InAlysicarpus vaginalis (L.) DC. nitrogen, ascorbic acid, proline and epicuticular wax (ECW) contents were higher in the plants growing in the coastal region whereas the protein, soluble sugars and starch contents were lower. The higher contents of proline, nitrogen and ascorbic acid recorded in the plants of the saline habitat are a physiological adaptation to overcome the salt stress. The higher ECW content in the plants of the saline habitat specially in the summer months seems to be an adaptation in these plants to survive in the saline habitat.

Potato spindle tuber viroid (PSTVd, severe strain) was isolated from tobacco plants transformed with a dimeric infectious expression construct which was maintained for a long time inAgrobacterium tumefaciens. Afterin vitro hybridization of PSTVd to complete minus transcripts of PSTVd (lethal), the resulting heteroduplexes were analyzed by electrophoresis under native conditions. Electrophoretic analysis revealed an appearence of electrophoretically distinguishable heteroduplexes, suggesting an accumulation of mutated sequence variants of PSTVd had occurred in the plant transformants. TGGE analysis of PSTVd cDNA, re-cloned from the original expression vector pCB1413 to plasmid pUC18 confirmed the accumulation of mutations in the cDNA and the instability of this sequence inA. tumefaciens maintained at 4°C for 2.5 years. One of these point mutations was identified by sequencing the PSTVd cDNAs isolated from the individualE. coli colonies. This transition (GC→AT) was localized at the position of 81 in the PSTVd genome, causing the change of C to U in PSTVd plus RNA. Transformation of tobacco with the freshly prepared expression vector containing the dimeric sequence of PSTVd lethal KF440-2 lead to the propagation of PSTVd electrophoretically identical to that derived from the original sequence and maintained in the tomato by a conventional infection.

Changes in the content and subcellular localization of ribonuclease isoenzymes were determined in mesophyll protoplasts prepared fromNicotiana tabacum L. cv. Samsun from healthy and potato virus Y (PVY) infected plants. Intact chloroplasts, mitochondria and soluble cytosolic proteins were obtained after protoplast disintegration by means of differential centrifugation. The 1 000g pellet from healthy protoplasts contained 7.3 %, the 15 000g pellet 13.5 % and 15 000g supernatant 82.1 % of the total activity of ribonucleases. The 1 000g pellet from infected protoplasts contained 10.4%, the 15 000g pellet 10.0% and 15 000g supernatant 89.6 % of the total activity of ribonucleases. The activity of these enzymes in infected protoplasts was enhanced in crude homogenate to 137.0 % (P<0.001), in 1 000g pellet to 194.8 % (P<0.001), in 15 000g pellet to 101.3 % (NS), and in 15 000g supernatant to 149.4 % (P<0.001) of that in healthy noninoculated protoplasts.

The regeneration ability of primary explants derived from mericlones of two commercial Bohemian hops was investigated. It was found that these hops are able to regenerate shoots by direct organogenesis on media containing BAP or zeatin at concentrations 0.5-2 mg dm^-3. The highest regeneration of shoots was achieved from either petioles or internodes at frequencies 21% and 52%, respectively, on the medium containing zeatin (2 mg dm^-3), while relatively low amount of regenerated shoots (1.3%) was observed for leaf blade explants. On the other hand, more efficient rooting occurred on the leaf blades then on other explants. A similar pattern of regeneration we observed for HLVd-infected mericlones of clone Osvald 31 even though viroid concentration inin vitro cultures was about 8-fold higher than in field-grown plants and was 31.1 pg mg^-1 of fresh mass in the average. These results suggest that HLVd infection did not impair organogenesis. We found that high 2,4-D concentration pretreatment (11 mg dm^-3) did not promote somatic embryogenesis. Although this treatment suppressed direct organogenesis, the inhibition was not complete and in low frequency the shoot regeneration was seen. Sensitivity of hop explants to antibiotics commonly used inAgrobacterium-mediated transformation was assayed. It was found that kanamycin (100-200 mg dm^-3) suppressed efficiently callogenesis, root formation and shoot proliferation. An estimation of effect of kanamycin (200 mg dm^-3) and ticarcillin (500 mg dm^-3) on morphogenesis was performed using regeneration medium. The inhibitory effects observed suggest that these conditions could be used inAgrobacterium transformation/selection system.

