Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response

Baumgartner, N. and Fondeville, J. C. 1989. Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response.
A statistical evaluation of the hypocotyl hook opening (hook opening index) was used for measurement of the hook angle in lots of etiolated Sinapis alba L. cv. Albatros seedlings. Studies of the kinetics for hook opening were carried out in continuous fluorescent white, blue and red light (6, 15 and 40 μmol m^-2s^-1) with 2-day-old dark-grown seedlings. At the beginning of the irradiation period the photoresponse in red light was the opposite to that in blue (low photon fluences). Blue rapidly induced the hook opening (in less than 20 min), while red produced hook tightening (photon fluences up to 70 mmol m^-2), which precedes the normal progressive hook opening. For low fluences, the data were consistent with the involvement of phytochrome and a specific blue light photoreceptor. A phytochrome effect was observed in the hook opening, dependent upon a high irradiance response (HIR). This HIR (like that for the inhibition of the hypocotyl elongation) was characterized by a wavelength response curve with maxima in the blue and far-red regions of the spectrum.     

Nutrients-mediated shift in temporal expression of phytochrome controlled β-amylase synthesis in mustard (Sinapis alba L.) cotyledons

Abstract. In cotyledons of mustard ( Sinapis alba L.) seedlings grown with distilled water (DW) phytochrome controlled increase in β-amylase (E.C. 3.2.1.2) level takes place at about 42 h after sowing (starting point), while the photoresponse escapes from photoreversibility at 30 h after sowing. The temporal onset of starting point is presumed to be determined by innate process of developmental homeostasis, which is not amenable to influence of environmental factors such as light and nutrients. However, the temporal appearance of onset of phytochrome controlled increase in β-amylase level (starting point) in seedlings grown with Hoagland's nutrient solution (HS) is delayed by 9 h as compared to DW-grown seedlings. Concomitantly, the temporal appearance of the loss of photoreversibility of phytochrome mediated increase in β-amylase level (coupling point) is also delayed by 9 h in HS-grown seedlings. HS does not influence the primary action of phytochrome, the lifetime of components involved in signal chain of above photoresponse and the turnover of β-amylase enzyme. These results indicate that HS-induced temporal shift in onset of starting point of above photoresponse is caused by interaction of nutrients with the process of developmental homeostasis.     

Hypocotyl growth in Sinapis alba L: the roles of light quality and quantity

Abstract. A comparison is made of the relative effectiveness of light quality and light quantity on the elongation growth of Sinapis alba hypocotyls. The results show that hypocotyl extension rate in plants which have not previously been exposed to light is controlled primarily by the prevailing photon fluence rate when the phytochrome photostationary state lies between ∼0.033 and ∼0.81. Below ∼0.033, changes in photostationary state also have a marked effect on extension rate. Elongation growth in light-adapted plants is controlled by both photon fluence rate and the spectral quality of the incident radiation at all photoequilibria. Photosynthesis can modify these responses but is not essential as a prior condition for a green plant to respond to changes in light quality and quantity.     

The 'end-of-day' phytochrome control of internode elongation in mustard: kinetics, interaction with the previous fluence rate, and ecological implications

Abstract The ‘end-of-day’ phytochrome control of internode growth was characterized in Sinapis alba, seedlings previously grown under continuous white light for 13 d. The transition from white light to darkness caused a reduction in internode extension rate with a lag of less than 10 min. Following this, extension rate remained almost constant for at least 48 h. i.e. ‘re-etiolation’ was not noticed. The phytochorme controlling the growth processes was stable in the Pfr form. The growth rate of plants receiving a red light pulse, and the growth promotion caused by a far-red light pulse, increased with increasing fluence rate of the previous white light treatment. In far-red treated plants a first growth rate acceleration peaked at 20–30 min after the end of white light, followed by a transient deceleration which led to a growth rate minimum at 40–60 min, followed by a final growth rate recovery yielding a more-or-less steady elevated rate. Pulses establishing different Pfr/P modified the extent, but not the early kinetics, of the growth response. The relative promotion of growth caused by low Pfr/P was limited by darkness as follows: (a), The growth promotion caused by far-red directed to the internode alone was transient. (b), The promotion caused by a reduction of Pfr/P in the whole shoot persisted in darkness for at least 48 h and also persisted if, after a 3–9 h dark period, the plants were returned to continuous white light. In darkness, however, the magnitude of this growth rate promotion decreased with time, particularly when the previous white light fluence rate was low, or the pulse preceding darkness provided the lowest Pfr/P. (c), When compared over the same period in darkness, growth rate was higher in those seedlings in which Pfr/P was reduced during the continuous white light pretreatment than in those ones in which the Pfr/P was only reduced immediately before darkness. It is proposed that in the natural environment, red/far-red signals could be more effective when provided during daytime than at the end of the photoperiod, as both the background growth rate and the relative promotion caused by low Pfr/P are reduced by darkness.     

