The loci of perception for phytochrome control of internode growth in light-grown mustard: Promotion by low phytochrome photoequilibria in the internode is enhanced by blue light perceived by the leaves

Under continuous white light (WL), extension growth of the first internode in Sinapis alba L. was promoted by low red (R): far-red (FR) ratios reaching the stem and-or the leaves. Conversely, the growth promotion by end-of-day light treatments was only triggered by FR perceived by the leaves and cotyledons, while FR given to the growning internode alone was tatally ineffective. Continuous WL+FR given to the internode was also in-effective if the rest of the shoot remained in darkness. Both the background stem growth, and the growth promotion caused by either an end-of-day FR pulse or continuous WL+FR given to the internode, increased with increasing fluence rates of WL given to the rest of the shoot. The increase by WL of the growth-stimulatory effect of low phytochrome photoequilibria in the internode appears to be mediated by a specific blue-light-absorbing photoreceptor, as blue-deficient light from sodium-discharge lamps, or from filtered fluorescent tubes, promoted background stem growth similarly to WL but did not amplify the response to the R:FR ratio in the internode. Supplementing the blue-deficient light (94 mol·m^-2·s^-1) with low fluence rates of blue (<9 mol·m^-2·s^-1) restored the promotive effect of low R:FR reaching the internode.Abbreviations BL blue light - FR far-red light - PAR photosynthetically active radiation - Pfr/P ratio between the FR-absorbing form and total phytochrome - R red light - SOX low-pressure sodium lamp - WL white light Supported by the Consejo Nacional de Investigaciones Cientificas y Técnicas (República Argentina) and the ORS scheme (UK)     

Phytochrome and internode elongation in Chenopodium polyspermum L. sites of photoreception

The elongation of the fourth internode of fully green Chenopodium polyspermum L. is modulated by far-red light (FR) given in addition to the main light period. Two different types of organs are responsible for the photoreception of FR producing the end-of-day effect; the stem and the leaves situated just above and below the reacting internode. Photoreversibility can be obtained within certain limits in the two organs. Evidence is presented which shows that in the fully green plant there is an interorgan reaction whose primary reaction is the photoconversion of phytochrome.Abbreviations and Symbols D darkness - FR far red light - R red light - P phytochrome - P_FR phytochrome in the FR absorbing form - 9+15 D (or light treatment) photoperiod of a 9 h main light period followed by 15 h of D (or light treatment)     

Impaired phytochrome-mediated shade-avoidance responses in the aurea mutant of tomato

Internode extension-growth responses to neighbouring plants and to red to far-red ratios (R:FR) were investigated in wild-type (WT) and aurea (au)-mutant seedlings of tomato grown under natural radiation. The genomic location of the au mutant is not known, but one of its consequences is the reduced phytochrome level. In WT seedlings, internode growth was promoted by the presence of non-shading neighbours reflecting far-red light (FR), the shade of a tall canopy, FR provided as a supplement during the photoperiod, and FR pulses either provided at the end of the day or delayed into the dark period. Supplementary FR during the photoperiod also promoted growth in herbicide-treated partially bleached WT seedlings. The au mutant showed higher background extension-growth rates, but only responded to the most severe treatments: deep shade light and very low R:FR at the end of the day, i.e. au-mutant seedlings were less sensitive than WT seedlings to R:FR signals. Wild-type seedlings were transferred from the glasshouse to a growth room and exposed to white light with two levels of phytochrome-absorbable radiation but similar phytochrome photoequilibria and radiation for photosynthesis. The plants exposed to the lowest level showed a transient increase of internode extension growth rate and a simultaneous reduction of response to FR pulses, i.e. reproduced some of the features of au-mutant seedlings. Phytochrome itself could set the degree of response to Pfr during neighbour detection.     

