This study deals with the effects of two cytokinins [kinetin (Kin) and N-(2-chloro-4-pyridyl)-N-phenylurea (CPPU)] and cytokinin antagonists [2-chloro-4-cyclobutyl-amino-6-ethylamino-1,3,5-triazine (ACK1) and N-(4-pyridyl)-O-(4-chlorophenyl)carbamate (ACK2)] in concentration of 1 μM on in vitro cultured Gypsophila. The application of Kin and CPPU stimulated bud opening and increased fresh and dry masses. Cytokinin antagonists reduced the number of sprouted buds and bud fresh and dry masses. In plants treated with CPPU the chloroplasts possessed well developed membrane system, which covered almost the entire chloroplasts volume. In ACK2 treated plants, the plastid apparatus in each cell was represented by two types of chloroplast in which the inner membrane system was differently organized. Cell wall adjacent chloroplasts possessed structure similar to the controls. In inner located chloroplasts part of thylakoids were semi-concentrically arranged and partially destructed.

Recent investigations on plant molybdenum-containing enzymes that include xanthine dehydrogenase (EC 1.1.1.204) and xanthine oxidase (EC 1.1.3.22), nitrate reductase (EC 1.7.1.1-3), aldehyde oxidase (EC 1.2.3.1), and sulfite oxidase (EC 1.8.3.1) are reviewed. The enzymes belong to closely related protein family and share common structural features. Special attention is being paid to the recently solved crystal structures their implications for the substrate binding and catalytic mechanism.

A field study was conducted to evaluate the drought tolerance of three sorghum [Sorghum bicolor (L.) Moench] cultivars, Gadambalia, Arous elRimal and Tabat, and quantify the physiological bases for differences in their drought tolerance. Water stress reduced shoot dry mass of Gadambalia, Arous elRimal and Tabat by 43, 46 and 58 %, respectively. The respective reduction in leaf area of the three cultivars was 28, 54 and 63 %. The reduction in net photosynthetic rate, stomatal conductance and transpiration rate due to water stress was lowest in Gadambalia and highest in Tabat. The leaf water potentials and relative water contents of Gadambalia under wet and dry treatments were similar, while those of Tabat were significantly reduced by water stress. The lowest and highest liquid water flow conductance was displayed by Tabat and Gadambalia, respectively. Drought tolerance in Gadambalia is associated with its smaller leaf area, higher liquid water flow conductance, and ability to maintain high leaf water potential, relative water content, stomatal conductance, transpiration rate and photosynthetic rate under drought stress.

In vitro regeneration of Melia azedarach L. was studied. Shoots were regenerated from calli initiated from leaflets of in vitro growing plants. The best medium for establishment of cultures was Murashige and Skoog (MS) medium with 4.44 μM benzylaminopurine (BAP) + 0.46 μM kinetin (KIN) + 16.29 μM adenine sulphate (ADE). Regenerated shoots were multiplied in MS + 0.44 μM BAP + 0.37 μM KIN + 3.26 μM ADE. Maximal rooting of 89 % was achieved by culture of regenerated shoots in MS + 12.26 μM indole-3-butyric acid for 3 d and subsequently in MS lacking growth regulators for 27 d. Rooted shoots were acclimatized and successfully transferred to soil.

A micro-propagating system based on the young stem node segments of Sophora flavescens Ait. (Fabaceae) was established. Murashige and Skoog (MS) basal medium supplemented with 8.88 μM 6-benzyladenine (BA) plus 2.69 μM α-naphthalene acetic acid (NAA) and that with only 5.37 μM NAA were found the best in promoting proliferation of shoots and induction of root, respectively. Percentages of shoot induction and number of shoot per explant were up to 93.4 % and 4.2 and rooting rate to 82.4 %, respectively. The segments of the regenerated shoots could be continuously induced to reproduce new shoots through subculture on the same medium in 30-d intervals and still kept this activity after being subcultured for 6 generations. After the regenerated plantlets were transplanted to field, they grew well, showing no any visible abnormalities.