Photocontrol of the cotyledonary blade epinasty of Sinapis alba seedlings. Effects of irradiance and quality of light

The effects of the fluence rate of continuous light (far-red, fluorescent white, blue and red light) on the increase of epinastic percentage of cotyledons were recorded for six days. The epinastic photoresponse was compared to the cotyledonary enlargement and to the inhibition of the hypocotyl extension of irradiated Sinapis alba L. seedlings. Fluence rate response curves and wavelength response curves showed that the photoepinasty is a typical high irradiance response (as is the inhibition of hypocotyl extension) with two maxima, one in the blue and one in the far-red. The epinastic photoresponse was not directly related to cotyledonary growth, which was greater in red and far-red light than in blue light.     

The role of pigments in germination and dark-growth of white mustard (Sinapis alba L.) seeds

Pigments leached from Sinapis alba L. seeds and extracted from dark-grown seedlings are described and investigated by spectrophotometry and chromatography and their functions examined. Evidence is given that they are quinonoid, and it is suggested that they form part of a complex which absorbs ultraviolet light and utilizes it to produce growth energy at stages before visible light becomes available to the plant, and that this process may be the means by which mutations are introduced into species.     

白芥自交亲和性分析

对不同来源的8份白芥材料,采用人工自交法分析其自交亲和性。结果显示:白芥的自交亲和性存在较大幅度的变异,自交亲和指数在0.01~4.10之间,8份参试材料中,自交亲和指数小于1的材料有3个,自交亲和指数大于1的材料有5个。表明白芥中存在自交亲和材料,白芥自交亲和性变异不仅存在于材料间,而且也存在于同一材料内不同个体间。按自交亲和指数的高低,可将参试材料分为3种类型:高自交亲和类型(自交亲和指数大于3.00,如民乐洪水芥麻、04(X)等)、自交亲和类型(自交亲和指数为1.00~2.99)、自交不亲和类型(自交亲和指数0.00~1.00)。     

Floral nectaries and nectar production in brown mustard (Brassica juncea) and white mustard (Sinapis alba) (Brassicaceae)

 The dynamics and abundance of nectar secretion as well as sugar productivity were studied in flowers of brown mustard (Brassica juncea) cv. Małopolska and white mustard (Sinapis alba) cv. Borowska. Moreover, floral nectaries were examined under LM and SEM. In both cultivars lateral and median pairs of nectaries secreted nectar. However, differences were found in morphology and activity of these pairs. The lateral nectaries produced more nectar than the median ones. Nectar secretion started at loose bud and peaked during anther dehiscence. Average amount of nectarsecreted by 100 flowers of cv. Małopolska and cv. Borowska were 119.9 mg and 134 mg. Mean concentration of nectar was 26.7% and 23.4%, respectively. One hundred flowers of cv. Małopolska and cv. Borowska secreted 28.4 mg and 24.9 mg of sugars in nectar. Estimated sugar productivity per 1 ha of crop was 65.5 kg and 71.2 kg, respectively. Received August 28, 2002; accepted November 2, 2002 Published online: June 2, 2003     

Control of hypocotyl phototropism by phytochrome in a dicotyledonous seedling (Sesamum indicum L.)