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     

补光对出口模拟贮运人参榕叶片生长和光合作用的影响

为减轻出口人参榕贮运暗胁迫下叶片的黄化与脱落,以人参榕(接穗为泰国榕)为材料,采用28 W荧光灯补充光照,研究不同补光时长(0~12h·d-1)处理28d后对模拟贮运人参榕生长和光合作用的影响,以探索人参榕贮运期间适宜的补光时长。结果显示:(1)模拟暗贮运28d时,补光0h·d-1处理的人参榕落叶率、黄化指数分别为89.64%、0.52,而补光8~12h·d-1处理的落叶率、黄化指数显著下降,落叶率比对照(0h·d-1)分别显著下降为35.7%、39.19%、26.08%,黄化指数分别显著下降为0.25、0.28、0.19。(2)随着补光时间的延长,人参榕叶片的相对含水量(RWC)显著降低,而比叶重(SLW)显著升高;其叶绿素a、叶绿素b、叶绿素(a+b)含量、类胡萝卜素含量、叶绿素a/b、净光合速率(Pn)、气孔导度(Gs)均呈上升趋势,且在补光8~12h·d-1处理下各指标均明显高于其他处理,但胞间二氧化碳浓度(Ci)呈下降趋势。(3)相关分析显示,模拟贮运人参榕的落叶率与黄化指数呈极显著正相关;落叶率、黄化指数均与其叶绿素含量、Pn呈极显著负相关,与Ci呈极显著正相关;且叶片Pn与叶绿素含量、Gs呈显著正相关,与Ci呈极显著负相关。研究表明,通过补光措施可显著减缓贮运人参榕叶片的黄化与脱落,28 W荧光灯光照8~12h·d-1的补光效果均较好,综合考虑成本认为在实际人参榕贮运过程中最适补光时长为8h·d-1;贮运时较长时间的暗胁迫环境对人参榕叶片光合系统造成损伤并导致Pn下降,其主要是叶绿素含量降低的非气孔限制因素所致。     

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     

Coupling of phytochrome B to the control of hypocotyl growth in Arabidopsis

Etiolated seedlings of the wild-type (WT) and of the phyB-1 mutant of Arabidopsis thaliana (L.) Heynh. were exposed to red-light (R) and far-red light (FR) treatments to characterize the action of phytochrome B on hypocotyl extension growth. A single R or FR pulse had no detectable effects on hypocotyl growth. After 24-h pre-treatment with continuous FR (FRc) a single R, compared to FR pulse inhibited (more than 70%) subsequent hypocotyl growth in the WT but not in the phyB-1 mutant. This effect of FRc was fluence-rate dependent and more efficient than continuous R (Rc) or hourly FR pulses of equal total fluence. Hypocotyl growth inhibition by Rc was larger in WT than phyB-1 seedlings when chlorophyll screening was reduced either by using broadband Rc (maximum emission 610 nm) or by using narrow-band Rc (658 nm) over short periods (24 h) or with seedlings bleached with Norflurazon. Hourly R or R + FR pulses had similar effects in WT and phyB-1 mutant etiolated seedlings. It is concluded that phytochrome B is not the only photoreceptor of Rc and that the action of phytochrome B is enhanced by a FRc high-irradiance reaction. Complementary experiments with the phyA-201 mutant indicate that this promotion of a phytochrome B-mediated response occurs via co-action with phytochrome A.Abbreviations D darkness - FR far-red light - FRc continuous FR - Pfr FR-absorbing form of phytochrome - HIR high-irradiance reaction - Pfr/P proportion of phytochrome as Pfr - phyA phytochrome A - phyB phytochrome B - R red light - Rc continuous R - WT wild-type I thank Professors R.E. Kendrick and M. Koornneef (Wageningen Agricultural University, The Netherlands) and Professor J. Chory (Salk Institute, Calif., USA) for their kind provision of the original WT and phyB-1 and phyA-201 seed, respectively. This work was financially supported by grants PID and PID-BID from CONICET, AG 040 from Universidad de Buenos Aires and A 12830/1-000019 from Fundación Antorchas.     

Indole-3-acetic acid levels after phytochrome-mediated changes in the stem elongation rate of dark- and light-grownPisum seedlings

