Influence of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and two ethylene inhibitors, silver nitrate (AgNO₃) and cobalt chloride (CoCl₂), on direct somatic embryogenesis were tested in vitro using leaf cultures of Oncidium cv. Gower Ramsey. Leaf cells of tips, adaxial sides and cut ends could directly form somatic embryos on a hormone-free 1/2-strength MS medium. The frequency of embryo-producing explants was 55, 52.5 and 30 %, respectively. The embryo numbers per embryo-producing explant was 20.3. ACC at lower concentrations (5 and 10 μM) significantly retarded direct embryo formation from cut ends. However, higher concentrations of ACC (20 and 50 μM) significantly promoted embryogenic response of leaf tips and adaxial sides. All concentrations of AgNO₃ and CoCl₂ significantly retarded direct embryo formation. The best response was found on 20 μM of ACC, and the frequency of embryo-producing explants were 90, 85 and 35 % on leaf tips, adaxial sides and cut ends, respectively. The embryo numbers per embryo-producing explant was 32.2.

The content of endogenous free abscisic acid (ABA) in the shoots of in vitro cultivated tobacco (Nicotiana tabacum L. cv. White Burley) and its changes during ex vitro acclimation of these plants to the greenhouse or growth chamber were estimated. The content of free ABA significantly increased at the 1^st and/or 2^nd day after plant transfer from in vitro to ex vitro. The ABA content of plants covered with transparent foil to maintain higher relative humidity (RH), did not significantly differ from ABA content of plants cultivated under ambient RH. Transfer to fresh medium also transiently increased the content of endogenous ABA. The ABA content in plants, which had been acclimated for 1 week to ex vitro conditions, decreased to the content found in the in vitro plants. Acclimation to ex vitro conditions affected the stomata on adaxial and abaxial sides differently: stomata on the adaxial side were less open than those on the abaxial one. The exogenous application of 5 μM ABA increased transiently its endogenous concentration in shoots of in vitro plants more than ten fold, but after 1 week the concentration in the shoots decreased.

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.

We studied the effects of a polyhydroxylated spirostanic brassinosteroid analogue (BB-16) on the activities of antioxidant enzymes in rice seedlings grown in vitro in culture medium supplemented with NaCl. Seedlings were grown in medium with 75 mM NaCl and 0.001 or 0.01 mg dm^-3 BB-16 for 16 d or 3-d-old seedlings were exposed for 4 d to 0, 0.001 or 0.01 mg dm^-3 BB-16 then further grown in medium with 75 mM NaCl without BB-16. Seedlings exposed to 0.01 mg dm^-3 BB-16 for 16 d showed significant increase in the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) and a slight increase in ascorbate peroxidase (APX). On the other hand, 4-d exposure to BB-16 only increased SOD and CAT activities at concentration 0.001 mg dm^-3. GR activity was not altered by this BB-16 treatment. These results indicated that BB-16, which is structurally modified in the lateral chain in relation to natural brassinosteroids, changes the activity of key antioxidant enzymes, which might confer tolerance to saline stress.

Flowers of Chrysanthemum morifolium Ramat cv. Lalima were greyed red and florets were flat spoon shaped. Ray florets after inoculation on the Murashige and Skoog's medium supplemented with 1.07 μM α-naphthaleneacetic acid and 8.87 μM benzyladenine were irradiated with γ-radiation (0.5 Gy and 1 Gy). All the regenerated shoots either from control or from γ-irradiated florets were isolated, rooted and transplanted in the field after hardening. Two mutants were obtained in the γ-irradiated plants (0.5 Gy). Both the mutants were yellow coloured but one having flat spoon shaped ray florets similar to the original cultivar, while the other having tubular florets. Both the mutants were propagated vegetatively and have produced true-to-type flowers.

