Polyethylene glycol (PEG)-treatment decreased chlorophyll and protein contents and increased NH₄ ⁺ content due to decreased glutamine synthetase activity in detached rice leaves. PEG-treatment also increased abscisic acid (ABA) content and decreased ethylene production. Addition of fluridone, an inhibitor of ABA biosynthesis, reduced ABA content in rice leaves but did not prevent chlorophyll and protein loss in rice leaves induced by PEG. Silver thiosulfate, an inhibitor of ethylene action, was effective in preventing PEG-promoted chlorophyll and protein loss, but had no effect on PEG-induced NH₄ ⁺ accumulation. The current results suggest that NH₄ ⁺ accumulation in rice leaves induced by PEG increases leaf sensitivity to ethylene, which in turn results in an enhancement of chlorophyll and protein loss.

Chenopodium rubrum, a short-day plant, and C. murale, a long-day plant, were grown in vitro in continuous darkness. Control C. rubrum plants exposed to continuous darkness for 15 d at cotyledonary phase, did not flower, while 80 % of plants flowered on the medium with 5 % glucose and 10 mg dm^-3 GA₃. Control C. murale plants exposed to continuous darkness for 10 d at the age of 4^th pair of leaves, did not flower, while GA₃ (1 - 5 mg dm^-3) stimulated flowering up to 65 %.

A greenhouse pot experiment with different phosphorus supply was conducted to study growth, photosynthesis and free polyamine (PA) content in Plantago lanceolata L. plants in relation to arbuscular mycorrhizal (AM) colonization. Inoculum of Glomus fasciculatum (BEG 53) was used. Inoculated plants had high colonization intensities which were related to the P supply. Non-mycorrhizal (NM) plants showed a typical yield response curve for P availability. Dry masses of mycorrhizal (M) plants were higher at the lowest soil P content than those of NM plants, but the opposite was found at the highest P supply. P contents in M plants were always higher. There were no differences in chlorophyll (Chl) concentrations (except the lowest soil P content) and ratios of variable to maximum Chl fluorescence (Fv/Fm) values between M and NM plants, whereas M plants had higher ratios of leaf area to fresh mass (A/f.m.) at low soil P contents and they had significantly higher CO₂ fixation capacities per unit leaf area. Free putrescine (Put), spermidine (Spd) and spermine (Spm) contents in NM plants were usually highest at the lowest P supply. The ratios of Put/(Spd+Spm) were identical in M and NM leaves. They were significantly higher, however, in NM roots at the two low P doses. It is concluded, that a P nutritional status might exist, below which PA concentrations and ratio are increased drastically, possibly indicating P deficiency or a certain state of plant development with a higher demand for AM symbiosis.

Effects of the superinfection with tobacco mosaic virus (TMV) on susceptible tobacco plants infected with potato virus Y (PVY) were determined. Dynamic changes in the TMV and/or PVY contents, the ribonucleases (RNases), the phosphomonoesterase (PME), the phosphodiesterase (PDE) and the glucose-6-phosphate dehydrogenase (G6P DH) activities were studied. The PVY infection caused a substantial reduction in the multiplication of TMV. The content of TMV in the PVY inoculated leaves amounts to 6 and 9 % in the PVY systemically infected leaves when compared with single TMV. Surprisingly, the challenging virus (TMV) enhanced the content of inducing virus (PVY) in the locally inoculated leaves up to 130 - 141 %. In contrast, the reduction of PVY content down to 35 - 40 % by TMV was seen in the PVY systemically infected leaves. The activities of the RNase, the PME, the PDE and the G6P DH were increased (when compared with the healthy plants) during the acute phase of single virus multiplication (PVY or TMV). The increase in the activities of the enzymes in the leaves with mixed infection was at least as high as the sum of the increases of single infections. Moreover, a higher increase than the sum was seen for G6P DH and PDE (by about 20 - 35 %).

