A hypothesis of existence of a general adaptation syndrome (GAS), in which different types of stress evoke similar coping mechanisms, resulting in adaptations, is tested for plants. As stress coping mechanisms, oxy-free radical scavengers and antioxidants, osmoregulation, the role of abscisic acid, jasmonates, nitric oxide, synthesis of heat shock proteins and phytochelatins as heavy metal detoxifiers are discussed.

Standardized laboratory techniques for the vegetative growth of the duckweedSpirodela polyrhiza (Lemnaceaé), and for formation as well as germination of their turions were described. Increasing photon fluence rates of blue or red light increased the yield of turions. A specific stimulating effect of blue light was demonstrated under autotrophic but not under mixotrophic conditions. Therefore the spectral composition of light is not important in mixotrophic formation of turions whereas in autotrophic formation light sources with a higher portion of blue light are recommended. Dark-grown (etiolated) turions showed accelerated germination and higher germination percentage in comparison with light-grown turions after induction by a single red light pulse. This difference was overcome in continuous red light by speeding up the germination response of light-grown turions. Use of Petri dishes (8 cm³ nutrient solution) instead of Erlenmeyer flasks (50 cm³ nutrient solution) retarded germination response. Especially for long term experiments the use of Erlenmeyer flasks is recommended. Storage of turions for 72 h at 25 ‡C following at 5 ‡C in darkness after-ripening resulted in a decreased lag phase of the light-induced germination both after induction by a single light pulse and in continuous light.

Phaseolus vulgaris L. seedlings were grown under different air humidities simulating conditions during micropropagation (very high humidity duringin vitro cultivation and low air humidity after transferex vitro). The functional stomatal apparatus developed after a short period of growth at low air humidity at the beginning of plant ontogeny or after transfer from high to low air humidity, but not in plants grown steadily under high air humidity. The ability of stomata to regulate gas exchange was not persistent and disappeared after transfer of plants from low to high humidity.

Qualitative and quantitative differences in cytokinin levels of gram seeds were observed during germination of control and 6-benzylaminopurine (BAP; 4.44 x 10^t-5 M) treated seeds. Zeatin riboside (ZR), zeatin (Z), dihydrozeatin (DHZ), isopentenyladenosine (iPA) and isopentenyladenine (iP) were determined using high pressure liquid chromatography. In the control seeds the ZR content increased markedly only after 24 h of germination. In BAP treated seeds, the increase in ZR content was stronger than in control seeds and it persisted during further germination. Z content increased during germination in both control and treated seeds. After 48 h of germination iP appeared in control and especially in treated seeds.

Maize (Zea mays L. cv. Ganga-5) seedlings were grown in the presence of ferulic acid (0.5 - 3.0 mM) for 8 d. Treatment with ferulic acid considerably decreased shoot and root length, increased the activity of peroxidase, catalase and indole-3-acetic acid (IAA) oxidase and decreased the activity of polyphenol oxidase. The increased activity of peroxidase correlated with pronounced increase in content of lignin and phenolic compounds

Concentration of cytokinins (CKs) of zeatin-type (Z) and isopentyladenine-type (iP) were determined using an enzyme-linked immunosorbent assay (ELISA) technique in xylem sap and bulk leaf extract of the hemiparasiteMelampyrum arvense before and after attachment to the host (Capsella bursa pastoris). In all the samples Z-type were dominant, though the iP-type was also frequent. The results also demonstrate that in comparison with the unattached hemiparasite after attachment to the host the concentration of Z-type in xylem sap increased about 92 and 182 times in the light and dark phase, respectively, and that of the iP-type about 34 times in the two phases. The concentration of Z-type and iP-type in leaves expressed per dm³ of cell water was at the level of 10^-7 M and 10^-8 M, respectively in the unattached hemiparasite. After attachment, the concentration of CKs increased to 10^-5 M and 10^-6 M for Z-type and iP-type, respectively. In xylem sap the concentration of Z-type was at the level of 10^-9 M and 10^-7 M and in the unattached and attached hemiparasite, respectively. The concentrations of iP-type were 10^-10 M and 10^-8 M for the unattached and attached hemiparasite, respectively. The diurnal oscillation of CK concentration was evident in the unattached hemiparasite, but after attachment their level was nearly constant and independent of the diurnal cycle.

