Myrosinase in Sinapis alba L.

Extracts from developing seeds, seedings, and different organsof mature plants of Sinapis alba L. were tested for the presenceof myrosinase. Three different patterns of isoenzymes were distinguishedby isoelectric focusing. One was found in developing seeds andseedlings, a second in mature leaves, stems, flowers, and podsand a third in roots. Sections of all the parts tested were examined for the presenceof myrosin cells by light microscopy. Developing seeds and seedlingsshowed a good correlation between the appearance of myrosinaseand the presence of myrosin cells. No myrosin cells were foundin root or flower parts although they showed myrosinase activity.     

The effects of light and cotyledon age on growth and root formation in excised cotyledons of Sinapis alba L.

Summary Root formation on excised mustard cotyledons was found to be determined by cotyledon age at excision and by light. Light treatment after excision enhanced root production in cotyledons excised 6 hours to 6 days after the start of imbibition and was essential for root production in cotyledons older than 6 days at excision. Three or more 12 hour light periods after excision were sufficient to induce root production in almost 100% of 7 day old cotyledons. The interposition of up to 5 days of darkness between excision and subsequent culture in the light did not reduce the final rooting percentage but delayed the onset of rooting by a time equivalent to the length of the dark period. The dry weight values of the cotyledons were directly related to the total light energy received after excision.The age and light effects on rooting may be mediated by their effects on the rate of breakdown and on the total levels of available reserves present in the cotyledons.     

Specificity of induction responses in Sinapis alba L.: Plant growth and development

