The effects of 4 or 8 drought cycles on four grass species,Cenchrus pennisetiformis, Leptochloa fusca, Panicum turgidum, andPennisetum divisum were assessed in a pot experiment. There were significant differences between the species in biomass production under water stress.C. pennisetiformis andP. turgidum produced significantly greater fresh and dry matter thanP. divisum and especially thanL. fusca. L. fusca had the lowest andP. divisum highest osmotic potentials compared with the other species after the completion of 4 or 8 drought cycles. Osmotic adjustment (difference between osmotic potential of droughted/rehydrated plants and control plants) was highest inL. fusca. The stomatal conductance was significantly decreased with increased drought stress inC. pennisetiformis. The elasticity ofC. pennisetiformis, P. turgidum andP. divisum increased with increase in number of drought cycles, whereas that ofL. fusca remained unchanged.L. fusca andP. turgidum had the lowest leaf hydration of all species after 8 drought cycles. The chlorophyllsa andb in all species remained unaffected by drought treatments. The proline content ofC. pennisetiformis andL. fusca increased significantly with increased drought stress, whereas that ofP. turgidum remained unaffected after 4 or 8 drought cycles.L. fusca synthesized great amount of leaf soluble proteins during 8 drought cycles, whereasP. divisum had low protein content after 4 drought cycles. The protein contents ofC. pennisetiformis andP. turgidum remained unaffected after 8 drought cycles. The leaf epicuticular wax ofL. fusca increased consistently with increased drought stress, but leaf wax ofP. divisum increased only at the highest drought stress and that ofC. pennisetiformis andP. turgidum increased after 4 drought cycles. On the basis of these results it was established thatC. pennisetiformis andP. turgidum were the most tolerant,P. divisum intermediate, andL. fusca the most sensitive to drought stress. The osmotic adjustment did not positively correlate with the degree of drought resistance.

Limitations on photosynthesis, characterized by leaf CO₂ exchange, chlorophyll fluorescence, and thylakoid structure, were studied under environmental conditions simulating culturein vitro. These were simulated by growingPhaseolus vulgaris plants in nutrient solution under high relative humidity of air (>90%), and CO₂ concentrations (c_a) that decreased with the development of photosynthetic activities during plant ontogeny (1200 to 300 mg m^-3). The ontogeny of such model plants was more rapid, primary leaves reached photosynthetic maturity 2 to 3 d earlier and their life span was 7 to 14 d shorter than in control plants. Their photosynthetic activityin situ was limited, after reaching "photosynthetic maturity", similarly to plants grownin vitro. When measured under optimal conditions, however, 50 to 70% higher net photosynthetic rates (P_N) were found in leaves of different ages as compared with plants grown under c_a of 700 mg m^-3 and a lower air humidity (30-35%). This increase in P_N was associated with a high conductance for CO₂ transfer by adaxial and abaxial epidermes. In model plants, the dark respiration rate (R_D) was almost twice that in the control, while the photorespiration rates were similar to controls; CO₂ compensation concentration was about 50% of that in controls. The ratios P_N/R_D were similar in control and in model plants. Chlorophylla+b content in leaves of the model plants was lower than that in the control plants. Grana extent increased with plant age in the model plants while it decreased in the control ones. In both the stromal and granal membranes of the chloroplasts in model plants, a marked accumulation of carotenoids occurred independent of age. The ratio of variable to maximal fluorescence, F_v/F_m, did not differ in the model and the control plants. In the control plants, photochemical quenching (q_P) slightly increased with plant age and was not affected by CO₂ concentration present during measurement. In the model plants, q_P increased with elevated CO₂ concentration in young plants and decreased in saturating CO₂ concentrations in older plants. Nonphotochemical quenching (q_NP) was lower in the model plants and increased under CO₂ saturating conditions. Vitality index, Rfd, was markedly lower in the model plants than in the control ones and a decline was found in saturating CO₂ concentration.

The influence of increasing copper concentrations on seed germination, seedling survival and radicle length ofMinuartia hirsuta, Silene compacta, Alyssum montanum andThlaspi ochroleucum was studied. Seed germination was highly affected by the higher Cu²⁺ concentrations (80 and 160 μM), while lower Cu²⁺ concentrations seemed to be necessary for seed germination, even for the plants originated from non-Cu²⁺-rich soils (i.e. A. montanum). Nevertheless, plants originated from Cu²⁺-rich soils (M. hirsuta, S. compacta) showed a higher demand of Cu²⁺ for rapid seed germination. Cu²⁺ at higher concentrations severely reduced growth rate of radicle, especially inA. montanum andT. ochroleucum. These data clearly indicate the reduced suitability of the above mentioned plant species for reclamation on Cu²⁺ soils. Lower Cu²⁺-concentrations had no influence on seedling survival inM. hirsuta andS. compacta, but a progressive reduction of a number of survived seedlings with increasing Cu²⁺ concentration was found, that was more pronounced inA. montanum andT. ochroleucum.

Changes in growth and phosphorus content in plants and seeds of fenugreek with increasing cadmium concentration was evaluated. Root length and shoot length ranged from 11.63 to 27.72 and from 9.70 to 54.78 cm, respectively. With the increasing Cd²⁺ concentration there was a significant decrease in root and shoot length, and fresh mass. Various phosphorus fractions of shoot decreased with increasing Cd²⁺ concentration except lipid P and nucleic acid P which increased at 65 and 95 d after sowing and protein P only increased at vegetative stage. In seeds (60 d after flowering) lipid P increased except at 2.5 μg(Cd²⁺) g^-1 (soil) while protein P decreased.