In two selected nitrogen-fixing cyanobacterial speciesAnabaena fertilissima andAnabaena variabilis pH, irradiance and different inocula sizes considerably modified the toxic effect of 50 % effective concentration (EC 50) dose of the pesticideFuradan (carbofuran 75 DB). Maximum growth and chlorophyll (Chl)a content ofA. fertilissima was observed in the pH range of 8 - 9 and that ofA. variabilis at pH 7-8, while at acidic pH (5 - 6) and at pH above 9 these parameters were considerably retarded. Toxicity of the EC 50 dose ofFuradan was increased further at pH 5-6, whereas reduction in the toxicity to the test cyanobacteria was observed at pH 7.8 - 9.0. The experimental organisms grew comparatively better and synthesized higher amount of Chl a at an irradiance of 12.5 than at 7.5 or 2.5 W m^-2. The toxicity of EC 50 dose of the pesticide gradually decreased with the increasing irradiance. The toxic effect ofFuradan was larger when the initial cyanobacterial population concentration was low andvice versa.

Potato virus A (PVA) was treated with different glutaraldehyde concentrations at a range of different pH values, and its immunochemical reactivity and integrity was tested in various types of ELISA using a panel of six monoclonal antibodies. Glutaraldehyde fixation was compared with formaldehyde fixation, and there was no significant difference in reactivity between PVA non-treated and treated with formaldehyde, but almost the entire immunochemical activity was lost after treating with glutaraldehyde.

The induction of sister chromatid exchanges (SCEs) inVicia faba root-tip cells after short-term (2 h) and long-term (24 h) treatments with alkylating agents (N-methyl-N-nitrosourea, ethyl methanesulphonate) and maleic hydrazide was studied. The primary roots were treated with mutagens before or after 5-bromodeoxyuridine (BrdU) incorporation into DNA and the influence of mutagen application on SCE induction in the cells with non- and BrdU-substituted chromosomal DNA. On the contrary, application of maleic hydrazide after the incorporation of BrdU into DNA strongly increased the rate of SCEs. The lowest limit concentrations of mutagens capable of significantly increasing SCE frequency in the cells with non-substituted DNA after the long-term treatment were estimated.

The interaction between native and introduced fungi and their effect on plant growth and mineral uptake were studied. The host plants wereLygeum spartum andAnthyllis cytisoides, the introduced fungus wasGlomus fasciculatum. The four soils used were selected from disturbed and contaminated by mining activities areas. Inoculated and uninoculated plants were grown in the unsterilized and sterilized soils (with and withouth native microflora, respectively). Plants inoculated withG. fasciculatum were higher and had higher tissue P concentration than uninoculated plants, especially inA. cytisoides. However, this inoculation was not effective in unsterilized substrates, suggesting a competition between introduced and native fungi. Concentration of mineral elements other than P varied depending on the host plant and soil. Decrease in Fe, Cu, Mn, Zn and Pb was observed in mycorrhizalA. cytiosides plants and a slight increase in Zn concentration was noted in mycorrhizalL. spartum plants. The study showed that the type of soil and their populations of native endophytes have a considerable effect on plant response to mycorrhizal symbiosis, especially in disturbed soils.

The effect of L-proline, glycinebetaine, L-and D-asparagine on rice seedling growth under NaCl stress was investigated. Glycinebetaine and L-asparagine were not effective in reducing NaCl inhibition in shoot growth of rice seedlings. L-Proline and D-asparagine were found to be able to reduce shoot growth inhibition under NaCl stress. However, L-proline, glycinebetaine, D- and L-asparagine further enhanced NaCl inhibition of root growth.

The barley (Hordeum vulgare L.) seeds were germinated in the non-saline conditions after 12 h imbibition in 2 % of NaCl solution. The results of treatment were: (l) the membrane system in meristematic cells of root tips developed well; (2) many profiles of endoplasmic reticulum and Golgi bodies appeared; and (3) the quantities of amoeboid plastids and amoeboid mitochondria increased. Thus the inhibitory effects of short-term NaCl stress on plants were reversible, and simultaneously NaCl treatment enhanced the metabolic activities in cells. The amoeboid form may be an adaptive form of plastids or mitochondria to an enhanced metabolic activity.

Decapitated pending vines are the most responsive parts of vanilla plants. Inflorescence localization along training vines showed a decreasing gradient from the decapitated end to the base in sun locality and was irregular and showed opposite gradient in shade locality. Soluble and ionic peroxidase activities, determined in the leaves and in the internodes, showed a marked peak during the end of June and a gradient along training vines which was inverse to the gradient of inflorescence localization and opposite between sun or shade conditions, supporting the utility of peroxidases as spatial and temporal biochemical markers of flowering processes.

