Effect of light and gibberellic acid on coleoptile and first-foliage-leaf growth in durum wheat (Triticum durum Desf.)

A comparison has been made of the relative effectiveness of light quality and quantity and gibberellic acid (GA₃) treatment on the elongation growth of the coleoptile and the first foliage leaf in durum wheat (Triticum durum Desf. cvs. Cappelli and Creso). The cultivar Creso is a shortstrawed variety carrying the Gai 1 gene on chromosome 4A, which influences both plant height and insensitivity to applied gibberellins. The main conclusions are as follows: 1) coleoptile elongation growth appears to be modulated via the fluencerate-dependent action of a blue-light receptor and via a low energy response of phytochrome; 2) the inhibition of first-foliage-leaf growth depends on the operation of a single blue-light-responsive photoreceptor; 3) high energy blue light produces the same inhibitory effect on the two wheat cultivars, whereas at relatively low fluences of white and blue light, the cultivar Creso is more sensitive; 4) the insensitivity to applied GA₃ exerted by the gene Gai 1 in Creso is independent of light; 5) in Cappelli, the action of light on coleoptiles appears to be independent of the applied GA₃, whereas the hormone is able to change the pattern of growth inhibition of the first-foliage-leaf.Abbreviations BL blue light - FR far-red light - GA gibberellin - GA₃ gibberellic acid - R red light - WL white light     

Effect of light and gibberellic acid on chromosome endoreduplication in leaf epidermis ofTriticum durum Desf.

Summary The first foliage leaf ofTriticum durum Desf., cvs. Capelli and Creso, was studied for the action of light and gibberellic acid on different aspects of plant growth. Creso is a short-strawed cultivar carrying theRht 1 gene, that influences both plant height and sensitivity to applied gibberellins. In this study, a cytophotometric analysis of chromosome endoreduplication in bulliform cells of the leaf epidermis was undertaken. The bulliform cells are arranged in long rows and comprise 4C, 8C, and 16C cells. The relative percentage of these cells was recorded under different light regimes and in the presence or absence of gibberellic acid (GA₃). Our data indicate that light strongly affects the occurrence of chromosome endoreduplication. Although cvs. Cappelli and Creso show the same frequency of endo-reduplicated cells in the dark, all light treatments induce lower endo-polyploidy in cv. Creso whereas, in cv. Cappelli, a reduction in endo-polyploidy is observed when plants are irradiated with blue-lacking lights. This indicates that the action of a blue-light responsive photo-receptor determines high endopolyploidy. With respect to GA₃ treatment, cv. Creso is again shown to be insensitive to hormone application, whereas in cv. Cappelli, gibberellic acid influences endopolyploidy level in the dark, causing very high frequencies of 8C cells and relatively high frequencies of 16C cells.This paper is dedicated to the memory of Sergio Baroncelli, Professor of Plant Breeding at the University of Pisa.     

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO₂ exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA₃) at the concentration of 25 g/1 (GA-plants), and then grown under 17 W/m² blue light (B-plants) or 11 W/m² red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA₃ suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.     

Gibberellins in dark- and red-light-grown shoots of dwarf and tall cultivars of Pisum sativum: The quantification,metabolism and biological activity of gibberellins in Progress no. 9 and Alaska