This study was conducted to determine effects of nitrogen supply (75 and 150 kg(N) ha^-1) and CO₂ enrichment on partitioning of macro and micro nutrients in wheat (Triticum aestivum L. cv. HD-2285). Plants were grown from seedling emergence to maturity inside open top chambers under ambient CO₂ (CA, 350 ± 50 μmol mol^-1) and elevated CO₂ (CE, 600 ± 50 μmol mol^-1). Leaves, stems and roots of the same physiological age were analyzed for carbon, nitrogen, calcium, copper, iron, zinc and manganese content at 40, 60 and 90 d after germination. C, Cu, Mn and Zn content was higher in the stem, leaves and roots on dry mass basis under CE than CA. However, N and Fe contents decreased in CE grown plants. Ca content was unaffected due to CE and variable N supplies.

Immature zygotic embryos were cultured on Murashige and Skoog's medium (MS) supplemented with various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA), benzyladenine (BA) and zeatin or with various concentrations of 2,4-D alone. The maximum number (8 per embryo) of adventitious buds formed from cotyledons of heart stage embryos cultured on MS medium with 1 mg dm^-3 BA and 0.01 mg dm^-3 NAA. The adventitious buds originated from procambial strands of immature embryo cotyledons and then developed into adventitious bud primordia within 20 d. Adventitious buds transferred to hormone free MS medium grew into shoots, but did not produce plantlets because the shoots failed to root.

Changes in the cytosotic (soluble) and the non-cytosolic (particulate) isozyme composition of hexokinases and in their properties were studied by ion exchange chromatography on DEAE cellulose after the subcellular fractionation both in the healthy and the tobacco mosaic virus (TMV) infected tobacco leaves. Three main isozyme complexes were obtained: one particulate fraction (the particulate hexokinase phosphorylating both glucose and fructose, EC 2.7.1.1), and two soluble fractions (the soluble hexokinase phosphorylating both the glucose and the fructose, and the soluble fructokinase, which phosphorylates primarily fructose, EC 2.7.1.4). The total fructokinase activities were nearly twice higher than the total glucokinase activities (188.6 % of glucokinase activity in healthy plants and 181.3 % in infected plants). The total particulate glucokinase activity was increased to 120.6 % and the fructokinase to 118.9 % in TMV infected tissue when compared with healthy control. The similar pattern of activity was observed for soluble hexokinase isozymes - the sum of soluble glucokinase activity was increased to 175.4 % and of fructokinase activity to 131.2 % in TMV infected tissue. The isozymes isolated both from the healthy control and TMV-infected leaves had the similar elution profiles, displayed Michaelis-Menten kinetics, showed the identical profiles of pH optima and were Mg²⁺ dependent with the highest enzyme activity at equimolar Mg²⁺ and ATP concentration.

Farnesyl diphosphatase (FDPase; EC 3.1.7.1) produces farnesol from farnesyl diphosphate (FDP) in a reaction that does not require Mg²⁺. This report shows that FDPase is constitutively expressed at a high level in the soluble and the microsomal fractions of Datura stramonium. Soluble and microsomal FDPase have a similar pH optimum (5.0 - 6.0) and a similar substrate specificity. Geranyl diphosphate (GDP) and geranylgeranyl diphosphate (GGDP) compete for FDP, but isopentenyl diphosphate (IDP), ATP, and para-nitrophenyl phosphate do not. Soluble FDPase activity was highest in fruit and flower followed by root, and leaf.

Barley (Hordeum vulgare L. cv. Alfa) seedlings were treated for 4 d before UV-B irradiation with 0.05 mM proline or 150 mM NaCl. UV-B exposure induced synthesis of yellow coloured compounds with maximum absorbance at 438 nm. The content of these compounds was increased in proline-treated and decreased in NaCl-treated plants. UV-B radiation reduced chlorophyll/carotenoids ratio, oxygen evolution rate and photochemical efficiency of PS 2 as estimated by chlorophyll fluorescence and increased proline accumulation, H₂O₂ generation and lipid peroxidation. Exogenous proline had no effect on the parameters studied and did not change the response of plants to UV-B radiation. NaCl inhibited photochemical efficiency of PS 2, reduced oxygen evolution and increased H₂O₂ concentration and lipid peroxidation. The combination of NaCl and proline treatment led to lowering the inhibitory effect of NaCl in non UV-B irradiated seedlings. There was not relationship between the level of UV-B-induced compounds and UV-B tolerance of barley seedlings.