Experiments were conducted to study the effect of plant type on canopy photosynthesis under field conditions. A chamber made of aluminium frame covered with clear plastic material was used to estimate canopy CO₂-exchange rates over a land area of 1.33 m². The plant type of maize "Shendan 7" [planophile type, original-type (OT)] was changed to erectophile type [altered-type (AT)] at silking stage. The rates of canopy apparent photosynthesis (CAP) were measured in both types of maize grown at five plant densities during the reproductive phase. It was shown that AT canopies had greater rates (about 17.2%) of CAP than did OT canopies and the yield increased by about 5.9-8.6% in AT canopies. The vertical distribution of photosynthetic photon flux density and CO₂ concentration in AT canopies were more uniform than those in OT ones. It was suggested that the compact architecture of maize canopy was excellent for photosynthesis and yield formation.

To determine some physiological parameters implicated in somatic embryogenesis in date palm (Phoenix dactylifera L.), peroxidases have been studied. Activated charcoal commonly used in date palm tissue culture as an essential antibrowning factor decreased cellular protein contents and peroxidase activities. During the first months of culture, the conventionally used medium (100 mg dm^-3 of 2,4-dichlorophenoxyacetic acid, 3 g dm^-3 charcoal) reduces 2 to 3 and 4 to 6 times protein contents and peroxidase activities, respectively, in comparison with the same one containing only 5 mg dm^-3 of 2,4-D and with or without 150 mg dm^-3 charcoal. In addition, the standard procedure decreased the embryogenic potential which is positively related to the intra- and extracellular (excreted into culture medium) peroxidase activities. In medium with embryogenic calli, extracellular peroxidase activity was three times as high as the activity determined in the same medium with non-embryogenic calli. There were two basic isoforms and four to five acidic bands characterizing the embryogenic calli. It can be suggested that peroxidases play a key role in somatic embryogenesis of date palm and the charcoal used at 3 g dm^-3 constitute a perturbating factor for this process.

The effect of 80 mM NaCl on the structure and ultrastructure of root cells ofPhaseolus vulgaris plants has been investigated. Roots of plants treated with NaCl were shorter and had less secondary roots than control plants. In control plants, epidermal cells were isodiametric and uniformly placed forming a thin layer, whereas in stressed plants, the shape and disposition of epidermal cells was less regular. The cortical cells of control plant were round-shaped and distributed allowing large and well defined intercellular spaces, whereas stressed plants presented irregular cells, which were interdigitated, thus decreasing the volume of the intercellular spaces. Presence of 80 mM NaCl did not result in significant differences in the number, shape or distribution of the cell organelles. Membrane vesiculation was often observed in cells of NaCl treated plants. Addition of 80 mM NaCl to the growth medium considerably increased the leakage of solutes from intact plant roots back to the solution especially K⁺ and Ca²⁺.

Hybridization between the nearly extinct speciesDiplotaxis siettiana andBrassica juncea is prevented because of strong prefertilization barriers. Use of mentor pollen ofD. siettiana irradiated with 1000 Gy gamma radiation before the incompatible pollination led to fertilization. 5 d after pollination 17% ovules showed entry of pollen tubes, 10 d after pollination 27% ovules showed small globular embryos which grew no further. No embryos were found in control pollinations. Thus , use of irradiated mentor pollen brings about fertilization in this difficult cross and hybrids can be obtained if embryos are rescued.

The influence of increasing copper concentrations on seed germination, seedling survival and radicle length ofMinuartia hirsuta, Silene compacta, Alyssum montanum andThlaspi ochroleucum was studied. Seed germination was highly affected by the higher Cu²⁺ concentrations (80 and 160 μM), while lower Cu²⁺ concentrations seemed to be necessary for seed germination, even for the plants originated from non-Cu²⁺-rich soils (i.e. A. montanum). Nevertheless, plants originated from Cu²⁺-rich soils (M. hirsuta, S. compacta) showed a higher demand of Cu²⁺ for rapid seed germination. Cu²⁺ at higher concentrations severely reduced growth rate of radicle, especially inA. montanum andT. ochroleucum. These data clearly indicate the reduced suitability of the above mentioned plant species for reclamation on Cu²⁺ soils. Lower Cu²⁺-concentrations had no influence on seedling survival inM. hirsuta andS. compacta, but a progressive reduction of a number of survived seedlings with increasing Cu²⁺ concentration was found, that was more pronounced inA. montanum andT. ochroleucum.

