Light requirement,phytochrome and photoperiodic induction of flowering of Pharbits nil Chois

The low chlorophyll content of cotyledons of Pharbitis nil grown for 24 h in far-red light (FR) or at 18° C in white light from fluorescent lamps (WL) allows spectrophotometric measurement of phytochrome in these tissues. The (A) measurements utilize measuring beams at 730/802 nm and an actinic irradiation in excess of 90 s. The constancy of the relationship between phytochrome content and sample thickness confirms that, under these conditions of measurement, a true maximum phytochrome signal was obtained. These techniques have been used to follow changes in the form and amount of phytochrome during an inductive dark period for flowering. Following exposure to 24h WL at 18° C with a terminal 10 min red (R), P_fr was lost rapidly in darkness and approached zero in less than 1 h; during this period there was no change in the total phytochrome signal. Following exposure to 24 h FR with a terminal 10 min R, P_fr approached zero in 3 h, and the total phytochrome signal decreased by about half. The relevance of these changes to photoperiodic time measurement is discussed.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Photomorphogenic and Chlorophyll Studies in the Bryophyte Marchantia polymorpha

The action of daily far-red (FR)-irradiations at the end of photoperiods of white fluorescent light was studied on orientation and chlorophyll content of green thalli of Marchantia polymorpha L. By the end of the night following the first FR-exposure, the chlorophyll content of the tips was already significantly lower than that of the controls, and there was a beginning of upward growth; by the end of the next 8-hour photoperiod and still before the second FR-irradiation, both the change in orientation and the pigment drop had become much more pronounced. After one week, a terminal 5 min FR treatment had resulted in 20 to 30% less chlorophyll for the tips after 8-hour days, and in ±10% less after 16-hour days; the morphogenic effects were also stronger after 8-hour than after 16-hour days. After three weeks under 8-hour photoperiods, the tips of the FR-treated thalli contained ±? less chlorophyll than the tips of the controls; for the basal parts of the thalli the drop was smaller. However, after 1-hour photoperiods, FR depressed the level of the basal parts much more than that of the tips: after one week 1 min FR caused a diminution of 20 to 30 per cent; a daily irradiation of 5 min caused a drastic bleaching, with 60 to 70 per cent less chlorophyll α than in the controls. The various FR-effects were always fully reversed by 2½ min R light. The results are interpreted in terms of the R, FR phytochrome-mediated system. The FR-induced change in orientation is thought to be linked to active growth. The FR-induced chlorophyll decrease can be explained by an effect on the regeneration of protochlorophyll as proposed for etiolated seedlings by several authors, but some of our data indicate the possibility of a greater chlorophyll catabolism in FR-treated than in control thalli.     

Light requirement,phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois

For dark-grown seedlings of Pharbitis nil capacity to flower in response to a single inductive dark period was established by 24 h white, far-red (FR) or ruby-red (BCJ) light and by a skeleton photoperiod of 10 min red (R)-24 h dark-10 min R. FR alone was ineffective without a brief terminal (R) irradiation, confirming that the form of phytochrome immediately prior to darkness is a crucial factor for flowering in Pharbitis. The magnitude of the flowering response was significantly greater after 24 h FR or white light (WL) (at 18° C and 27° C) than after two brief skeleton R irradiations, but the increased flowering response was not attributable to photosynthetic CO₂ uptake because this could not be detected in seedlings exposed to 24 h WL at 18° C. Photophosphorylation could have contributed to the increased flowering response as photosystem I fluorescence was detectable in plants exposed to FR, BCJ, or WL, but there were large differences between flowering response and photosystem I capacity as indicated by fluorescence. We conclude that phytochrome plays a major role in photoresponses regulating flowering. There was no simple correlation between developmental changes, such as cotyledon expansion and chlorophyll formation during the 24-h irradiation period, and the capacity to flower in response to a following inductive dark period. Changes in plastid ultrastructure were considerable in light from fluorescent lamps and there was complete breakdown of the prolamellar body with or without lamellar stacking at 27 or 18° C, respectively, but plastid reorganization was minimal in FR-irradiated seedlings.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing from of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Interaction of Brassinosteroids with Light Quality and Plant Hormones in Regulating Shoot Growth of Young Sunflower and <Emphasis Type="Italic">Arabidopsis</Emphasis> Seedlings