Substitution of wheat (Triticum aestivum L.) chromosomes 7A, 1D, 3A, 3B, 3D, 4A and 4D of cultivar Cappelle Desprez by their homologues of cultivar Bezostaya-1 increased the seedling tolerance to high concentrations of copper (1 μM CuSO_4⋅ 5 H₂O). Substitution of chromosome 1A had negative effects on seedling tolerance.

Five different methods for measuring transpiration, which include gravimetric analysis (control), heat pulse velocity (HPV), time domain reflectometry (TDR), single leaf and whole plant infrared gas-exchange measurements, have been tested on two cultivars (Redcort and Empire) of young apple trees (Malus communis L.). The objective was to compare these methods and establish the most affordable one to be used in greenhouse conditions in order to determine and/or estimate the amount of water for an efficient irrigation management. Results obtained with TDR were particularly accurate and not statistically different with respect to the control (-4.2 %) and this was supported by the correlation coefficient (r = 0.94) found. The HPV method was sufficiently accurate and reliable for small stems, however, in our conditions this method generally underestimated the transpiration (-32.4 %). Single leaf and particularly whole plant infrared gas-exchange measurements suffered an overestimation of the transpiration with respect to the control.

Volatile essential oils from Prinsepia utilis L. have been shown to inhibit stomatal opening in Vicia faba L. epidermal peels as well as whole leaves as shown by measurement of pore width and stomatal conductance (g_s). The stomatal closure was associated with inhibition of K⁺ influx in the guard cells. Gas chromatography/mass spectroscopy analysis of the steam distillate from P. utilis L. leaves showed the presence of over twenty compounds; of which thirteen compounds have been identified.

Induction of both somatic embryogenesis and organogenesis in presence of thidiazuron is reported in peanut tissues. However the histological evidence of thidiazuron induced somatic embryogenesis was unclear. Thidiazuron triggered multiple shoot differentiation in the plumule of the embryos. Keeping in view the ability of thidiazuron to induce both organogenesis and embryogenesis in peanut tissues, experiments were conducted to define the pathway of morphogenesis in the plumule of rooted somatic embryos. On exposure to thidiazuron, projections appeared from the plumule. These projections closely resemble the somatic embryos. However histological examination revealed that these are caulogenic buds and not somatic embryos. In concurrence with the earlier reports on thidiazuron induced organogenesis it is concluded that this growth regulator induces organogenic response in peanut tissues.

The present investigation has been performed to evaluate nitrate reductase (NR) and nitrogenase activities as well as growth and mineral nutrition of wheat plants grown under drought stress and inoculated with different Azospirillum strains (NR^- and NR⁺). Fresh, dry mass and water content decreased with decreasing soil moisture content, which was accompanied with low soluble sugars and soluble protein content and increase in the total amino acids content. Azospirillum inoculation with either bacterial strain (NR^- and NR⁺) significantly increased the above characteristics even at 40 % moisture content. NR activity decreased in both the shoots and roots by decreasing soil moisture content. NR⁺ strain exhibited increased root NR activity compared with uninoculated plants or inoculated with NR^- strain. However, plants inoculated with NR^-strain increased NR activity in the shoot more than in the root of the same plant and in the shoot of control plants. Inoculation with either NR^- and NR⁺ Azospirillum strains gave higher nitrogenase activity than uninoculated control plants. The low N supply (0.5 mM) did not affect nitrogenase activity. NR^-strain was less effective than NR⁺strain in promoting total N-yield, spike numbers and their mass per pot. Azospirillum inoculation exhibited no significant changes in wheat Mg²⁺ content. However, K⁺ and Ca²⁺ have shown significantly increased values. Azospirillum beneficial effect on plant N balance and growth are most probably composed of multiple mechanisms and beneficial NR is one of them. The importance of Azospirillum NR⁺strains for increasing wheat resistance to water stress is also supported by the obtained data.