Plant defenses are expected to be negatively correlated with plant growth, development and reproduction. In a recent study, we investigated the specificity of induction responses of chemical defenses in the Brassicaceae Sinapis alba.¹ It was shown that glucosinolate levels and myrosinase activities increased to different degrees after 24-hours-feeding by a specialist or generalist herbivore or mechanical wounding. Here, we present the specific influences of these treatments on organ biomasses which were recorded as a measure of growth. Directly after the treatments, organ biomasses were reduced locally and systemically by herbivore feeding, but not by mechanical wounding compared to control plants. Induction of glucosinolates, which increased in all treatments, is thus not necessarily expressed as cost in terms of reduced growth in S. alba. No significant long-term differences in plant development between herbivore treated and control plants were found. Thus, tissue loss and increased investments in chemical defenses could be compensated over time, but compensation patterns depended on the inducing agent. Furthermore, herbivore treatments resulted in an increased mechanical defense, measured as abaxial trichome densities. Plants respond highly dynamic with regard to defense and growth allocation and due to different inductors.Key words: Brassicaceae, organ biomass, plant development, specialist, generalist, herbivore, mechanical wounding, costs, trichome densityPlant defenses are generally thought to impose costs in relation to growth and fitness.² The ability to increase defense levels only after herbivory, i.e., induction, is one possible mechanism of lowering these allocation costs.³ In Brassicaceae, the glucosinolate-myrosinase system is known to hold a defensive function.⁴ The constitutive and induced production of glucosinolates and myrosinases is thought to be connected to allocation and ecological costs.^2,5In a recent study, we investigated the specificity of short-term induction patterns of chemical defenses in Sinapis alba L. var. Silenda damaged by a glucosinolate-sequestering specialist herbivore (turnip sawfly, Athalia rosae (L.), Hymenoptera), a generalist herbivore (fall armyworm, Spodoptera frugiperda J. E. Smith, Lepidoptera) or mechanical wounding (cork borer).¹ Feeding by the specialist as well as mechanical wounding led to 3-fold increases in both glucosinolate- and myrosinase-levels, whereas generalist feeding induced up to 2-fold increases in glucosinolates only.Different strengths of plant chemical responses might be mirrored in differences of subsequent fitness-related parameters of the plants.⁶ To assess short-term effects within 24 hours of induction on organ growth in S. alba, organ dry biomasses were calculated from the previous plant set.¹ Water content was determined of the organ halves which were freeze-dried and analyzed for glucosinolate content¹ and organ dry weights were calculated from water content and total organ fresh weight. The percentage of removed tissue area was determined by photo analysis and organ dry weights of treated leaves were corrected for the respective area. The percentage of lost area in damaged leaves was 7.9 ± 0.5 % after mechanical wounding, 15.1 ± 2.3 % after feeding by S. frugiperda and 15.6 ± 2.3 % after feeding by A. rosae (mean values ± SE, n = 7–8). The plants'' habits and total number of leaves did not vary between the tested plant groups (Fig. 1B; ANOVA: f = 2.36, df = 3, p = 0.095).Open in a separate windowFigure 1Organ dry biomasses of leaves and stems (A) and total numbers of leaves (B) of Sinapis alba cv. Silenda directly after induction. The second youngest leaves of three weeks old plants were treated with either mechanical wounding (cork borer), one Spodoptera frugiperda caterpillar (third instar) or one larva of Athalia rosae (third instar) enclosed in a muslin bag for 24 hours. Bagged leaves without any further treatment served as controls (mean values ± SE, n = 6–8 per treatment). Letters above bars indicate significant differences (ANOVA, Tukey-HSD tests: p < 0.05; n.s., not significant). DL, damaged leaf; OL, older leaf; YL, younger leaf; OS, older stem; YS, younger stem.The short-term growth responses were highly specific between treatments. Herbivore damage did not only result in reduced organ biomass growth of the damaged leaf (ANOVA: f = 11.29, df = 3, p < 0.001), but also of adjacent tissues compared to organs from bag treated and mechanically wounded plants after 24 hours of treatment (Fig. 1A; older leaf - ANOVA: f = 3.87, df = 3, p = 0.021; younger leaf - ANOVA: f = 6.02, df = 3, p = 0.003; younger stem - ANOVA: f = 4.12, df = 3, p = 0.017). Significant differences from bag treated control plants were found for damaged and systemic younger leaves of plants treated with A. rosae larvae. Differences of organ dry biomasses between mechanically wounded and herbivore treated plants were more pronounced, with reduced growth in the latter of 15 to 36 % in leaves and 23 to 48 % in stem parts. This specificity in growth response could be brought about by elicitors introduced to the wounded plant tissues from the herbivores'' saliva which can influence C-allocation to roots.⁷ The reduced growth of organ biomasses observed in herbivore treated leaves could be the result of specifically saliva elicited resource allocation away from leaf tissue,⁸ and might not represent costs of increased chemical defense.Long-term effects of herbivore feeding on development of S. alba were monitored in a second set of plants which were treated (as described previously in ref. ¹) for 24 hours with either the specialist or the generalist, enclosed in a bag. About three weeks later, on the day when the first flower opened, several parameters were recorded (9^,10 Thereby, thresholds for damage seem to exist, beyond which no compensation of tissue loss is possible.¹¹ The percentages of damage in S. alba were, however, below the threshold values reported for other Brassicaceae.¹¹ Influences on growth rates can be obviously transitory. In Arabidopsis thaliana (L.) Heynh., reduced growth rates were observed directly after treatment, but later growth increased so much, that these plants overcompensated and were even larger than control plants.⁹ Such plastic plant responses can be again modified by elicitors.^7,12

Table 1

Developmental responses of 3-week-old Sinapis alba plants treated for 24 hours with either one larva of the specialist Athalia rosae or one caterpillar of the generalist Spodoptera frugiperda