Sunflower hypocotyls elongate as light quality changes from the normal red to far-red (R/FR) ratio of sunlight to a lower R/FR ratio. This low R/FR ratio-induced elongation significantly increases endogenous concentrations of indole-3-acetic acid (IAA) and also of three gibberellins (GAs): GA₂₀, GA₁, and GA₈. Of these, it is likely GA₁ that drives low R/FR-induced growth. Brassinosteroids are also involved in shoot growth. Here we tested three R/FR ratios: high, normal, and low. Significant hypocotyl elongation occurred with this stepwise reduction in R/FR ratio, but endogenous castasterone concentrations in the hypocotyls remained unchanged. Brassinolide was also applied to the seedlings and significantly increased hypocotyl growth, though one that was uniform across all three R/FR ratios. Applied brassinolide increased hypocotyl elongation while significantly reducing (usually) levels of IAA, GA₂₀, and GA₈, but not that of GA₁, which remained constant. Given the above, we conclude that endogenous castasterone does not mediate the hypocotyl growth that is induced by enriching FR light, relative to R light. Similarly, we conclude that the hypocotyl growth that is induced by applied brassinolide does not result from an interaction of brassinolide with changes in light quality. The ability of applied brassinolide to influence IAA, GA₂₀, and GA₈ content, yet have no significant effect on GA₁, is hard to explain. One speculative hypothesis, though, could involve the brassinolide-induced reductions that occurred for endogenous IAA, given IAA’s known ability to differentially influence the expression levels of GA20ox, GA3ox, and GA2ox, key genes in GA biosynthesis.     

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     

The influence of chlorophyll on in-vivo difference spectra of phytochrome

Summary A comparison was made between in-vivo phytochrome difference spectra of light- and dark-grown plant material. Spectral differences were found to be caused, at least to a large extent, by screening by chlorophyll and not by differences in phytochrome. Presence of chlorophyll affects the phytochrome in leaves differently from that in stems. In cotyledons the absorption maximum in the R part of the spectrum shifts towards shorter wavelengths, in FR to longer ones. Concomitantly, the R/FR ratio diminishes; this was confirmed in a model experiment. In stem tissue the peak positions remain the same but the isosbestic point shifts towards longer wavelengths and the R/FR ratio increases.In Viola, however, the phytochrome appears to be different from the normal type. In the etiolated hypocotyl, where the difference spectrum of phytochrome is presumably not distorted by chlorophyll, the R and FR maximum was found to be at a shorter wavelength than in hypocotyls from Cornus and turnip or from stem tissue of dark-grown pea. Abbreviations. R = red; FR = far-red; R/FR ratio = (A) red max./(A) far-red max. of difference spectrum; FR/R ratio = (A) far-red max./(A) red max. The peak positions and the isosbestic point for each curve are estimated from the difference spectrum and are approximate only. They are given in the figure legends in the sequence: absorption maximum of P_r (red-absorbing form of phytochrome), P_fr (far-red-absorbing form), isosbestic point in nm, R/FR ratio.Holder of a Research Grant from the Netherlands Organisation for Pure Scientific Research (Z.W.O.).311th Communication.     

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.     

Differential response of Scots pine seedlings to variable intensity and ratio of red and far‐red light

We investigated the response to increasing intensity of red (R) and far‐R (FR) light and to a decrease in R:FR ratio in Pinus sylvestris L. (Scots pine) seedling. The results showed that FR high‐irradiance response for hypocotyl elongation may be present in Scots pine and that this response is enhanced by increasing light intensity. However, both hypocotyl inhibition and pigment accumulation were more strongly affected by the R light compared with FR light. This is in contrast to previous reports in Arabidopsis thaliana (L.) Heynh. In the angiosperm, A. thaliana R light shows an overall milder effect on inhibition of hypocotyl elongation and on pigment biosynthesis compared with FR suggesting conifers and angiosperms respond very differently to the different light regimes. Scots pine shade avoidance syndrome with longer hypocotyls, shorter cotyledons and lower chlorophyll content in response to shade conditions resembles the response observed in A. thaliana. However, anthocyanin accumulation increased with shade in Scots pine, which again differs from what is known in angiosperms. Overall, the response of seedling development and physiology to R and FR light in Scots pine indicates that the regulatory mechanism for light response may differ between gymnosperms and angiosperms.     

