Zeitschrift für Pflanzenphysiologie最新文献

Bud formation, a fundamental step in the morphogenesis of the protonema of Funaria hygrometrica and other mosses, is, as is well known, regulated by external cytokinins like kinetin, zeatin etc. The first visible effect of kinetin (10 μM l⁻¹) is an arrest in the lengthwise growth of the side branches of caulonema. This effect is observed in less than three hours after hormone application. Thereafter, growth in the cell tip takes place in the widthwise dimension. Branches longer than 80 μm continue the filamentous growth. Within a few hours after removal of kinetin, tip growth is restored. From these observations it can be concluded that the effect of cytokinins is to change the growth form in the tip region of the side branches. Furthermore, the extent of this reaction depends on the caulonema cells themselves. For example, in isolated single cells it is always observed that the sixth cell of a filament produces the highest number of buds upon treatment with cytokinin.

CO₂ compensation concentrations (Γ) and rates of net photosynthetic CO₂ uptake and of respiration in light and darkness were determined at 20°C, 300 μmol photons m_-2s_-1 and 21% O₂ in some foliose and fruticose lichens. Large differences were found in the values of F which ranged between 5 and 70 μl CO₂ l_-1 air. Γ values higher than typical for vascular C₃ plants (30 to 35 μll_-1 under the same conditions) may be due to fungal respiration but were found in foliose and fruticose lichens irrespective of the mass proportion of the phycobiont to mycobiont. Low Γ levels were detected in a lichen with a cyanobacterium as phycobiont (Peltigera polydactyla) but also in lichens with green algae (Cladonia rangiferina, C stellaris, Evernia prunastri). In low Γ species with green algae a dense plectenchyma of fungal hyphae forms the thallus surface and this high diffusive resistance may assist a CO₂-concentrating mechanism. There was no correlation between the values of Γ and the absolute rates of the other CO₂ exchange parameters investigated.

The resistance of the photosynthetic apparatus of primary leaves from Phaseolus vulgaris to short-term heat-shock (5 min) and to long-term heat-stress (1 to 5h) is studied. A model system is used, in which the aging of primary leaves is retarded by decapitation (removal of the apex). This offers the opportunity to compare leaves from the same calendary age (25 to 32 d) but being in different physiological states (mature or senescing). Photosynthetic CO₂-uptake, chlorophyll fluorescence and the field-indicating absorbance change at 518 nm are measured with intact leaves after different heat-stress to characterize the pattern of heat-damage. It is shown, that there is no significant difference between the sensitivity of mature or aged leaves to short heat-treatments. However, the ability of leaves to increase their thermal stability during incubation at high, but not yet damaging temperatures (heat-hardening), clearly demonstrated in mature leaves, declines during aging and is almost absent in senescent leaves. This loss in adaptive changes may account for the decline in the overall resistance of the photosynthetic apparatus to longterm heat-stress observed during leaf-senescence.

The mutagenicity of the plant tissue culture medium and its hormonal composition was tested in the Tradescantia stamen hair system. Although this system is highly sensitive to chemical mutagens, no alteration was observed in the frequency of somatic mutations following direct application of the culture medium to Tradescantia inflorescences regardless of its hormonal composition. It is suggested that plant tissue culture media have no direct effect on the induction of mutations in cells cultured in vitro.

Permeability of erythritol to lipid bilayers composed of several types of phospholipids is enhanced by the plant hormones abscisic acid and kinetin. Abscisic acid increases permeability in its undissociated form and requires the presence of phosphatidylethanolamine in the bilayers. The abscisic acid-induced permeability can be completely inhibited by kinetin. A new model based on the kinetin blockage of abscisic acid-phosphatidylethanolamine channels is proposed to explain the antagonistic effect of these two hormones on membranes.

Induction of callus formation, growth rate and differentiation pattern of calli derived from potato tuber tissue or from stolons were investigated depending on the hormone content and composition of nutrient media. Media are described giving callus induction, various types of organ differentiations (roots, shoots with or without tubers) and regenerates. Metabolic activity of various tissues was examined by following [¹⁴CO₂]-fixation via the phosphoenol-pyruvate-carboxylase pathway and by studying uptake and metabolisation of U-[¹⁴C]-glucose. On a fresh weight basis, both tissues of intact potato tubers and derived calli showed a rather similar rate and labelling pattern of [¹⁴CO₂]-fixation. Native potato tuber tissue, however, metabolized added U-[¹⁴C]-glucose with a much higher rate than callus tissue. Also, in the former a major part of label from U-[¹⁴C]-glucose was found in sucrose, whereas callus tissue from the same plant material showed little sucrose formation. Starch formation from U-[¹⁴C]-glucose was equally low in both kinds of tissue.

Barley chloroplasts contain a latent chlorophyll-bleaching activity. It is closely associated with the thylakoid, and depends on the presence of free fatty acids such as linolenic acid. Chlorophyll-bleaching is strictly dependent on oxygen. The principle responsible for the linolenate-dependent bleaching effect is tentatively termed «chlorophyll oxidase».

The effects of various inhibitors, particularly chelators of Cu and Fe on «chlorophyll oxidase» resemble the effects on the bleaching of chlorophyll by soybean lipoxygenase in the presence of linolenic acid. However, «chlorophyll oxidase» differs clearly from lipoxygenase in that pigment-bleaching is not associated with the production of linolenate hydroperoxide. Moreover, «chlorophyll oxidase» is active in the presence of oleic- and even stearic acid and thus is distinct from lipoxygenase which requires fatty acids containing a 1,4 pentadiene unit.

Young and old leaves from 22 mangrove species of Northern Queensland (Australia) were investigated for inorganic ions and organic acids. Na⁺ and Cl⁻ concentrations expressed on plant water basis were close to sea water with the exception of Heritiera littoralis and Hibiscus tiliaceus, which are both regarded as brackish water species. Leaf age did not appear to effect Na⁺ and Cl⁻ storage much. SO₄²⁻ and Mg²⁺ increased markedly in old leaves of salt-secreting species such as Avicennia marina, Avicennia eucalyptifolia, Aegialitis annulata, Aegiceras corniculatum and Acanthus ilicifolius as well as in the members of the Rhizophoraceae.

Free oxalate was found in all salt-secreting species and young leaves of Lumnitzera racemosa. Malate and citrate were present in all species, while quinate and shikimate occurred frequently. The contribution of organic acids to the anion content was important in only a few cases.

Mechanisms of salt-regulation and problems in the classification of mangroves are discussed.

A system for the regeneration of callus and albino plantlets from protoplasts of proso millet is described. Rapidly growing albino suspensions derived from mature seeds were used as the source of protoplasts. Protoplasts were cultured in drops of 0.07–0.25 ml in KM medium containing 1.0 mg · l⁻¹ 2,4-D and BAP. After 5 days, 7% of protoplasts had reformed cell walls and divided to form microcalli, but only 0.4% of plated protoplasts formed macrocalli. Over 20 albino shoots, 5 plantlets, and many roots were initiated by apparent somatic embryogenesis from protoplast-derived calli cultured for one or more passages on LS medium minus hormones.

Protoplasts isolated from shoot tips of Sorbus aucuparia L. were cultivated in original and modified V-KM media at densities of 10⁵ per ml, a temperature of 25±1°C, and 800 lx of cool white fluorescent light. Within six days of culture, 3% of the protoplasts showed mitotic activity. After 30 days, the cell clusters were transferred to medium B5C with 2.5 μM BA resulting in vigorous callus proliferation. So far, no organogenesis has been obtained even though various culture conditions have been applied.