Two forage grasses, timothy (Phleum pratense L.) and ryegrass (Lolium multiflorum Lam.) were exposed to flooding, and activities of alcohol dehydrogenase (ADH) and their isozyme profiles were determined. The flooding stress increased ADH activities in both species. This increase was 2-times greater in timothy than in ryegrass. Only one ADH isozyme was found in non-flooded seedlings of both species, whereas two and four bands were identified in ryegrass and timothy seedlings, respectively, under flooding stress.

The aim of this work was to evaluate how the Falling Number (FN) in introgressive triticale lines is influenced by introduced Triticum monococcum genes responsive for mature spikes sprouting resistance (SR). These lines were developed in two independent series (A and B) by incorporating of diploid wheat (T. monococcum) genes in two different strains of hexaploid triticale (LT 176/10 and LT 522/6) using the synthetic allotetraploid T. monococcum/Secale cereale (A^mA^mRR) as a bridging form. In three consecutive vegetation seasons the mature spikes response to artificial wetting was tested to assess SR. FN was evaluated in full milling of seeds to characterize the level of starch-protein matrix damage in 57 introgressive triticale lines. The obtained results showed twofold higher coefficients of variation of the SR than FN. SR-FN correlation was generally significant in a B-series of lines and statistically insignificant in an A-series showing dependence on the triticale recipient parent and year. In opposite to SR, in both series there was not a line having FN comparable with that of diploid wheat parent. This demonstrates that genetic background of the FN is more complicated in relation to inheritance of SR.

Eight cultivars/lines of Gossypium hirsutum (CIM-443, CIM-448, CIM-1100, FH-634, S-111, S-113, Cedix, and LRA 5166) resistant to cotton leaf curl virus (CLCuV), one moderately-resistant (cv. NIAB-Krishma), and one susceptible (cv. S-12) were used. All the resistant lines remained free of all disease symptoms, whereas in moderately-resistant and susceptible cvs. leaf curling and vein thickening occurred. Cultivars with varying degree of CLCuV-resistance had different pattern of accumulation of macronutrients. Leaf N content was lowest in S-12, but increased considerably due to disease. Leaf K and Ca contents of S-12 were lower in the diseased leaves than in healthy ones. Chlorophyll a and b contents were highest in lines S-111, S-113 and S-12. A marked reduction in chlorophyll b content was observed in the diseased leaves of S-12. Leaf water potential in S-12 and NIAB-Krishma was also decreased due to disease. The most distinctive characteristic to differentiate between lines was epicuticular wax content, since all the resistant lines had considerably higher wax content on their leaf surfaces than the moderately-resistant or susceptible cultivars.

The influence of potassium sulfate, abscisic acid (ABA) and indole-3-acetic acid (IAA) solutions on xylem exudation rate and potassium efflux from the apical cut end of root tips of intact maize (Zea mays L. cv. Dnepropetrovskaya) seedlings was studied. Foliar application of 5 mM K₂SO₄ considerably stimulated the exudation rate. The application of ABA and IAA (1 mM) also induced a high rate of xylem exudation, K⁺ efflux being simultaneously increased.

In Solanum nigrum, the initiation of root primordia occurred directly on stem explants or microshoots cultured on half strength MS medium supplemented with 1 mg dm^-3 indolebutyric acid (IBA), indole-3-acetic acid, or naphthalene acetic acid, IBA being most effective. Initiation of shoot primordia occurred on B5 medium supplemented with 0.5 mg dm^-3 benzylaminopurine (BAP) or kinetin; BAP was more active. During shoot formation, the increased content and the expression of new isoenzymes of peroxidase (POX), esterase and malate dehydrogenase was found. On the other side, expression of new indophenol peroxidase isoenzyme was detected during root formation. Organogenesis of S. nigrum has no effect on glutamate oxaloacetate transaminase and glutamate dehydrogenase content. Differential expression of POX could be detected between basal and upper side of explants.

Activities of host ribonucleases and glucose-6-phosphate dehydrogenase were studied in three cultivars (Monosvalof, Steffi and Rimini) of sugar beet differing in their resistance to beet necrotic yellow vein virus (BNYVV). No differences were found in the susceptibility of cultivars to BNYVV between mechanically inoculated and Polymyxa betae (a natural fungal vector of the virus) infected plants, but the culmination of reproduction curves of BNYVV in mechanically inoculated plants was observed one week earlier than in plants inoculated by means of P. betae. The activities of ribonucleases corresponded with virus multiplication. In roots, activities of ribonucleases reached a maximum at day 7; in leaves, maximum activity was found at day 21 in cv. Monosvalof, and at day 14 in cv. Steffi. The relatively resistant cultivar Rimini showed much lower activities. The activity of glucose-6-phosphate dehydrogenase was only slightly increased at the time of culmination of the BNYVV reproduction curve in cvs. Monosvalof and Steffi.

