Heide Schnabl

Effects of salicylic acid on growth and stomatal movements ofVicia faba L.: Evidence for salicylic acid metabolization

The influence of salicylic acid on the growth and stomatal movements ofVicia faba L. was investigated. Whereas shoot length, fresh weight, and transpiration rates, which are directly correlated with stomatal pore widths, were only affected at salicylic acid concentrations higher than 3.5 mM after long-term treatments, guard cells in epidermal peels exhibited a high sensitivity at concentrations as low as 0.001 mM, resulting in stomatal closing. HPLC analysis of methanolic extracts from roots and leaves revealed the presence of free salicylic acid and a metabolite, whose amount increased with time in plants previously incubated with a medium containing salicylic acid. The possible ability ofVicia faba to detoxify the phenolic acid may be one explanation of the discrepancy between the stomatal reaction in epidermal peels directly treated with the phenolic acid and after application through the transpiration stream. The results indicate that, under natural conditions, salicylic acid will not act as an allelopathic compound whose toxic properties severely affect the growth ofVicia faba.

Effects of 2,4-dihydroxy-1,4-benzoxazin-3-ones on the activity of plasma membrane H+-ATPase

Abstract The action of 2,4-dihydroxy-1,4-benzoxazin-3-ones and their corresponding benzoxazolinone (BOA) derivatives on the activity of plasma membrane H + -ATPase from roots of Avena sativa and Vicia faba was investigated. Significant inhibitory effects were found with 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one in concentrations of 0.25 mM or higher. Benzoxazolinone compounds caused a weaker inhibition of the enzyme. At low effector concentrations stimulatory effects were observed. The H + -ATPase activity of A. sativa and V. faba was reduced by DIBOA to the same extent. The allelopathic effects of DIBOA and BOA on radicle elongation of A. sativa are correlated with the H + -ATPase activity.

Phytotoxins from shoot extracts and root exudates of Agropyron repens seedlings

Abstract Allelopathic constituents of ethylacetate extracts from shoots and root exudates of 10-day old Agropyron repens seedlings were investigated. The allelochemicals were identified by GC-mass spectrometry and comparison of retention times and mass spectra to data of respective reference compounds. In shoot extracts the cyclic hydroxamic acids 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-2H-1,4-benzoxazin-3-one (DIBOA), as well as the corresponding lactam derivative 2-hydroxy-1,4-benzoxazin-3-one (HBOA), were found. The concentration of major component DIBOA was 0.5 mg g−1 fr. wt, the concentration of DIMBOA was 0.02 mg g−1 fr. wt. Futhermore maleic, t-aconitic and citric acid were found. In order to estimate the allelopathic potential of living plants an investigation of root exudates was performed. The cyclic hydroxamic acids were identified as important constituents. Their concentrations were 0.4 μmoll−1 DIMBOA and 0.2 μmoll−1 DIBOA. Additionally 2,4-dihydroxy-7,8-dimethoxy-2H-1,4-benzoxazin-3-one (DIM2BOA) was detected. Vanillic, ferulic and β-hydroxybutyric acid are also phytotoxins released by intact, living quackgrass seedlings.

A Novel Method For Determining Phytotoxicity In Composts

Phytotoxicity of compost in various degrees of maturity has been extensively reported. It is usually determined by a seed germination index assay or by plant growth tests. The main deficiency of these tests is the length of time required for their performance. Therefore, we tested new biosensor techniques in this study based on oxygen consumption and fluorescence measurements of isolated freshly suspended or lyophilized chloroplast thylakoids (Vicia faba L.). These methods were compared with traditional phytotoxicity tests. The new systems proved to be suitable for evaluating the function of the photosynthetic electron transport (PET) between photosystem II and photosystem I. When PET was inhibited by phytotoxic substances, fluorescence increased whereas oxygen consumption decreased. Germination index data as well as plant growth bioassay data exhibited high correlations with data obtained from the novel biosensor techniques. Thus, we propose application of these methodologies based on freshly isolated or...

Regeneration and Evacuolation of Protoplasts from Mesophyll, Hypocotyl and Petioles from Helianthus annuus L.

Summary Different sources of plant organs were tested in order to isolate, regenerate and evacuolate protoplasts of sunflower. Protoplasts from mesophyll and petioles were successfully isolated with yields between 2–9x 106 protoplasts per gram fresh weight and from hypocotyl with 4–5 x 105. Protoplasts from mesophyll and hypocotyl showed a regeneration rate of 60–65 % when immobilized in alginate or agarose, those of petioles even 90%. Adding 2,4-D stimulated the calli to form rhizoides consisting of 2–3 cells. Early somatic embryogenic stages were observed. The evacuolation rate of mesophyll protoplasts was 70%. Two partners of protoplasts are suggested for future electrofusion processes. The evacuolated mesophyll protoplasts and the highly regenerable protoplasts of petioles which contain their vacuoles.