The stem growth in darkness or in continuous red light of two pea cultivars, Alaska (Le Le, tall) and Progress No. 9 (le le, dwarf), was measured for 13 d. The lengths of the first three internodes in dark-grown seedlings of the two cultivars were similar, substantiating previous literature reports that Progress No. 9 has a tall phenotype in the dark. The biological activity of gibberellin A₂₀ (GA₂₀), which is normally inactive in le le geno-types, was compared in darkness and in red light. Alaska seedlings, regardless of growing conditions, responded to GA₂₀. Dark-grown seedlings of Progress No. 9 also responded to GA₂₀, although red-light-grown seedlings did not. Gibberellin A₁ was active in both cultivars, in both darkness and red light. The metabolism of [¹³C³H]GA₂₀ has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [¹³C³H]GA₂₀ is converted to [¹³C³H]GA₁, [¹³C³H]GA₈, [¹³C]GA₂₉, its 2-epimer, and [¹³C³H]GA₂₉-catabolite. [¹³C³H] Gibberellin A₁ was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [¹³C³H]GA₈, was detected. However results do indicate that the tall growth habit of Progress No. 9 in the dark, and its ability to respond to GA₂₀ in the dark may be related to its capacity to 3-hydroxylate GA₂₀ to give GA₁. In red light the overall metabolism of [¹³C³H]GA₂₀ was reduced in both cultivars. There is some evidence that 3-hydroxylation of [¹³C³H]GA₂₀ can occur in red light-grown Alaska seedlings, but no 3-hydroxylated metabolites of [¹³C³H]GA₂₀ were observed in red light-grown Progress. Thus the dwarf habit of Progress No. 9 in red light and its inability to respond to GA₂₀ may be related, as in other dwarf genotypes, to its inability to 3-hydroxylate GA₂₀ to GA₁. However identification and quantification of native GAs in both cultivars showed that red-light-grown Progress does contain native GA₁. Thus the inability of red light-grown Progress No. 9 seedlings to respond to, and to 3-hydroxylate, applied GA₂₀ may be due to an effect of red light on uptake and compartmentation of GAs.Abbreviations AMO-1618 2-isopropyl-4-(trimethylammonium chloride)-5-methylphenyl piperidine-1-carboxylate - cv. cultivar - GC-MS gas chromatography-mass spectrometry - GA_(n) gibberellin A_(n) - HPLC high-pressure liquid chromatography     

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     

Cell elongation and cell division in elongating lettuce hypocotyl sections

The roles of cell division and cell elongation in the growth of sections excised from hypocotyls of lettuce (Lactuca sativa L. cv. Arctic) were investigated. Elongation of sections incubated in the light is inhibited compared to dark-grown sections and this inhibition is reversed by gibberellic acid (GA₃). The elongation of both dark-grown and GA₃-treated, light-grown sections can be enhanced by 10mM KCl. Under all conditions of incubation, elongation growth is greatest in the uppermost quarter of the hypocotyl section while the basal quarter does not elongate. In darkness the two apical segments of sections marked into four equal parts grow at the same rate, while in light, growth of the apical segment exceeds that of the second segment. Cell division in cortical or epidermal cells, as measured by mitotic index or cell number, is not affected by illumination conditions nor by GA₃ or KCl treatments. Although -irradiation and FUDR pretreatment eliminate or cause a marked reduction in cell division in the excised hypocotyl, sections from seeds irradiated with -rays or incubated in 5-fluorodeoxyuridine elongate in response to GA₃ and KCl treatment as do sections from non-pretreated controls. Therefore, since neither GA₃ nor darkness affect celldivision activity and since treatments which eliminate or significantly reduce cell division do not affect growth, we conclude that the effect of GA₃ and darkness in this material is to increase cell elongation.Abbreviations FUDR 5-fluorodeoxyuridine - GA(s) gibberellin(s) - GA₃ gibberellic acid     

Determination of femtomol quantities of gibberellic acid by radioimmunoassay

A highly sensitive and specific radioimmunoassay which allows the detection of as little as 5 fmol (2 pg) of gibberellic acid (GA₃) in crude plant extracts is described. Antisera of high affinity and titer were obtained by immunizing rabbits with a conjugate of carboxyl-coupled GA₃ and bovine serum albumin. [¹²⁵I]Gibberellic acid-[N-(p-hydroxybenzyl) putrescine]amide of high specific activity, used as the immunotracer, is readily displaced by gibberellic acid methyl ester but not by free gibberellic acid. Thus, methylation of extracts prior to analysis is required. The assay is very specific; besides GA₃, only the closely related GA₇ is highly immunoreactive. Various gibberellins, related compounds, as well as other classes of plant hormones do not interfere with the assay. Levels of immunoreactive gibberellins (GA₃, GA₇) in actively growing tissues, among them cell suspension cultures of 33 different species, were determined.Abbreviations ABA abscisic acid - GC-MS gas chromatography-mass spectroscopy - TLC thin-layer chromatography - GA gibberellin Part 17 in the Series: Use of Immunoassay in Plant Science     