Light effects upon dry lettuce seeds

Germination of certain dry seeds (achenes) of Lactuca sativa L. cv. Grand Rapids was increased to ca. 75% after irradiation with 665 nm red light (R; 1x10³ J m^-2); this response was eliminated by far-red light (FR) following the R. The response of dry seeds required an order of magnitude more light than that of wetted seeds, and was not maximal until 48 h after irradiation. Other seeds, which could not be stimulated by R in dry state, showed a partial response after 10 min hydration. Irradiation of dry seeds (or seeds wetted 1 h) with FR (1x10³ J m^-2) reduced dark germination from 26% to 2%. Seeds dehydrated in an oven (60°C, 90 min) showed a decrease in germination if irradiated with R (1x10⁵ J m^-2) before wetting. The results show that phytochrome is present in dry lettuce seeds (and functional in some seed lots) prior to wetting; and that in other seed lots the molecule becomes functional within minutes after wetting the seeds. Transformation of the FR absorbing from of phytochrome (P_FR) to the inactive from (P_R) occurs at lower seed moisture content than the reverse reaction. It appears that dormancy in seeds ripened in sunlight might be assured during seed drying and maturation by the more effective transformation of P_FR to P_R than vice versa as phytochrome is dehydrated.Abbreviations FR far-red - R red - CAL seeds from California - NC seeds from North Carolina (see text)     

Different Phototransduction Kinetics of Phytochrome A and Phytochrome B in Arabidopsis thaliana

The kinetics of phototransduction of phytochrome A (phyA) and phytochrome B (phyB) were compared in etiolated Arabidopsis thaliana seedlings. The responses of hypocotyl growth, cotyledon unfolding, and expression of a light-harvesting chlorophyll a/b-binding protein of the photosystem II gene promoter fused to the coding region of β-glucuronidase (used as a reporter enzyme) were mediated by phyA under continuous far-red light (FR) and by phyB under continuous red light (R). The seedlings were exposed hourly either to n min of FR followed by 60 minus n min in darkness or to n min of R, 3 min of FR (to back-convert phyB to its inactive form), and 57 minus n min of darkness. For the three processes investigated here, the kinetics of phototransduction of phyB were faster than that of phyA. For instance, 15 min R h⁻¹ (terminated with a FR pulse) were almost as effective as continuous R, whereas 15 min of FR h⁻¹ caused less than 30% of the effect of continuous FR. This difference is interpreted in terms of divergence of signal transduction pathways downstream from phyA and phyB.     

Role of Calcium Channels in Phytochrome-Mediated Regulation of Gravitropic Response

The effect of the inhibitors of calcium channels on red-light (R)-mediated inhibition of gravitropic bending was studied in excised wheat (Triticum aestivumL.) coleoptiles. The effect of a short R pulse (2 min) preceding the gravitropic stimulation was completely alleviated by a similar pulse of far-red light (FR), when the latter preceded the gravitropic stimulation and the delay between R and FR pulses did not exceed 20 min. Plant memory of the R pulse lasted up to 40 min. Neither R nor FR exerted any effect on the gravitropic reaction when applied after gravitropic stimulation. Treatment with 1 M of verapamil, LaCl₃, GdCl₃, or ruthenium red before the gravitropic stimulation prevented or released the R-exerted suppression of the gravitropic response (GR). The GR in coleoptiles is apparently regulated by the phytochrome system at the induction phase and involves calcium channels.     

<Emphasis Type="Italic">Petunia</Emphasis> × <Emphasis Type="Italic">hybrida</Emphasis> during transition to flowering as affected by light intensity and quality treatments

