5-Aminolevulinic acid synthase (ALAS) has been detected in a normal (auxin- and cytokinin-dependent) green sugar beet callus under light and under darkness. ALAS activity was lower when the callus was grown under light. The supply of precursors of the Shemin pathway (glycine and succinate) to dark-grown callus enhanced considerably the capacity of the 5-aminolevulinic acid (ALA) formation. Glutamate, γ-aminobutyrate or α-ketoglutarate also increased ALA accumulation. Such an accumulation was also obtained after inhibition of polyamine synthesis. The results show that glutamate or its derivatives might feed the Shemin pathway in conditions preventing glutamate to be used through the Beale pathway.

Protocols were developed for plant regeneration from callus induced in mature embryos of rice. Somaclonal variation was scored by genome mutation, chromosome mutation and plasmon mutation in R₀, R₁ and R₂ plant progenies. The frequency of haploids and diploids appeared in the ratio of 20:33. Variation in the chromosome number in callus cells was found to be high and age dependent. Different types of chlorophyll deficient mutants including albinos appeared in R₂ plant progeny where gene mutation frequency was the highest (52.4 %). The results revealed that a high frequency of somaclonal variation is possible to generate by tissue culture techniques.

Normal callus and embryogenic suspensor mass (ESM) were induced from the same immature embryo of Abies alba Mill. These two tissues were found to differ in their isoenzyme patterns of peroxidase, glutamate dehydrogenaseand non-specific esterase and in their requirement for myo-inositol inculture medium.

Explants of Chenopodium rubrum, a short-day plant, were decapitated and exposed to floral inductive treatment, and the extent of flowering of axillary buds was afterwards assessed. Isolated buds never responded to induction, whereas the presence of the petiole of the subtending leaf already assured a high degree of flowering. We may assume either that the petiole is the receptor organ of the photoperiodic signal or that its transporting role is indispensable.

The effect of five Azotobacter chroococcum strains and nitrogen content in nutrient media on callus growth of two Beta vulgaris L. cultivars were investigated, as well as the activity of nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in inoculated callus tissue. On medium with full nitrogen content (1 N) the inoculation with A. chroococcum strain A2 resulted in the highest calli mass, while strains A8 and A14 maximally increased NR activity. On media with 1/8 N the highest effect on calli growth, GS and GDH activity had the strain A8. The strain A2/1 significantly increased callus proliferation on medium without N. Asymbiotic association between sugar beet calli and Azotobacter depended on genotype/strain interaction and was realised in presence of different nitrogen levels.

The involvement of ethylene in shoot formation in vitro was studied in one year old lavandin (Lavandula officinalis Chaix x Lavandula latifoliaVillars) callus. A peak in ethylene evolution characterized thenon-regenerating leaf callus line, as compared to the shoot-forming calyxcallus line, on the growth medium provided with 2,4-dichlorophenoxyacetic acid (1 mg dm-3) and kinetin (0.5 mg dm-3). After one year in culture, calyxcallus attained the capacity to grow on auxin-reduced media, showing decreased ethylene production and faster shoot bud emergence, when transferred onto the regeneration medium, supplemented with 10 mg dm^-3 benzyladenine. Shoot formation was also inhibited by addition of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, indicating an involvement of ethylene in the failure of regeneration.

The present study was carried out to study the effect of salt stress on cell membrane damage, ion content and antioxidant enzymes in wheat (Triticum aestivum) seedlings of two cultivars salt-tolerant KRL-19 and salt-sensitive WH-542. Seedlings (4-d-old) were irrigated with 0, 50 and 100 mM NaCl. Observations were recorded on the 3^rd and 6^th day after salt treatment and 2^nd day after salt removal. The relative water content declined with induction of salt stress, more in WH-542 than in cv. KRL-19. K⁺/Na⁺ ratio in KRL-19 was higher than in WH-542. WH-542 suffered greater damage to cellular membranes due to lipid peroxidation as indicated by higher accumulation of H₂O₂, MDA and greater leakage of electrolytes than KRL-19. The activities of catalase, peroxidase and ascorbate peroxidase and glutathione reductase increased with increase in salt stress in both the cultivars, however, superoxide dismutase activity declined. Upon desalanization, partial recovery in the activities of these enzymes was observed in KRL-19 and very slow recovery in WH-542.