A reliable protocol for plant regeneration from mature embryo derived calli of nine barley (Hordeum vulgare) cultivars has been developed. The auxins 2,4-dichlorophenoxyacetic acid, picloram and dicamba proved effective in inducing callus from mature embryos of most of the barley cultivars. The induced primary callus was loose, friable and translucent. It ultimately yielded creamy white and compact callus after 2 - 3 transfers on fresh medium of the same composition. Callus induction and regeneration capacity were highly cultivar dependent. Addition of a high concentration of picloram (4 mg dm^-3) promoted regeneration in 3 cultivars (Tallon, Grimmett and Sloop). In cv. Arapiles, abscisic acid and betaine were crucial in generating morphogenic callus from the mature embryos. Plants regenerated from these calli were hardy and developed roots readily when transferred to hormone free medium.

Sunflower (Helianthus annuus L.) seeds were germinated and grown in the presence of 50, 100 and 200 µM CdCl₂. The lower concentration (50 µM) of Cd² ions produced slight decrease in reduced glutathione (GSH) content and overall increase (except superoxide dismutase) in antioxidant enzyme activities, and in H₂O₂ concentration. Chlorophyll content, lipid peroxidation and protein oxidation were not affected under 50 µM CdCl₂. GSH content was diminished under 100 and 200 µM CdCl₂, and except for superoxide dismutase, which activity remained unaltered, overall decreases in the antioxidant enzyme activities (catalase, ascorbate peroxidase, dehydroascorbate peroxidase, glutathione reductase) and in guaiacol peroxidase were observed. These Cd² concentrations caused a decrease in chlorophyll content as well as an increase in lipid peroxidation, protein oxidation and H₂O₂ concentration. All the observed effects were more evident with the highest concentration of cadmium chloride used.

The shoot apices of ten groundnut interspecific hybrids, showing peanut stripe virus symptoms were used as explants. Murashige and Skoog (MS) medium containing 1 mg dm^-3 each of naphthaleneacetic acid (NAA) and benzylaminopurine (BAP) supported maximum callusing of the hybrids J 11 × Arachis sp. PI 30008 as well as J 11 × A. sp. Manfredi # 5 (86.3 and 82.6 %, respectively). On MS medium with 3.5 mg dm^-3 NAA and 0.2 mg dm^-3 BAP, the meristems of J 11 × A. stenosperma as well as J 11 × A. otavioi gave good response (79.7 and 77.2 %). The regeneration frequencies ranged from 16.7 to 76.9 % and was more than 30 % in all hybrids except for J 11 × PI 30085. Shoots (5 cm) regenerated from the virus-free (ELISA tested) calli rooted well (60 - 80 %) on MS basal medium supplemented with 0.4 % activated charcoal and 200 mg dm^-3 casein hydrolysate. In addition, long shoots which failed to produce roots, when transferred to soil during rainy season and protected from direct sun got established.

Contents and functioning of photosynthetic pigments and gas exchange of Nicotiana tabacum L. leaves were studied in platlets cultivated in vitro under different CO₂ supply. The plantlets were grown for six weeks either in glass vessels tightly closed with aluminium foil (G-plants) or in polycarbonate Magenta GA-7 vessels covered with closures with microporous vents (M-plants). M-plants (better supplied with CO₂) had higher contents of chlorophyll (Chl) a. Chl b. and β-carotene, higher photochemical activities of photosystem 2 and whole electron transport chain, and lower contents of xanthophyll cycle pigments. Differences in Chl a fluorescence kinetic parameters between G-plants and M-plants were not statistically significant. M-plants had higher net photosynthetic rate, and lower transpiration rate and stomatal conductance than G-plants.

Diurnal patterns of CO₂ exchange and fluctuations of tissue malic acid concentrations were investigated in the resurrection angiosperm Haberlea rhodopensis Friv. grown under irradiances of 30 or 300 μmol(photon) m^-2 s^-1 at transition from biosis to anabiosis and vice versa. Different degree of CAM-cycling were exhibited under well-watered conditions and extreme desiccation under both irradiances. The CAM-cycling was proved as efficient mechanism of saving water.

The increase in water use efficiency (the ratio of photosynthetic to transpiration rates) is likely to be the commonest positive effect of long-term elevation in CO₂ concentration (CE). This may not necessarily lead to decrease in long-term water use owing to increased leaf area. However, some plant species seem to cope better with drought stress under CE, because increased production of photosynthates might enhance osmotic adjustment and decreased stomatal conductance and transpiration rate under CE enable plants to maintain a higher leaf water potential during drought. In addition, at the same stomatal conductance, internal CO₂ concentration might be higher under CE which results in higher photosynthetic rate. Therefore plants under CE of the future atmosphere will probably survive eventual higher drought stress and some species may even be able to extend their biotope into less favourable sites.