The effect of red (R) and far-red (FR) light on stem elongation and indole-3-acetic acid (IAA) levels was examined in dwarf and tall Pisum sativum L. seedlings. Red light reduced the extension-growth rate of etiolated seedlings by 70–90% after 3 h, and this inhibition was reversible by FR. Inhibition occurred throughout the growing zone. After 3 h of R, the level of extractable IAA in whole stem sections from the growing zone of etiolated plants either increased or showed no change. By contrast, extractable IAA from epidermal peels consistently decreased 3 h after R treatments. Decreases of 40% were observed for epidermal peels from the top 1 cm of tall plants receiving 3 h R. Brief R treatments resulted in smaller decreases in epidermal IAA levels and these decreases were not as great when FR followed R. In lightgrown plants, end-of-day FR stimulated growth during the following dark period in a photoreversible manner. The uppermost 1 cm of expanding third internodes was most responsive to the FR. Extractable IAA from epidermal peels from the upper 1 cm of third internodes increased by 30% or more 5 h after FR. When R followed the FR the increases were smaller. Levels of IAA in whole stem sections did not change and were twofold greater than in dark-grown plants. In both dark- and light-grown tall plants, IAA levels were lower in epidermal peels than in whole stem segments. These results provide evidence that IAA is compartmentalized at the tissue level within the growing stem and that phytochrome regulation of stem elongation rates may be partly based on modulating the level of IAA within the epidermis.Abbreviations IAA indole-3-acetic acid - R red light - FR farred light We thank Yu-Xian Zhu for helping to develop methods for IAA analysis, James Reid for supplying the genetic lines of Pisum and Richard Cyr for the use of microscopy equipment. This work was supported by NSF grant DCB-8801880 and by Hatch funds from the College of Agriculture and Life Sciences at Cornell University. The gas chromatograph-mass spectrometer was funded by NSF grant DMB-8505974 and funds from the College of Agriculture and Life Sciences at Cornell University. A preliminary report of some of these experiments has appeared in Plant Growth Substances, 1991 (Behringer et al. 1992 b).     

Persistent effects of changes in phytochrome status on internode growth in light-grown mustard: Occurrence,kinetics and locus of perception

Extension growth of the first internode in fully de-etiolated mustard (Sinapis alba L.) seedlings (11–12.5 d old) is under the control of both the current phytochrome photoequilibrium (Pfr/P, ratio of the far-red-absorbing form of phytochrome to total phytochrome) and that established by short (<12 h) pretreatments. Plants were pretreated with either light pulses providing different calculated Pfr/P followed by dark incubations of different durations (a), or with a 12-h period of white light establishing different Pfr/P (b). After the pretreatments, the plants received either light pulses providing different Pfr/P, followed by dark incubations (c), or continuous white light with or without addtional far-red light (d). Thus, four experimental approaches were followed: (a)(c); (a)(d); (b)(c) and (b)(d). Extension growth during the second period (c or d) was not only affected by the current phytochrome status, but also by that established during the pretreatment period (a or b). The results show the existence of a long-term promotion of stem growth which persists after the end of the low Pfr/P pretreatment. This effect is different from the previously reported rapid effect of far-red light added to background white light as follows: (i) the duration of low Pfr/P required to effect a full response is longer (2.5 h); (ii) the duration of the promotion after returning to high Pfr/P is longer (approx. 24 h) and (iii) the locus of perception is mainly in the leaves, rather than the growing internode.Abbreviations FR far-red light - PAR photosynthetically active radiation - Pfr/P ratio between the FR-absorbing form and total phytochrome - R red light - WL white light     

Identification of the alga known as <Emphasis Type="Italic">Nannochloropsis</Emphasis> Z-1 isolated from a prawn farm in Hainan,China as <Emphasis Type="Italic">Chlorella</Emphasis>

An alga known as “Nannochloropsis”, isolated from a prawn farm in Hainan, China, has been critically investigated and identified as Chlorella, a member of the Chlorophyceae based on fatty acid composition, ultrastructure, and 18S rDNA. Cells of this alga were spherical, measured by 1–6 μm in diameter and were enclosed in thin walls of approximately 0.04 μm thickness. They contained several small mitochondria, two to three thylakoids and had no vacuoles. There were many pyrenoids in the algal cells and their thylakoid lamellae were sparse and not translucent. Many lipid droplets were present in the cytoplasm. The total lipid content of this alga was 3% per gram dry weight and its major fatty acids were C_16:0, C_18:0, C_18:1, C_18:2, C_18:3 and C_20:0. Eicosapentaenoic acid (C_20:5, EPA) was not detected. The length of its 18S rDNA sequence was 1,712 bp. 18S rDNA sequence analyses indicated that this alga was a species of Chlorella.     

Floral initiation in sorghum hastened by gibberellic acid and far-red light

Combinations of far-red light (FR) (4 min) and gibberellic acid (GA₃), given at the beginning of a daily 12-h dark period in a growth room, were used to study floral induction in four maturity genotypes of the milo group of sorghum (Sorghum bicolor (L.) Moench). The 12-h dark period without GA₃ application or FR induced flowering in only the early genotype; FR hastened initiation in the early genotype, while GA₃ hastened floral initiation in the two intermidiate-flowering genotypes. GA₃ and FR together had a strong synergistic effect, hastening floral initiation by 30 to more than 80 d in the early and intermediate genotypes. Red light (R) did not hasten flowering; FR preceded by R gave the same effect as FR alone. GA₃ promoted stem elongation equally whether floral initiation occurred or not; thus, its effect on stem elongation was independent of floral initiation. The capacity of GA₃ to induce flowering in sorghum, a short-day plant, seems to be enhanced by phytochrome being in the P_R form at the beginning of the night when GA₃ was applied.Abbreviations FR far-red light - GA(s) gibberellin(s) - GA₃ gibberellic acid - R red light     