Zea mays ssp. mays (2n=40) and Z. mays ssp. parviglumis (2n=20) were crossed to obtain hybrid plants by embryo rescue. Hybrid embryos were isolated and cultured on García et al. (1992) basic medium supplemented with 2,4-dichlorophenoxyacetic acid and/or kinetin in different concentrations. Caryopses harvested 23 d after pollination (DAP) were turgid, with 0.3 to 0.5 mm long embryos, while those harvested 30 DAP were shrunken, with 1 to 1.5 mm long embryos. Twenty days after plating, 100 % of the younger embryos gave rise to white, compact embryogenic calli. Subsequently, coleoptiles, leaf-like structures, shoots and roots originated from them and 35 hybrid plants were regenerated from 60 embryos. Embryogenic or organogenic calli frequencies did not differ among hormonal treatments, but they decreased, on average, from 90.5 to 44.3 %, comparing 50 and 120-d-old cultures. The older embryos regenerated plants only by germination, although they gave rise to organogenic callus with low frequencies. Regenerated plants showed a somatic chromosome number of 2n=30, pollen fertility of 40 to 80 % and 15 % viable naked caryopses.

Multiple shoots were induced by culturing nodal explants excised from 1-month-old aseptic seedlings of red pepper (Capsicum annuum L. cv. Pusa Jwala) on Murashige and Skoog (MS) medium supplemented with (0.1-10 μM) thidiazuron (TDZ). The rate of multiple shoot induction per explant was maximum (14.4 ± 0.06) on MS medium supplemented with 1.0 μM TDZ. Regenerated shoots were elongated well on growth regulator free MS medium. Adventitious roots were induced two weeks after transfer of elongated shoots to MS medium supplemented with auxins (IAA, IBA or NAA) in different concentrations. Optimum root formation frequency was obtained in medium containing 1.0 μM IBA. Ex-vitro rooting was also achieved by pulse treatment with 300 μM IBA for 10 min. Rooted shoots were transplanted in plastic pots containing garden soil (with 90 % survival rate), where they grew well and attained maturity. Regenerated plants were phenotypically and cytologically normal.

The effect of thidiazuron (TDZ) was studied on in vitro axillary shoot proliferation from nodal explant of Psoralea corylifolia - an endangered medicinal plant. Proliferation of shoots was achieved on Murashige and Skoog (MS) medium supplemented with 0.5, 1, 2, 3, 4 and 5 μM TDZ. The maximum number (13.6 ± 1.4) of shoots per explant were obtained from nodal segment cultured on 2 μM TDZ for 4 weeks and this increased to 29.7 ± 2.1 on hormone free MS medium after 8 weeks. The in vitro proliferated and elongated shoots were transferred individually on a root induction medium containing 0.5 μM indole-3-butyric acid (IBA) and within 4 weeks 4.5 ± 0.5 roots per shoot were produced. The regenerated plantlets were transferred to 1:1 soil and vermiculite mixture and acclimatized with 80 % survival rate. Fully acclimatized plants were grown in garden soil in greenhouse and their morphological and physiological parameters were comparable with seedlings.

Biomass growth and ginsenoside production in cell suspension and adventitious roots of Panax ginseng C.A. Meyer cultures cultivated both in Erlenmayer flasks and a 3 dm³ bioreactor were studied. The maximum content of ginsenosides was found in the suspension culture cultivated in the bioreactor (4.34 % dry mass), however the saponin content was limited to two major ginsenosides, Rb₁ and Rg₁. The production of ginsenosides in adventitious roots was lower (1.45 or 1.72 % dry mass), nevertheless, the full range of ginsenosides was detected.

A rapid and efficient in vitro plant regeneration method was developed for Aristolochia indica. Multiple shoot formation was induced from shoot tip and nodal explants on Murashige and Skoog (MS) medium with 1 - 6 mg dm^-3 2-isopentenyl-adenine (2-iP) or 1 - 4 mg dm^-3 6-benzyladenine (BA). Maximum number of shoots were induced with 5 mg dm^-3 2-iP alone (about 12 - 14 shoots). Shoot differentiation occurred directly from the leaf bases as well as from the internodes when cultured on 1 - 4 mg dm^-3 BA and 0.8 - 2 mg dm^-3 α-naphthaleneacetic acid (NAA) containing medium. Regeneration from the callus occurred when the calli initiated on MS medium containing 0.6 - 4 mg dm^-3 NAA in combination with 0.8 - 3 mg dm^-3 BA were transferred to 1 - 6 mg dm^-3 BA alone containing medium. Elongated shoots were separated and rooted in MS medium containing 1 mg dm^-3 indole-3-butyric acid. These were then transferred to soil after gradual acclimatization.