Seeds of Citrus reticulata were germinated efficiently when they were sown directly after their extraction from fruits harvested in January, and incubated at constant temperature (25 °C). Seed drying decreased both the percentage of seed germination and the number of seedling per seed. Germination of seeds was better on Murashige and Skoog (MS) medium supplemented with 0.5 mg dm^-3 benzylaminopurine (BAP) than in a soil. Shoot cuttings obtained from germinated seeds were subcultured on B5 medium supplemented with 1 mg dm^-3 BAP, 0.5 mg dm^-3 kinetin (KIN) and 0.5 mg dm^-3 naphthalene acetic acid (NAA), where shoots grew and multiplied. They were rooted on half strength MS medium supplemented with 0.25 mg dm^-3 BAP, 0.5 mg dm^-3 NAA and 1 mg dm^-3 isobutyric acid (IBA). Rooting under light was better than under dark. Seedlings and shoot cuttings with roots were transferred successfully to the soil after three weeks of acclimatization.

An extent of helper component protein (HC-Pro) sequence variability within virus population of single Czech isolate of potato virus Y^NTN (PVY^NTN) Nicola was identified by temperature-gradient gel electrophoresis (TGGE) and heteroduplex analysis. HC-Pro region was approximated with 6 pairs of primers derived from Hungarian PVY^NTN isolate (sequence AC M95491). Immunocapture reverse transcription - polymerase chain reaction (RT-PCR) was used to obtain six mixtures of individual overlapping polymerase chain reaction (PCR) products. cDNA libraries were prepared by cloning of purified PCR products in pCR-Script vector and screened by heteroduplex analyses. 15 different subfragments within the HC-Pro region were isolated and sequenced. In comparison to AC M95491, 19 nucleotide changes were identified, 13 led to amino acid (aa) changes. In comparison to available post-transcriptional gene silencing (PTGS) specific suppressor HC-Pro sequences of potyviruses we found out 4 aa changes in conserved regions.

A simple and rapid method for multiple shoot formation in vitro from immature embryo axis explants of Carica papaya L. cvs. Honey Dew, Washington and Co2 is described. Multiple shoot regeneration was achieved by culture of the explants on modified Murashige and Skoog (MS) medium supplemented either with thidiazuron (TDZ; 0.45-22.7 μM) or a combination of benzylaminopurine (BAP; 0.2 - 8.84 μM) and naphthalene acetic acid (NAA; 0.5 - 2.64 μM). Highest frequency of shoot regeneration occurred on medium supplemented either with 2.25 μM TDZ or a combination of BAP (4.4 μM) and NAA (0.5 μM). Composition of the basal media influenced the frequency of multiple shoot initiation. Stunted shoots regenerated at 4.5 μM and higher concentrations of TDZ. Such shoots could, however, be elongated by transfer to medium containing 5.7 μM GA₃. Rooting of the regenerated shoots was achieved in presence of indolebutyric acid (IBA; 4.92 - 19.68 μM), however, least response was in presence of 14.7 μM IBA. Rooted plants were hardened and transferred to pots.

The report describes in vitro plant regeneration from embryo axis explants of six cultivars of cotton. Induction of a maximum number of multiple shoots in all six cultivars could be achieved on Murashige and Skoog's (MS) salts and Gamborg's (B5) vitamins supplemented with 0.4 μM benzyladenine (BA) and 0.1 μM napthaleneacetic acid (NAA). Elongated shoots could be rooted on half strength medium supplemented with 0.5 μM NAA. Rooted shoots survived (92 %) after hardening in the greenhouse and grew to maturity (100 %) after transfer to field.

An Agrobacterium rhizogenes-mediated transformation system for Aesculus hippocastanum L. has been developed. Wounded androgenic embryos of A. hippocastanum were inoculated with bacteria containing the pRiA4 plasmid, with the uid A sequence as a reporter gene. The hairy roots emerging from the wounded sites of androgenic embryos were isolated and maintained in Murashige and Skoog's (MS) liquid hormone-free medium. Five hairy root lines have been maintained in vitro for 4 years with unchanged growth rate and might be a suitable source for secondary metabolite production. The transformation events have been confirmed by a polymerase chain reaction specific to the rol A, B, C and D genes. The absence of residual contaminating bacteria has been shown by a polymerase chain reaction specific to the vir D1 sequence.