Phytochrome action in light-grown mustard: kinetics,fluence-rate compensation and ecological significance

Internode extension in young, light-grown mustard plants was measured continuously to a high degree of resolution using linear voltage displacement transducers. Plants were grown in background white light (WL) and the first internode was irradiated with supplementary far-red (FR) from fibre-optic light guides, depressing the Pfr/P (ratio of FR-absorbing form of phytochrome to total spectrophotometrically assayable phytochrome) within the internode and causing an acceleration of extension rate. The internode was sensitive to periods of FR as brief as 1 min, with a sharp increase in extension rate occurring after the return to background WL only. The mean latent period of the response to FR was approx. 10 min. Periods of FR longer than approx. 35 min caused an apparently biphasic growth response, with an initial sharp acceleration in extension rate (Phase 1) being followed by a brief deceleration and a further acceleration to a more-or-less steady elevated rate, somewhat less than the first peak (Phase 2). With such longer-term FR, extension rate decelerated upon FR switch-off after a mean lag of approx. 6 min, achieving the prestimulation extension rate within 16 min. The magnitude of the FR-induced increase in extension rate, expressed as a percentage of the rate in WL alone, was an inverse, linear function of the phytochrome photoequilibrium (i.e. Pfr/P, measured in etiolated test material irradiated under the same geometry) over the range 0.17 to 0.63. This relationship was not significantly affected by variations in backround WL fluence rate over the range 50–150 mol·m^-2·s^-1 and was held both for Phase 1 and Phase 2 of the response. The data provide evidence for rapid coupling/uncoupling between phytochrome and its transduction chain in the light-grown plant and for fluence-rate compensation of the regulation of extension rate. The extensive linearity of the relationship between phytochrome photoequilibrium and proportional extension rate increment allows for fine tuning in shade avoidance. The results are discussed with respect to recent evidence on the nature of phytochrome in light-grown plants and in relation to the function of phytochrome in plants growing in the natural environment.Abbreviations FR far-red light - LVDT linear voltage displacement transducer - P total spectrophotometrically assayable phytochrome - PAR photosynthetically active radiation (400–700 nm) - Pfr FR-absorbing form of phytochrome - Pr R-absorbing form of phytochrome - R red light - WL white light     

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     

Effect of cultural conditions on the lipid profile of Thiobacillus ferroxidas

The intensitive investigations on the lipid profile of Thiobacillus ferrooxidans at various culture ages suggest some correlations of the lipid constitutents with the membrane-bound iron oxidation system. Phosphatidic acid, phosphatidyl serine and phosphatidyl ethanolamine were the major polar components; hydrocarbon, triglyceride and diglyceride were the main neutral components. Major fatty acids were C_16:0, C_16:1, C_16:3, C_18:1, C_18:3, C_22:1 while C_20:1, C_20:2, C_12:0, C_14:2, C_18:0, C_18:2, C_20:0, C_22:0 were found in trace amounts which also depended upon the phase of the growth. One lipoamino acid was identified as ornithine lipid in the polar fraction. Each and every component varied to some extent at different growth phasesindicating relationship of these lipids to the iron oxidation system of the strain.     

Gibberellin physiology of safflower: endogenous gibberellins and response to gibberellic acid

Endogenous gibberellins (GAs) were extracted from safflower (Carthamus tinctorius L.) stems and detected by capillary gas chromatography-mass spectrometry from which GA₁, GA₃, GA₁₉,, GA₂₀, GA₂₉, and probably, GA₄₄ were detected. The detection of these GAs suggests that the early 13-OH biosynthetic pathway is prevalent in safflower shoots. Deuterated GAs were used as internal standards and GA concentrations were determined in stems harvested at weekly intervals. GA₁ and GA₁₉ levels per stem increased but concentrations per gram dry weight decreased over time. GA₂₀ was only detected in young stem tissue.Gibberellic acid (GA₃) was also applied in field trials and both GA₃ and the GA biosynthetic inhibitor, paclobutrazol, were applied in growth chamber tests. GA₃ increased epidermal cell size, internode length, and increased internode cell number causing stem elongation. Conversely, paclobutrazol reduced stem height, internode and cell size, cell number and overall shoot weight. In field tests, GA₃ increased total stem weight, but decreased leaf weight, flower bud number and seed yield. Thus, GA₃ promoted vegetative growth at the expense of reproductive commitment. These studies collectively indicate a promotory role of GAs in the control of shoot growth in safflower, and are generally consistent with gibberellin studies of related crop plants. Author for correspondence     