Abstract The phototropic response in stems of higher plants is brought about by blue/UV light. The problem studied here is to what extent long-wavelength light, which is absorbed by phytochrome, affects the phototropic response. A refined measurement of phototropism — a curvature index — was applied to the hypocotyl of the sesame seedling (Sesamum indicum L.). The time course of the phototropic response was followed in continuous unilateral weak blue light (B, 460 nm, 8 mW m^?2). Long term red light (R) pretreatments, operating through phytochrome, strongly increase the rate and extent of the phototropic response once it is elicited by unilateral B, while the pretreatments decrease the sensitivity towards B. If a R pulse is given immediately prior to the onset of unilateral B, the rate of the response is strongly reduced compared to the time course of curvature observed when the pretreatment was terminated with a long wavelength far-red light (FR) pulse. R and FR were then applied simultaneously with unilateral B to manipulate the status of the phytochrome system during actual curvature. It was found that a low Pfr/P ratio (established by FR) stimulates the phototropic response far above the control (B alone), while a high Pfr/P ratio (established by R) reduces the response below the control. During bending a positive effect of phytochrome on the rate and extent of the phototropic response, which is saturated at a low level of Pfr, appears to be counteracted by an inhibitory effect which dominates at higher levels of Pfr, such as established by omnilateral R. However, if R is applied unilaterally from the same direction as B, R increases the rate of curvature. Apparently the sesame seedling is capable of detecting the direction of R relative to the direction of B. While a mechanistic explanation of these effects cannot be advanced at present, it is clear that the seedling is capable of super-imposing information about the actual light conditions during bending on a ‘memory’ of the light conditions prior to the onset of bending. Thus, the previous as well as the actual light conditions determine its phototropic responsiveness.     

Accumulation of Storage Materials,Precocious Germination and Development of Desiccation Tolerance During Seed Maturation in Mustard (Sinapis alba L.)

Under defined environmental conditions (20°C, continuous light of 15 klx) development of mustard seeds from artificial pollination to maturity takes about 60 d. After surpassing the period of embryo cell division and histodifferentiation (12–14d after pollination = dap), the seed enters into a maturation period. The time courses of various physiological, biochemical, and structural changes of embryo and testa during seed maturation were analyzed in detail (dry and fresh mass changes, osmotic and water potential changes, respiration, DNA amplification by endomitosis, total ribosome and polysome formation, storage protein synthesis and accumulation, storage lipid accumulation). In addition to the final storage products protein and lipid, embryo and testa accumulate transiently large amounts of starch within the chloroplasts during early maturation. Concomitantly with the subsequent total breakdown of the starch, the plastids lose most of their internal structure and chlorophyll and shrink into proplastids, typical for the mature seed. At about 30 dap the seeds shift from a desiccation-sensitive to a desiccation-tolerant state and are able then to germinate rapidly upon drying and reimbibition. If isolated from the immature fruit and sown directly on water, the seeds demonstrate precocious germination from about 13 dap onwards. Young seeds (isolated ≦ 38 dap) germinate only after surpassing a lag-phase of several days (after-ripening) during which the embryo continues to accumulate storage protein and lipid at the expense of the surrounding seed tissues. We conclude from these results that the maturing seed represents a rather closed developmental system which is able to continue its development up to successful germination without any specific regulatory influence from the mother plant. Immature seeds are able to germinate without a preceding dehydration treatment, which means that partial or full desiccation does not serve as an environmental signal for reprogramming seed development from maturation to germination. Instead, it is argued that the water relations of the seed are a critical element in the control of maturation and germination: during maturation on the mother plant the embryo is subject to a considerable turgor pressure (of the order of 12 bar) accompanied by a low water potential (of the order of ?12 bar). This turgor permits maturation growth but is subcritical for germination growth. However, upon imbibition in water, the low water potential provides a driving force for a burst of water uptake overcoming the critical turgor threshold and thereby inducing germination.     

Degradation of phytochrome A and the high irradiance response in Arabidopsis: a kinetic analysis

The ability to respond to far‐red‐rich light is essential for seedlings germinating below dense canopies. Physiological and genetic studies have demonstrated that phytochrome A is the only photoreceptor mediating responses to far‐red light. However, all phytochromes including phytochrome A are believed to be activated by red light and to be inactivated by far‐red light. To address the fundamental question of why phytochrome A has its highest physiological activity at presumably inactivating wavelengths, we analysed light‐induced degradation of phytochrome A in Arabidopsis. Rate constants were obtained for all reaction events in a two‐step model of degradation. Based on biochemical data, the model includes a tagging mechanism preceding degradation. The parameterized model describes Pr accumulation, wavelength dependencies of degradation kinetics and steady‐state levels as well as Pfr‐induced Pr degradation. Subsequently, experimentally derived fluence rate response curves, action spectrum and response curves to dichromatic irradiation were compared to simulations based on the model of degradation. Two kinetically defined phytochrome subspecies, untagged Pfr and tagged Pr, have steady‐state levels closely matching the physiological response curves. Therefore, sensing of far‐red light by phytochrome A can be quantitatively explained based exclusively on regulated protein degradation.     

