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In the present report the suggestion (Paech, K. 1950. Biochemie und Physiologic der sekundären Pflanzenstoffe. - Springer, Berlin,. pp. 201-203) was tested that the photosynthetic apparatus requires light protection during the early phase of its development and that this is the reason (in a teleonomic sense) for the transient formation of large amounts of juvenile anthocyanin in outer tissue layers of seedlings and young leaves of deciduous trees and shrubs. Seedlings of two species (Sinapis alba L. and Sesamum indicum L.) which differ in their potential to produce anthocyanin were compared under identical light conditions. The results obtained are compatible with the idea that juvenile anthocyanins are involved in photoprotection. However, the experimental results also indicate that full photostability of the plastid is attained - irrespective of the presence or absence of anthocyanin - once a certain amount of chlorophyll has been accumulated. Thus, photosensitivity of a seedling under natural light conditions is restricted to an early phase of development prior to intense greening. [ABSTRACT FROM AUTHOR]

A simple method is proposed for quantitative evaluation of stomatal and non-stomatal components of the decline in leaf CO2 uptake during rapid water stress. The changes in leaf conductance were measured during the stress and were used to calculate the photosynthetic rate which would he observed if stomatal closure were the only cause of the decline in photosynthesis. Photosynthesis-CO2 response curves, determined just before the stress, were used for this calculation. The difference between the calculated and the actual rate is a measure of the non-stomatal effect of water stress. This analysis was tested on Sinapis alba submitted to rapid and severe water stress by excising leaves or roots. Experiments were performed at saturating light conditions under high (61 Pa), normal (34 Pa) or low (11 Pa) ambient CO2 pressure. The non-stomatal effect on de-rooted plants reaches a maximum at the beginning of the stress and is dependent on the CO2 pressure; after 45 min its influence is stilt about 100%, 70% and 8%, respectively, at high, normal and low CO2. In the excised leaf system in which desiccation was more rapid, the non-stomatal effect accounted for nearly 100% of the assimilation decline whatever the CO2 pressure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The myrosinase-glucosinolate system is considered to be a major component of the preformed defence system of Brassicaceae species. This hypothesis has influenced the belief that the components of the myrosinase-glucosinolate system are present at fixed levels which are independent of environmental factors. In the present study we show that external availability of nutrients can modulate the expression levels of myrosinase enzymes (EC 3.2.3.1). Nutrients such as sulphate, iron, copper, zinc and manganese were tested for their modulation effect on myrosinase expression levels and activity in roots, stems, cotyledons and buds of Sinapis alba seedlings at four different developmental stages. The most sensitive organ was the bud where iron deficiency approximately doubled the myrosinase activity. Removal of sulphate and all four micronutrients reduced the myrosinase activity to approximately half of the activity in plants supplemented with all these nutrients. The myrosinase polypeptides can be divided into classes based on molecular mass after reduction. The nutritional status influenced mainly the 68-kDa class of myrosinases as revealed by western blot and laser scan densitometry of the immunolabelled blots. [ABSTRACT FROM AUTHOR]

The natural auxins, 4-chloroindoleacetic acid and its methyl ester have strong herbicidal effects on pea, Pisum sativum, a plant in which they occur naturally. The standard herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) is only 5 times more effective than 4-chloroindoleacetic acid. The I50, the dose inhibiting yield by 50%, for 4-chloroindoleacetic acid and its methyl ester is 0.5 kg ha-1 or 15 mg kg-1 fresh weight, close to the concentration of 4-chloroindoleacetic acid methyl ester in maturing pea seeds. Naphthaleneacetic acid and indoleacetic acid are also inhibitory, but at much higher concentrations. In its inhibiting effect on white mustard, Sinapis alba, 4-chloroindoleacetic acid approximates that of 2,4-D, whereas in barley, Hordeum vulgare, it is a stronger herbicide than 2,4-D. All auxins tested killed white mustard at low doses, but none killed barley. Both 4-chloroindoleacetic acid and 2,4-D killed pea. The chloroindole auxins of pea may be the hypothetic death hormones or senescence factors that are secreted from the developing seeds into the parent plant which is strongly inhibited or killed and from which the nutrients are mobilized and translocated to the seeds. The action mechanism of auxin type herbicides may be to simulate the action of endogenous herbicides. [ABSTRACT FROM AUTHOR]