Narrow-band light regulation of ethylene and gibberellin levels in hydroponically-grown <Emphasis Type="Italic">Helianthus annuus</Emphasis> hypocotyls and roots

Both hypocotyl and root growth of sunflower (Helianthus annuus) were examined in response to a range of narrow-band width light treatments. Changes in two growth-regulating hormones, ethylene and gibberellins (GAs) were followed in an attempt to better understand the interaction of light and hormonal signaling in the growth of these two important plant organs. Hydroponically-grown 6-day-old sunflower seedlings had significantly elongated hypocotyls and primary roots when grown under far-red (FR) light produced by light emitting diodes (LEDs), compared to narrow-band red (R) and blue (B) light. However, hypocotyl and primary root lengths of seedlings given FR light were still shorter than was seen for dark-grown seedlings. Light treatment in general (compared to dark) increased lateral root formation and FR light induced massive lateral root formation, relative to treatment with R or B light. Levels of ethylene evolution (roots and hypocotyls) and concentrations of endogenous GAs (hypocotyls) were assessed from both 6-day-old sunflower plants either grown in the dark, or treated with FR, R or B light. Both R and B light had similar effects on hypocotyl and root growth as well as on ethylene and on hypocotyl GA levels. Dark treatment resulted in the highest ethylene levels, whereas FR treatment significantly reduced ethylene evolution for both hypocotyls and roots. R- and B-light treatments elevated ethylene evolution relative to FR light. Endogenous GA₅₃ and GA₁₉ levels in hypocotyls were significantly higher and GA₄₄, GA₂₀ and GA₁ levels significantly lower, for dark and FR light treatments compared to R and B light-treatments. The patterns seen for changes in GA concentrations indicate FR-, R- and B-light-mediated effects [differences] in the metabolism of the early C₂₀ GAs, GA₅₃ → GA₄₄ → GA_19. Surprisingly, GA₂₀, GA₁ and GA₈ levels in hypocotyls were very much reduced by treatment of the plants with FR light, relative to B and R-light treatments, e.g. the increased hypocotyl elongation induced by FR light was correlated with reduced levels of all three of the downstream C₁₉ GAs. The best explanation, albeit speculative, is that a more rapid metabolism, i.e. GA₂₀ → GA₁ → GA₈ → GA₈ conjugates occurs under FR light. Although this study provided no evidence that elevated ethylene evolution by roots or hypocotyls of sunflower is controlling growth via endogenous GA biosynthesis, there are differences between soil-grown and hydroponically-grown sunflower seedlings with regard to trends seen for hypocotyl GA concentrations and both root and hypocotyl ethylene evolution in response to narrow band width R and FR light signaling.     

Photocontrol of stem elongation in light-grown plants of Fuchsia hybrida

Stems of the caulescent long-day plant, Fuchsia hybrida cv Lord Byron, showed 2 types of response to light. In one, internode length was increased by far-red irradiation given at the end of an 8 h photoperiod: the response was no greater with prolonged exposure and was less when the start of far-red was delayed. The effect of far-red was reversible by a subsequent exposure to red light. Internode length was inversely proportional to the P_fr/P ratio established before entry to darkness and there was no evidence for loss of P_fr during a 16 h dark period. The inhibitory effect of P_fr acted at a relatively late stage of internode growth. With the development of successive internodes a second response appeared in which stems lengthened following prolonged daily exposures to red or far-red light, or mixtures of the two, or to brief breaks with red or white light. In these later internodes, a short exposure to far-red near the middle of the night was not reversible by red because red alone promoted elongation at this time. Internode length increased with increase in the daily duration of light and, when light was given throughout an otherwise dark period of 16 h, with increase in illuminance to a saturation value of 200 lx from tungsten lamps. Elongation increased as a linear function of decrease in photostationary state of phytochrome down to P_fr/P0.3; however, internodes were shorter in far-red light than in 25% red/red+far-red. It was concluded that stem length is a net response to two modes of phytochrome action. An inductive effect of P_fr inhibits a late stage in internode expansion, and a phytochrome reaction which operates only in light (and may involve pigment cycling) promotes an early stage of internode development. Stem elongation is thus a function both of the daily duration of light and its red/red+far-red content. The outgrowth of axillary buds was controlled by the first type of phytochrome action only.Abbreviations and symbols FR far red light - R red light - P phytochrome - P_fr phytochrome in the far-red light absorbing form - SD 8 h short days - LDP long-day plant - SDP short-day plant     

