The effect of red and far-red light in the high irradiance reaction of phytochrome (hypocotyl growth in dark-grown Sinapis alba L.)

Abstract. Fluence-rate response curves were determined for the inhibition of hypocotyl growth in 54-h-old dark-grown Sinapis alba L. seedlings by continuous or hourly 5 min far-red light irradiation (24 h). Just as in red light ( Heim & Schäfer, 1982 ), a fluence-rate dependence was observed for both kinds of irradiations, even if only 35% of the continuous light effect could be substituted for by hourly far-red pulses. The same total fluence was used for the two different light regimes. Measurements of Pfr and Pfr/Ptot showed a strong fluence-rate dependence under continuous light which only partially paralleled the fluence-rate response curves for the inhibition of the hypocotyl growth. It was concluded that neither spectrophotometrically determined levels of Pfr nor Pfr/Ptot can be the only light-dependent factor controlling hypocotyl lengthening under continuous irradiation.     

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.     

Intergeneric Somatic Hybridization Between Brassica napus L. And Sinapis alba L.

Electrically induced protoplast fusion was used to produce somatic hybrids between Brassica napus L. and Sinapis alba L. Seven hybrids were obtained and verified by the simple sequence repeat and cleaved amplified polymorphic sequence analysis of the genefael, indicating that the characteristic bands from S. alba were present in the hybrids. The hybridity was also confirmed by chromosome number counting because the hybrids possessed 62 chromosomes, corresponding to the sum of fusion-parent chromosomes. Chromosome pairing at meiosis was predominantly normal, which led to high pollen fertility,ranging from 66% to 77%. All hybrids were grown to full maturity and could be fertilized and set seed after self-pollination or back-crosses with B. napus. The morphology of the hybrids resembled characteristics from both parental species. An analysis of the fatty acid composition in the seeds of F1 plants was conducted and the seeds were found to contain different amounts of erucic acid, ranging from 11.0% to 52.1%.     

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.     

Obtention d'épinastie des cotylédons de Sinapis alba en éclairement rouge Iointain continu.

Obtention of epinasty in the cotyledons of Sinapis alba under continuous far-red illumination. Relation to the development of hypocotyl and cotyledons. Treatment by far red light induces epinasty of the cotyledonary leaf. The effects of light treatments of different intensities were recorded for hypocotyl length, percentage of epinasty and the cotyledon leaf area. The percentage of epinasty increases as a function of treatment duration and light intensity. As from the second day of treatment a correlation is obtained between the percentage of epinasty and hypocotyl length when the seedlings are given far-red light treatment of different durations.     

Effects of temperature on the development of Sinapis alba L. phytochrome-control of nitrate reductase activity at 10°C

Abstract. An analysis of three biochemical parameters during growth of white mustard in continuous white light (WL) has been undertaken at 10°, 15° and 20°C. The time required for anthocyanin and chlorophyll content and nitrate reductase [E.C. 1661 NAD(P)H: nitrate oxidoreductase] activity (NRA) to reach a peak in the cotyledons is shown to be temperature dependent, the rise in chlorophyll content being delayed to a much greater extent than anthocyanin content. In addition, with NRA, there is a significant increase in the level of the peaks with a lowering of temperature.
The NRA in dark-grown plants has been investigated in detail at 10°C. The pre-competence time for this response is increased to 20–24 h, compared with 14 h in seeds grown at 25°C. Other responses are affected far more by the lower temperature; for example, time for 50% loss of photoreversibility of a red (R) pulse in 48-h-old seeds is approximately 13 h, compared with 8 min in seeds grown at 25°C. At 25°C, light treatments during precompetence have been found to increase significantly the effectiveness of a subsequent R pulse on NRA; at 10°C, this effect appears to be almost entirely absent.     

Photocontrol of stem elongation in plant neighbourhoods: effects of photon fluence rate under natural conditions of radiation