A simple procedure for the detection of extracellular plant proteolytic enzymes using insoluble dye stained gelatin substrates incorporated into an appropriate culture medium is described. Extracellular proteinases produced by the tested plant cells (callus culture and cell suspension) hydrolyzed the substrates and dyed peptide fragments were released. Dyed zones around and under the proteinase-producing callus cultures were formed on the agar medium. Similarly, coloration of the culture media using proteinase-producing cell suspensions was observed.

A rapid and highly-effective method for micropropagation from nodal segment and shoot tip explants was established for Coleus blumei Benth. Nodal segments and shoot tips were inoculated on MS medium containing 0.7 % agar, 3 % commercial sugar, and different combinations of 6-benzyladenine (BA) with indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) or α-naphthaleneacetic acid (NAA). Hundred percent shoot induction from both explants was achieved on the medium containing BA (2 mg dm^-3) and NAA (1 mg dm^-3). Shoot tips were proved to be the better explant in comparison to nodal segments in having high rate of shoot induction and more number of shoots. The same media conditions were found suitable for shoot multiplication. Multiplied shoots rooted best on MS medium supplemented with IBA (2 mg dm^-3). Micropropagated plants were successfully established in soil after hardening, with 100 % survival rate.

The effects of carbon sources (sucrose, glucose, fructose and mannitol) and auxins [indolebutyric acid (IBA) and α-naphthaleneacetic acid (NAA)] on in vitro propagation of banana (Musa spp. AAA) were studied. Over all carbon sources tested, sucrose induced highest frequency of shoot proliferation. Optimal shoot proliferation rates were achieved on the Murashige and Skoog (MS) medium supplemented with sucrose and glucose combination (1:1) at the concentration of 30 g dm^-3. Similarly, higher frequency of root induction was obtained at IBA and NAA combination (1:1; concentration of 2 mg dm^-3) than at other concentrations of IBA or NAA alone or their combinations.

An efficient system for shoot regeneration and Agrobacterium-mediated gene transfer into Brassica napus was developed through the modification of the culture conditions. Different concentrations of benzyladenine (1.5, 3.0 and 4.5 mg dm^-3) and thidiazuron (0.0, 0.15 and 0.30 mg dm^-3) were evaluated for shoot regeneration of 7, 14 and 21-d-old hypocotyl explants. Maximum shoot regeneration frequency was obtained in 21-d-old explants using 4.5 mg dm^-3 benzyladenine and 0.3 mg dm^-3 thidiazuron. Under above culture condition, the highest percentage of shoot regeneration frequency was 200 %. Agrobacterium-infected explants grown on the selection medium gave rise to transgenic shoots at a frequency of 11.8 %. Transformed shoots rooted when cultured on a medium supplemented with 2 mg dm^-3 of indolebutyric acid and 10 mg dm^-3 kanamycin. The rooted plantlets were successfully established in the soil and developed fertile flowers and viable seeds. Evidences for transformation were confirmed by GUS assay and PCR analysis.

We induced an oxidative stress by means of exogenous hydrogen peroxide in two wheat genotypes, C 306 (tolerant to water stress) and Hira (susceptible to water stress), and investigated oxidative injury and changes in antioxidant enzymes activity. H₂O₂ treatment caused chlorophyll degradation, lipid peroxidation, decreased membrane stability and activity of nitrate reductase. Hydrogen peroxide increased the activity of antioxidant enzymes, glutathione reductase and catalase. These effects increased with increasing H₂O₂ concentrations. However, no change was observed in the activity of superoxide dismutase and proline accumulation.

We describe the multi-step regeneration system of medicinal plant Schisandra chinensis (Turcz.) Baill. The seeds were pre-treated with 0.005 μM thidiazuron. Subsequently the zygotic embryos of the early heart stage were cultured on medium with 50 μM of 2,4-dichlorophenoxyacetic acid (2,4-D) and after three weeks the embryogenic calli were transferred to a medium with 10 μM of 2,4-D and 4 μM of 6-benzyladenine and were sub-cultured at the 4-week intervals. Abscisic acid (30 μM) and polyethyleneglycol (3 %) significantly influenced the synchronization of development of the somatic embryos (SEs) to the globular stage. The following culture on a medium without growth regulators resulted in full developed cotyledonary stage SEs. Indole-3-butyric acid (0.05 μ) contributed to their rapid conversion to plantlets.