Lotus corniculatus has been transformed byAgrobacterium tumefaciens harbouring therolABC, rolAB, and 35S-rolC constructs. Growth, shoot and root morphology, cytokinin and auxin concentrations in the shoots, chlorophyll content in the leaves, nodulation and nodule nitrogenase activity of clonal progenies of selected transformants, in which the transferredrol sequences were proved, were compared with control plants.
The most striking alterations were observed in the 35S-rolC transformants (dwarfism, shoot and root branching, shorter internodes, delayed nodule formation, decreased nitrogenase activity, reduced content of leaf pigments) in comparison with either therolAB, rolABC, or controls. TherolAB androlABC transformants were very similar to the control plants in their morphology as well as in most other traits measured.

Several morphological characteristics differed when wheat (Triticum aestivum L. cv. Doha 88) was grown under a cool (10 °C), warm (20 °C), and hot (30 °C) regime. Development of leaves was linearly related to shoot meristem temperature, and the time between appearance of successive leaves on the main culm was independent of growth temperature. Area and dry mass of leaves and roots increased exponentially with time, and variations between growth temperature regimes were reduced when plants were compared at a similar developmental age. In isolated thylakoids thermal stability of photosystem 2 and of whole electron transport chain was enhanced with the increase in growth temperature. Therefore this cultivar is able to acclimate to contrasting temperature regimes.

Small callus pieces excised from theAgrobacterium transformed root line D₂ ofDatura stramonium, were cultured onto solidified MS medium supplemented with a 1.0 μM kinetin and three different concentrations (0.1, 0.5 and 1.0 μM) of 2,4-dichlorophenoxyacetic acid (2,4-D), and were examined for their alkaloid productivity in relation to organization level and growth rate. Growth of transformed roots (in a MS liquid medium without plant growth regulators) was greater than that of transformed calli excised from them and cultured separately. The addition of 1.0 μM 2,4-D to the culture medium had a positive effect on callus biomass production, while it inhibited root formation by this tissue (the lower the 2,4-D concentration in the medium the greater the number of roots which emerged from the calli). Hyoscyamine production was also higher in the transformed roots than in the transformed calli, and in these tissues the production of hyoscyamine was positively correlated with organogenesis index (i.e. its ability for rooting). At the same time, the epoxidation of hyoscyamine to scopolamine only took place in the transformed calli. This occurred to a greater extent at the lower concentrations of 2,4-D in the culture medium. The mode through which the 2,4-D could control the alkaloid production of transformed callus is discussed.

Anin vitro procedure for large scale multiplication ofBoswellia serrata Roxb. has been developed using cotyledonary node segments. In average 4 shoots per node were obtained on Murashige and Skoog's (MS) medium containing 0.5 mg dm^-3 6-benzylaminopurine (BAP) and 0.05 mg dm^-3 napthaleneacetic acid (NAA) within 22 d. By repeated subculture technique 90-100 shoots per node could be obtained after 88 d of initial culture. Shoots could be rooted on MS medium containing 1/4 salts, 1% saccharose, and a combination of 0.5 mg dm^-3 indole-3-butyric acid (IBA) and 0.25 mg dm^-3 indole-3-acetic acid (IAA). Addition of antioxidants like polyvinylpyrrolidone (PVP-50 mg dm^-3) and ascorbic acid (100 mg dm^-3) in both multiplication and rooting media prevented browning of cultures. Approximately 80% of shoots rooted within 8-10 d. Rooted plantlets were kept for 15 d in culture bottles containing Soilrite^TM irrigated with a nutrient solution containing 1/4 MS salts and finally transferred to pots containing soil: Soilrite^TM (1∶1), mixture with 70% transplantation success.

Agrobacterium tumefaciens induced transgenosis by treatment of germinatingArabidopsis thaliana seed embryos has been achieved with differentAgrobacterium strains including the strain LBA4404, which was ineffective in seed transformation experiments of the other authors. The frequency of transgenosis was increased several times by application of acetosyringone to the growingA. tumefaciens suspension cultures. The DNA demethylating agent 5-azacytidine partly restored the distorted Mendelian segregation ratios in the offspring of transgenic plants.