The effect of different NaCl regimes was examined on the growth and ion accumulation in whole plants and callus cultures ofVigna radiata. Whole plants grown in sand culture were watered with Hoagland's solution supplemented with 0-350 mol m^-3 of NaCl. Callus cultures were initiated from leaves of 7-d old seedlings of the same seed stock and grown in modified PC-L2 medium containing the same levels of NaCl as in Hoagland's solution. Callus showed the same tolerance to salt as did the whole plant suggesting thatV. radiata appears to have a mechanism(s) for salt tolerance which operates at the cellular level. Ion analysis of whole plant showed that root sodium concentrations of the tolerant cultivar G-65 was much higher while shoot sodium was much less than those of salt sensitive cultivar ML-1. Callus cultures of cv. G-65 also accumulated higher Na⁺ levels. Thus, the greater salt tolerance of cv. G-65 was associated with the control of sodium accumulation at the shoot or cellular level.

Net photosynthetic rate (P_N), productivity and the first phases of the fluorescence induction curve were investigated in leaves of two potato cultivars exposed to water stress. Water stress applied to potato plants at the beginning of their development (planting-bud formation) increased productivity but decreased P_N and variable fluorescence (F_v) of leaves. The short-term influence of water stress on the same plants also diminished the F_v.

Addition of either abscisic acid (ABA) or kinetin at 10^-6 M to salinized media (20-120mM NaCl) induced remarkable effects on growth ofPhaseolus vulgaris plants. Whereas ABA inhibited the plant growth and the rate of transpiration, kinetin induced stimulation of both parameters. Moreover, ABA increased proline and phosphorus concentrations in the salinized plants whilst kinetin decreased them.
ABA induced stimulation of the transport of K, Ca and Cl from root to shoot, accumulation of K, Na and Cl in root cells and inhibits the transport of Na and accumulation of Ca. Kinetin appeared to inhibit the transport and accumulation of Na and Cl, transport of K, and stimulates the accumulation of K and Ca as well as the transport of Ca. The highest influence of both ABA and kinetin was mostly observed when these hormones were used in combination with the highest concentration of NaCl (120 mM) in the medium.

The interactive effects of certain phytohormones (GA₃, IAA or kinetin) and drought on plant-water relations and mineral accumulation of the three crop plants; maize, cowpea and broad bean, were studied. Phytohormone applications were capable of counteracting to some extent, the adverse effects of drought on transpiration, stomatal frequency, and leaf area.

C. rubrum plants of different age were treated with methyl jasmonate (JA-Me), in some cases in combination with photoperiodic flower induction. Plants treated with JA-Me (3×10^-4, 3×10^-5 and 5×10^-7M) showed inhibition of growth and flowering. No effect of JA-Me application on ethylene formation was observed.

In concentration range of 10^-15 to 10^-5 3-allyl-6-nitro-2-benzothiazolinone (ANB) did not affect the algaChlorella vulgaris L. and intact dicotyledonous plantVicia saliva L. However, it stimulated growth and chlorophyll production inZea mays L., showing different effects on individual plant organs, and in the callus obtained from the root ofDaucus carota L. At high concentration (10^-4 M), ANB inhibited all the characteristics studied.

Effects of a short-term pre-irradiation of etiolated wheat seedlings by radiation of various wavelengths and various irradiances on the rates of photophospho-rylation, Hill reaction, and chlorophyll accumulation were studied. The curves, constructed for the dependence of inhibitory effect in different processes on pre-irradiance doses, have a saturation level corresponding to photostationary state of the phytochrome system and a pre-threshold site where the inhibition is absent. For an interpretation of the experimental data we suggest a general model that includes both the threshold concept of Mohr and the presence of an additional control mechanism not sensitive to far-red radiation. According to the model, the phytochrome-controlled biological effect is pro-portional to the time during which the level of active phytochrome is higher than the threshold one and may be analysed according to the inhibition degree. The difference in control by red (RR) and green radiation (GR) pretreatments is attributed to the difference of the phytochrome photoconversion rate under RR and GR.

