Two experiments were conducted independently with plants of cassava (Manihot esculenta Crantz) growing in sand with nutrient solutions with four nitrate concentrations (0.5, 3, 6 or 12 mM). In leaves, nitrate-N was undetectable at the low nitrate applications; total-N, ammonium-N, amino acid-N, reduced-N and insoluble-N all increased linearly, while soluble proteins did it curvilinearly, with increasing nitrate supply. In contrast, soluble-N did not respond to N treatments. Total-N and soluble proteins, but not nitrate-N or ammonium-N, were much higher in leaves than in roots. Plants grown under severe N deficiency accumulated ammonium-N and amino acid-N in their roots. Further, plants were exposed to either 3 or 12 mM nitrate-N, and leaf activities of key N-assimilating enzymes were evaluated. Activities of nitrate reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase were considerably lower in low nitrate supply than in high one. Despite the low nitrate reductase activity, cassava leaves showed an ability to maintain a large proportion of N in soluble proteins.

Twenty genotypes of Stylosanthes consisting four species were evaluated under rain fed condition employing biochemical and physiological attributes to select drought tolerant lines. Relative water content measured at 50 % flowering stage of the plants showed significant variations among the lines which ranged from 32.11 in S. scabra RRR94-86 to 83.33 % in S. seabrana 2539. The results indicated that S. scabra genotypes were more tolerant to drought over other lines as evidenced by high leaf thickness, proline accumulation, content of sugars and chlorophyll, and nitrate reductase activity.

The content of glucose, fructose and saccharose as well as changes in the activities of enzymes involved in their biosynthesis and degradation were studied in tobacco plants infected with potato virus Y (necrotic strain) during the acute-infection period. Over the first part of this period, accumulation of saccharose, glucose and fructose was observed concurrently with decreased activities of the enzymes metabolizing saccharose, glucose and fructose (saccharases, saccharose synthase and hexokinases) and enhancement in the activities of enzymes synthesizing these carbohydrates (saccharosephosphate synthase, glucose-6-phosphate and/or fructose-6-phosphate phosphatases). The subsequent period was characterised by a reduction in both phosphatases that (together with just slightly raised saccharosephosphate synthase) could hardly produce enough sugars for the highly stimulated enzymes such as saccharases, saccharose synthase, and both kinases. Presumably for this reason, the previously increased content of sugars was considerably reduced to the level of control plants. The activities of glucokinase, fructokinase, saccharases and saccharose synthase were strongly increased at the culmination of virus multiplication and negatively correlated with the content of free glucose, fructose and saccharose.

Callogenesis, somatic embryogenesis and regeneration capacity in twenty-three agronomically important spring barley (Hordeum vulgare L.) cultivars on induction media with 2,4-dichlorophenoxyacetic acid (2,4-D) or 3,6-dichloro-o-anisic acid (dicamba) and on modified regeneration media were studied. The frequency of zygotic embryos exhibiting callogenesis varied from 88 to 100 % according to genotype. Dicamba was more suitable for somatic embryogenesis induction and exhibited a higher frequency of regenerants than did 2,4-D. Green regenerants were obtained in all cultivars, and there were no albino plants. Except for cv. Victor all cultivars used in the experiment showed lower regeneration capacity as compared to the model cv. Golden Promise.

Effect of pre-treatments of 1 and 5 μM epibrassinolide or homobrassinolide prior to water stress induction on changes in root nodulation and contents of endogenous abscisic acid (ABA) and cytokinin trans-zeatin riboside (ZR), and nitrogenase activity was investigated in the nodulated roots of Phaseolus vulgaris L. cv. Arka Suvidha. Brassinosteroids in the unstressed plants increased root nodulation, ZR content and nitrogenase activity, and also ameliorated their stress-induced decline in the nodulated roots. The ABA contents in the nodules of control or stressed plants were not altered by brassinosteroids treatment. There was an increase in pod yield by brassinosteroids treatment (5 μM) in the irrigated control as well as stressed plants without influencing pod number or pod length. Among the brassinosteroids, epibrassinolide was relatively more effective.

Zilla spinosa plant part extracts exhibited significantly different inhibitory effect on the seed germination and seedling growth of its associate species. Shoot extract reduced the percentage germination and seedling length of different test species more than root extract. Except of Z. coccineum, seedling growth was more sensitive than seed germination. Shoot/root ratio of all test species increased significantly with increase in extract concentration. Mycelia growth of the two rhizosphere fungal species was more significantly reduced by Z. spinosa shoot extract than root extract. The effects of the different extracts on total protein and total carbohydrate contents of the two test species were comparable. Non-significant increase was recorded at low concentration of both shoot and root extract. However, with the rise of extract concentration, highly significant reduction in the content of these metabolites was recorded.