Turgor Pressure and Phototropism in Sinapis alba L. Seedlings

Rich, T. C. G. and Tomos, A. D. 1988. Turgor pressure and phototropismin Sinapis alba L. seedlings.—J. exp. Bot 39: 291-299. Phototropic responses were studied in light-grown mustard hypocotyls.Phototropism was induced by adding 0.27 µmol m^–2s^–1 unilateral blue light to a background of low pressuresodium (SOX) lamp light. Curvatures of some 6° from thevertical were reached by 60 min, the curvature rate between20 min and 60 min being 0.14° min^–1. From the axialgrowth rate and tissue geometry the local growth rates of illuminatedand shaded sides of the hypocotyl were calculated to be 1.5and 4.5 µmin^–1 respectively. Turgor pressures ofexpanding cells in control plants and in the shaded and illuminatedsides of the blue light illuminated hypocotyls were measuredto be 0.40-0.55 MPa with a pressure probe. No changes in turgorpressure were observed on initiation of curvature. The decayof pressure in the cells of non-transpiring plants followingexcision indicated that the yield stress threshold of the tissuemay be as low as 0.1 MPa. These results indicate that the phototropicgrowth response in this tissue is not mediated by changes inturgor pressure. Key words: Sinapis alba L., phototropism, turgor pressure     

Evolution and distribution of growth in etiolated hypocotyls ofLupinus albus

The variations in length and fresh and dry mass of etiolated hypocotyls of lupin during the growth have been studied. The growth exhibited by the different zones delimited along the hypocotyl was dependent on the localization of the zone as well as on the age of seedlings, but in both cases the pattern of growth was similar. During the period of growth studied (seedlings 7 to 21 d old), the growth of hypocotyl was basically due to cell elongation, since the relative elongation of cells was positively correlated with the relative elongation of the hypocotyl.     

Dark Reversion of Phytochrome in Sinapis alba L

Phytochrome in Sinapis alba L. (white mustard) seedlings undergoes both decay and reversion after an exposure to red light. This is typical of other crucifers and of dicotyledons in general. In the presence of sodium azide, decay is inhibited, and reversion continues at about the same rate as in buffer alone. The reversion has been demonstrated both in cotyledon plus hypocotyl hook and in hypocotyl hook samples alone and is of the same order of magnitude in both. Contrary conclusions in the literature that there is no reversion in Sinapis are based on indirect measurements and are unjustified.     

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%.     

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.     

Light-controlled inhibition of hypocotyl growth inSinapis alba L. seedlings

Fluence rate-response curves were determined for the inhibition of hypocotyl growth in 54 h old dark-grownSinapis alba L. seedlings by continuous or hourly 5 min red light irradiation (24 h). In both cases a fluence rate-dependence was observed. More than 90% of the continuous light effect could be substituted for by hourly light pulses if the total fluence of the two different light regimes was the same. Measurements of the far red absorbing form of phytochrome ([P _fr]) and [P _fr]/[P tot] (total phytochrome) showed a strong fluence rate-dependence under continuous and pulsed light which partially paralleled the fluence rate-response curves for the inhibition of the hypocotyl growth.Abbreviations R red - HIR high irradiance response - P _rfr phytochrome in its red, far-red absorbing form - [P _tot]=[P _r]+[P _fr] =k ₁/(k ₁+k ₂): photoequilibrium of phytochrome at wavelength , wherebyk _1,2 rate constants ofP _rP _fr,P _frP _r photoconversion - [P _fr]/[P _tot]     

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.     

Bee visits and the nectar of Echium vulgare L. and Sinapis alba L.

Abstract. 1. The time-course of anthesis of Echium vulgare is described.
2. Diel changes in the sugar concentration of the nectar, the quantity of nectar and the quantity of sugar per flower are illustrated for E.vulgare and for Sinapis alba.
3. These changes are interpreted in terms of (a) the periodicity of secretion and (b) the influence of microclimate and insect visits on post-secretory changes in the composition and volume of nectar.
4. There was hour-to-hour and day-to-day variation in the species composition and the proportion of workers taking nectar rather than nectar plus pollen among the social bees visiting E.vulgare.
5. Honeybee visits to E.vulgare were more numerous in humid weather, when there was enough nectar per flower for their relatively short tongues to reach, and in an area where the corollas grew shorter than they did elsewhere.
6. The significance of changes in the caloric content, volume, concentration, viscosity and sugar composition is discussed from the points of view of insects and ecologists.     