Multiple shoots were initiated from nodal and shoot tip explants collected from mature trees of Morus alba L. cultivars Chinese White, Kokuso-27 and Ichinose, and M. multicaulis Perr. cultivars Goshoerami and Rokokuyaso after 2 weeks of culture. Nodal explants were more responsive than shoot tip explants. Murashige and Skoog basal medium was found to be most suitable medium and 6-benzylaminopurine was the most effective cytokinin for shoot induction. Explants collected between April and September evoked better response than the explants collected between October and March. Shoots were multiplied by transferring nodal explants excised from in vitro raised shoots onto a medium containing cytokinins. Sucrose was the most suitable carbon source examined for shoot multiplication. An increase in shoot multiplication rate was noticed upto 4 - 5 subcultures. Nodal explants rooted on an auxin-supplemented medium. The acclimatized plants were successfully transplanted in the field.

Influence of various saline media on Chlorella fusca growth, contents of photosynthetic pigments, and activity of the nitrate reductase (NRA) was determined. KCl, CaCl₂, and MgCl₂ in concentrations relative to NaCl as 1:1, 2:1, and 3:1 promote cell number, dry mass, and contents of photosynthetic pigments. The activity of NR was enhanced by Mg²⁺ and K⁺ and in some cases by Ca²⁺ at all ratios applied.

The possibility was examined whether the pool of sequence variants of HLVd which accumulated as progeny of "thermomutants" induced upon heat-treatment of hop could initiate infection of non-host solanaceous plants. It was found that HLVd microevolution led to the appearance of HLVd population in tomato. This viroid population was maintained at levels detectable by molecular hybridisation, showing the highest concentration in apical leaves. HLVd was further transferred from tomato to Nicotiana benthamiana, where distinct HLVd sequence variants appeared and were stably maintained at low levels. Our results show that replication of HLVd under heat stress resulted in the production of viroid quasispecies, potentially important for viroid evolution in so-called non host plants.

The modified nucleotide content of the ribosomal RNAs in wheat is greatly influenced by light. The rRNAs of etiolated seedlings contain far fewer modified derivatives. The modified nucleotide composition characteristic of green plants develops gradually as a result of irradiation. In the course of the experiments changes in the state of modification of 5.8S and 18S rRNAs were examined during the greening of etiolated wheat seedlings. Three types of minor nucleotides, O^2'-methyladenosine, O^2'-methylguanosine and pseudouridine were found in the 5.8S rRNA of green wheat leaves, none of which was detected in etiolated wheat. The minor nucleotides appeared in the 5.8S rRNA only after 48 h irradiation. The sequences of 5.8S rDNA, TTS1, ITS2 and 18S rDNA were also determined and the presence of the hyper-modified nucleotide 1-methyl-3-(α-amino-α-carboxypropyl)-pseudouridine was detected in green wheat 18S rRNA. This minor component was not demonstrable in etiolated wheat 18S rRNA, but appeared after irradiation for 48 h.

Black plum (Syzygium cuminii) explants were grown in vitro on Murashige and Skoog medium. Among the various saccharides tested, the best caulogenic response was afforded by sucrose both in terms of explant response and shoot developing potential. Within monosaccharides, mannose was totally inhibitory as on the medium supplemented with this the shoot buds failed to develop, while, fructose and xylose completely inhibited the opening as well as the elongation of shoot buds. Glucose and galactose did not completely inhibit the caulogenic response. Among disaccharides, other than sucrose, maltose totally inhibited the elongation of the developed shoot buds while lactose supported it to a limited extent. Sugar alcohols, though not as good as sucrose, proved better sources of carbon and energy than the other tested sugars. Sucrose at concentration 4 % proved to be the best in developing 4.2 shoots per explant.

Potted tomato plants (Lycopersicon esculentum Mill. cv. Amalia) were submitted to three different treatments: control (C) plants were maintained at day/night temperature of 25/18 °C; preconditioned plants (PS) were submitted to two consecutive periods of 4 d each, of 30/23 and 35/28 °C before being exposed to a heat stress (40/33 °C lasting 4 d) and non-preconditioned (S) plants were maintained in the same conditions as the C plants and exposed to the heat stress. The inhibition of plant growth was observed only in PS plants. Heat stress decreased chlorophyll content, net photosynthetic rate and stomatal conductance in both PS and S plants. However, PS plants showed good osmotic adjustment, which enabled them to maintain leaf pressure potential higher than in S plants. Furthermore, at the end of the recovery period PS plants had higher pressure potential and stomatal conductance than in S plants.