We have designed and constructed four oligonucleotides corresponding to the most conserved regions of ornithine decarboxylases (ODC; EC 4.1.1.17) of plant origin. These oligonucleotides were used for the amplification of homologous fragments from several plants (Zea mays, Capsicum annuum, Sorghum bicolor, Phaseolus vulgaris, Carica papaya and Daucus carota). The amplified fragments were cloned and sequenced, revealing high homology to other ODCs. Peptide sequences coded by these fragments were compared by Clustal analyses. These analyses identified the location of the conserved sequences corresponding to the binding sites of substrate and cofactor. Data demonstrated that the plant ODCs fragments lacked intron sequences and were extremely homologous (over 80 %), constituting a compact group separated from other eukaryotic ODCs.

Maize (Zea mays ssp. mays) and eastern gamagrass (Tripsacum dactyloides) are known for their susceptibility to chilling injuries. Their hybrid (Z. mays × T. dactyloides) showed higher tolerance to low temperatures (-2 °C) in the field than its parents. Exposure to 5 °C for 2 or 3 d reduced the variable to maximal chlorophyll fluorescence ratio (F_V/F_M), an indicator of the maximum photochemical efficiency of the photosystem 2, and the variable to minimal fluorescence ratio (F_V/F₀) more in maize and eastern gamagrass than in hybrid plants. Chlorophyll contents for rewarming plants (25 °C for 3 d) were lower than before chilling in both parents while values for hybrid plants were similar. Electrolyte leakage was higher in chilled than control plants but it did not show significant differences among genotypes. Our data suggest that hybrid plants have higher capacity to recover from chilling injury in controlled conditions than their parents.

Suckers collected from different populations of Musa acuminata ssp. malaccensis were found to be highly resistant to race 4 of Fusarium oxysporum f. sp. cubense (FOC) suggesting that local wild banana populations co-evolved with the pathogen. Seedlings from these wild banana plants segregated for resistance to the pathogen. The infected seedlings were characterized based on external and internal symptoms and the variable response to FOC was mainly due to the genetic factors. Using the technique of random amplified polymorphic DNA (RAPD), 96 major amplification products from 15 primers were identified. Only 10 out of 96 markers were monomorphic and shared among the seed progenies, whereas the remaining 86 were highly polymorphic. Three primers showed banding patterns specific to resistant or susceptible seedlings. These results showed the great potential of the wild Musa acuminata ssp. malaccensis as a source for banana improvement and also for the synthesis of segregating populations for linkage mapping, gene cloning and DNA markers related to FOC resistance.

We employed continuous irradiation (CL) for induction of premature senescence caused by enhanced production of reactive oxygen species. As a model plant we used bean (Phaseolus vulgaris L. cv. Jantar) cotyledons because they have well defined and a quite short life span. Senescence of bean cotyledons induced by CL progressed more rapidly than natural senescence: the life span of CL cotyledons was 13 d compared to 16 d in controls (C). Chl content was significantly lower in 10- and 13-d-old CL plants than in C plants and the change with age was not statistically significant. Activities of all antioxidative enzymes declined either with senescence onset or during whole life span. Activity of antioxidative enzymes, except ascorbate peroxidase, was lower in CL plants compared to C plants. On the contrary, contents of non-enzymatic antioxidants β-carotene and ascorbate were higher in CL plants than in C plants. No significant difference, except in the youngest cotyledons, was observed in glutathione content.

Salt stress (50 and 150 mM NaCl) effects on sucrose metabolism was determined in Lupinus albus L. Sucrose synthase (SS) activity increased under salt stress and sucrose phosphate synthase activity decreased. Acid invertase activity was higher at 50 mM NaCl and decreased to control levels at 150 mM NaCl. Alkaline invertase activity increased with the salt stress. Glucose content decreased with salt stress, sucrose content was almost three times higher in plants treated with 150 mM NaCl and fructose content did not change significantly. The most significant response of lupin plants to NaCl excess is the increase of sucrose content in leaves, which is partially due to SS activity increase under salinity.