The adventitious bud development was induced in epicotyl segments of Valencia sweet orange (Citrus sinensis L. Osbeck). Seeds were cultured in vitro for three weeks in the dark, followed by one week at a 16-h photoperiod. Epicotyl segments were cultured horizontally for the induction of organogenesis in Murashige and Tucker (1969, MT) culture medium supplemented with 1.0 mg dm^-3 benzylaminopurine. Samples were observed by light and scanning electron microscopy from day zero to day 25, when buds were well grown. It was shown that the adventitious buds originated directly from the cambial region on the cut ends of the explants.

Leaf explants of Phalaenopsis amabilis var. formosa formed clusters of somatic embryos directly from epidermal cells without an intervening callus within 20 - 30 d when cultured on 1/2-strength modified Murashige and Skoog medium supplemented with 0.1, 1 and 3 mg dm^-3 TDZ. Repetitive production of embryos involved secondary embryogenesis could be obtained by culturing segments of embryogenic masses on TDZ-containing media. Plantlet conversion from embryos was successfully achieved on regulator-free growth medium.

Plant regeneration was achieved from coleoptile tissue of wheat (Triticum aestivum L. cv. Kharachia-65). Coleoptiles (1.0 - 3.5 cm long) were excised from 2- to 5-d-old seedlings and cultured on Murashige and Skoog's (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D - 0.5, 2.5, and 5.0 mg dm^-3). Cream, friable callus was obtained after 6 weeks of inoculation. This callus was sub-cultured on MS medium supplemented with 2,4-D (2.5 mg dm^-3) and 5 % coconut water. After 6 weeks of sub-culturing white, cream or pale, friable, nodular callus was obtained. Plant regeneration occurred when this callus was sub-cultured on MS medium supplemented with 0.2 mg dm^-3 1-naphthalene acetic acid + 1.0 mg dm^-3 6-benzylaminopurine. For rooting, regenerated shoots or plantlets were transferred on MS medium supplemented with 0.5 mg dm^-3 indole-3-acetic acid. Rooted plantlets were directly transferred into pots and grown under field conditions. Seed setting invariably occurred in all plants.

The inoculation of the seedling roots of the resistant (Bousthami Noir) and susceptible (Jihel) date palm (Phoenix dactylifera) cultivars by Fusarium oxysporum f. sp. albedinis induced an increase in phenylalanine ammonia-lyase (PAL) activity. The response of the PAL activity in the resistant cultivar was faster and higher than in the susceptible one. However, the elicitation of the seedlings with the hyphal wall elicitor (HWE) of the pathogen induced identical PAL activity in both cultivars. In the resistant cultivar, the the PAL activity elicited with the HWE was not influenced by the addition of the fungal culture filtrate (FCF) whereas it was suppressed in the susceptible cultivar. This FCF suppressor effect was dose-dependent, not influenced by sodium periodate, whereas it was strongly reduced by the heat (121 °C for 45 min) and pronase E. These results show that differential induction of the defence mechanisms in both cultivars was not related to differences in the induction of the PAL activity, but to the suppression of its elicitation in the susceptible cultivar.

Thirteen flavonoid aglycons, contained in the strongly allelopathic epicuticular exudates of Dittrichia viscosa, were investigated for their effects on lettuce seedling radicle growth. Concerning radicle length and mass, variable results were obtained, with most of the substances having no effect, some being inhibitory and some even promotive. Shoot mass was slightly reduced in four cases. Seed germination rates, root hair and lateral root formation were not affected either. Three of the compounds (namely quercetin 3,3-dimethylether, naringenin and eriodictyol) induced a strong ageotropic response in radicle growth.

Induction and growth of soybean callus cultures were influenced by NaCl, especially at the highest concentration tested (150 mM). Protein content was raised as NaCl was increased in the Murashige and Skoog medium. Total sulfhydryl group (-SH) and glutathione (GSH) concentrations were also increased in NaCl treated cultures. The affinity (Km) of glutathione reductase (GR) for oxidized glutathione (GSSG) was gradually increased as NaCl level was raised in the medium. The GSH/GSSG ratio was raised significantly as the result of GR activity. The increase in GR activity may constitute an adaptive response of soybean callus to NaCl.

Cultural conditions affecting the induction of rhizogenesis in vitro were evaluated in cashew (Anacardium occidentale L.) shoot-node-derived microshoots. The application of auxins was essential for the formation of adventitious roots. A 5-d indole-3-butyric acid (IBA) induction period was more suitable than continuous IBA treatment or a shorter induction period. N⁶-[2-Isopentenyl]adenine in low concentrations (0.3 - 1 µM) in the root induction medium supported root formation. Precultivation of microshoots with gibberellic acid (GA₃) suppressed the subsequent rhizogenesis. Activated charcoal did not affect rooting. No significant differences in rooting abilities of cashew shoots were observed between 25, 29 and 35 °C and roots did not develop at 19 °C. Salts of low osmotic composition were more suitable than richer media. Microshoots originated from cotyledonary nodes showed higher rooting when compared to standard microshoots.