Petunia × hybrida was grown under high (H), medium (M) and low (L) light intensity [photoperiod; 16 h d⁻¹, photosynthetic photon flux density (PPFD); 360, 120 and 40 μmol m⁻² s⁻¹, respectively] as well as under end-of-day (EOD) red (R) and far-red (FR) light quality treatments [photoperiod; 14.5 h d⁻¹, PPFD; 30 μmol m⁻² s⁻¹ EOD; 15 min, Control (C) light; without EOD light treatment]. Shoot growth, leaf anatomical and photosynthetic responses as well as the responses of peroxidase (POD) isoforms and their specific activities following transition to flowering (1–6 weeks) were evaluated. Flower bud formation of Petunia × hybrida was achieved at the end of the 4th week for H light treatment and on the end of the 6th week for FR light treatment. No flower bud formation was noticed in the C and R light treatments. H and M light treatments induced lower chlorophyll (Chla, Chlb, Chla+b) concentrations in comparison to L light. On the other hand R and FR light chlorophyll content were similar to C light. Photosynthetic parameters [CO₂ assimilation rate (A), transpiration rate (E) and stomatal conductance (g _s) values] were higher in the H light treated plants in comparison to M and L light treated plants. A, E and g _s values of R and FR light were similar to C light plants. Leaf anatomy revealed that total leaf thickness, thickness of the contained tissues (epidermis, palisade and spongy parenchyma) and relative volume percentages of the leaf histological components were differently affected within the light intensity and the light quality treatments. POD specific activities increased from the 1st to the 6th week during transition to flowering. Native-PAGE analysis revealed the appearance of four anionic POD (A₁–A₄) isoforms in all light treatments. On the basis of the leaf anatomical, photosynthetic and plant morphological responses, the production of high quality Petunia × hybrida plants with optimal flowering times could be achieved through the control of both light intensity and light quality. The appearance of A₁ and A₂ anionic POD isoforms could be also used for successful scheduling under light treatments.     

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     

Photoresponses of transgenic tobacco plants expressing an oat phytochrome gene

The physiological responses of transgenic tobacco (Nicotiana tabacum L.) plants that express high levels of an introduced oat (Avena sativa L.) phytochrome (phyA) gene to various light treatments are compared with those of wild-type (WT) plants. Seeds, etiolated seedlings, and light-grown plants from a homozygous transgenic tobacco line (9A4) constructed by Keller et al. (EMBO J, 8, 1005–1012, 1989) were treated with red (R), far-red (FR), or white light (WL) with or without supplemental FR light, revealing major perturbations of the normal photobiological responses. White light stimulated germination of both WT and transgenic seed, but addition of FR to the WL treatment suppressed germination. In the WT, all fluence rates tested inhibited germination, but in the transgenics, reduction effluence rate partially relieved germination from the FR-mediated inhibition. It is suggested that the higher absolute levels of the FR-absorbing form of phytochrome (Pfr) in the irradiated transgenics, compared to the WT, may be responsible for the reduced FR-mediated inhibition of germination in the former. Hypocotyl extension of dark-grown seedlings of both WT and transgenic lines was inhibited by continuous R or FR irradiation, typical of the high-irradiance response (HIR). After 2 d of de-etiolation in WL, the WT seedlings had lost the FR-mediated inhibition of hypocotyl extension, whereas it was retained in the transgenics. The FR-mediated inhibition of hypocotyl extension in the transgenic seedlings after de-etiolation may reflect the persistence of an, FR-HIR response mediated by the overexpressed oat PhyA phytochrome. Light-grown WT seedlings exhibited typical shade-avoidance responses when treated with WL supplemented with high levels of FR radiation. Internode and petiole extension rates were markedly increased, and the chlorophyll ab ratio decreased, in the low-R: FR treatment. The transgenics, however, showed no increases in extension growth under low-R: FR treatments, and at low fluence rates both internode and petiole extension rates were significantly decreased by low R FR. Interpretation of these data is difficult. The depression of the chlorophyll ab ratio by low R FR was identical in WT and transgenic plants, indicating that not all shade-avoidance responses of light-grown plants were disrupted by the over-expression of the introduced oat phyA gene. The results are discussed in relation to the proposal that different members of the phytochrome family may have different physiological roles.Abbreviations FR far-red light - PAR photosynthetically active radiation - Pr, Pfr red- and FR-absorbing forms of phytochrome - Ptot total phytochrome - PhyA (PhyA) gene (encoded protein) for phytochrome - R red light - WL white light - WT wild type This work was supported by an Agricultural and Food Research Council research grant to H.S. and A.C.M.; the production of the transgenic seed was funded by the U.S. Department of Energy (DE-F602-88ER13968) to R.D.V., and by E.I. du Pont de Nemours; Dr. G.C. Whitelam is thanked for the provision of monoclonal antibodies for the immunoblot analyses.     