Abstract. We investigated the effects of photon fluence rate on internode elongation in fully de-etiolated plants growing under sunlight. Our goal was to find out whether perception by the stems of fluence rate changes related to canopy density may be involved in the modulation of internode growth in canopies formed by plants of similar stature (e.g. crop stands). Using Datura ferox L. and Sinapis alba L. seedlings growing under natural radiation, we found that internode elongation is promoted by localized shading. This effect was observed with internodes receiving light with a high (>0.9) or a low (0.3) red (R) to far-red (FR) photon ratio. Selective removal of the different wavebands from the light impinging on the internodes showed that part of the response to fluence rate is due to photons in the R + FR range. The blue (B) component, most likely acting through a specific photoreceptor, also inhibited elongation. However, changes in the fluence rate of B light did not have detectable effects on the response of the internodes to R:FR ratio. Fibre-optic studies and measurements with integrating-cylinder sensors in even-aged populations of seedlings showed that both the quality and quantity of radiation received by the stems are profoundly influenced by changes in canopy density. When density is very low (leaf area index = LAI ≥ 1) only the R:FR ratio is reduced, due to FR reflected from nearby leaves. In the LAI range of 1 to 2, though a large proportion of the leaf area is still receiving full sunlight, the photon fluence rate at the stem level drops dramatically. These results suggest that in even-aged populations of LAI > 1 elongation growth is promoted by the low R:FR ratio and the reduced fluence rate. Perception of these two factors at the stem level may elicit morphological adaptations in the canopy before the onset of severe competition among neighbours for the resource of light.     

Early detection of neighbour plants by phytochrome perception of spectral changes in reflected sunlight

Abstract We have tested the hypothesis that a plant may detect the presence of a neighboug42r, before being shaded by it, through the perception of the spectral composition of reflected sunlight. Within seedling canopies the red: far-red ratio (R: FR) of the light received by a sensor with a geometry approximating that of a stem was significantly reduced by selective reflection. This effect was observed before any reduction in the amount of photosynthetic light energy received by an individual seedling could be detected. Small green fences of grass, east-west orientated, altered the spectral distribution of the light on the north (sunlit) side of them. Fully illuminated seedlings of Sinapis alba grown on the north side of these green fences produced longer internodes and had a lower leaf: stem dry weight ratio than those grown in front of fences of bleached grasses. A similar redistribution of growth was elicited in seedlings of Chenopodium album, Datura ferox and S. alba growing in full sunlight by exposing plants to additional small quantities of far-red reflected by selective mirrors. These results suggest that the change in the R: FR ratio serves as an early warning signal of oncoming competition.     

Isolation and Characterization of Mustard (Sinapis alba L.) Seed Storage Proteins

A total storage protein fraction was prepared from mustard (Sinapis alba L.) seeds via isolated protein bodies and characterized by sedimentation, immunological, and electrophoretic techniques. Mustard seed storage protein consists of three fractions (1) a “legumin-like” 13-S complex composed of two pairs of disulfide-linked polypeptides (16.5 + 28.5 kDa and 19.5 + 34 kDa, respectively) and two single polypeptides (18 kDa and 26 kDa), (2) a “vicilin-like” 9-S complex composed of two glycoproteins (64 kDa and 77 kDa), and (3) two small polypeptides (10 kDa and 11 kDa) which probably represent the 1.7-S complex found in other Cruciferae. In contrast to related species, no glycosylated polypeptide was found in the 13-S complex. Immunological relationships were found between the paired polypeptides of the 13-S complex but not between polypeptides of the 13-S complex and polypeptides of the 9-S complex. Pulse-chase labeling and in vitro translation of polysomal RNA from young embryos demonstrated that the polypeptides of the 13-S complex originate from high molecular mass precursors, except for the 18 kDa polypeptide which appears to be synthesized in its final size. The amino-acid composition of the major polypeptides of the mustard storage protein is given.     

Photo-inhibition of internode elongation rate in light-grown Vigna sinensis L. Control by light quality

Abstract. In white light(W) stem elongation of green plants is stimulated when some far-red light (F) is added to W (Holmes & Smith, 1975, 1977b). The effect of adding F to a background W was quantified using Vigna sinensis L. plants and relatively high fluence rate W. F was given selectively to the 1st internode and the internode elongation rate (E.R) was recorded using linear voltage displacement transducers. Results confirm that adding F to background W stimulates internode E. R. The stimulation is very quickly measurable after switching F on and falls off rapidly after switching F off. The stimulation is not dependent on F fluence rate per per se but is strictly dependent on the quantum flux ratio F/W. These data are strongly in favour of phytochrome as the receptor, whose activity is controlled by the P_FR content or the [P_FR]/[P] ratio. A common mode of action for phytochrome in W and in darkness is suggested. The results indicate independence and additivity of the E. R.modulation by W light quantity and of the modulation by light quality.     

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.     