Sinapis alba L. was induced to flower by either a long day or a displaced short day. Following collection of leaf (phloem) and root (xylem) exudates from induced and non-induced plants, polyamines in the exudates were extracted, separated and analyzed quantitatively. The titers of free and conjugated putrescine, the major polyamine fractions in all samples, increased early and markedly in leaf exudates during the floral transition, coinciding closely with movement of the floral stimulus out of the induced leaf. By contrast, putrescine liter in the root exudate did not increase. A spray of difluoromethylornithine (DFMO), an irreversible inhibitor of the putrescine-biosynthetic enzyme ornithine decarboxylase, at hour 8 of the long day considerably reduced the titer of free and con conjugated putrescine in leaf exudates, and at the same tune, markedly decreased the flowering response of induced plants. This effect of DFMO on flowering was substantially reversed by a simultaneous application of putrescine to the roots DFMO sprayed on induced plants also suppressed early activation of indices of both mitosis and DNA synthesis in the shoot apical meristem. These results support the view that the extra putrescine synthesized in induced leaves is a necessary component of the floral stimulus Sinapis. [ABSTRACT FROM AUTHOR]

Carbon allocation and partitioning were investigated in the first intemode of light-grown Sinapis alba L. seedlings exposed to white light (WL) with or without supplementary far-red light (FR). In the intemode, supplementary FR increased the rates of extension-growth and the accumulation of radiolabeled carbon (fed through the leaves), reducing sugars (even per unit volume), starch, hemicellulose and cellulose, but had no effect on the levels of sucrose and ammonium oxalate-solubilised cell wall carbohydrates, on invertase activity or on the use of additional sucrose fed through the leaves. In source leaves, supplementary FR had no effect on photosynthesis rates and reduced the accumulation of radiolabeled carbon. Mechanical reduction of stem extension-growth responses to supplementary FR did not affect internode carbohydrate or carbon accumulation responses. Supplementary FR provided only to one leaf had no effect on internode extension growth but increased carbon accumulation in the internode, provided that supplementary FR and radiolabeled carbon were both given to the same leaf. Phytochrome-mediated effects on carbon partitioning are not the mere consequence of internode extension-growth responses. Some additional control point(s) (e.g. leaf-source strength) must be under the direct influence of phytochrome. [ABSTRACT FROM AUTHOR]

In Sinapis alba, a long-day plant (LDP) which can be induced by a single long day (LD), it has been suggested that cytokinins may be part of a multicomponent floral stimulus. In order to determine cytokinin fluxes during floral transition, we developed a technique to collect phloem sap reaching the apical part of the shoot, close to the target bud. Exudates collected from roots, leaves, and the apical part of the shoot were analysed by radioimmunoassay for cytokinins. Such analyses confirm previous observations, obtained using the Amaranthus bioassay, indicating that cytokinin export from the roots and mature leaves is enhanced 2-5 fold during floral transition. The flux of cytokinins directed to the upper part of the shoot through the phloem is also rapidly increased (ca 1.5-2 fold) by the inductive treatment, between 9 and 25 h after start of the LD. We suggested that the shoot apical meristem of 2-month-old Sinapis plants probably has a low cytokinin level. Induced leaves rapidly produce a signal which is transported to the roots where it alters cytokinin production and/or export. In addition, or as a consequence, leaf-cytokinins are exported via the phloem to the apical meristem where they induce a mitotic peak and some other events normally associated with the floral transition. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Entire plants of Sinapis alba exposed to a single long day were induced to flower. However, if only the shoot tip was exposed to the long day, no flowering ensued. In the apical meristem of plants with only the shoot tip exposed to the long day, none of the ultrastructural changes normally observed in the meristem of induced plants were detected, except for a marked increase in the number of mitochondria per cell. We conclude that the great majority of ultrastructural changes normally occurring in the shoot meristem during floral transition are not direct effects of daylength on the tip but are caused by signal(s) generated in induced leaves. [ABSTRACT FROM AUTHOR]