The effect of application of jasmonic acid (JA) and salicylic acid (SA) on the induction of resistance in wheat to Stagonospora nodorum and on the induction of μ-1,3-glucanase and thaumatin-like proteins (TLPs) was studied. Western blot analysis revealed that two β-1,3-glucanases with apparent molecular masses of 31 and 33 kDa that cross-reacted with a barley glucanase antiserum were induced in wheat leaves after treatment with JA and SA. When wheat plants were treated with SA and JA, a TLP with an apparent molecular mass of 25 kDa and several other isoforms of TLP were induced. Pre-treatment of wheat plants with SA and JA significantly reduced (up to 56 %) the incidence of leaf blotch disease incited by S. nodorum compared with untreated control plants.

Mature zygotic embryos of Paspalum scrobiculatum L. cv. PSC 1 on MS or N₆ nutrient medium supplemented with various concentrations of 2,4-D (4.5 - 22.5 µM) formed embryogenic callus, which differentiated into somatic embryos within 5 weeks of culture. The somatic embryos after transfer to hormone-free regeneration medium germinated and formed plantlets. Of the two nutrient formulations, N₆ was relatively better than MS for somatic embryogenesis. A culture for 11 d on 100 µM 2,4-D was essential for the establishment of an embryogenic callus. Shorter duration, 4-d or 7-d culture on 2,4-D medium, supported some proliferation and subsequent differentiation into shoot-buds or multiple-shoots, in high-frequency cultures. This is first instance in monocots of a controlled regeneration response; either somatic embryogenesis or shoot formation.

Changes in antioxidant systems in sunflower (Helianthus annuus L.) inbred lines were studied in relation to different concentrations (0, 2, 3 and 4 mM) of oxalic acid. A great variability of the total superoxide dismutase (SOD) activity was observed in different genotypes after application of oxalic acid. Genotypes showing no change in SOD activity, as well as those with decreased and increased activities, have been found. The highest guaiacol peroxidase (GPX) activity was recorded in the leaves of Ha-26A genotype where the activity of SOD was low. In genotypes with increased GPX activity the malonyldialdehyde content was low. The increase in reduced glutathione content occured in almost all of the genotypes studied with the increase in oxalate concentration. Some genotypes such as PR-ST-3B, showed distinctive and combined activity of several antioxidant systems. Also, obtained results for the content of total phenols support the idea of using soluble phenols as molecular markers and confirm the hypothesis of the defensive role of these compounds in plants.

The effects of different concentrations of NaCl on the activities of antioxidative enzymes in the shoots and roots of soybean (Glycine max [L.] Merr cv. Pershing) inoculated or not with an arbuscular mycorrhizal fungus, Glomus etunicatum Becker & Gerdemann, were studied. Furthermore, the effect of salt acclimated mycorrhizal fungi on the antioxidative enzymes in soybean plants grown under salt stress (100 mM NaCl) was investigated. Activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased in the shoots of both mycorrhizal (M) and nonmycorrhizal (NM) plants grown under NaCl salinity. Salinity increased SOD activity in the roots of M and NM plants, but had no effect on CAT and polyphenol oxidase activities in the roots. M plants had greater SOD, POD and ascorbate peroxidase activity under salinity. Under salt stress, soybean plants inoculated with salt pre-treated mycorrhizal fungi showed increased SOD and POD activity in shoots, relative to those inoculated with the non pre-treated fungi.

Image analysis was used in studying stomatal morphology during acclimatization of tobacco plantlets to ex vitro conditions, 45 d after transfer leaf area was 15 times, and total number of stomata per leaf four times increased. During acclimatization stomatal density was decreased considerably on both leaf sides, and was compensated by an increase in stomatal sizes, e.g., in stomatal length and in stomatal area (both guard cells and pore). Elongation of stomata was increased indicating that the originally circular stomata of in vitro plantlets were changed into elliptical ones in ex vitro acclimatized plants.

