeMonascus pigments (monascorubrin and rubropunctatin). The new pigments have several advantages over the known redMonascus pigments (rubropunctamine and monascorubramine) including very high water-solubility, higher absorption coefficient, and greater resistance to decoloration by light. Adding glutamate, glycine or leucine to a resting-cell system led to the formation of specific water-soluble red pigments corresponding to the exogenous amino acid. The water-soluble red pigments produced by resting-cells have retention times identical to those of the corresponding red derivatives made chemically from the orange pigments in methanol-phosphate buffer at pH 7. The hydrophobicities of the amino acid sources correspond to the HPLC retention times of the red pigments derived from them.     

Photosynthetic metabolism and cell-wall polysaccharide accumulation inGelidium sesquipedale (Clem.) Born. et Thur. under different light qualities

The influence of different light qualities on the photosynthetic rate, dark respiration, intracellular carbon and nitrogen content, and accumulation of photosynthetic pigments and cell-wall polysaccharides during short-term incubation (5 h) of the red algaGelidium sesquipedale was investigated. The same photon irradiance of 50mol m^–2 s^–2 below the light saturation point of photosynthesis was applied in each case. Blue light stimulated photosynthesis, dark respiration and the accumulation of chlorophyll and biliproteins, phycoerythrin in particular. The accumulation of internal carbon and nitrogen was greater under blue light than under the other light qualities. In contrast, the percentage of cell-wall polysaccharides was higher in red light. The content of cell-wall polysaccharides decreased during the time of incubation in all light treatments except in red light. The action of a non-photosynthetic photoreceptor in the control of cell-wall polysaccharide synthesis is suggested because the accumulation of cell-wall polysaccharides was not correlated with net photosynthesis in contrast to what occurred with carbon, chlorophyll and phycoerythrin accumulation.     

Ionic mechanism and role of phytochrome-mediated membrane depolarisation in caulonemal side branch initial formation in the mossPhyscomitrella patens

In caulonemal filaments of the mossPhyscomitrella patens (Hedw.), red light triggers a phytochrome-mediated transient depolarisation of the plasma membrane and the formation of side branch initials. Three-electrode voltage clamp and ion flux measurements were employed to elucidate the ionic mechanism and physiological relevance of the red-light-induced changes in ion transport. Current-voltage analyses indicated that ion channels permeable to K⁺ and Ca²⁺ are activated at the peak of the depolarisation. Calcium influx evoked by red light coincided with the depolarisation in various conditions, suggesting the involvement of voltage-gated Ca²⁺ channels. Respective K⁺ fluxes showed a small initial influx followed by a dramatic transient efflux. A role of anion channels in the depolarising current is suggested by the finding that Cl^– efflux was also increased after red light irradiation. In the presence of tetraethylammonium (10 mM) or niflumic acid (1 M), which block the red-light-induced membrane depolarisation and ion fluxes, the red-light-promoted formation of side branch initials was also abolished. Lanthanum (100 M), which inhibits K⁺ fluxes and part of the initial Ca²⁺ influx activated by red light, reduced the development of side branch initials in red light by 50%. The results suggest a causal link between the red-light-induced ion fluxes and the physiological response. The sequence of events underlying the red-light-triggered membrane potential transient and the role of ion transport in stimulus-response coupling are discussed in terms of a new model for ion-channel interaction at the plasma membrane during signalling.Abbreviations [Ca²⁺]_c cytosolic free Ca²⁺ - I-V current-voltage - E equilibrium potential - Pr red-light-absorbing phytochrome form - Pr far-red-light-absorbing phytochrome form - SPQ 6-methoxy-l-(3-sulphonatopropyl)quinolinium - TEA tetraethylammonium     

Phytochrome-mediated induction of phenylalanine ammonia-lyase in the cotyledons of tomato (Lycopersicon esculentum Mill.) plants

Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5.) induction in cotyledons from 96-h dark-grown Lycopersicon esculentum Mill. was studied in response to continuous light and hourly light pulses (blue, red, far red). The increases of PAL promoted by blue and red pulses are reversed completely by immediately following 758 nm irradiations. The response to continuous red light could be substituted for by hourly 6-min red light pulses. The effect of continuous red treatments is mainly due to a multiple induction effect of phytochrome. In contrast to red light, hourly light pulses with far red and blue, light can only partially substitute for continuous irradiation. The continuous blue response could be due to a combination of a multiple induction response and of a high irradiance response of phytochrome. The continuous far red response, could represent a high irradiance response of phytochrome. Dichromatic irradiations indicate that phytochrome is the photoreceptor controlling the light response (PAL) in tomato seedlings.Abbreviations Norflurazon NF-4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-tolyl)-3 (2H) pyridazinone - PAL phenylalanine ammonia-lyase - phytochrome photoequilibrium P_fr/P_tot - P_fr far-red absorbing form of phytochrome - P_r red absorbing form of phytochrome - P_tot total phytochrome: P_r+P_fr     

Are NADP-dependent isocitrate dehydrogenases and ferredoxin-dependent glutamate synthase co-regulated by the same photoreceptors?