Indole-3-acetaldehyde (IAAld) was identified as a natural compound in Chinese cabbage (Brassica campestris L. ssp. pekinensis cv. Granat) seedlings by chemical conversion to indole-3-acetaldoxime (IAOX) followed by mass spectroscopy. The IAAld reductase (EC 1.2.3.1), an enzyme with a molecular mass of 32 kDa, was extracted, purified 5-fold and characterized. The enzymatic IAAld reduction showed a pH optimum at 6–7 and a marked preference for NADPH as cofactor. The Km value for IAAld was 125 µM, for NADPH 36 µM. The enzyme reaction was inhibited at high NADPH concentrations (> 200 µM) and modulated by IAA and indole-3-ethanol (IEt). Sulfhydryl reagents inhibited IEt formation, suggesting the participation of SH-groups in the reaction. Phenylacetaldehyde and benzaldehyde were competitive substrates, while acetaldehyde acted partly as an inhibitor, and partly as an activator on the IAAld reduction. IAAld reductase activity was also detected in other Brassica species. The importance of this enzyme is discussed with respect to the possibilities of IAA biosynthesis in the Brassicaceae. [ABSTRACT FROM AUTHOR]

Prolonged application of ammonium as a source of nitrogen leads to serious physiological and morphological disorders in many plants, including mustard (Sinapis alba L.) seedlings (ammonium toxicity syndrome). Ammonium tolerance was previously observed in mustard seedlings in the presence of considerable amounts of nitrate in the medium. In the present study, the question was addressed as to what extent accumulation of nitrate and ammonium occurs in the mustard seedling and how this relates to ammonium toxicity and tolerance. Emphasis was on light control of accumulation in the attached cotyledons. Both NO-3 and NH+4 became strongly accumulated in the mustard cotyledons once the concentration in the medium exceeded 1 mM. In the cotyledons, we measured concentrations > 30 mM in the case of nitrate and > 50 mM in the case of ammonium 4 days after sowing. Accumulation of inorganic nitrogen in the mustard cotyledons did not depend on photosynthesis nor on intact chloroplasts. However, the rate of nitrate accumulation was strongly stimulated by light, operating through phytochrome, while ammonium accumulation was not affected by light in short-term experiments, i.e. within 24 h and only weakly (and probably indirectly) in long-term light. We conclude that strong interaction between NO-13 and NH+4 is characteristic for accumulation of inorganic nitrogen. In the presence of NO-3, accumulation of NH+4 is diminished and, to a lesser extent, vice versa. Using [15N]-labelling it was found that incorporation of inorganic nitrogen into organic compounds was stimulated strongly whenever nitrate and ammonium were provided simultaneously. It appears from the data that accumulation of nitrate is strictly controlled by the mustard cotyledons while the accumulation of ammonium is not. The data indicate that the level of ammonium is governed primarily by the rate of ammonium assimilation. Stimulation of ammonium assimilation by simultaneously applied nitrate appears to explain nitrate-mediated ammonium tolerance in the mustard plant. [ABSTRACT FROM AUTHOR]