The effects of different paraquat, alachlor and metolachlor concentrations on superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) activities and pigment contents in lettuce, bean and pea seeds and leaves were studied. Under paraquat (1.0 and 2.0 μM) treatment declined SOD and CAT activities were observed in seeds and undetectable ativity of GPX. Germination of all investigated seeds was completely inhibited. All used concentrations of alachlor and metolachlor inhibited antioxidant enzyme activities in seeds but did not prevent germination and growth. In leaves, lower concentrations of these herbicides increased activities of antioxidant enzymes but at the highest herbicide concentrations (200 μM) activities of investigated enzymes declined. The pigment contents the leaves decreased due to alachlor and metolachlor treatment in a concentration dependent manner.

A full-length cDNA encoding phosphoenolpyruvate carboxylase (PEPC) was isolated from tropical epiphytic CAM orchid Mokara Yellow. The cDNA designated as Mpepc1 is 3 450 bp in length with an open reading frame of 2 862 bp encoding 954 amino acids. The deduced amino acid sequence of Mpepc1 shows 83 % identity with pepc2 of sorghum, 82 % with pepc1 and pepc2 of maize and 81 % with pepc of Arabidopsis thaliana. RT-PCR analysis showed that Mpepc1 was expressed in mature leaves, immature leaves, and aerial roots of M. Yellow. No expression was detected in the flower.

Somatic embryogenesis in pigeonpea [Cajanus cajan (L.) Millsp.] has been achieved using cotyledon segments of mature seeds as explants. A large number of globular somatic embryos were induced directly from cotyledons of genotypes T-15-15, GAUT-82-90 and GAUT-82-99 when cultured on EC6 basal medium supplemented with 2.22, 4.44, 13.32 or 22.2 μM N⁶-benzylaminopurine (BAP) and 0.45, 1.36, 2.27, 4.54 and 13.62 μM thidiazuron. Somatic embryos developed into cotyledonary stage when the globular embryos were transferred to Murashige and Skoog's (MS) basal medium containing 2.89 - 14.43 μM gibberellic acid. Maturation of somatic embryos was achieved on half strength MS medium with 0.38 μM abscisic acid. The mature somatic embryos were germinated on MS medium supplemented with 0.44 μM BAP and the plantlets were hardened and transferred to soil.

Accelerated ageing of Dendrocalamus strictus Ness seeds at 42 ± 1°C and 100% relative humidity for 1 to 8 d was conducted. Seeds lost viability and changed their biochemical constituents. Reductions in the contents of sugars, starch, proteins and lipids were found. Decrease in the activity of the peroxidase as well as acid and alkaline phosphatase were also observed. Increase in total free amino acids content and the activity of amylase confirmed the degradation of seed reserves.

The influence of nitrogen deprivation on leaf development and the biomechanics of leaf growth were studied using maize (Zea mays L.) seedlings grown under low irradiance. Although the nitrogen deprivation had no significant effect on photosynthesis, the leaf length, the leaf area, and the total assimilation area of plants decreased. The mature size of the epidermal cells was not altered, while the cells of nitrogen-deprived plants reached their final length closer to the leaf base than the epidermal cells of control plants. Decreases in the length of the growing zone (from 50 to 30 mm) and in the maximum value of relative elemental growth rate (from 0.08 to 0.06 mm mm^-1 h^-1) were observed in the nitrogen deprived plants. The maximal value of growth velocity in the control treatment was higher along the elongation zone, except for the basal 20 mm, where there was no significant difference between the control and the N-deprived plants. The net deposition rates of water and dry matter were also affected by nitrogen deprivation: the values of these features decreased and the spatial position of the maximum of the deposition rates shifted towards the leaf base.