The effect of 50 to 200 mM NaCl on two lines (CP with solid stem and CV with hollow stem) of ×Haynaldoticum sardoum was studied. NaCl significantly reduced root and shoot fresh and dry masses, root length and less markedly shoot length of CP and CV plants. The sodium accumulated in the leaves in relation to the concentration of NaCl and length of the treatment; CP leaves contained twice as much sodium as CV leaves. The leaf chlorophyll a/b ratio was not affected by NaCl. NaCl decreased the leaf water and osmotic potentials. The pressure potential increased due to the increased concentration of dissolved solutes in the leaf, particularly sodium. The proteinase and exopeptidase activities increased during NaCl treatment.

Matured somatic embryos of different embryogenic cell lines of Picea abies formed as a response to abscisic acid and polyethylene glycol were categorised into three main groups: well-developed, less-developed and undeveloped type. Only the well-developed embryos were able to convert into normal plants. They were positively influenced by prolonged proliferation up to 4 months in contrast to the less-developed ones. Seed extract positively affected both well-developed and less-developed embryos, but only in the beginning of tested period. Intermediate cell lines after a peak of acquisition of maximum maturation competence decrease the maturation frequency with prolonged culture.

The changes in the autofluorescence spectra of intact Philadelphus grandiflorus, Epiphyllum hybridum, and Plantago major pollen have been observed with microspectrofluorometric method after 100-h exposure to ozone (3 h per day for 5 d per week in total dose 5.0 cm³ m^-3). The fluorescence maximum at 530 - 550 nm disappeared in carotenoid-containing pollen of Philadelphus grandiflorus and Epiphyllum hybridum and new maximum at 475 - 480 nm arose that correlated with lipofuscin-like substances observed in the extracts from the pollen grains. The carotenoid-less pollen of Plantago major showed only the increase of the maximum at 470 nm, and no lipofuscin in the extracts. It is supposed that main indicator of the pollen damage by ozone in carotenoid-containing microspores are the lipofuscin-like compounds.

The activities of enzymes involved in ammonia metabolism ferredoxin-dependent glutamate synthase (Fd-GOGAT), glutamine synthetase (GS) and glutamate dehydrogenase (GDH), the rates of photosynthetic oxygen evolution, dark respiration, and the activity of RuBP carboxylase (RuBPC) were determined in alfalfa (Medicago sativa L.) leaves taken from the apex (apical leaves), from the second to the fourth internode (mature leaves) and from the bottom of the canopy (basal leaves). Photosynthetic rate and the activities of RuBPC, GS and Fd-GOGAT showed their maximum in the mature leaves. The respiration rate together with amino acid and ammonium contents decreased with leaf age, whereas the opposite was true for GDH activity. Basal leaves still maintained substantial levels of chlorophylls, GS and Fd-GOGAT activities and oxygen evolution rate, thus suggesting that photosynthesis has some role in the reassimilation of the nitrogen liberated during protein degradation.

Spirodela polyrhiza L. Schleid. plants developed anthocyanin (AC) on the abaxial frond surface when grown on Hoagland nutrient solution diluted 1:≥40; AC content was maximum at 1:80 dilution. Till 1:20 dilution there was no or very little AC formation. The formation of AC seems to rely on the availability of excess carbon skeleton in relation to nitrogen in plants. Thus, addition of saccharose to 1:20 diluted medium resulted in a concentration-dependent AC formation. Also fructose, glucose, mannitol, and sorbitol induced AC synthesis. Conversely, urea and ammonium nitrate, when added to the 1:80 diluted medium, suppressed the AC formation. Omission of micronutrients from the growth medium led to the formation of a little amount of AC whereas polyethylene glycol and Cd treatments were ineffective. AC produced under starvation (7 d on distilled water) did not get turned over upon the transfer of plants to nutrient sufficient (1:5 diluted medium) conditions indicating that AC formed does not serve as a reversible C-reserve.

Gemma morphology, histology and ultrastructure before and after germination in vitro were studied in Drosera pygmaea. The histology of the gemma is similar to that of a seed, being characterized by an embryo-like structure and storage tissue, although no seed coat is formed. One embryo-like structure within the gemma, which gives origin to a new plant, expresses polar organisation with distinct meristematic regions. Storage tissue surrounding the embryo-like structure resembles endosperm and it is built of parenchyma cells possessing plastids with starch grains and dense material within vacuoles. The regeneration from the gemma may provide useful system to study plant morphogenesis under stress conditions including in vitro culture.

Expression of esterase isoenzymes in 1272 seeds was used to estimate hybridity of Lycopersicon esculentum Mill. Individual seeds (440) of the parental cultivars taken from different experimental stations in Bulgaria were also analysed. The banding patterns were obtained by means of vertical block electrophoresis in polyacrylamide gels. It was established that quantitative variation of locus Est-1 can be applied to prove hybridity of F₁ tomato seeds. This marker is related to the genetic nature of tomatoes and is not the result of the environmental influence. The reason for this conclusion is the fact that the isoenzymes of the Est-1 locus are indicative for hybridity determination of all examined seeds taken from different regions in Bulgaria. Use of this locus is to be recommended for both its universality and the fact that the reagents for esterase isoenzymes staining are not expensive.