Variations in Tiller Dynamics and Morphology in Lolium multiflorum Lam.Vegetative and Reproductive Plants as affected by Differences in Red/Far-Red Irradiation

Lolium multiflorum Lam, plants were grown in a growth room undertwo light sources with red/far-red ratios of 1·62 and0·84 but similar photosynthetically active radiation.In both situations the capacity to produce new tillers and thelight available per tiller decreased with canopy growth. Tilleringwas further reduced by the low red/far-red ratio while lightinterception and plant dry weight were unaffected by this treatment.In both reproductive and vegetative plants under the lower red/far-redratio the time between leaf expansion and the appearance ofa tiller in its axil was increased and the proportion of ‘maturebuds’ that developed was reduced. Irradiation with lowred/far-red advanced the reproductive development and increasedthe number of fertile tillers per plant. It also caused longerleaf sheaths, blades and reproductive shoots. The results suggestthat as canopy density increases the lower light interceptionper tiller and the photomorphogenic effect of low red/far-redratios may reduce the capacity to produce new tillers. Lolium multiflorum, Lam., annual ryegrass, tillering, tiller growth, leaf growth, flowering, light quality.     

Morphogenetic Changes Induced by a Low Red: Far-Red Ratio and their Growth Consequences in Water Hyacinth (Eichhornia crassipes)

Plants of water hyacinth (Eichhornia crassipes) were grown undertwo red/far-red ratios (Z) to investigate the effects on morphologyand growth of the light quality component of canopy shade. Experimentswere conducted in diffuse sunlight in the presence or absenceof far-red radiation. Under low Z conditions, fewer new ramets were produced and theirstolons were shorter. The number of leaves per ramet was unchanged,but petiole length and blade area were increased. This changein biomass partitioning resulted in a lower investment in themain resource-acquiring organs (leaf blades and roots). Thelower allocation of biomass to the leaf blades was compensatedfor by a higher net assimilation rate, such that relative growthrate remained unchanged. Key words: Biomass partitioning, Eichhornia crassipes, growth, morphogenesis, red: far-red ratio     

Tillering Responses to the Light Environment and to Defoliation in Populations of Perennial Ryegrass (Lolium perenneL.) Selected for Contrasting Leaf Length

Tillering responses to the light environment and to defoliationwere studied in two populations of perennial ryegrass (LoliumperenneL.) selected for contrasting leaf lengths. The objectiveof this study was to determine whether differences in tilleringresponses between populations, as a result of management practices,affected their competitive ability. Young seedlings were exposed,under controlled conditions, to defoliation, neutral shading(decreased photosynthetic photon flux), low red:far-red ratioand/or decreased blue light. Selection for longer leaves reducedthe tillering rate. After defoliation, this difference betweenshort- and long-leaved populations was magnified. Defoliationdecreased both site filling and phyllochron of the long-leavedpopulation but had no effect on the short-leaved population.Lowering the photosynthetic photon flux reduced the phyllochronin both population. Decreasing the red:far-red ratio reducedtillering rate by reducing site filling, whereas decreasingblue light had no significant effects on tillering. Tilleringresponses to photosynthetic photon flux and to red:far-red ratiowere similar in the two populations selected for contrastingleaf length. The implication of these tillering responses indefining the competitive ability of the grass plants is discussedin relation to their management.Copyright 1999 Annals of BotanyCompany Blue light, defoliation, far-red, irradiance, leaf size,Lolium perenne(L.), perennial ryegrass, photomorphogenesis, phyllochron, shading, site filling, tiller production.     

Tillering Responses of Lolium multiflorum Plants to Changes of Red/Far-Red Ratio Typical of Sparse Canopies

Casal, J. J., Sáchez, R. A. and Deregibus, V. A. 1987.Tillering responses of Lolium multiflorum plants to changesof red/far-red ratio typical of sparse canopies.—J. exp.Bot. 38: 1432–1439. Plants of Lolium multiflorum were grown either in growth roomsunder radiation sources providing equivalent PAR but differentR/FR ratios between 0·46 and 2·36, or under sunlightsupplemented with a series of small fluence rates of FR throughoutthe photoperiod. In both kinds of experiments a reduction oftillering was found along with small depressions of R/FR ratiobelow the values typical of sunlight. In this range both thesquare-root-transformed rate of tillering and the site-fillingrate were linearly related to the estimated phytochrome photo-equilibriaand the slope was very steep under conditions that allowed hightillering rates. The addition of low fluence rates of red lightat the base of the shoots raised tillering of plants exposedto low R/FR ratios to the level of plants grown under high R/FRratios in spite of the ratios received by the rest of the plant.Moreover, irradiation of plant bases with intermediate-low R/FRratios reduced tillering indicating that this would be one siteof perception. These results show a high sensitivity to changesof R/FR ratio typical of different degrees of shade in sparsecanopies. This suggests that by monitoring these changes Loliummultiflorum plants would be able to perceive an anticipatedsignal of impending competition in growing canopies.     