Dimorphic seeds of Atriplex prostrata were removed from cold dry storage monthly over a one year period to test for fluctuations in seed dormancy and germination rate. For each seed type, four replicates of 25 seeds were exposed to four alternating night/day temperature regimes mimicking seasonal fluctuations in Ohio: 5/15 °C; 5/25 °C; 15/25 °C and 20/35 °C with a corresponding 12-h photoperiod (20 μmol m^-2 s^-1; 400 - 700 nm). We found a significant three-way interaction of seed size, temperature and month for both percent germination and the rate of germination. Large seeds showed the greatest germination at the 20/35 °C and 5/25 °C temperature regimes and small seeds at the 5/25 °C regime. Large seeds had greater germination at all temperatures as compared to small seeds. Large seeds had the fastest germination rates at 20/35 °C followed by 5/25 °C whereas small seeds had the fastest rates at 5/25 °C followed by 20/35 °C.

Overexpression of antifungal pathogenesis-related (PR) proteins in crop plants has the potential for enhancing resistance against fungal pathogens. Thaumatin-like proteins (TLPs) are one group (PR-5, permatins) of antifungal PR-proteins isolated from various plants. In the present study, a plasmid containing a cDNA of rice tlp (D34) under the control of the CaMV-35S promoter was introduced into tobacco plants through Agrobacterium-mediated transformation system. A considerable overproduction of TLP was observed in transformed tobacco plants by Western blot analysis. There was a large accumulation of tlp mRNA in transgenic plants as revealed by Northern blot analysis. Southern blot analysis of the DNA from transgenic tobacco plants confirmed the presence of the rice tlp gene in the genomic DNA of transgenic tobacco plants. Immunoblot analysis of intracellular and extracellular proteins of transgenic tobacco leaves using a Pinto bean TLP antibody demonstrated that the 23-kDa TLP was secreted into the extracellular matrix. T₂ progeny of regenerated plants transformed with TLP gene were tested for their disease reaction to Alternaria alternata, the brown spot pathogen. Transgenic tobacco plants expressing TLP at high levels showed enhanced tolerance to necrotization caused by the pathogen.

In the present study three species of Heritiera Aiton (Sterculiaceae) were characterized using 9 amplified fragment length polymorphism (AFLP) primer combinations and the genetic relationship among these three species was assessed, Nine AFLP primer combinations yielded 445 bands out of which 210 were monomorphic and 235 were polymorphic. Out of the 235 polymorphic bands 79 were present only in a single species. Among the total amplified bands 255 were shared between H. fomes and H. littoralis, 225 were shared between H. fomes and H. macrophylla and 306 bands were shared between H. littoralis and H. macrophylla. The cluster analysis showed H. littoralis is closer to H. macrophylla than H. fomes. The similarity between H. fomes and H. littoralis was higher than that of H. fomes and H. macrophylla. The present study indicates that H. littoralis is better classified as mangrove associate or back mangal than a true mangrove.

Effective protocol was established for micropropagation of the medicinal plant Eupatorium triplinerve Vahl through rapid axillary bud proliferation and ex vitro rooting. Murashige and Skoog (MS) medium fortified with 8.87 μM benzylaminopurine (BAP) and 2.46 μM indole-3-butyric acid (IBA) was the best for axillary bud proliferation and developed a mean of 8.1 shoots per node. Excision and culture of the node segments of the in vitro shoots on medium supplemented with the same concentration of growth regulators developed more than 30 shoots within 40 d. Shoot multiplication did not exhibit decrease in the number of shoots even at 7^th subculture. Dipping of the basal end of shoots in 2.46 μM IBA solution for 10 d induced roots and its transfer to small pots facilitated the survival of all rooted shoots (100 %). Ex vitro rooting by direct transfer of the shoots from multiplication medium showed 92 % survival.

Callus cells of potato (Solanum tuberosum L.) cv. Désirée were exposed to various subzero temperatures and examined for the freezing damage. In the cells subjected to -3 °C, plasma membranes appeared to be intact, while tonoplast seemed to be damaged and organelles to be swollen. After freezing at -6 °C, the damage became severe and plasma membranes were ruptured. After exposure to -10 °C, the damage was so severe that the cell organelles could not be recognised and cytoplasm became fragmented.