Stomatal resistance (r_L) and leaf water potential (Υ_L), soil moisture and the course of meteorological factors were measured in irrigated and non-irrigated sugar beet canopies during three years. By means of the canopy water balance equation, theoretical analysis of observed dependencies of stomatal resistance upon leaf water potential was made. The changes of r_L were not induced by the change of (Υ_L) but by that of external and internal factors, (Υ_L) correlates with. Therefore the empirical dependence of stomatal resistance upon leaf water potential cannot be generalized.

Nitrate content in lucerne stems and leaf blades immersed by cut ends in distilled water or in KNO₃ solution increased with the increase in KNO₃ concentration and with the duration of exposure under irradiance of 100 or 230 W m^-2 PAR. The nitrate content increased from basal stem parts to apical stem parts and leaves. Nitrate was transported mainly with transpiration stream. Some flow variations occurred in stems causing time changes in nitrate content in different parts of stems.

Haploid and dihaploid female and rare dihaploid male plants were produced inMelandrium album throughin vitro induced androgenesis. In the seed progeny obtained from cross-hybridization between dihaploid androgenic males (supermales) and standard females only male plants were observed. The microspores containing Y chromosome gave rise to supermales.

Salinity inhibited growth, and affected the contents of chlorophylls, carotenoids, saccharides, amino acids, proteins, DNA and RNA in broad bean plants. Foliar application of NaH₂PO₄ and NaNO₃ greatly ameliorated the adverse effects of NaCI. This counteraction was associated with an increase in contents of saccharides, proteins, DNA and RNA.

The protein coding region of theE. coli DNA repair geneada combined with the CaMV 35S promoter has been transferred to tobacco by means ofAgrobacterium tumefaciens Ti plasmid. In transgenic plants having theada gene in a sense orientation, detectable amounts of O⁶-alkylguanine-DNA-alkyltransferase has been found whereas in non-transformed plants this activity is absent. Cell suspension cultures derived from the former plants showed lower sensitivity to the toxic (growth inhibiting) effects of the bifunctional alkylating agent 1-(2-chloroethyl)-1-nitroso-3-(aminomethyl-1,3-diazinylo)-methylurea compared with cell cultures derived from a control non-transformed plant or from transgenic plants harbouring theada gene in an opposite, non-sense orientation.

A disease of spiraea(Spiraea xvanhouttei) manifested in leaves by very mild, mostly hardly perceptible mosaic, was found to be caused by cucumber mosaic virus (CMV) infection. The proof was given on the basis of responce of differential plants after virus transmission, by immunosorbent electron microscopy and ELISA.

Total nonstructural saccharides (TNS) content in young plant ofAlopecurus pratensis was always above 4% of dry matter even at several types of stress treatment (nitrogen deficiency, low irradiance). TNS content was in negative correlation with concentration of total nitrogen in all cases. Positive correlation was found between the TNS content in plants and relative increase in their root growth rate.

DNA methylation of two repetitive sequences in tobacco nuclear genome was studied in the course ofin vitro dedifferentiation and differentiation. Using 5-mC sensitivè restriction enzymes and DNA/DNA hybridization with 25S-rDNA probe it has been shown that during the early phase of callus induction prominent changes in the methylation pattern occur which are stably maintained during subsequent callus growth. The following protoplast recovery and plant regeneration have again displayed some more modifications of the methylation status. Comparing the patterns of R₀ plants with the original plant material and the calli it can be assumed that both share in the resulting methylation status. The experiments analyzing the HRS60 family of non-transcribed highly repetitive sequences have displayed a quite monotonous methylation status thus indicating no random methylation perturbations in silent DNA sequences.