Phytochrome Control of Chlorophyll Content in Mature Attached Leaves of Petunia axillaris

Petunia axillaris plants were grown under white light (photoperiod10 h). Pulses of end-of-day far-red light, but not red lightat the end of the day slowed down the accumulation of chlorophyllin expanding, greening leaves and reduced chlorophyll contentin mature leaves. The chlorophyll a / b ratio was unaffected.Low phytochrome photoequilibria reduced chlorophyll contentin mature leaves without affecting leaf area or d. wt. Thiseffect occurred even before senescence was triggered in thecontrol plants having high phytochrome photoequilibria     

Photocontrol of petiole elongation in light-grown strawberry plants

Summary The mode of phytochrome control of elongation growth was studied in fully-green strawberry (Fragaria x Ananassa Duch.) plants. Petiole growth showed two distinct types of response to light. In one, the end-of-day response, petioles were lengthened by low-intensity far-red irradiation for 1 h immediately following the 8 h photoperiod. The response was little or no greater with prolonged exposure and less when the start of far-red was delayed. It was already evident in the first leaf to emerge after treatment began. With the development of successive leaves a second, photoperiodic, type of response appeared, in which petioles lengthened following only prolonged exposure to red, far-red, mixtures of the two, or tungsten lighting, all at low levels of intensity. As with the inhibition of flowering in previous experiments, irradiation with red light during the second half of the otherwise long dark period gave the greatest response.Abbreviations and Symbols FR far-red light - HIR high irradiance response - R red light - P_r phytochrome in the red light absorbing form - P_fr phytochrome in the far-red light absorbing form - SDP short-day plant - LDP long-day plant - PAR photosynthetically active radiation     

Phytochrome Control of Turion Formation in Spirodela polyrhiza L. Schleiden

Turion yield in Spirodela polyrhiza, strain SJ, is increasedby increasing the daily light period. This effect is more pronouncedin autotrophic than in mixotrophic conditions. Night-break irradiation(15 mins) increased turion yield by 150 % under the conditionsof an 8-h daily light period. Besides the effect of night-breakirradiation, end-of-day far-red irradiation decreased turionyield with increasing photoperiod, whereas end-of-day red irradiationwas without any effect. This demonstrates the promoting effectof the P_fr form of phytochrome on formation of light-grown turions. Formation of dark-grown turions was increased by about 240%by a single red light pulse and was reversed by an immediatelyapplied far-red light pulse. Consequently, under heterotrophicconditions phytochrome modulates the turion formation process. Spirodela polyrhiza L. Schleiden, duckweed, Lemnaceae, photomorphogenesis, phytochrome, turion     

Far red end-of-day treatment restores wild type-like plant length in hybrid aspen overexpressing phytochrome A

Shoot elongation in woody plants is modulated by a multitude of light signals, including irradiance, photoperiod and spectral composition, for which the phytochrome system is the probable photoreceptor. In hybrid aspen ( Populus tremula  ×  tremuloides ) overexpression of the oat phytochrome A ( PHYA ) prevents growth cessation in response to short photoperiod, and plants exhibit dwarf growth that is related to reduced cell numbers and reduced gibberellin contents. End-of-day far-red treatment significantly enhances internode elongation in PHYA overexpressors as well as in the wild type, and this was found here to be caused by stimulation of cell division and cell extension. In PHYA overexpressors the effects were substantially larger than in the wild type, and resulted in complete restoration of wild type-like plant length as well as cell numbers, and gibberellin content was greatly increased. No clear effect of far-red end-of-day treatment on gibberellin levels could be detected in the wild type. It thus appears that the far-red end-of-day treatment might modify the responsiveness of the tissue to GA rather than the GA levels. The observed effects were completely reversed by a subsequent irradiation with red light. The present data show that dwarfism due to PHYA overexpression can be completely overcome by far red end-of-day treatment, and the observations indicate that effects of far red end-of-day treatments appear to be mediated by phytochrome(s) other than phytochrome A.     