Biosynthesis of wax esters in tissues of Sinapis alba L. seeds

The biosynthesis of wax esters has been investigated in maturing seeds of Sinapis alba. Exogenous long-chain alcohols are incorporated exclusively into alkyl moieties of wax esters. Oxidation of the long-chain alcohols is not detected. Exogenous fatty acids are incorporated into acyl moieties of wax esters to a low extent. A reduction of fatty acids to alcohols is not observed. Synthesis of wax esters is localized exclusively in the testa; both outer and inner integument are equally active in wax ester biosynthesis. The biosynthesis of wax esters is specific with regard to both chain length and degree of unsaturation of long-chain alcohols. Exogenous and endogenous sterols are not esterified.     

The mosaic of ancestral karyotype blocks in the Sinapis alba L. genome

The organisation of the Sinapis alba genome, comprising 12 linkage groups (n = 12), was compared with the Brassicaceae ancestral karyotype (AK) genomic blocks previously described in other crucifer species. Most of the S. alba genome falls into conserved triplicated genomic blocks that closely match the AK-defined genomic blocks found in other crucifer species including the A, B, and C genomes of closely related Brassica species. In one instance, an S. alba linkage group (S05) was completely collinear with one AK chromosome (AK1), the first time this has been observed in a member of the Brassiceae tribe. However, as observed for other members of the Brassiceae tribe, ancestral genomic blocks were fragmented in the S. alba genome, supporting previously reported comparative chromosome painting describing rearrangements of the AK karyotype prior to the divergence of the Brassiceae from other crucifers. The presented data also refute previous phylogenetic reports that suggest S. alba was more closely related to Brassica nigra (B genome) than to B. rapa (A genome) and B. oleracea (C genome). A comparison of the S. alba and Arabidopsis thaliana genomes revealed many regions of conserved gene order, which will facilitate access to the rich genomic resources available in the model species A. thaliana for genetic research in the less well-resourced crop species S. alba.     

Influence of ACC and Ethephon on cell growth in etiolated lupin hypocotyls. dependence on cell growth state

The possible implication of ethylene on the growth regulation of etiolated lupin hypocotyls was investigated. Excised hypocotyl sections from actively growing seedlings produced ethylene at a rate of 3 nmol h^-1 g^-1 min^-1. The rate of ethylene production was increased about 7 times when sections were treated with 10 mM 1-aminocyclopropane-1-carboxylic acid (ACC). Measurement of endogenous ACC showed that 95 % of total ACC (64.2 nmol g^-1 min^-1) corresponded to conjugated ACC. Treatments to intact seedlings with the ethylene precursor ACC, and the ethylene generating compound, 2-chloroethyl phosphonic acid (ethephon) during the cell elongation phase of the hypocotyl (from 7 to 21 dage), modified the cell growth of the organ. ACC (1 or 5 mM) or low concentrations of ethephon (0.66 mM) produced a transient decrease in the growth rate without modifying the final length of the hypocotyls. Higher concentrations of ethephon reduced the final length; the younger the seedlings were, the greater the reduction. Simultaneously to inhibition of cell elongation, ethephon produced stimulation of the radial expansion of cells in pith and cortex. The growth inhibition period, which lasted for 2 days after the treatments, was followed by another period in which the growth rate of treated plants surpassed that of the control. In both cases differences were observed along the hypocotyls due to the different growth status of the cells. It is suggested that the sensitivity to ethylene and the metabolism of ethylene depend on the growth status of the cells.     