The regulation of proline accumulation in polyethylene glycol (PEG, -1.5 MPa) treated rice leaves was investigated. PEG treatment resulted in a decrease in relative water content, indicating that PEG treatment caused water stress in rice leaves. Proline accumulation caused by PEG was related to protein hydrolysis, an increase in ornithine-δ-amino- transferase activity, an increase in the content of ammonia, and an increase in the contents of the precursors of proline biosynthesis, glutamic acid, ornithine, and arginine. Results also show that abscisic acid accumulation is not required for proline accumulation in PEG-treated rice leaves.

The effects of aluminum on lipid peroxidation and activities of antioxidative enzymes were investigated in detached rice leaves treated with 0 to 5 mM AlCl₃ at pH 4.0 in the light. AlCl₃ enhanced the content of malondialdehyde but not the content of H₂O₂. Superoxide dismutase activity was reduced by AlCl₃, while catalase and glutathione reductase activities were increased. Peroxidase and ascorbate peroxidase activities were increased only after prolonged treatment, when toxicity occurred. The results give evidence that Al treatment caused oxidative stress and in turn, it caused lipid peroxidation.

The nature of nucleolar associate bodies in the meristematic cells of the root of Lupinus luteus L. was investigated using immunocytochemical methods, in situ hybridisation with light, confocal, and electron microscopy. The nuclear bodies of lupin proved to be structures containing fibrillarin and coilin, but devoid of rRNA and DNA, like animal coiled bodies (CBs). In lupin cells we have observed the occurrence of small nuclear ribonucleoprotein (snRNP) in the cytoplasm, in nucleoplasm, CBs and in nucleoli. This type of snRNP localisation pattern is in agreement with recently presented models of the small nuclear RNA cycle.

The effect phosphinothricin (PPT), an inhibitor of glutamine synthetase (GS), on proline accumulation in detached rice leaves was investigated. During 12 h incubation, PPT inhibited GS activity and induced accumulation of NH₄ ⁺, and accumulation of proline in the light but not in darkness. Proline accumulation caused by PPT in the light was related to protein hydrolysis, and increase in the contents of precursors of proline, ornithine and arginine. Abscisic acid accumulation was not required for proline accumulation in PPT-treated rice leaves.

Rhododendron shoot regeneration was accomplished using either flower explants (each consisting of ovary with pedicel) of Rhododendron cvs. Nova Zembla and Irina or leaves isolated from in vitro grown Rhododendron catawbiense Michx. Multiple shoot tip clumps were obtained on Anderson's medium containing 0.5 to 1.5 mg dm^-3 thidiazuron (TDZ) in combination with 12 to 15 mg dm^-3 N⁶-[2-isopentenyl]adenine (2iP) and 1 to 3 mg dm^-3 indole-3-butyric acid (IBA). After 16 weeks on the regeneration media, explants with shoot tip clumps were transferred for shoot elongation to Anderson's medium with 3 mg dm^-3 2iP. Two months later, the shoots have reached 5 to 40 mm in length and were fit for subcultivation.

A rice (Oryza sativa L.) homolog of mammalian Rac-GTPase, OsRac1, characterized only in transgenic rice, was proposed to involve in cell death/disease resistance. However, its role in wild-type rice remains uncharacterized and unclear. We examined expression of the OsRac1 mRNA in response to stress signalling components, jasmonic acid (JA), hydrogen peroxide (H₂O₂), and two protein phosphatase inhibitors, cantharidin (CN) and endothall (EN), using rice (cv. Nipponbare) seedlings. The OsRac1 transcript, whose accumulation required certain de novo synthesized protein factor(s), increased in the leaves upon CN/EN and H₂O₂ treatment, but not by JA. Using two pathogenesis-related (PR) protein gene markers, OsPR5 and OsPR10, our results also reveal OsRac1 mRNA accumulates later than that of these two important defense/stress-related OsPR genes.