Regeneration of fertile interspecific hybrids from protoplast fusions between Helianthus annuus L. and wild Helianthus species

Abstract The use of interesting characteristics from wild Helianthus species in sunflower breeding is limited by poor crossability or sterility of interspecific hybrids. To overcome this barrier, mesophyll protoplasts of Sclerotinia sclerotiorum-resistant clones of Helianthus maximiliani, H. giganteus and H. nuttallii were fused with hypocotyl protoplasts of H. annuus in the presence of polyethyleneglycol and dimethylsulfoxide. Fusion products were embedded in agarose and subjected to a regeneration protocol developed for sunflower protoplasts. Organogenic calli were transferred onto solid medium and emerging shoots were elongated in the absence of plant growth regulators. Rooting of shoots was induced by a 1-naphthaleneacetic acid treatment and putative hybrid plants from fusions between H. annuus + H. maximiliani and H. annuus + H. giganteus were transferred into the greenhouse. All of them exhibited a hybrid phenotype with a high percentage of rhizome producing plants. Their hybrid origin was confirmed by random amplified polymorphic DNA analysis. Plants flowered after 3–4 months and set seeds, of which 70–80% germinated.

Uptake and detoxification of salicylic acid by Vicia faba and Fagopyrum esculentum

Abstract Roots of Vicia faba and Fagopyrum esculentum showed a characteristic tri-phasic uptake of salicylic acid. During the first, short phase, absorption was unaffected by O 2 depletion, vanadate or cysteine, which suggests a diffusion of salicylic acid into the apoplast and some penetration into the cytoplasm. The second phase, continuing for about 6–8 ( V. faba ) and 5–8 hr ( F. esculentum ), was stationary and no obvious uptake was observed. The third phase was characterized by an active uptake. The absorbed salicylic acid was differently detoxified by the two species and the resulting compounds were identified. Vicia faba glucosylated salicylic acid to form o -β- d -glucosylhydroxybenzoic acid, whereas F. esculentum oxidized it to 2,5-dihydroxybenzoic acid and glucosylated this product at the 5-OH group. The enzymes involved seemed to be induced by salicylic acid. Most of the detoxification occurred during the phase of active uptake.

A regeneration protocol for sunflower (Helianthus annuus L.) protoplasts

SummaryHypocotyl protoplasts of four different Helianthus annuus genotypes were cultivated for 22–28 days in agarose droplets covered with liquid medium. In the first week, supplementation of the medium with plant growth regulators was at a 0.8/1 ratio of cytokinin and auxin followed by a high auxin concentration in the second week and a cytokinin to auxin ratio of 8/1 in the third and fourth week. Following transfer onto solid medium containing cytokinin and auxin in a proportion of 40/1 morphogenic callus started to form globular structures that developed into leaf primordia. Subsequent shoot elongation and rooting were obtained on hormone free medium after dipping the cut shoots into high auxin solution. Thirteen weeks after protoplast isolation, plantlets could be transferred to the greenhouse. Shoot regeneration was obtained for all four cultivars (Florom-328, Cerflor, Euroflor, Frankasol) at different rates reflecting their regenerative potential.

24-Epi-secasterone and 24-epi-castasterone from Lychnis viscaria seeds

The brassinosteroids 24-epi-castasterone and the hitherto unknown (22R, 23R, 24R)-22,23-dihydroxy-2β,3β-epoxy-24-methyl-5α-cholestan-6-one (24-epi-secasterone) could be identified from seeds of Lychnis viscaria (Caryophyllaceae). In the phytosterol fraction of the same plant material spinasterol was found as the main component.

On the properties of fluorescing compounds in guard and epidermal cells of Allium cepa L.

Onion guard cells, in contrast to those of Vicia and Pisum, do not require an alkaline treatment in order to fluoresce. Fluorescing compounds of Allium cepa L. were characterized using in-vivo microspectrophotometry; furthermore, invitro chemical analysis for epidermal tissue, intact guard and epidermal cells, and isolated guard-cell protoplasts was performed. The emission intensity (λmax 520 nm) decreased when intact onion guard cells were excited with 436 nm light, but increased (λmax 470 nm) when excited at 365 nm. This photodecomposition at 436 nm is typical of flavins or flavoproteins whereas an increase in fluorescence intensity with excitation at 365 nm may be explained by the presence of other substances. The presence of flavins could not be unambiguously confirmed from these results. Indeed, the absorption spectra of the vacuolar area of guard cells did not show the peak at 445 nm which is characteristic for flavins. Furthermore, there was no decrease of absorption at the excitation wavelengths of 440 and 330 nm. Since spectral data indicate the presence at high amounts of flavonoids in guard and epidermal cells, this may reduce the sensitivity for the detection of flavins in guard cells. Using thin-layer chromatography and high-performance liquid chromatography together with hydrolytic procedures, flavonol glycosides with kaempferol and quercetin as aglycones substituted with sulphate and glucuronate were identified. Further studies on guard-cell metabolism should consider the presence of flavonoids in stomata of onion and other plants.