Activities of NADP-dependent isocitrate dehydrogenases (cytosolic and plastidic isoforms, ICDH1 and ICDH2; EC 1.1.1.42) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) in turions of Spirodela polyrhiza were all stimulated by light. Single or repeated red light (R) pulses induced the activity of the enzymes and this effect was reverted by subsequent far-red light (FR) pulses. The enzymes are, therefore, co-regulated by the low-fluence response of phytochrome. For ICDH, this is reported here for the first time. Neither an effect of the very low-fluence response nor of the FR-mediated high-irradiance response was detectable. Irradiance with continuous R resulted in enhanced enzyme activities and protein levels (Western analysis using polyclonal antibodies against ICDH1 and Fd-GOGAT). These additional effects of continuous R (called a non-induction effect) could be inhibited for ICDH1 and ICDH2 by the inhibitor of photosynthetic electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and are therefore related to the effect of photosynthesis. In contrast, the non-induction effect of Fd-GOGAT was resistant against this inhibitor. Moreover, hourly R pulses did not replace the effect of continuous R. The non-induction effect of light on the activity and protein level of Fd-GOGAT was therefore tentatively classified as an R-mediated high-irradiance response. The activity of Fd-GOGAT but not that of ICDHs was additionally regulated by a specific blue-light receptor. It can be concluded that the levels of ICDHs and Fd-GOGAT were coordinated by light but were not co-regulated by the same photoreceptors. Nitrate is necessary for the light regulation of both enzymes, contributing to the coordinated expression of the relevant genes.Abbreviations DCMU 3-(3,4-Dichlorophenyl)-1,1-dimethylurea - Fd-GOGAT Ferredoxin-dependent glutamate synthase - FR Far-red light - HIR High-irradiance response - ICDH NADP-dependent isocitrate dehydrogenase - ICDH1 Cytosolic ICDH - ICDH2 Chloroplastic ICDH - LFR Low-fluence response - R Red light - SDS–PAGE Denaturing polyacrylamide gel electrophoresis - VLFR Very low-fluence response     

Redistribution of growth during phototropism and nutation in the pea epicotyl

First positive phototropism of the third internode of intact, 5-d-old pea (Pisum sativum L.) seedlings, grown under continuous, dim red light, showed maximal response following a photon fluence of 3 mol·m^-2 blue light. Greater or lesser fluences (with irradiation time 100 s or less) caused less bending, no response being detectable above 300 or below 0.03 mol·m^-2. Bilateral irradiation with blue light caused no detectable inhibition of growth rate over that range of fluences. The linear nutation of the pea third internode was shown to be driven by a balanced oscillation of growth rate such that the overall growth rate was little changed during the oscillation. Phototropic stimulation changed neither the amplitude nor the period of nutation. Nutation and phototropism probably regulate growth independently. Phototropism in response to the optimal blue light fluence was caused by concomitant depressed growth on the irradiated side and stimulated growth on the shaded side of the bending internode. These results are consistent with the Cholodny-Went hypothesis which states that unilateral blue light induces a lateral redistribution of a growth regulator.Abbreviations R red light - BL blue light Carnegie Institution, Department of Plant Biology paper No. 921     

Absence of red-light enhancement of phototropism in pea seedlings at limiting irradiances of blue light

The effect of different light qualities (blue, green, white, red and far-red) on ethylene production in leaf discs and flower petal discs of Begonia × hiemalis cv. Schwabenland Red was studied. All the light qualities, except far-red, reduced the ACC-conversion to ethylene in leaf discs by about 70% at a photosynthetic photon flux density (PPFD) of 20 mol m^–2s^–1.Blue and green light were less inhibitory than white and red light at lower PPFD. In all treatments far-red light at 0.5 mol m^–2s^–1 of photon flux density (PFD) stimulated the ACC-conversion to ethylene in leaf discs by about 60–90% compared to the dark-incubated control. White and red light strongly inhibited the -naphthalene-acetic acid (NAA) stimulated ethylene synthesis in leaf discs. The results may suggest that the ethylene production is controlled by phytochrome in the leaves but not in the petals. Lack of coaction of any light quality with silver ions on ethylene production in leaf and petal discs was also observed.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme - NAA -naphthalene-acetic acid - PFD photon flux density - PPFD photosynthetic photon flux density - RH relative air humidity - SAM S-adenosylmethionine - STS silver thiosulphate