In a fructose-containing medium in which rye root-microsomal membrane vesicles had reached the equilibrium of uptake of fructose, the presence of both Mg²⁺ and ATP caused the efflux of fructose from the vesicles. Among nucleotides examined, ATP caused the largest efflux of fructose. The efflux of fructose dependent on Mg²⁺ and ATP was quite insensitive to a protonophore, carbonylcyanide m-chlorophenylhydrazone (CCCP), which actually abolished MgATP-dependent proton accumulation in the vesicles, while it was largely inhibited by vanadate, which inhibits ATP-binding cassette transporters (ABCTs). The Michaelis-Menten constant (Km) of the efflux of fructose was 0.4 mM. It was observed that fructose stimulated the ATPase activity of the vesicles and that vanadate markedly decreased the fructose-stimulated ATPase activity.

To examine the ion accumulation and membrane lipid metabolism in response to salinity we compared two tomato cvs. Pera and Hellfrucht Fruhstamm (HF), considered to be salt-tolerant and sensitive respectively. Na⁺ and K⁺ accumulation was significantly higher in roots of cv. Pera after 24 h and 72 h of 100 mM NaCl. While in cv. HF, a temporary increase in K⁺ accumulation at 24 h was accompanied by a sustained increase in Na⁺ content. Both cultivars enhanced incorporation of [³²P]orthophosphate into phosphatidylinositol 4,5-bisphosphate at 24 h and 72 h of NaCl. In parallel to the increase of phosphatidylinositol 4,5-bisphosphate a decrease in phosphorylation of phosphatidic acid and phosphatidylcholine were observed in the sensitive cv. HF. Structural and signal lipid changes in response to salinity were more evident in the sensitive cv. HF. Salt tolerant cv. Pera accumulated Na⁺ ions in the roots without considerable modifications in lipid metabolism.

Five cultivars of Plantago ovata Forsk. (medicinal plant) have been developed by different agricultural universities in India. Genetic variability of these cultivars was estimated using RAPD markers. The data were correlated to morphological characters and a dendrogram was obtained from Jaccard's coefficient.

An effort has been made to assess the role of reactive oxygen species in germination and subsequent growth of Amaranthus lividus under elevated temperature. Transfer of A. lividus seeds from 25 to 45 °C for 4, 8 and 12 h, during early imbibitional period reduced percentage of germination, relative germination performance, relative growth index and seedling length. Heat shock during early germination decreased also the activities of free radical scavenging enzymes like catalase, peroxidase and superoxide dismutase, increased the accumulation of superoxide, hydrogen peroxide and induced lipoxygenase mediated membrane lipid peroxidation. Membrane injury index and relative leakage ratio revealed a rise with concomitant reduction in membrane protein thiol content in heat shock raised seedlings. The results indicate that heat shock in A. lividus seeds induced an excessive generation of ROS and led to an oxidative membrane damage, causing early growth impairment.

Here we studied whether early development of Silene latifolia is accompanied with changes in acetylation of nucleosomal histones H4. Using acid-urea-triton polyacrylamide gel and immunoblotting with specific antisera the histone acetylation in relationship with transcriptional activity, measured by [¹⁴C]-uridine incorporation, was analysed in dry and germinating seeds, seedlings, and adult leaves. We show that quiescent and germinating seeds, until the root tip is released from testa, are characterised by an absence of transcriptional activity and by a low H4 acetylation level: only mono-acetylated isoforms were present. During the postgermination period and early plantlet development, a high increase of transcriptional activity started and a sharp H4 hyperacetylation, up to the penta-acetylated isoform, was detected. We conclude that epigenetic modification by nucleosomal histone deacetylation plays a role in maintenance of global genome silencing in quiescent seeds.

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.