The Effect of Light and Exogenously Supplied Ammonium Ions on Glutamate Dehydrogenase Activity and Isoforms in Young Mustard (Sinapis alba L.) Seedlings

Glutamate dehydrogenase (GDH, E.C. 1.4.1.3) of mustard cotyledons was investigated during the first 4 days of seedling development. The enzyme was found to be composed of seven catalytically active isoforms (each with a molecular mass of 270 kDa) which exhibited a charge heterogeneity when investigated by isoelectric focusing. Antibodies against the purified isoform 7, raised in rabbits, cross-reacted with each of the isoforms in Western blotting experiments. In addition, each of the isoforms was composed of four immunopositive reacting polypeptides with 19, 21, 23 and 25 kDa. During development of the seedlings, a shift in the isoform pattern towards the more acidic forms was found which was more pronounced when the seedlings were supplied with 15 mM NH₄Cl. The time course of changes in total GDH level can be correlated with the time course of disappearance of storage proteins. Both parameters are negatively regulated by light possibly via the photoreceptor, phytochrome. There are some indications that GDH in young mustard cotyledons mainly acts in the deaminating direction.     

Amino-acid biosynthesis in the cotyledons of Sinapis alba L. in darkness and far-red light studied by deuterium labelling and mass spectrometry

The incorporation of deuterium from deuterium oxide into the free amino acids of the cotyledons of Sinapis alba L. was studied by gas chromatography-mass spectrometry and was similar, both qualitatively and quantitatively, after incubation of the seedlings in darkness or far-red light. The results support studies which show that phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) is synthesised de novo, rather than activated, in response to far-red light.Abbreviations GC-MS Gas chromatography-mass spectrometry - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - HFB n-propyl heptafluorobutyryl n-propyl     

The influence of light quality on the phytochrome content of light grown Sinapis alba L. and Phaseolus aureus Roxb.

The effect on the phytochrome system of light regimes establishing a range of photoequilibria was studied in two light grown dicotyledonous plants, both of which were treated with the herbicide SAN 9789 to prevent chlorophyll accumulation. In Sinapis alba L. cotyledons the results are comparable with phytochrome behaviour in etiolated mustard seedlings; the level of Pfr becomes independent of wave-length whereas the total phytochrome level is wave-length dependent. Contrasting properties are exhibited in Phaseolus aureus Roxb. leaves in which total phytochrome is unaffected by light quality; consequently the Pfr level is dependent on wavelength. Nevertheless, the amount of phytochrome in mung leaves increased after transfer to darkness suggesting that light still has a profound influence on the phytochrome system, even though light quality during the light period and prior to darkness does not.Abbreviations FR far-red light - WL white light - PAR photosynthetically active radiation - Pfr far-red light absorbing form of phytochrome - Pr red light absorbing form of phytochrome - Ptot total phytochrome level (=Pr+Pfr) - Pfr/Pfr+Pr - SAN 9789 4-chloro-5-(methylamino) 2(,, trifluoro-m tolyl)-3(2H)-pyridazinone     

Control of hypocotyl gravitropism by photochrome in a dicotyledonous seedling (Sesamum indicum L.)

Abstract The present study was prompted by the question as to whether the strong effect of red and far-red light treatments on blue-light-mediated phototropism in the sesame (Sesamum indicum L.) hypocotyl (Woitzik & Mohr, 1988) should be attributed in part to changes initialed by light in the gravitropic counter-response. Light treatments, operating through phytochrome, do indeed strongly affect the gravitropic response. However, the direction of the light effect is the same in gravitropism, as in phototropism. Thus, the gravitropic counter-response leads to an underestimate, rather than an overestimate, of the importance of phytochrome action on phototropic responsiveness. The effect of red and far-red light, operating via phytochrome, on the gravitropic response of the sesame hypocotyl could be studied in the present paper without any interference due to phototropism or light control of longitudinal growth. It was found that the effects of red and far-red pretreatments (given prior to the onset of the stimulus) as well as the action of simultaneously applied red or far-red light (simultaneous to the phototropic or gravitropic stimulus) are very similar in both phototropism and gravitropism. In particular, the seedling is capable of superimposing information about the actual light conditions during bending on the ‘memory’ it has about the light conditions prior to the onset of phototropism or gravitropic stimulation, This striking similarity between the phototropic and gravitropic responses possibly indicates that phytochrome affects the signal-response-chain at a relatively late stage, after the phototropic and the gravitropic signal-response chains have merged. From a teleonomic point of view the action of red and far-red light on phototropic, as well as gravitropic, responsiveness can be conceived as part of a shade escape strategy.     