This study examined the effect of mycorrhizal colonization with Glomus intraradices on physiological parameters and foliar nutrient concentrations in Olea europaea L. subsp. sylvestris and Rhamnus lycioides L. seedlings subjected to well-watered or drought-stressed conditions. Under drought stress, mycorrhizal O. europaea seedlings showed significantly higher photosynthetic and transpiration rates, stomatal conductance and foliar P concentration than its similarly-sized non-mycorrhizal counterpart. The intrinsic water use efficiency (photosynthetic rate to stomatal conductance ratio) was not change in O. europaea and decreased in R. lycioides seedlings due to mycorrhizal colonization under both well-watered and drought-stress conditions.

Effect of environmental conditions on formation of Nicotiana tabacum L. megagametophyte was studied. It was established, that unfavorable temperatures can specifically modify the structure of embryo sacs (ES). At low temperature (9/5 °C), ES with a reduced number of cells or with egg-like synergide(s) can be formed; at high variable (40/25 °C) or constant (37 °C) temperatures, ES with excessive numbers of cells or with synergide-like egg cells arise. Total frequencies of the changed ES patterns varied from 8 up to 35 % per plant and depended on the plant genotype and conditions of exposure.

Leaves from mature in vitro grown plants of Drosera spathulata Labill. regenerated new plantlets on solid induction medium in light. Especially vascular sheath parenchyma cells located close to basal part of tentacule showed high embryogenic potential. Proembryoids arrising from the tentacule base part were visible by scanning electron microscopy. Their surface cells were linked and covered with thin external, fibrilar network representing an extracellular matrix (ECM). Proembryogenic surface cells were later connected by coarse strands of fibrils. Young protoderm was formed arround globular embryoids and its cells were characterized by "brain-like" surface structure. However, the surface of fully developed protodermal cells was practicaly smooth and cells were stick to each other very tightly in torpedo and cotyledonary shaped embryoids. The presence of ECM was typical only for somatic proembryos and globular embryos. The ECM network was never observed on the surface of heart and torpedo shaped embryos.

Changes in contents of pigments, chlorophyll-protein complex, and photosynthetic activities were investigated in field grown apple (Malus pumila Mill.) leaves infected by Apple Proliferation phytoplasma. The contents of chlorophyll a+b (Chl) and carotenoids (Car) markedly decreased in infected leaves. Similar results were also observed for content of total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused a marked inhibition of whole chain and photosystem 2 (PS2) activity. Smaller inhibition of photosystem 1 (PS1) activity was observed even in severely infected leaves. The artificial exogenous electron donors, MnCl₂ diphenyl carbazide, and NH₂OH, did not restore the loss of PS2 activity in both mildly and severely infected leaves. Similar results were obtained by Chl fluorescence measurements. The marked loss of PS2 activity in infected leaves was due to the reduction of contents of chlorophyll and light-harvesting chlorophyll-protein 2 complexes.

Experiments were performed to evaluate the capacity of quince (Cydonia oblonga Mill.) leaves to regenerate somatic embryos and shoots and/or roots simultaneously. Leaves, treated for 2 d in liquid medium containing 2.5 mg dm^-3 2,4-dichlorophenoxyacetic acid were cultured for 0, 3, 6, 9, 12, 15, 18, 21 d on a gelled medium supplemented with 1 mg dm^-3 kinetin (Kin) and 0.1 mg dm^-3 naphthalenacetic acid (NAA) and were transferred to a medium either without growth regulator (GR-) or containing 0.6 mg dm^-3 6-benzylaminopurine (BA) + 0.2 mg dm^-3 gibberellic acid (GA₃) + 0.06 mg dm^-3 indole-3-butyric acid (IBA) (GR+). Leaves producing somatic embryos (SEs) only, or adventitious roots (Rs) only, or SEs+Rs simultaneously, were detected on GR- culture medium; on GR+ medium, leaves producing adventitious shoots (Ss) only, SEs+Ss or SEs+Rs+Ss simultaneously, also appeared. Leaves producing both Ss+Rs were never detected. Proportions among the various types of regenerating leaves varied according to both the length of Kin+NAA treatment and the presence or absence of GR in the transfer medium. The greatest variations, both on GR- and on GR+, took place within the first 9 d of culturing on Kin+NAA. After this period, no further substantial differences in the trend of each type of regenerating leaf were observed. The length of the treatment with Kin+NAA also modified the proportions between the different types of morphogenic structures.