Phytochrome and internode elongation in Chenopodium polyspermum L. the light fluence rate during the day and the end-of-day effect

The elongation of the fourth internode of fully green Chenopodium polyspermum L. is strongly stimulated by far-red light (FR) given at the end of the day. The end-of-day effect is more important when the plants had been cultivated for several days with a main light period of 140 Wm^-2 than with a main light period of 85 Wm^-2. There exists a quantitative relationship between the FR end-of-day effect mediated by phytochrome and the value of the light fluence during the day.Abbreviations D darkness - FR far-red light - HWL white light at 140 Wm^-2 - LWL white light at 85 Wm^-2 - PAR photosynthetically active radiation - R red light - WL white light     

Inhibition by light of growth and Golgi-localized glucan synthetase in the maize mesocotyl

When dark-grown maize (Zea mays L.) seedlings were exposed to red light (R), Golgi-localized glucan synthetase activity in the mesocotyl began to decrease within 1 h, and fell by approx. 70% in 12 h. The response required at least 10^-2 mol m^-2 R and saturated at 100 mol m^-2. Far-red light (FR) alone inhibited glucan synthetase, and FR reversed the inhibition by R back to the level caused by FR alone. Density gradient fractionation indicated that of the major membrane markers only the Golgi-localized glucan-synthetase activity was affected by R. Golgi-localized latent inosine-diphosphatase activity was unaffected. The kinetics of the response, the photon fluence dependence, and the reversibility by FR all correlated with the inhibition by light of elongation of the mesocotyl, indicating that light inhibits growth and glucan synthetase activity by a similar mechanism.Abbreviations FR far-red light - GS glucan synthetase - IAA indole-3-acetic acid - R red light     

Uncoupling light quality from light irradiance effects in Helianthus annuus shoots: putative roles for plant hormones in leaf and internode growth

An attempt has been made to uncouple the effects of the two primary components of shade light, a reduced red to far-red (R/FR) ratio and low photosynthetically active radiation (PAR), on the elongation of the youngest internode of sunflower (Helianthus annuus) seedlings. Maximal internode growth (length and biomass) was induced by a shade light having a reduced R/FR ratio (0.85) under the low PAR of 157 micromol m(-2) s(-1). Reducing the R/FR ratio under normal PAR (421 micromol m(-2) s(-1)) gave similar growth trends, albeit with a reduced magnitude of the response. Leaf area growth showed a rather different pattern, with maximal growth occurring at the higher (normal) PAR of 421 micromol m(-2) s(-1)), but with variable effects being seen with changes in light quality. Reducing the R/FR ratio (by enrichment with FR) gave significant increases in gibberellin A(1) (GA(1)) and indole-3-acetic acid (IAA) contents in both internodes and leaves. By contrast, a lower PAR irradiance had no significant effect on GA(1) and IAA levels in internodes or leaves, but did increase the levels of other GAs, including two precursors of GA(1). Interestingly, both leaf and internode hormone content (GAs, IAA) are positively and significantly correlated with growth of the internode, as are leaf levels of abscisic acid (ABA). However, changes in these three hormones bear little relationship to leaf growth. By implication, then, the leaf may be the major source of GAs and IAA, at least, for the rapidly elongating internode. Several other hormones were also assessed in leaves for plants grown under varying R/FR ratios and PARs. Leaf ethylene production was not influenced by changes in R/FR ratio, but was significantly reduced under the normal (higher) PAR, the irradiance treatment which increased leaf growth. Levels of the growth-active free base and riboside cytokinins were significantly increased in leaves under a reduced R/FR ratio, but only at the higher (normal) PAR irradiance; other light quality treatments evoked no significant changes. Taken in toto, these results indicate that both components of shade light can influence the levels of a wide range of endogenous hormones in internodes and leaves while evoking increased internode elongation and biomass accumulation. However, it is light quality changes (FR enrichment) which are most closely tied to increased hormone content, and especially with increased GA and IAA levels. Finally, the increases seen in internode and leaf GA content with a reduced R/FR ratio are consistent with FR enrichment inducing an overall increase in sunflower seedling GA biosynthesis.