Effects of photoperiod in the glasshouse on the growth of leaves and tillers in three perennial grasses

Leaf and tiller development in vegetative plants of S.₃₇ cocksfoot (Dactylis glomerata L.), S.₂₁₅ meadow fescue (Festuca pratensis Huds.) and S.₂₄ perennial rye-grass (Lolium perenne L.) were measured in photoperiods varied by extending a basic period of natural light with low-intensity artificial illumination so that all plants received approximately the same amount of light each day. Increasing the photoperiod usually increased leaf length and sometimes leaf width, but decreased rate of production of leaves. However, the rate of production of new leaf surface increased with photoperiod. Increasing the photoperiod generally decreased the rate of tillering; thus, plants grown in long days had few tillers with large leaves and sheaths, in short days, plants developed more but smaller tillers.     

Photomodulation of Stem Extension in Light-Grown Plants: Evidence for Two Reactions

Internode elongation was measured in plants of Phaseolus vulgarisand Glycine max grown under 8 h photoperiods at 25 W m^–2in white fluorescent light, followed by light-extensions varyingin quality, irradiance and duration. Two distinct responsesto light were observed under these conditions. A reduction in P_FR/P increased elongation, but elongation wasalso modified by a second reaction in which internode lengthincreased with increase in the duration and irradiance of theday-extension. This light-promoted response occurred in bothred and blue light. In the P_FR-inhibition response, light acteddirectly on the expanding internode. The light-promoted response,in contrast, required irradiation of the leaf. The response to a short end-of-day exposure to far-red lightprogressively diminished as successive internodes expanded underthe treatment, whereas the light-promoted response increased.The two processes appeared to interact and, in the later-expandinginternodes, the effect of a reduction in P_FR was greater underlong day-extensions with mixed red and far-red light than inthe end-of-day treatments. ¹ Present address: British Telecom, Brunel House, 2 FitzalanRoad, Cardiff, U.K.     

Phytochrome A affects stem growth, anthocyanin synthesis, sucrose-phosphate-synthase activity and neighbour detection in sunlight-grown potato

Phytochrome action in fully de-etiolated sunlight-grown potato (Solanum tuberosum L.) was studied by comparing wild-type (WT) plants and transgenic plants with either a sense or an anti-sense phytochrome A (phyA) construction. Radial stem growth, anthocyanin levels, and sucrose-phosphate-synthase activity were directly related to the levels of phyA (severely reduced in transgenics with anti-sense phyA, normal in WT and increased in transgenic with sense phyA). In contrast, longitudinal stem growth was inversely related to the levels of phyA. Phytochrome A influenced stem-extension growth responses to red/far-red ratios perceived by stable phytochrome[s]. First, far-red light reflected by non-shading neighbours promoted stem growth in WT plants but transgenic plants with either increased or reduced phyA levels failed to respond to this light signal. Second, plants with low phyA levels also showed impaired sensitivity to reductions in end-of-day red/far-red ratios. In addition, phyA appears to perceive changes in irradiance reaching the stem: lowering the amount of red plus far-red light reaching the stem promoted stem growth in WT plants. This effect was exaggerated in phyA overexpressors and absent in phyA underexpressors. Thus, phyA is active in fully de-etiolated, sunlight-grown plants. Received: 4 October 1997 / Accepted: 24 October 1997     

Photoreversibility of flower initiation in Lemna perpusilla as affected by the light quality of the main light period

Reversible floral responses of Lemna perpusilla to red and far-redlights appeared only at the beginning of the inductive darkperiod when the 8 hr photoperiod consisted of white or red light.When blue or far-red light was given during the 8 hr photoperiod,the far-red given at the beginning of the dark period scarcelyinhibited flowering; red/far-red reversibility newly appearedat the middle of the dark period. This indicates that the photoregulationsystem in the flowering of L. perpusilla can be converted fromthe Pharbitis type to the Xanthium type by changing the lightquality of the main photoperiod from white or red to blue orto far-red, which is known to be effective for the so-calledhigh-energy photoreaction of photomorphogenesis. (Received July 2, 1975; )     

Shade-avoidance responses in two common coastal redwood forest species,Sequoia sempervirens (Taxodiaceae) and Satureja douglasii (Lamiaceae), occurring in various light quality environments