The fungal colonization of the angiosperm root parasiteCynomorium coccineum and the halophytic hostsLimonium delicatulum andArthrocnemum glaucum were investigated in a Mediterranean salt marsh in March 1992. The main fungal inhabitants on the leaves or shoot surface of the test plants wereAspergillus niger, Penicillium chrysogenum andCladosporium herbarum. The qualitative analysis of the fungal species associating the parasite, the hosts and the non-infected plants showed similar pattern. However, the total population exhibited quantitative differences coupled with the amount and the chemical composition of the exudates on plant surface and the quantity of transpired water. The fungal catch from the aerial shoot (inflorescence) of the parasite was higher than that collected from either the leaves or aerial shoots of non-infected or host plants. The fungal density on the leaves ofL. delicatulum was higher than those isolated from the aerial shoots ofA. glaucum. Infection byC. coccineum caused a marked drop in the total fungal population on leaves or shoot surfaces of the hosts as compared to the corresponding non-infected individuals. The stimulative effect of washings on spore germination of some isolated fungal species was matched with the density of fungi on the target plants.

The study of in vitro growth of Crepis tectorum revealed 100 % callusing and 40 % plantlet regeneration. The root and leaf used as explants showed the normal diploid (2n=8) chromosome constitution. In one month old culture 95 % callus cells were diploid. The callus maintained in 2,4-D 1 mg 1-1 for two years showed 62 % diploid, 5 % tetraploid and 33 % hyperdiploid cells. The differentiation of shoot occurred in two year old calli after subeulturing in 2 mg I-1 BAP and the potentiality of regeneration was retained for more than one year. The leaf-tips of regenerated plants were homogeneous and identical to the donor plant both in number and morphology of chromosomes.

The dependence of luciferase activity in the homogenate of leaves of transgenic tobacco plants with chimeric firefly luciferase gene on ATP concentration and temperature was studied. The optimum ATP concentration was between 0.625 mM and 2.5 mM. The activity rapidly decreased if the homogenate was kept in 25°C and is completely lost during 30 min.

Pressure-volume technique was utilized to evaluate salinity response among three populations ofSpartina patens (Ait.) Muhl. from Louisiana Gulf coast marshes. Plants were subjected to salinities of 85 and 425 mol m^-3 for 77 d in a greenhouse. Ψ_w and Ψ_π decreased in all populations in response to increases in salinity. There were 32% decrease in Ψ_sat, 42% decrease in Ψ_tlp in response to salinity changes from 85 to 425 mol m^-3 in the Ferblanc population. Similarly, there were 35% and 41% decrease in Ψ_sat in the Clovelly and Lake Tambour populations, respectively. All populations showed the ability to adapt to the increased salinity as was evidenced by osmotic adjustment. However, the Lake Tambour population appeared to have superior ability to adapt to high salinity through having a significantly lower osmotic potential at saturation (Ψ_sat), osmotic potential at turgor loss point (Ψ_tlp), and maximum turgor potential (Ψ_P(max)) compared to other populations. Ferblanc and Clovelly populations revealed the ability to adapt to saline environments to a lesser extent as compared to the Lake Tambour population. Results indicate that there is a potential for selection of superior strains ofSpartina patens for use in marsh restoration projects aiming at prevention of wetland loss in certain coastal areas.

Selected factors affecting somatic embryogenesis efficiency have been studied, namely genotype, explant type and its orientation in the medium, different basal media, different auxins for somatic embryo induction, and two ways of donor plant cultivation. The key role is played by genotype and auxin used, the minimum effect was observed due to basal media. In the series of subsequent experiments we have found the best combination of individual factors as follows: cv. Altona, 10 uM 2,4-D, L2 basal medium, central part of immature cotyledon as initial expiant oriented by adaxial side down on the agar medium, and field grown donor plants. This combination exhibited 100 % embryogenic explants with 5.43 ± 0.65 somatic embryos per expiant,i.e. somatic embryogenesis efficiency 5.43.

Spring oilseed rapeBrassica napus L. ssp.oleifera cv. HM-81 was transformed with T_L-DNA of the Ri plasmid of the agropine strainAgrobacterium rhizogenes 15834. Selfed progenies (R₂ and R₃ generations) were studied for changes in values of growth characteristics and fatty acids contents. Transformants are 'homozygous' for T_L-DNA. Both generations of transformants differed significantly from the nontransformed control plants in reduced length, lower number of pods per plant, lower total mass of seeds and the higher number of branches. The contents of palmitic, linoleic and linolenic acids were significantly higher in transformants when compared with the control. On the contrary, the contents of both stearic and oleic acids were in most of transformants significantly lower. Only traces of erucic acid (less than 0.05 % ) were found, both in transformed and nontransformed plants.