Effets du rapport RC:RS sur les jeunes feuilles de trèfle blanc. Assimilation nette de CO2, activité photochimique et morphologie foliaire

Young leaves of white clover are subjected to low irradiance and low red to far-red (R:FR) ratio within canopies. The objectives were to investigate the consequences of low R:FR ratio on morphology, net CO₂ assimilation and photochemical activity of leaves developed under simulated light environment of canopy. We used far-red (FR) light emitting diodes to modify the R:FR ratio only at the developing leaf under a low irradiance. Net CO₂ assimilation rate, stomatal conductance and leaf morphology were not affected by low R:FR ratio. FR exposure slightly reduced the photochemical quantum yield of PSII but there were no consequences on electron flow through photosystem II. The carbon fixation by the leaf was therefore not modified by light quality. However, low R:FR ratio decreased the leaf chlorophyll content by 21 %. Those effects were only attributed to just unfolded leaves as they were not persistent in mature leaves and there were no consequences on plant biomass accumulation.     

The role of phytochrome in photoperiodic time measurement and its relation to rhythmic timekeeping in the control of flowering in Chenopodium rubrum

Summary To follow changes in the status of phytochrome in green tissue and to relate these changes to the photoperiodic control of flowering, we have used a null response technique involving 1.5-min irradiations with mixtures of different ratios of R and FR radiation.Following a main photoperiod of light from fluorescent lamps that was terminated with 5 min of R light, the proportion of P_fr in Chenopodium rubrum cotyledons was high and did not change until the 3rd hour in darkness; at this time, P_fr disappeared rapidly. When the dark period began with a 5-min irradiation with BCJ or FR light to set the proportion of P_fr low P_fr gradually reappeared during the first 3 h of darkness and then disappeared again.The timing of disappearance of P_fr is consistent with the involvement of phytochrome in photoperiodic time measurement. Reappearance of P_fr after an initial FR irradiation explains why FR irradiations sometimes fail to influence photoperiodic time measurement or only slightly hasten time measurement. A R light interruption to convert P_r to P_fr delayed, the timer by 3 h but only for interruptions after and not before the time of P_fr disappearance. Such 5-min R-light interruptions did not influence the operation of the rhythmic timekeeping mechanism. Continuous or intermittent-5 min every 1.5 h-irradiations of up to 6 h in duration were required to rephase the rhythm controlling flowering. A skeleton photoperiod of 6 h that was began and terminated by 5 or 15 min of light failed to rephase the rhythm.The shape of the curves for the rhythmic response of C. rubrum to the length of the dark period are sometimes suggestive of clocks operating on the principle of a tension-relaxation mechanism. Such a model allows for separate timing action of a rhythm and of P_fr disappearance over the early hours of darkness. Separate timing action does not, however, preclude an interaction between the rhythm and phytochrome in controlling flowering.Abbreviations FR far-red - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - R red - BCJ photographic ruby-red irradiation A grant in aid of research from the National Research Council of Canada to B. G. Cumming is gratefully acknowledged.     

光质和光周期对山白兰苗木生长、生理的影响

为筛选出山白兰(Michelia baillonii)苗木培育过程中适宜的光环境，该研究以一年生山白兰幼苗为试验材料，设置12、16 h·d^-1两个光周期，配合使用红蓝复合光(8R1B、6R1B)、红蓝紫绿复合光(8R1B1P1G、6R1B1P1G)4种光质和白光(W)对照，采用双因素随机区组试验设计和隶属函数法，探讨了山白兰苗木生长、光合色素、内源激素含量对不同光质和光周期处理的响应规律。结果表明：(1)光质、光周期及其交互作用对山白兰苗高增长量、叶面积、叶绿素a、玉米素(ZR)、脱落酸(ABA)的含量、内源激素比值[IAA/ABA、(IAA+GA₃+ZR)/ABA]等均有显著影响(P<0.05)。(2)16 h·d^-1光周期有利于苗高增长量、叶面积、苗木质量指数、生物量、叶绿素a、生长素(IAA)、ZR的含量、内源激素比值的提高。(3)当光周期为16 h·d^-1时，8R1B处理下的苗高增长量、叶面积和苗木质量指数均最大，分别为21.84 cm、158.39 cm²和2...     