Shade-avoidance responses were examined for two species common to the coastal redwood forest, Sequoia sempervirens and Satureja douglasii. Sequoia seedlings demonstrated a shade-avoidance response when given end-of-day far-red light by increased hypocotyl, epicotyl, and first-node extension, and greater total number of needles and reduced anthocyanin concentration. Thus, Sequoia seedlings respond as sun-adapted plants. Satureja has several leaf monoterpene chemotypes that occur in different light environments including the redwood forest, and the types responded differently to the light treatments. The pulegone type responded to end-of-day far-red light as a sun-adapted plant with significant extension growth, increased leaf area and chlorophyll, and reduced anthocyanin. The isomenthone type responded as a shade-tolerant plant and did not exhibit extension growth nor a change in other parameters with end-of-day far-red light. However, the carvone and bicyclic types had variable responses depending on the parameter studied, which indicated genetic variation for these traits.     

Is the far-red-absorbing form of Avena phytochrome A that is present at the end of the day able to sustain stem-growth inhibition during the night in transgenic tobacco and tomato seedlings?

Avena phytochrome A (phyA) overexpressed in tobacco (Nicotiana tabacum L.) and tomato (Lycopersicon sculentum Mill) was functionally characterised by comparing wild-type (WT) and transgenic seedlings. Different proportions of phytochrome in its far-red-absorbing form (Pfr/P) were provided by end-of-day (EOD) light pulses. Stem-length responses occurred largely in the range of low Pfr/P (3–61%) for WT seedlings and in the range of high Pfr/P (61–87%) for transgenic seedlings. A similar shift was observed when the photoperiod was interrupted by short light pulses providing different Pfr/P ratios and followed by 1 h dark incubation. In other experiments, Avena phyA was allowed to re-accumulate in darkness and subsequently phototransformed to Pfr but no extra inhibition of stem extension growth was observed. In transgenic tomato seedlings the response to EOD far-red light was faster and the response to a far-red light pulse delayed into darkness was larger than in the WT. Avena phyA Pfr remaining at the end of the photoperiod appears intrinsically unable to sustain growth inhibition in subsequent darkness. Avena phyA modifies the sensitivity and the kinetics of EOD responses mediated by native phytochrome.Abbreviations EOD end-of-day - FR far-red light - Pfr/P pro-portion of phytochrome in its FR-absorbing form - phyA phyto-chrome A - phyB phytochrome B - R red light - RFR R to FR ratio - WT wild type We thank Dr Brian Thomas for providing the antibodies used in this work, and Federico Guerendiain for his excellent technical assistance. This work was financially supported by grants UBA AG 040 and Fundacion Antorchas A-12830/1-19 (both to J.J.C.), PID-CONICET (to R.A.S. and J.J.C.), United States Department of Energy DE-FG02-88ER13968 (to R.D.V.).     

Phenotypic Analysis of a Dwarf Wheat (Triticum aestivum L.) with Altered Phytochrome-Mediated Growth Responses

The influence of the amount of red light relative to far red light (red/far red ratio) on leaf-sheath elongation, leaf length, tillering, assimilate partitioning to shoots and roots, and chlorophyll content in a dwarf wheat (Triticum aestivum L. cv Tibet Dwarf) and seven other dwarf and standard cultivars was determined. All cultivars tested showed far red-stimulated leaf and leaf-sheath elongation except Tibet Dwarf. Tibet Dwarf was also unresponsive to a brief end-of-day exposure to far red light, although the other cultivars exhibited increased leaf-sheath and leaf length. In these cultivars, the effects of an end-of-day 5-min far red exposure were reversible by a subsequent 5-min red light exposure. Shoot/root ratios were higher and tillering was suppressed by increased far red irradiance in all cultivars except Tibet Dwarf. In addition, Tibet Dwarf was less responsive to dark-induced leaf and leaf-sheath elongation (etiolation) and retained chlorophyll in dark-adapted leaves longer than control cultivars. Tibet Dwarf did not differ from the other cultivars in leaf chlorophyll content. Western blot analysis, using an antibody against phytochrome A, showed that dark-grown Tibet Dwarf shoots contained at least twice the amount of detectable phytochrome A protein present in the other wheat cultivars. These results, plus the short, thick-stemmed, dark-pigmented phenotype of Tibet Dwarf suggest the possibility of a mutation in the phytochrome/signal transduction pathway.     