The in vitro regeneration of three flax (Linum usitatissimum L.) breeding lines (cv. Jitka, cv. Areco and NLN 245) and selection of transgenic plants were studied. A. tumefaciens derived binary vector GV3101 (pPM90RK)(pPCVRN4) bearing tetramer of 35S promoter enhancer was used in transformation experiments. Following 3 weeks of cultivation on shoot inducing Murashige and Skoog agar medium containing BAP (0.1 µM) and NAA (0.005 µM) from 82.6 % to 98 % of hypocotyl segments formed shoots. While ticarcillin (500 mg dm^-3) used to eliminate Agrobacterium following the transformation decreased the organogenic response by about 10 % only, the addition of 20 mg dm^-3 hygromycin to ticarcillin efficiently suppressed the regeneration of untransformed control plants. To look up for genomic mutations caused by T-DNA insertion from Agrobacterium transformation or originated from somaclonal variation over 500 regenerated plants have been cloned, transferred into soil and evaluated especially for their morphological characteristics. Up to now among plants of cv. Areco-background at least 8 genotypes showed changes either in flower or filament and stigma colour and one clone of plants with pollen sterility was identified. Among fifty four plant clones evaluated in 7 clones the presence of transgene specific sequence hpt was detected and simultaneously Agrobacterium contamination of tissues was firmly excluded.

Potato (Solanum tuberosum L. cv. Bintje) was transformed with a cDNA clone encoding an osmotin-like protein. Transgenic and non-transgenic in vitro plants were subjected to NaCl for 3 weeks. The shoot and root development was slightly affected by salinity indicating that the salt condition used was a mild stress. The endogenous proline content of the osmotin-like transformed clone only raised slightly as compared to the non-transformed genotype, where a marked increase in proline content could be observed as a result to salt stress. These data provide evidence for the involvement of osmotin-like proteins in the mechanisms of salt tolerance in potato plants.

Various ecophysiological investigations are presented in Aldrovanda vesiculosa, a rootless aquatic carnivorous plant. A distinct polarity of N, P, and Ca tissue content per dry mass (DM) unit was found along Aldrovanda shoots. Due to effective re-utilization, relatively small proportions of N (10 - 13 %) and P (33 - 43 %) are probably lost with senescent leaf whorls, while there is complete loss of all Ca, K, and Mg. The total content of starch and free sugars was 26 - 47 % DM along adult shoots, with the maximum in the 7^th - 10^th whorls. About 30 % of the total maximum sugar content was probably lost with dead whorls. The plant was found to take up 5 - 7 times more NH₄⁺ to NO₃^- from a mineral medium. Under nearly-natural conditions in an outdoor cultivation container, catching of prey led to significantly more rapid growth than in unfed plants. DM of the fed controls was 48 % higher than in the unfed plants. The controls produced 0.69 branches per plant, while the unfed plants did not produced any. However, the N and P content per DM unit increased by 6 - 25 % in the apices and the first 6 whorls in the unfed variant, as compared to the fed controls. It may be suggested that carnivory is very important for Aldrovanda.

Exogenously applied methyl jasmonate (MeJA) might induce the formation of necrotic lesions that closely resemble hypersensitive response lesions. Cellular damage, restricted to the infiltrated zone, was accompanied with the production of H₂O₂ from the oxidative burst. H₂O₂ generated in response to MeJA can be histochemically detected in cells surrounding the necrotic lesions as well as in the vascular tissues. The response is systemic and maximizes with time. Among 12 plant species from different families that were assayed for both hypersensitive reaction (HR)-like response and H₂O₂ generation, only woody species exhibited both MeJA-inducible HR cell death and the generation of H₂O₂. To assess the role of H₂O₂ in MeJA-induced HR-like cell death, a gain and loss of function strategy was employed. The cumulative results indicate that H₂O₂ is neither necessary nor sufficient for MeJA-inducible cell death and that O₂^- rather than H₂O₂ might be responsible.

The cloning of a 465 bp fragment from the 5'-flanking region of the gene encoding a cytosolic cyclophilin from periwinkle was achieved through inverse polymerase chain reaction. The DNA fragment was fused to a gusA-intron marker then introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. Histochemical analysis of the transgenic shoot cultures demonstrated that the construct was able to drive GUS expression in stomata guard cells, but not in mesophyll cells when shoots were still attached to the callus from which they were initiated. In separated transgenic shoots and in seedlings, GUS was expressed in external and internal phloem and root hairs, respectively. GUS activity in transgenic tobacco seedlings was also investigated by fluorimetric assays. Treatments with NaCl or ABA decreased promoter activity whereas treatment with yeast extracts increased it.

Barley (Hordeum vulgare L., cv. Hemus) plants were grown in nutrient solution with or without 54 µM Cd²⁺ for 12 d. A treatment with Cd²⁺ inhibited the growth of young barley plants. The main factor limiting plant growth was net assimilation rate, due to decreased photosynthetic rate and accelerated dark respiration rate. One of the reasons for the reduced photosynthetic rate was the lower chlorophyll and carotenoid content. Cd²⁺ decreased water potential and transpiration rate, but relative water content in leaves of the treated plants was not significantly changed.