Growth and photosynthesis of soybean (Glycine max (L.) Merr.) in simulated vegetation shade: influence of the ratio of red to far-red radiation*

Abstract. Glycine max (L.) Merr. was grown under several light conditions to determine the role of red and far-red radiation in plant adaptation to vegetation shade. Neutral density,‘neutral’ density with elevated far-red radiation, and green shade treatments were used in a greenhouse, producing calculated phytochrome photostationary state (P_fr/P_r+P_fr) values of 0.68, 0.63 and 0.51, respectively. Cool-white fluorescent lamps either alone or in conjunction with far-red fluorescent lamps were used in a growth chamber, providing P_fr/P_r+P_fr of 0.79 and 0.61, respectively. Daily photo-synthetically active radiation was about 25% of daylight and was approximately equal for both greenhouse (2.15MJ m^?2) and growth chamber (2.57MJ m^?2). Developmental stage 4 weeks after sowing was similar for all treatments, but axillary growth and rates of leaf area and dry matter accretion differed between plants from greenhouse and growth chamber. Light conditions simulating vegetation shade (i.e. a low ratio of red to far-red radiation) significantly promoted petiole elongation and retarded the rate of stem elongation in both greenhouse and growth chamber experiments. Other aspects of growth either were not significantly altered by spectral quality or were not modified consistently in both greenhouse and growth chamber environments. Net photosynthetic rates measured under growth conditions for unifoliate and first trifoliolate (TF₁) leaves of growth chamber plants between 9 and 21 d after sowing were generally unaffected by spectral quality, but supplemental FR enhanced TF₁ leaf area expansion. The latter effect was not correlated with increased dry matter accumulation. The significance of spectral quality for adaptation of soybeans to canopy closure and intercropping is discussed.     

The kinetics of type 1 phytochrome in green,light-grown wheat (Triticum aestivum L.)

The kinetics of type 1 phytochrome were investigated in green, light-grown wheat. Phytochrome was measured by a quantitative sandwich enzyme-linked immunosorbent assay using monoclonal antibodies. The assay was capable of detecting down to 150 pg of phytochrome. In red light, rapid first-order destruction of the far-red-light-absorbing form of phytochrome (Pfr) with a half-life of 15 min was observed. Following white light terminated by red, phytochrome synthesis was delayed in darkness by about 15 h compared to plants given a terminal far-red treatment. Synthesis of the red-light-absorbing form of phytochrome (Pr) was zero-order in these experiments. Phytochrome synthesis in far-red light was approximately equal to synthesis in darkness in wheat although net destruction occurred in light-grown Avena sativa tissues in continuous far-red light, as has been reported for other monocotyledons. In wheat, destruction of Pfr apparently did not occur below a certain threshold level of Pfr or Pfr/total phytochrome. These results are consistent with an involvement of type 1 phytochrome in the photoperiodic control of flowering in wheat and other long-day plants.Abbreviations ELISA enzyme-linked immunosorbent assay - FR far-red light - HIR high-irradiance response - Pfr farred-light-absorbing form of phytochrome - Pr red-light-absorbing form of phytochrome - Ptot total phytochrome (Pr + Pfr) - R red light The authors wish to thank Prof. Daphne Vince-Prue (University of Reading) for many helpful discussions regarding this work. Hugh Carr-Smith was supported by a Science and Engineering Research Council studentship and Chris Plumpton by an Agricultural and Food Research Council (AFRC) studentship. B. Thomas and G. Butcher were supported by the AFRC.     

Effect of light on the development of glyoxysomal functions in the cotyledons of mustard (Sinapis alba L.) seedlings

The degradation of storage fat in the cotyledons of mustard seedlings is unaffected by phytochrome and photosynthesis (irradiation with continuous red or far-red light from sowing of the seeds) although light imposes a strong constraint on the translocation of organic matter from the cotyledons into the seedling axis. Likewise, the development and disappearance of glyoxysomal enzyme activities (isocitrate lyase, malate synthase, citrate synthase) takes place independently of light. It is concluded that the mobilization of storage fat (fatcarbohydrate transformation) is independent of photomorphogenesis. The surplus of carbohydrate produced from fat in the light seems to be converted to starch grains in the plastids, which function as a secondary storage pool in the cotyledons.Abbreviations CS citrate synthase - ICL isocitrate lyase - MS malate synthase