A set of 28 fibre flax and linseed cultivars differing in plant morphology and technological parameters were analysed by isozyme markers in five ontogenetic phases. Relatively high isozyme polymorphism was observed using polyacrylamide gel electrophoresis. Altogether 18 isozyme systems produced 145 different bands; 66 of them (45.52 %) have been found to be polymorphic. The highest level of polymorphism was found in acid phosphatase and esterase, polymorphism was detected in aconitase, diaphorase, glutamate dehydrogenase, peroxidase and superoxide dismutase as well. The highest number of unique isozymic spectra (cultivar × enzyme × ontogenetic phase) was detected in the phase of shoot with removed cotyledons. Electrophoretic analysis of all polymorphic isozymes enabled to distinguish 20 cultivars (71 %) in the screened cultivar set.

The seasonal dynamics in content and distribution of N-rich compounds between overwintering organs of Calamagrostis epigeios were examined. Samples were taken both from plants grown in natural conditions and in containers with controlled nutrient supply. There were significant changes in content of nitrate, free amino acids and soluble protein in all investigated plant parts during the course of a year. Amino acids showed both the highest maximum and seasonal fluctuation among the all N compounds observed and, therefore, appear to have a central role in N storage. Their content rises in the autumn, remains stable during winter and declines quickly at the beginning of spring. The most abundant amino acids in the end of winter storage period - asparagine, arginine and glutamine - constituted about 90 % of N in fraction of free amino acids. The portion of N stored in soluble proteins, however, was considerably smaller compare to both amino acids and nitrate. The amount of N stored in rhizomes of C. epigeios was smaller than in roots and stubble base before the onset of spring re-growth. This indicates that roots and stubble base are particularly important for winter N storage in this species.

Vigna radiata (L.) seedlings (5-d-old) were exposed to different concentrations of NaCl in light and in dark. The content of proline in the shoots increased with an increase in NaCl concentration, in light as well as in dark. But, irrespective of the concentration of NaCl, proline accumulation in the shoots was higher in light than in dark. Pretreatment of seedlings with dichlorophenyl dimethyl urea (DCMU) did not make any significant difference in light promoted stress induced proline accumulation. As DCMU is a potent inhibitor of photosynthetic electron transport, the light reaction of photosynthesis was not responsible for the observed light promotion of stress induced proline accumulation. In another set of experiments, 5-d-old green as well as etiolated seedlings were exposed to NaCl stress in the presence of different concentrations of sucrose. Irrespective of the concentration of sucrose used, proline content in shoots of stressed seedlings was higher in light than in dark. Although, sucrose enhanced NaCl stress induced increase in proline content in dark by about 32 %, this enhancement was not comparable to the 286 % increase in proline content brought about by light. These results showed that certain factors other than photosynthesis play a role in light promotion of stress induced proline accumulation.

Diurnal and seasonal changes of net photosynthetic rate (P_n) and the efficiency of photosystem 2 (F_v/F_m) were measured on two perennial species growing on a soil catena in semi-arid south-east Spain. Stipa tenacissima, a tussock grass, grows on shallow soil at the top of the catena and Retama sphaerocarpa, a leguminous shrub, grows in the valley bottom. A linear relationship was found between light saturated photosynthetic rates (P_max) and diffusive leaf conductance (g_l) in both Retama and Stipa indicating that the intercellular CO₂ concentration (c_i) was maintained constant in both species diurnally. Relatively high values of calculated c_i in Retama cladodes suggested that was not the primary limitation to carbon assimilation. F_v/F_m for the two species when well watered was around 0.8. Although Retama cladodes maintained this value throughout the year, F_v/F_m decreased to a minimum of 0.43 in Stipa leaves, at the end of the dry season. Our data suggest that plants in the Rambla Honda can substantially reduce transpiration without reducing photosynthetic rates to the same extent by closing their stomata, because P_n is reduced primarily by high respiration, decreased mesophyll conductance and by photoinhibition or permanent damage of photosystem 2.