Induced mutagenesis in callus tissues was studied in the medicinal plant Scilla indica irradiated with different doses of γ-radiation ranging from 2.5 to 20 Gy. Low doses accelerated the cell division and growth rate of the tissues whereas high doses repressed growth rate and resulted in lethality of tissues. Various cytological and chromosomal abnormalities were observed in the irradiated calli, the degree of which depended upon the dosage. Low doses of irradiation also promoted the regenerating capacity of the calli tissues and plants regenerating from them exhibited better growth and vigour compared to normal plants. High doses led to loss of regenerating capacity and promoted formation of malformed and stunted plants. Cytological study of regenerants revealed both diploid and mixoploid plants but no tetraploids were obtained.

Two tomato (Lycopersicon esculentum L.) cultivars: Robin (tolerant) and Roma (sensitive to heat stress) were studied. Chlorophyll fluorescence induction parameters (F_v/F_p, A_max, and Rfd) at 25 °C showed that the PS2 activity was similar for both cultivars. The parameters, measured at 38 °C, decreased in both cultivars, but more in cv. Roma. Exogenous application of 4 mM spermidine improved the plant heat-resistance in both cultivars, and especially in cv. Roma. Analysis of chlorophyll fluorescence changes during linear increase in temperature showed that cv. Robin plants have higher ability to hardening and higher resistance to thermal damage of the pigment-protein complexes structure and the activity of PS2 than cv. Roma.

Nodal explant cultures from field-grown five jojoba genotypes (EC 99690, EC 99692, EC 99692, EC 267779 and EC 171284; male and female plants), could be established on Murashige and Skoog (MS) medium. The nodal explants of different genotypes as well as sex elicited differential requirements of N⁶-benzyladenine (BA) for optimum shoot regeneration and medium-term conservation. Female nodal explants of EC 99692 produced maximum shoots (10 shoots per explant) followed by male of EC 171284 (9.3 shoots per explant) on MS + 10 μM BA. The pulse treatment of 50 μM indole-3-butyric acid for 20 min caused in vitro rhizogenesis in 44 - 67 % cultures of various genotypes tested. A significant difference was observed for the conservation period of male and female cultures of all the genotypes. MS + 10 μM BA supported the shoot cultures of EC 99690, EC 99691 and EC 267779 for maximum conservation period, while MS + 5 μM BA proved to be optimum for conserving the shoots of EC 99692 and EC 171284. Generally, the female shoot cultures of genotypes survived for longer period than male ones.

Somatic embryogenesis of European chestnut (Castanea sativa Mill.) was obtained using juvenile tissue cultured on P24 medium with 5 μM 2,4-dichlorophenoxyacetic acid plus 0.5 μM 6-benzylaminopurine (BA) for three weeks and then cultured on 0.89 μM BA. Induction frequency with ovaries ranged from 2.0 to 19.1 % and was observed in tissue collected 2 to 8 weeks postanthesis, ovules used as a starting tissue gained 0.8 to 7.8 %, 3 to 9 weeks postanthesis. Zygotic embryos collected 5 to 10 weeks postanthesis formed 10.5 to 57.1 % somatic embryos, respectively. The culture lines were maintained via secondary embryogenesis on P24 medium with 0.89 μM BA. Development and maturation were stimulated on P24 medium with increased agar concentration (1.1 %). Five plantlets were transferred to substrate and acclimatized successfully in greenhouse.

In order to establish an efficient system for in vitro plant regeneration of a short day plant Chenopodium rubrum L. and a long day plant Chenopodium murale L., optimum culture conditions for somatic embryogenesis were investigated. The effects of different growth regulators, their combination and their concentrations on somatic embryos induction in different explant types (root, hypocotyl, cotyledon and leaf) were tested. Somatic embryogenesis was induced in both plants on Murashige and Skoog (MS) medium supplemented with sucrose (3 %), agar (0.7 %) and 1 - 10 μM 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole growth regulator. The largest embryogenic capacity was found in root explants of Chenopodium rubrum on 1 μM 2,4-D and in basal parts of cotyledons in C. murale plants on 10 μM 2,4-D.