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      

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     

Gibberellins and phytochrome regulation of stem elongation in pea

In garden pea (Pisum sativum L.) neither etiolation nor the phytochrome B (phyB)-response mutation lv substantially alters the level of the major active endogenous gibberellin, GA₁ in the apical portion of young seedlings. The phyB-controlled responses to continuous red light and end-of-day far-red light are retained even in a GA-overproducing mutant (sln). Comparison of the effects of the lv mutation and GA₁ application on seedling development shows important differences in rate of node development, cell extension and division, and leaf development. These results suggest that in pea the control of stem elongation by light in general and phyB in particular is not mediated by changes in GA₁ content. Instead, the increased elongation of dark-grown and lv plants appears to result from increased responsiveness of the plant to its endogenous levels of GA₁. Three GA₁-deficient mutants, na, ls and le have been used to investigate these changes in responsiveness, and study of these and the double mutants na lv, ls lv and le lv has demonstrated that the relative magnitude of the change in responsiveness is dependent on GA₁ level. The difference in pleiotropic effects of GA₁ application and the lv mutation suggest that light and GA₁ interact late in their respective transduction pathways. A model for the relationship between light, GA₁ level and elongation in pea is presented and discussed.Abbreviations B blue light - cv cultivar - EOD-FR end-of-day far-red light - FR far-red light - GA_n Gibberellin A_n - GC-SIM gas chromatography-selected ion monitoring - HIR high irradiance response - W white light We thank Prof. L.N. Mander for provision of deuterated internal standards, Peter Bobbi, Noel Davies, Omar Hasan, and Katherine McPherson for technical assistance, Stephen Swain for discussion and provision of GA-level data, and the Australian Research Council for financial assistance. J.L.W. is in receipt of an Australian Postgraduate Research scholarship.     

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     

The Interaction of Plant Growth Regulators and Vernalization on the Growth and Flowering of Cauliflower (Brassica oleracea var. botrytis)

The growth and flowering response of a cold-requiring cauliflower (Brassica oleracea var. botrytis cv. 60 day) to a range of temperatures under 10 h photoperiod and to growth regulator application were investigated. Endogenous gibberellin A₁(GA₁) concentrations were also assessed under these treatments. Flowering and growth of the inflorescence stalk were correlated with plant developmental stage at the time of a vernalizing cold treatment. Temperature and its duration also affected flowering and inflorescence development. The most effective temperature for inflorescence induction was 10 °C. Flowering did not occur in non-vernalized plants (25 °C) even though they had been treated with GA₃. Application of GA₃ promoted inflorescence stalk elongation greatly in vernalized plants (10 °C), but less so in partially vernalized plants (15 °C or 20 °C). Paclobutrazol (PP₃₃₃) sprayed at the 8–9 leaf stage significantly suppressed inflorescence stalk length and slightly delayed flower bud formation and anthesis. Vernalization at 10 °C increased endogenous GA₁ content in both leaves and the inflorescence stalk irrespective of GA₃ or PP₃₃₃ treatment. Application of GA₃ tended to increase GA₁ levels, while PP₃₃₃ significantly reduce GA₁, both irrespective of vernalization. Vernalization is an important factor for flowering, but not curd formation in this cauliflower cv. 60 day and GA₁ is likely a causal factor in inflorescence stalk elongation.     