Cation fluxes in the saps of Sinapis alba during the floral transition

Plants of Sinapis alba L. were induced to flower by either a single long day or a single displaced short day. The levels of three cations. Ca²⁺, Mg²⁺ and K⁺, were measured by atomic absorption spectrophotometry in exudates from roots, leaves and apical stem tips. The export of all three cations out of the root system (root exudate) was increased in induced as compared to non-induced plants. No changes were observed in cation export out of the mature leaves (leaf exudate). The supply of cations to the apical bud (apical exudate) did not originate from the phloem and, so, should mainly be of apoplastic origin. Only the supply of Ca²⁺ to the apical bud was increased, not the supply of Mg²⁺ or K⁺. The increase in Ca²⁺ supply was transient and occurred at about the same time as a conspicuous stimulation of cell division, previously detected in the apical bud.     

Effects of windspeed on the growth and biomass allocation of white mustard Sinapis alba L.

Summary We examined how different wind speeds and interactions between plant age and wind affect growth and biomass allocation of Sinapis alba L. (white mustard). Physiological and growth measurements were made on individuals of white mustard grown in controlled-environment wind tunnels at windspeeds of 0.3, 2.2 and 6.0 ms^–1 for 42 days. Plants were harvested at four different dates. Increasing wind speed slightly increased transpiration and stomatal conductance. We did not observe a significant decline in the photosynthetic rate per unit of leaf area. Number of leaves, stem length, leaf area and dry weights of total biomass and plant parts were significantly lower in plants exposed at high wind speed conditions. There were no significant differences in the unit leaf rate nor relative growth rates, although these were always lower in plants grown at high wind speed. Allocation and architectural parameters were also examined. After 42 days of exposure to wind, plants showed higher leaf area ratio, root and leaf weight ratios and root/shoot ratio than those grown at control treatment. Only specific leaf area declined significantly with wind speed, but stem and reproductive parts also decreased. The responses of plants to each wind speed treatment depended on the age of the plant for most of the variables. It is suggested that wind operates in logarithmic manner, with relatively small or no effect at lower wind speeds and a much greater effect at higher speeds. Since there is no evidence of a significant reduction in photosynthetic rate of Sinapis with increasing wind speed it is suggested that the effect of wind on plant growth was due to mechanical effects leading to changes in allocation and developmental patterns.     

Enhancement of Pfr-mediated responses by light pretreatments: persistence of the pretreatment effects

Abstract. In germinating seedlings of Sinapis alba , nitrate reductase activity is under phytochrome control and becomes accessible to phytochrome at about 15 h from sowing. The induction of the enzyme with pulses of light is strongly affected by pretreatments given prior to 15 h, also acting through phytochrome. It is shown that the effects of these pretreatments can persist undiminished for a considerable time (>40 h) but do not alter the pattern of the subsequent responsiveness to P_fr. The nitrate reductase response is compared with other data pertaining to a similar response.     

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.     

The Flowering Process: On the Track of Controlling Factors in Sinapis alba

The major physiological theories of the control of the flowering process are first presented and their inferences tested in the long-day plant Sinapis alba. Then, the genetic analyses of the control of flowering time in Arabidopsis thaliana are also summarized with a brief overview of the several pathways, each including several genes, identified. Clearly, both the experimental data of physiological experiments and the multiplicity of interacting genetic pathways best support the theory of the multifactorial control of flowering. This is further shown by the fact that a critical gene expressed in the shoot meristem at floral transition in S. alba, MADS A (orthologous to A. thaliana SOC1), can be upregulated by a single dose of a cytokinin or a gibberellin, without leading to flowering. This indicates that the floral shift requires upregulation of other genes by other factors.     

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     

Phytochrome action in light-grown plants: the influence of light quality and fluence rate on extension growth in Sinapis alba L.

Using light-grown plants of Sinapis alba an analysis has been made of the effect on extension growth of adding far red light to a background photosynthetic source. It has been possible to distinguish between the increase in fluence rate and the reduction of the amount of phytochrome present as Pfr, which are both consequences of the addition of supplementary far red light, and to determine that the response of increased extension growth is due only to the latter. It is shown that the degree of fluence rate dependency varies with photoequilibrium and the significance of this interaction is discussed in terms of the mode of action of phytochrome and of its role in the natural light environment.Abbreviations PAR photosynthetically active radiation - SAN 9789 4-chloro-5-(methylamino)-2-(,,-trifluoro-m-tolyl)-3(2H) pyridazinone - Pfr far-red absorbing form of phytochrome - Pr red-absorbing form of phytochrome - LER logarithmic extension rate     

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.