A simple protocol for mass multiplication of Crataeva nurvala, a medicinal tree, from seedling-derived explants is described. Six different types of explants (cotyledonary nodes, epicotyl nodes, hypocotyl segments, first pair of leaves, cotyledons, and root segments) developed shoots on Murashige and Skoog's (MS) basal medium or the same supplemented with different concentrations of 6-benzylaminopurine (BAP). Among the explants tested for caulogenic potential, only the epicotyl and cotyledonary nodal explants developed shoots on MS basal medium, while on BAP (0 - 2.0 mg dm^-3) adjuvated media all the explants exhibited caulogenesis. The optimum concentration of BAP varied for these explants. The shoots could be rooted on half strength MS with 0.02 mg dm^-3 α-naphthalene acetic acid to get plants, which have been transferred to soil. The explants from in vitro regenerated shoots also possessed a similar caulogenic potential.

Responses of 20 d-old plants of two Brassica napus L. cultivars Dunkeld and Cyclon to NaCl salinized soil [electrical conductivity 2.4 (control), 4.0, 8.0 or 12.0 dS m^-1] were examined. The salt tolerant line Dunkeld had significantly higher fresh and dry masses of shoots, and seed yield than salt sensitive line Cyclon in all salinities. The effect of salt stress on reduction in total leaf soluble sugars was markedly greater in Dunkeld as compared to that in Cyclon. No effect of salt stress was observed on leaf soluble proteins but there was a slight increase in total free amino acids of both cultivars. Leaf proline content increased markedly in both cultivars and Dunkeld had greater proline content than Cyclon at all salinities. Salt stress had no significant effect on seed oil content and erucic acid content of seed oil, however, content of glucosinolates in the seed meal increased and Cyclon had greater content of glucosinolates than Dunkeld.

In four experiments, the chromosome doubling effect of acenaphthene vapour was tested on androgenic embryoids and/or plantlets of tobacco. The maximum rate of plants with doubled chromosome numbers (41.3 % diploids plus 2.7 % tetraploids) was recorded when approx. 100 mg acenaphthene in small and sterilized cheese-cloth bags were hanged for 72 h, into the culture jars (6.0 × 11.5 cm), containing 4 - 6 androgenic plantlets newly transferred from culture tubes. Acenaphthene treatments performed at the earlier stages of culture resulted in lower percentages (from 0.0 to 6.3 %).

A protocol for multiple shoot induction from cotyledonary node explants of Terminalia chebula Retz. has been developed. Germination frequency of embryos (up to 100 %) was obtained on Murashige and Skoog (MS) medium supplemented with 0.5 mg dm^-3 gibberellic acid (GA₃). Maximum number of shoots (6.4 shoots per cotyledonary node) was obtained on half-strength MS + 0.3 mg dm^-3 GA₃+ 1.0 mg dm^-3 indole-3-butyric acid (IBA) + 10.0 mg dm^-3 benzylaminopurine (BAP) after 4 weeks of culture. When the cotyledonary nodes along with the axillary shoot buds were allowed to grow in the same medium upto 19.2 shoots were obtained after 8 - 9 weeks. Best rooting (100 %, 5.5 roots per shoot) was observed when shoots were excised and transferred to half-strength MS medium containing 1.0 mg dm^-3 IBA + 1 % mannitol and 1.5 % sucrose. Survival of rooted plants in vivo was low (35 - 40 %) when they were directly transferred to soil in glasshouse. However, transfer to soil with MS nutrients and 1.0 mg dm^-3 IBA in culture room for a minimum duration of 2 weeks increased the survival percentage of plants to 100 %.

An antiviral factor (AVF) was separated by removing virus particles from extracts of tobacco mosaic virus (TMV) infected leaves using calcium phosphate gel and by column chromatography on DEAE cellulose. AVF was not found in the extracts from healthy plants. The AVF restricted the virus infectivity "in vivo" and significantly decreased the activity of key enzymes of metabolic pathways tending to the purine and pyrimidine nucleotides biosynthesis of viral- RNA (glucose-6-phosphate dehydrogenase, ribonucleases, phosphomonoesterase and phosphodiesterase). No inhibition of these enzymes was observed "in vitro" when the effect of different concentrations of AVF (0.25 - 250 µg cm^-3) was examined.