7 days or 7 weeks old alfalfa plants (Medicago sativa L.), susceptible (S) and resistant (R) to bacterial wilt, were inoculated withCorynebacterium michiganense pv.insidiosum and on day 8 and 15 after inoculation the levels of acid-soluble phosphate esters (P-esters) were determinated by means of³²P labelling in the shoots or roots. The most significant changes were recorded in the roots of the older R plants grown in full Knop nutrient solutions on day 8 after inoculation. The marked reduction of inorganic phosphate (P₁) uptake by whole R plants is accompanied by a decrease in the levels of fructose-l, 6-bisphosphate (Fru-P₂), glucose-6-phosphate (Glc-6-P), fructose-6-phosphate (Fru-6-P), adenosine mono-, and diphosphate (AMP and ADP), phosphorylcholine (P-choline) and a proportional increase in the level of P₁. In the S plants, infection affected neither P₁ uptake nor P₁ proportions. In the plants grown after inoculation in diluted Knop's solutions (0.147 mM KH₂PO₄), infection induced a reduction of the radial transport of P₁ to the segments of R roots whereas a reduction of the levels was only recorded in some P-esters [AMP, ADP, dihydroxyacetone phosphate (DHAP), and P-choline, but no decrease of Fru-P₂, Glc-6-P and Fru-6-P]. In the S plants, P₁ transport and the levels of P-esters were increased by the infection. P₁ transport exhibited considerable metabolic dependence (DNP, DCCD). Bacterial infection probably had no influence on the activity of the plasma membrane ATPases.

The angiosperm root parasiteCynomorium coccineum and the halophytic hostsLimonium delicatulum andArthrocnemum glaucum were invesrigated under natural conditions in a Mediterranean salt marsh in March 1992. The diurnal transpiration rate of the parasite was low and parallel to the climatic factors. The non-infected plants showed higher transpiration rates than the parasite and its hosts. Compared to the non-infected plants, it is apparent that the perennial herbL. delicatulum is more sensitive to infection since its reduction in the fresh and dry mass was higher than that found inA. glaucum.

Uptake of³⁵S-sulphate by bundle sheath strands (BSC) from leaves of maize plants (Zea mays L. ev. Dekalb L 72 A) was higher than that by isolated mesophyll protoplasts (MC) of maize. Ion uptake followed the Michaelis-Menten kinetic satuiation curves. SO² ₄-uptake increased after addition of malate, NADPH, malate + NADP+ to BSC suspensions, but not to MC susp: nsions.

Floral induction in the long day plant spinach (Spinacia oleracea) has been shown to be accompanied by a thickening of plasmalemma. This change was observed at early evocation, in both shoot apices and leaves, as well as after inducing GA₃ treatment. To get further information on this thickening, plasma membranes from spinach leaves were isolated, in the present study, using aqueous two phase partitioning and the effect of variousin vitro treatments on their thickness was investigated. The average plasmalemma thickness was unaffected by Na⁺ and K⁺ ions. It was increased upon the effect of either Ca²⁺ or gibberellic acid. A thickening of plasmalemma was also observed when plasma membranes from vegetative plants were incubated with a cytosolic preparation from photoinduced plants. The results were discussed in relation with the plasmalemma modifications previously reported in spinach.

SC₂ and SC₃ progenies of nineteenin vitro regenerated barley plants (SC₁) from resistant calli selected against purified culture filtrate ofHelminthosporium sativum and one parent 'Dissa' genotype were studied for stability of resistance and protein, soluble protein, maltose and saccharose contents. Cytological studies were also carried out on the SC₃ generation. Stability of resistance toHelminthosporium sativum was found in 50% of the somaclonal lines. Significant variation among different somaclonal lines and among different callus lines from which the plants were regenerated were found for yield, disease score and biochemical characters assessed except saccharose content in the somaclonal lines. Significant increase and decrease over the donor parent for most of the characters were obtained. Cytological abnormalities such as multilobed nuclei, multinucleate cells, abnormal anaphase and mixoploidy were also observed.