Phytochrome inhibits the effectiveness of gibberellins to induce cell elongation in rice

Red light controls cell elongation in seedlings of rice (Oryza sativa L.) in a far-red-reversible manner (Nick and Furuya, 1993, Plant Growth Regul. 12, 195–206). The role of gibberellins and microtubules in the transduction of this response was investigated in the rice cultivars Nihon Masari (japonica type) and Kasarath (indica type). The dose dependence of mesocotyl elongation on applied gibberellic acid (GA₃) was shifted by red light, and this shift was reversed by far-red light. In contrast, coleoptile elongation was found to be independent of exogenous GA₃. Nevertheless, it was inhibited by red light, and this inhibition was reversed by far-red light. The content of the active gibberellin species GA₁ and GA₄ was estimated by radio-immunoassay. In the mesocotyl, the gibberellin content per cell was found to increase after irradiation with red light, and this increase was far-red reversible. Conversely, the cellular gibberellin content in japonica-type coleoptiles did not exhibit any significant light response. Microtubules reoriented from transverse to longitudinal arrays in response to red light and this reorientation could be reversed by subsequent far-red light in both the coleoptile and the mesocotyl. This movement was accompanied by changes in cell-wall birefringence, indicating parallel reorientations of cellulose deposition. The data indicate that phytochrome regulates the sensitivity of the tissue towards gibberellins, that gibberellin synthesis is controlled in a negative-feedback loop dependent on gibberellin effectiveness, and that at least two hormone-triggered signal chains are linked to the cytoskeleton in rice.Abbreviations D darkness - FR far-red light - GA₃ gibberellic acid - GC-SIM gas chromatography-selected ion monitoring - R red light This work was supported by a grant of the Human Frontier Science Organization to P.N. Advice and organizational support by Prof. M. Furuya (Hitachi Advanced Research Laboratory, Hatoyama, Japan) and Prof. N. Murofushi (Department of Agricultural Chemistry, University of Tokyo, Japan) is gratefully acknowledged. Seeds of both rice cultivars were kindly provided by Dr. O. Yatou (Institute for Radiation Breeding, Hitachi-Ohmiya, Japan), and the antiGA₁ Me-antiserum for the radio-immunoassays by Dr. I. Yamaguchi (Department of Agricultural Chemistry, University of Tokyo, Japan).     

Photoregulation of germination in seed of transgenic lines of tobacco and Arabidopsis which express an introduced cDNA encoding phytochrome A or phytochrome B

Photoinduction and photoinhibition of germination in seed from a homozygous tobacco (Nicotiana tabacum L.) line containing an introduced oat phyA cDNA (encoding phytochrome A) is compared with that of isogenic wild-type (WT) tobacco. Under continuous irradiation by a light source with a low redfar-red (RFR) ratio the transgenic tobacco seed appeared to be less susceptible to photoinhibition of germination compared with WT seed. However, induction of germination following a short pulse by R (666 nm) was not enhanced in the genotype transformed by oat phyA cDNA compared with the WT; neither did germination of the transgenic tobacco seed show an increased sensitivity to saturating pulses of light of longer wavelengths (666–730 nm). In seeds of transgenic Arabidopsis thaliana (L.) Heynh. which contained an introduced phytochrome-B-encoding cDNA, levels of dark germination were enhanced, consistent with mediation of response by phytochrome B-P_fr. The germination behaviour of Arabidopsis genotypes wich contained an introduced cDNA encoding phytochrome A, however, did not significantly differ from that of the WT.Abbreviations ABO seed transformed with Arabidopsis phyB - cDNA; CaMV cauliflower mosaic virus - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_tot total phytochrome - P_fr/P_tot phytochrome photoequilibrium - R red light - RBO seed transformed with rice phyB cDNA - RFR quantum ratio of red and far-red light - WL white light - WL + FR whitelight supplemented with far-red light - WT wild type The authors wish to thank R.D. Vierstra (Department of Horticulture, University of Wisconsin-Madison, USA) for providing the transgenic tobacco line, and M.T. Boylan, D. Wagner and P.H. Quail (U.C. Berkeley/USDA Plant Gene Expression Center, Albany, Calif. USA) for providing the transgenic Arabidopsis lines. The work presented in this paper was funded by grants from the Agricultural and Food Research Council (H.S., A.C.M., G.C.W.).     