光敏核不育水稻开花和育性转变不同的光反应

从光敏核不育水稻"农垦585"幼穗分化至二次枝梗期开始,在每天的短日照光期（10h日光）结束、暗期开始时（EOD）进行15d的远红光（FR）照射实验,以比较开花、育性转变过程对短暂的远红光（FR）或红光（R）的反应。EODFR明显抑制水稻植株开花（穗分化）,导致"农垦585"和原种"农垦58"的抽穗期均比短日照下推退7d,表现为长日照效应,而"农垦58S"的结实率与原种相比却无显著变化。这暗示诱导农垦58S开花、育性转变过程的光反应可能有差异,前者不仅与光周期有关,且受EODFR的剧烈影响,而育性主要受光周期（临界暗期）控制,基本上不受EODFR的调控。     

Morphology and Photosynthetic Efficiency of Tobacco Leaves That Received End-of-Day Red and Far Red Light during Development

Shaded leaves in plant canopies receive a higher proportion of far red relative to red light than is received by unshaded leaves. Brief end-of-day irradiations with red or far red light, acting through the phytochrome system, reversibly control morphological development of tobacco plants. Leaves that received far red light for 5 minutes at the end of each day during development were longer and narrower than those that received end-of-day red light. The far red treated leaves weighed less, had fewer stomata, and had less chlorophyll per unit area of leaf. Net CO₂ assimilation rates did not differ significantly between red- and far red-treated leaves on an area basis; however, the far red-treated leaves assimilated significantly more CO₂ on a leaf weight basis.     

Endogenous Abscisic Acid Content Correlates with Photon Fluence Rate and Induced Leaf Morphology in Hippuris vulgaris

This research focused on studying how light and endogenous abscisic acid regulate leaf development in Hippuris vulgaris, a species of heterophyllic aquatic plant. Amounts of photosynthetically active radiation greater than 300 micromoles per square meter per second caused submerged H. vulgaris shoots to produce aerial-type leaves. Abscisic acid was not detected in shoots grown under noninducing light quantities (100 micromoles per square meter per second), but was present at 13.4 nanograms per gram fresh weight in shoot tips after plants were exposed to 1 photoperiod of inducing light (500 micromoles per square meter per second). This supports a role for abscisic acid in the high light-induced heterophylly in H. vulgaris, and provides additional support for the general hypothesis that abscisic acid regulates leaf development in heterophyllic aquatic plants. No relationship was observed here between postphotoperiodic light treatments of various red/far red ratios and heterophylly in H. vulgaris.     

The response of Cuscuta planiflora seedlings to red and far-red, blue light and end-of-day irradiations

Irradiation of excised stem segments from de-etiolated seedlings of Cuscuta planiflora for 24 h with mixtures of red and far-red light with red to far-red ratios between 0.02 to 1.0 enhanced coiling and formation of prehaustoria. Maximum number of prehaustoria were recorded when red:far-red was near 0.1. Coiling and prehaustoria were observed whenever estimated in vivo Pfr/Ptotal at photoequilibrium was between 0.06 and 0.67. Irradiation of excised stem segments from white light grown seedlings with 12 h blue light also promoted coiling and prehaustoria formation after another 38 h in darkness. Coiling and prehaustoria were not observed in segments pulsed with 10 min red light at the end of 12 h in blue light. Coiling and prehaustoria were observed after photoreversible end-of-day far-red/red/far-red pulses but not after red/far-red/red pulses. A far-red pulse may not reverse inhibition by end-of-day red pulse when far-red is given more than 12 h after the red pulse.     

The relationship between red and far-red light on flowering of the long-day plant, Lemna gibba

Lemna gibba, a long-day duckweed, can be induced to flower whenthe 10 hr white photoperiod is extended with red or far-redlight. The 10 hr red photoperiod is also effective in inducingflowering when followed by a far-red extension, but a red extensionis ineffective. When 2 hr of far-red light are given immediately after the 10hr red photoperiod, the following red as well as the far-redextension can induce flowering, indicating that the 2 hr far-redlight plays an important role as a starting factor for induction.This red or far-red extension is effectively replaced by a redbreak given at a proper time in the darkness which follows the2 hr far-red light as the starting factor. The effect of thered break in not cancelled by subsequent exposure to far-red,which synergistically promotes flowering. However, a red break given immediately after a proper periodof far-red extension further promotes flowering. The phase sensitiveto the red break coincides with that sensitive to the red breakgiven in darkness. The effect of the red break is reversed bysubsequent exposure to far-red, contrary to the effect of thered break in darkness. Using these results, relation between red and far-red lighton flowering in L. gibba is discussed. (Received July 17, 1971; )