Cell suspension culture of Eschscholtzia californica Cham. were permeabilized by Tween 20 or 80, and immobilized by glutaraldehyde. The highest invertase activity was at pH 4.5 and temperature 50 °C. The hydrolysis of the substrate was linear for 5 h reaching 60 % conversion. The cells had high invertase activity and a good stability, and in long-term storage they showed convenient physico-mechanical properties.

Treatment of spruce, fir and oak trees with herbicides, which may be one of the forest damage inducing agents, caused pronounced changes in the contents and distribution of indole-3-acetic acid (IAA) and cytokinins (CKs) one year after treatment, i.e. at the time of the first microscopically visible damage in treated trees. In Picea pungens IAA content increased in the terminal buds by about 105 % and in the apical buds of the first order branches by 220 %. The same was true for young sprouts of Abies nordmanniana, while in leaves of oak trees IAA content was decreased by 15 % after glyphosate treatment and by 30 % after 2,4-dichlorophenoxyacetic acid (2,4-D) treatment. Another striking feature was a significantly decreased content of IAA in the lower parts of roots in Picea pungens (50 % of the control), which is accompanied by an increase in IAA content in the middle part of the roots (130 %). On the other hand, the IAA content of both sprouts and roots of A. nordmanniana was significantly increased after herbicide treatment.
In P. pungens, the content of free cytokinins (sum of zeatin, zeatin riboside, isopentenyladenine and isopentenyladenosine) decreased due to herbicide treatment. The strongest decrease was seen in roots, especially in their upper and middle parts (the average reduction of cytokinin content in roots was 63 %). In the above-ground organs the reduction was seen namely for isopentenyladenine and isopentenyladenosine, while the abundance of zeatin riboside was, on the other hand, higher in treated plants. In Quercus robur leaves, the total content of cytokinins also decreased, namely after glyphosate treatment. In consequence of these changes, CK/IAA ratio decreased pronouncedly in all organs of herbicide-treated trees, with the exception of oak leaves treated by 2,4-D.

Treatment of Taxus chinensis cell suspension cultures with fungal elicitor resulted in an oxidative stress characterized by H₂O₂ production, malondiadehyde (MDA) accumulation and cell death. This oxidative stress was dependent on the concentration of elicitor. Cells exposed to elicitor accumulated taxol, however, not proportional to elicitor concentration. High production of taxol occurred in cells treated with the suitable elicitor concentration. We concluded that oxidative stress had the deleterious effect on taxol production. Simultaneous treatment with elicitor and ascorbic acid (ASA) changed the oxidative stress and taxol production. Production of taxol in cells treated with 200 mg dm^-3 elicitor and ASA was enhanced compared with that in cells treated with only 200 mg dm^-3 elicitor, while production of taxol in cells treated with 100 and 50 mg dm^-3 elicitor and ASA was decreased compared with that in cells treated with 100 and 50 mg dm^-3 elicitor.

Ornithine carbamoyltransferase (OCT) from spinach (Spinacea oleracea L.) was purified to homogeneity and studied for some kinetic and structural properties. The enzyme showed a specific activity of 436 U mg^-1, its molecular mass was approximately 118 kDa as estimated by Sephacryl S-200 gel filtration chromatography, the purified protein ran as a single band of 38 kDa in sodium dodecyl sulfate-polyacryamide gel electrophoresis. The enzyme catalyses an ordered bi-bi-sequential reaction in which carbamoyl phosphate binds first, followed by L-ornithine; L-citrulline leaves first, followed by phosphate. The Michaelis constant was 0.19 mM for L-ornithine and 13.1 µM for carbamoyl phosphate; the dissociation constant for the enzyme and carbamoyl phosphate complex was of 19 µM. The K_m of the reaction decreases from pH 6.0 to pH 10.4. The enzyme is heat-labile, but it was protected from thermal inactivation by substrates; more by ornithine alone than by two substrates acting together.