Rapid photomodulation of stem extension in light-grownSinapis alba L.

Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR _max 719 nm and supplementary FR _max 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.Abbreviations B blue light - FR far-red light - R red light - WL white light - Pfr far-red absorbing form of phytochrome - Pr red absorbing form of phytochrome - P_tot total phytochrome level (=Pr+Pfr); -Pfr/Ptot, measured - ER difference in stem extension rate, before and after treatment     

Promotion of flowering in apple trees with gibberellin A4 and C-3 epi-gibberellin A4

The proportion of spurs flowering on apple trees (Malus domestica Borkh. cv Golden Delicious) displaying a high degree of alternate-year flowering was increased in the off year by gibberellin A₄ (GA₄) and C-3 epi-GA₄ applied in the previous year. When applied 4.5 weeks after anthesis amounts of GA₄ ranging from 3 to 300 g per spur and 25 or 50 g of C-3 epi-GA₄ per spur were effective. Treatments with GA₄ made seven weeks after anthesis were less effective. A combination of 30 g GA₄ and 30 g zeatin (6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine) promoted flowering at both treatment times, and tended to be more effective than GA₄ alone.Abbreviation GA gibberellin or gibberellin-like substance Contribution No. 618     

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     

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     

Identification of gibberellin A4 in Pisum sativum L. and the effects of applied gibberellins A9, A4, A5 and A3 on the le mutant

Gibberellin A₄ (GA₄) was identified for the first time in the garden pea (Pisum sativum) L.), by gas chromatography-mass spectrometry. However, in wild-type shoots the level of GA₄ was only about 6% of the level of GA₁, and it is therefore unlikely that GA₄ plays a major role per se in the control of pea stem elongation. In shoots of the le mutant, GA₄ was not detected, while the level of GA₉ was approximately twice that found in the wild-type. The le mutation also markedly reduced the elongation response to applied GA₉. It appears, therefore, that in Pisum the le mutation blocks the 3-hydroxylation of GA₉ to GA₄, in addition to the 3-hydroxylation of GA₂₀ to GA₁. In contrast, the le mutation did not reduce the response to applied GA₅, suggesting the step GA₅ to GA₃ is not catalysed by the enzyme controlled by the Le gene. The step GA₅ to GA₃ was confirmed in peas by metabolite analysis after treatment with deuterated GA₅.     

Enzymes from seeds of Phaseolus vulgaris L.: Hydroxylation of gibberellins A20 and A1 and 2,3-dehydrogenation of gibberellin A20

A time-course study is described relating the enzyme activities for GA₂₀ metabolism with seed development in Phaseolus vulgaris L. Enzyme activity for the 3-hydroxylation of GA₂₀ to GA₁, and for the 2,3-desaturation of GA₂₀ to GA₅, was confined to the cotyledons and showed maximal specific activity at 21 d after anthesis. These enzyme activities co-occurred, together with a much lower level of activity for the 2-hydroxylation of GA₂₀ to GA₂₉. The observed rates of GA₁, GA₅ and GA₂₉ formation from GA₂₀ were constant under a range of incubation conditions. Enzyme activity for the conversion of GA₁ to GA₈ was detected only in embryos of seed from 40 d after anthesis. By deuterium-labelling and analysis of the products by gas chromatography-selected ion monitoring it was shown that 2-hydroxylation of GA₁ to GA₈ and 3-hydroxylation of GA₂₀ to GA₁ occur with retention of configuration and that the conversion of GA₂₀ to GA₅ occurs with loss of the 2- and 3-hydrogens. These results establish that GA₁ is not formed from GA₂₀ via GA₅.Abbreviations GA_n Gibberellin A_n - GC gas chromatography - HPLC high-performance liquid chromatography - MS mass spectrometry - SIM selected-ion monitoring - THO tritiated water