In many plant species, prolonged application of ammonium (NH4+) as a source of nitrogen results in physiological and disorders ('ammonium toxicity'). In the mustard (Sinapis alba L.) seedling we have previously observed particularly severe symptoms of ammonium toxicity in the absence of external nitrate (NO3--) or with increasing NH4+/NO3- rations. In the present investigation we have studied the symptoms of this 'toxicity' in more depth, i.e. at the morphological, plastidic, enzyme and mRNA levels, in an effort to elucidate the causation of the syndrom. It could be confirmed that the syndrome is specific for ammonium and is not caused by a surplus of nitrogen. The syndrome is caused neither by pH changes in the medium nor by non-specific osmotic effects. Furthermore, the syndrome is not causally related to the fact that nitrate reudctase (NR; EC 1.6. 6.1.) is induced by ammonium. Development of the syndrome required neither photosynthesis nor intact plastids. Nevertheless, the plastids are severely affected by ammonium application as is anthocyanin synthesis. Enzymes are differently affected. Among the plastidic enzymes, levels of ribulose-1, 5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) and NADP-dependent glyceradehyde-3-phosphate dehydrogenase (NADP-GPD; EC 1.2.1.13) are strongly reduced and abundance of translatable mRNA of the small subunit of RuBPCase is decreased, whereas nitrite reduced (NIR; EC 1.7.7.1) is not affected. Among extraplastidic enzymes, the level of chalcone synthase (CHS; EC 1.7.7.1) is not affected. Among extraplastidic enzymes, the level of chalcone synthase (CHS; EC 2.3.1.74) is strongly reduced, the NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD-GPD; EC 1.2.12) level is unaffected, whereas the isocitrate lyase (ICL; EC 4.1.3.1) level is strongly promoted. The fat → carbohydrate transformation seems to be impaired by ammonium: fat degradation is reduced, starch accumulation is strongly inhibited and the levels of glucose and fructose are decreased. It appears from the present data and from results obtained in a companion study (U. Hecht and H. Mohr, in preparation) that the ammonium toxicity syndrome is detectable as soon as ammonium accumulation occurs in the plant. However, the actual mechanism through which the excess ammonium affects metabolism remains unclear at present. [ABSTRACT FROM AUTHOR]

The activity of glutamine synthetase (GS) in mustard (Sinapis alba L.) and Scots pine (Pinus sylvestris L.) seedlings was used as an index to evaluate the capacity to cope with excessive ammonium supply. In these 2 species GS activity was differently affected by the application of nitrogen compounds (NH4+ or NO3-). Mustard seedlings older than 5 days showed a considerable increase in GS activity after NH4+ or NO3- application. This response was independent of the energy flux, but GS activity in general was positively affected by light. Endogenous NH4+ did not accumulate greatly after nitrogen supply. In contrast, seedlings of Scots pine accumulated NH4+ in cotyledons and roots and showed no stimulation of GS activity after the application of ammonium. In addition, root growth was drastically reduced. Thus, the pine seedlings seem to have insufficient capacity to assimilate exogenously supplied ammonium. NO3-, however, did not lead to any harmful effects. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Senescence of mustard (Sinapis alba L.) cotyledons was studied by monitoring the levels of ribulose-1,5-bisphosphate carboxylase (RuBP carboxylase. EC 4.1.1.39) activity, enzyme protein and translatable mRNA of the small subunit (SSU-mRNA) of RuBP carboxylase. In continuous white light (cWL) RuBP carboxylase began to decline 6 days after sowing and the decrease in SSU-mRNA preceded the drop in enzyme protein. The decline in RuBP carboxylase was more pronounced when the seedlings were transferred to darkness. This dark-mediated senescence was affected by phytochrome (Pfr) primarily by retardation of enzyme degradation and to a lesser extent by the maintenance of gene expression. When seedlings were reirradiated with cWL or red light after being kept for 6-8 days in darkness the levels of enzyme protein and SSU-mRNA again increased. Thus, even after long periods of darkness the seedlings retained their ability to respond to light with renewed gene expression which was affected by Pfr. Under short-day conditions (8 h light/l6 h dark), almost no decline of RuBP carboxylase occurred, whereas SSU-mRNA decrease followed the same pattern as in cWL or darkness. [ABSTRACT FROM AUTHOR]