Effects of 4 potentially selective agents for transformed cells, 3 antibiotics [kanamycin, geneticin (G418) and hygromycin] and bialaphos, as well as 2 antibiotics for eliminating Agrobacterium, carbenicillin and cefotaxime on growth and somatic embryogenesis of embryogenic calli of Muscari armeniacum cv. Blue Pearl were evaluated. Callus growth was completely inhibited by 75 mg dm^-3 hygromycin or 4 mg dm^-3 bialaphos, and somatic embryos were never produced on media containing 25 mg dm^-3 hygromycin or 3 mg dm^-3 bialaphos. Kanamycin and G418 less inhibited growth and somatic embryogenesis of the calli. On the contrary, carbenicillin and cefotaxime promoted both callus growth and somatic embryogenesis at all concentrations tested.

The influence of cold storage of cuttings on the transport and metabolism of indole-3-acetic acid (IAA) and the rooting were studied in two carnation (Dianthus caryophyllus L.) cultivars (Oriana and Elsy), which are known to exhibit very distinct rooting characteristics. The percentage of rooting at 11 d after planting increased with the storage period particularly in Oriana, but the values in Elsy were higher than in Oriana. Auxin transport was measured by applying ³H-IAA to stem sections. Irrespective of the section localization, the oldest node (node) or the basal internode (base), the transport increased as the storage period increased from 2 to 12 weeks in Oriana and from 2 to 8 weeks in Elsy cuttings. The auxin transport rate was higher in bases than in nodes and also in Elsy than in Oriana at a given storage period. IAA oxidation and hydrolyzation of IAA conjugates (determined by extracting the sections with acetonitrile and NaOH once the basipetal IAA movement ceased after a 24 h transport period) showed a negative, highly significant correlation with the amount of IAA transported. Although the rooting percentage and IAA transport were higher in Elsy than in Oriana, the differences in rooting between the cultivars could not be explained solely by differences in IAA transport.

Radish (Raphanus sativus L. cv. Redondo Vermelho) seedlings were analysed by light and scanning electron microscopy to characterize the structural changes caused by the exposure to 0.5 or 1.0 mM cadmium chloride for 24, 48 and 72 h. The analyses showed changes in the anatomical and morphological characteristics of roots, stems and leaves of two-week-old seedlings. In all tissues, pressure potential was decreased. Premature death with the disintegration of the epidermis and an increase in the number of root hairs was observed in roots exposed to Cd. The stem of seedlings exposed to Cd exhibited more cells layers in the cambial region. The main effects observed in leaves in response to Cd were stomatal closure, lack of cell wall thickening and alterations in the shape of the chloroplasts. It is suggested that the structural changes observed in seedlings treated with Cd were mainly caused by a Cd-induced decrease in water uptake.

A study of the genetic variability of a population of Hypericum brasiliense was made using several isozyme systems as well as an investigation of the morphogenic potential of apical buds from plants at different development stages (juvenile and adult) using in vitro culture. The results from nine isozymes systems showed low polymorphism in the alleles. Apical buds from juvenile plants originated plantlets with apical dominance and fast growth while those from adults led to the development of flower buds.

The effect of an extended drought (from 1992 to 1995) on water relations was assessed on evergreen oak (Quercus ilex L.) in a dehesa ecosystem (Seville, Southern Spain). Diurnal and seasonal transpiration patterns were analysed at leaf (porometry) and whole-tree level (sap flow), focusing on the relationship between tree transpiration rates (E_t) and potential evapotranspiration rates (PET). Daily maximum E_t varied over the year, becoming higher between May and August, and lower between November and April. Annual E_t (169 - 205 mm y^-1) accounted for less than 40 % of annual rainfall. The prolonged drought did not affect the water relations of the Q. ilex, mainly due to strong stomatal regulation avoiding the loss of water. Stomatal control was found in all seasons, although it was stronger in summer. This behaviour leads to low water consumption and low E_t/PET ratios throughout the year (0.05 to 0.27).