PHYTOCHROME CONTROLLED NYCTINASTY IN ALBIZZIA JULIBRISSIN. II. POTASSIUM FLUX AS A BASIS FOR LEAFLET MOVEMENT

Excised Albizzia leaflet pairs exposed to red (R) light close within 30–90 min after transfer to darkness. Interruption of darkness by far-red (FR) light at any time after R inhibits closure within ca. 10 min. Similarly, irradiation with R at any time after prior FR promotes closure within ca. 10 min, and the increased rate of closure is independent of the time lapse between the FR and R irradiations. Closure in the dark is inhibited by NaN₃ and DNP (5 X 10^–4 m ), by anaerobic conditions and by externally applied salts of monovalent cations, especially K; it is also temperature sensitive. Pulvinule cells are very high in K. Electron microprobe analysis of cryostated, lyophilized pulvinules reveals that during closure, K is lost from ventral cells and enters dorsal cells. FR before darkness inhibits the former but not the latter process. Thus, K flux appears to control the changes in volume of the pulvinule cells that control leaflet movement. While leaflet closure normally requires a dark period, salts of organic acids such as sodium acetate, propionate, and butyrate cause closure in the light.     

Phytochrome-mediated polarotropism of Adiantum capillus-veneris L. protonemata as analyzed by microbeam irradiation with polarized light

Summary Perception of polarized light inducing phytochrome-mediated polarotropism in protonemata of the fern Adiantum capillus-veneris L. was analyzed using brief microbeam irradiation with polarized red (R) or far-red light (FR). The polarotropic response inducible by irradiation of the subapical 10–30-m part with polarized R vibrating parallel to the cell axis was nullified by subsequently giving R at the apical 0–2.5-m region. This inhibitory effect of R showed an action dichroism, that is, polarized R vibrating normal to the cell axis was effective but the parallel-vibrating R was not. On the other hand, FR irradiation of the extreme tip after irradiation of the whole cell with depolarized R effectively induced a tropic response. This FR effect also showed action dichroism, with parallel-vibrating polarized FR being more effective than FR vibrating normal to the cell axis. When the apical-dome region and the adjacent subapical 10–20-m region were sequentially irradiated with polarized R vibrating obliquely in different directions, polarotropism took place depending on the vibrating direction of the light given to the apical-dome region. Obliquely vibrating polarized FR given to the apical dome after irradiation of the whole cell with depolarized R also induced polarotropism. Thus, the difference in amount (or percent) of the far-redabsorbing form of phytochrome (Pfr) between the extreme tip and the subapical region appears to be crucial in regulating the direction of apical growth; the difference in Pfr level between the two sides of the protonemal apex may occur mainly at the apical dome. Furthermore, the transition moments of the red-absorbing form of phytochrome (Pr) and Pfr seem to be aligned parallel and normal, respectively, to the cell surface at the periphery of the apical hemisphere.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Far-red light-insensitive, phytochrome A-deficient mutants of tomato

We have selected two recessive mutants of tomato with slightly longer hypocotyls than the wild type, one under low fluence rate (3 mol/m²/s) red light (R) and the other under low fluence rate blue light. These two mutants were shown to be allelic and further analysis revealed that hypocotyl growth was totally insensitive to far-red light (FR). We propose the gene symbol fri (far-red light insensitive) for this locus and have mapped it on chromosome 10. Immunochemically detectable phytochrome A polypeptide is essentially absent in the fri mutants as is the bulk spectrophotometrically detectable labile phytochrome pool in etiolated seedlings. A phytochrome B-like polypeptide is present in normal amounts and a small stable phytochrome pool can be readily detected by spectrophotometry in the fri mutants. Inhibition of hypocotyl growth by a R pulse given every 4 h is quantitatively similar in the fri mutants and wild type and the effect is to a large extent reversible if R pulses are followed immediately by a FR pulse. After 7 days in darkness, both fri mutants and the wild type become green on transfer to white light, but after 7 days in FR, the wild-type seedlings that have expanded their cotyledons lose their capacity to green in white light, while the fri mutants de-etiolate. Adult plants of the fri mutants show retarded growth and are prone to wilting, but exhibit a normal elongation response to FR given at the end of the daily photoperiod. The inhibition of seed germination by continuous FR exhibited by the wild type is normal in the fri mutants. It is proposed that these fri mutants are putative phytochrome A mutants which have normal pools of other phytochromes.