Modification by ethylene of the cell growth pattern in different tissues of etiolated lupine hypocotyls

The influence of ethylene on growth in etiolated lupine (Lupinus albus L.) hypocotyls was studied in ethephon-treated plants. Ethephon reduced the length and increased the diameter of hypocotyls. At the end of the hypocotyl growth period (14 days), the fresh weight was reduced by 53%, and the dry weight was reduced by 16%. Thus, ethylene reduced water uptake in the tissues to a greater extent than the incorporation of new materials. Light microscopic measurements showed that the thickness of tissues was stimulated by ethylene, the vascular cylinder and cortex exhibiting greater increases (55 and 45%, respectively) than pith (26%) or epidermis (12%). Ethephon modified the cell growth pattern, stimulating lateral cell expansion and cell wall thickness, while reducing cell elongation. The response to ethylene varied in the different tissues and was higher in cortex and pith cells than in the epidermis cells. The ethylene-induced cell expansion in the cortex varied according to the localization of cells in the tissue: the central and subepidermal layers showed little change, whereas the innermost layers exhibited the greatest increase. Electron microscopy revealed that ethylene increased both the rough endoplasmic reticulum and dictyosomes, suggesting that ethylene stimulated the secretion of cell wall materials. In untreated seedlings, the pattern of cell growth was similar in cells from the epidermis, cortex, and pith. The final cell size varied along the hypocotyl, the cells becoming shorter and broader the closer to the basal zones of the organ.     

The development of protein and oil bodies in the seed of Sinapis alba L.

Summary The cotyledons of Sinapis alba L. seed are the storage organs and first photosynthetic organs. The development of the cotyledon cell contents was studied using electron and light microscopy. From the heart shaped embryo (11 days from petal fall) to the mature seed, nine stages were examined.Both types of protein grains (designated aleurone grains and myrosin grains) were found to form within vacuoles, but the mode of protein accumulation differed with each type of grain.Oil bodies were apparent with the EM from 18 days onwards, but could not be seen to arise from the ER. They were granular in appearance at early stages, but later became electron transparent.     

Localization of arabinogalactan proteins in the membrane system of etiolated hypocotyls of Phaseolus vulgaris L.

The subcellular distribution of arabinogalactan protein (AGP) in etiolated bean hypocotyls was studied by isopycnic density centrifugation on sucrose gradients at different Mg²⁺ concentrations. The distribution of hydroxyproline (a major amino acid in AGP) in the membrane-containing fractions indicated that hydroxyproline-containing proteins were associated with rough endoplasmic reticulum, possibly with the Golgi apparatus, and with the plasma membrane. Non-specific binding of hydroxyproline-containing molecules to membranes could be excluded. To detect AGPs, fractions obtained after isopycnic density centrifugation were isoelectrofocused on polyacrylamide gels, and the gels were stained with β-Gal-Yariv reagent. Bands appeared only at low pH values, where also most hydroxyproline was found. In the fractions at low densities (presumably membranefree), several bands were visible supporting the idea of the heterogeneous character of soluble AGP. The distribution of AGP in the membranous fractions strongly indicated that AGP was associated with the plasma membrane. Specific agglutination of protoplasts in the presence of β-Gal-Yariv reagent indicated that AGP was exposed at the outside of the cell membrane.     

Formation of protein storage bodies during embryogenesis in cotyledons of Sinapis alba L.

An electron microscopic investigation of fine structural changes in post-meristematic cotyledon mesophyll cells during the period of storage protein accumulation (16–32 d after pollination) showed that the rough ER, the Golgi apparatus and the developing vacuome are intimately involved in the formation of storage protein bodies (aleurone bodies). At the onset of storage protein accumulation (16–18 d after pollination) storage protein-like material appears within Golgi vesicles and preformed vacuoles. At a later stage (24 d after pollination) similar material can also be detected within vesicles formed directly by the rough endoplasmic reticulum (ER). It is concluded that there are two routes for storage protein transport from its site of synthesis at the ER to its site of accumulation in the vacuome. The first route involves the participation of dictyosomes while the second route bypasses the Golgi apparatus. It appears that the normal pathways of membrane flow in the development of central vacuoles in post-meristematic cells are used to deposit the storage protein within the protein bodies. Thus, the protein body can be regarded as a transient stage in the process of vacuome development of these storage cells.Abbreviation ER endoplasmic reticulum