The effects of NaCl and polyethylene glycol (PEG) on superoxide dismutase (SOD) and peroxidase (P) activities, lipid peroxidation (LP) and proline content in seeds and leaves of drought tolerant (FC-506 and MS-100) and drought sensitive (MS-612 and MS-13) sugar beet cultivars were examined. After PEG and NaCl treatment in tolerant cultivars both in seeds and leaves SOD activity mainly increased, though P activity increased only in leaves of tolerant cultivars. In drought sensitive cultivars the decrease of SOD and P activity was mostly observed. LP increased in seeds and leaves of all examined cultivars. The proline content increased in the leaves of examined cultivars and was significantly higher in drought tolerant plants. On the other hand, in the seeds only slight increase in proline content was found. The results obtained indicated that drought tolerance could be correlated with high proline content and enzymatic defense against lipid peroxidation.

Proline content, ion accumulation, cell wall and soluble peroxidase activities were determined in control and salt-treated calli (150 nM NaCl) and whole plants (30 mM NaCl) of two rice cultivars (salt sensitive cv. IKP and salt tolerant cv. Aiwu). Under salinity, the highest accumulation of Na⁺, Cl^- and proline occurred in calli, roots and younger leaves of cv. IKP, coupled with the highest decrease in K⁺ content; accumulations of Na⁺ and Cl^- were restricted to older leaves in cv. Aiwu. Relative growth rates of calli and roots or shoots from both cultivars were not linked to peroxidase activities. High concentrations (1 M) of exogenously applied glycerol did not inhibitin vitro activities of soluble peroxidase extracted from control and salt-treated calli or plants. Conversely, 35-55% (in cv. IKP) or 60-80% (in cv. Aiwu) of soluble peroxidase activities were found in presence of isosmotic proline concentration. There were no differences between proline and glycerol effects onin vitro cell wall peroxidase activities.

Several morphological characteristics differed when wheat (Triticum aestivum L. cv. Doha 88) was grown under a cool (10 °C), warm (20 °C), and hot (30 °C) regime. Development of leaves was linearly related to shoot meristem temperature, and the time between appearance of successive leaves on the main culm was independent of growth temperature. Area and dry mass of leaves and roots increased exponentially with time, and variations between growth temperature regimes were reduced when plants were compared at a similar developmental age. In isolated thylakoids thermal stability of photosystem 2 and of whole electron transport chain was enhanced with the increase in growth temperature. Therefore this cultivar is able to acclimate to contrasting temperature regimes.

Rates of whole chain and photosystem 2 activities in chloroplasts isolated fromVigna unguiculata L. seedlings grown under ultraviolet-B (UV-B) enhanced radiation were less affected by 3, 6 and 9 mM CdCl₂ for 60 min at 0 °C in the dark than the rates in chloroplasts from control plants grown under normal irradiation. The results are in agreement with changes in contents of chloroplast 55, 47, 43, 33, 29, 27-25, 23 and 17 kDa polypeptides that were significantly lowered at 3, 6 and 9 mM CdCl₂ only in chloroplasts from control plants. On the other hand, in the simultaneous treatment of chloroplast isolated from control plants the UV-B supported the inhibitory effect of all applied concentrations of CdCl₂. The photosystem 1 activity was only marginally affected in the all experimental variants.

Life span of the second leaf of wheat(Triticum aestivum L., cv. Grana) plants was studied from day 8 to day 50 of plant age in a variant with nitrogen (+N) and in a variant in which plant senescence was induced by the omission of nitrogen from the nutrient solution (-N). Seed protein was the sole source of nitrogen for these plants. Specific leaf mass (SLM) in the -N variant, and specific leaf area (SLA), the mass of fresh leaf, soluble protein content and total nitrogen content in the +N variant peaked by day 22 of plant age (that is by day 19 of leaf age). Dry matter content, leaf length and leaf area, and SLM in the +N variant peaked by day 29 of plant age (that is by day 26 of leaf age). The ontogeny of the second leaf in the variant with enhanced senescence was shorter by at least 14 days. Plants from this variant showed typical symptoms of N deficiency, that is yellowing of leaves, tip burn, and lack of tillering. However, the growth and biochemical characters studied did not indicate an earlier onset of the senescence of the second leaf of -N plants. Both +N and -N variants reached their peaks (with the exception of an earlier peak by day 12 in case of total nitrogen content in the -N variant) on the same day of leaf age. Thus the first part of the leaf life span from leaf growth initiation to full expansion was of the same length in both the control and N-def icient plants. The stage of the proper senescence of the second leaf of -N plants was very short; the leaf completely died away within 7 days after senescence onset.

Lotus corniculatus has been transformed byAgrobacterium tumefaciens harbouring therolABC, rolAB, and 35S-rolC constructs. Growth, shoot and root morphology, cytokinin and auxin concentrations in the shoots, chlorophyll content in the leaves, nodulation and nodule nitrogenase activity of clonal progenies of selected transformants, in which the transferredrol sequences were proved, were compared with control plants.
The most striking alterations were observed in the 35S-rolC transformants (dwarfism, shoot and root branching, shorter internodes, delayed nodule formation, decreased nitrogenase activity, reduced content of leaf pigments) in comparison with either therolAB, rolABC, or controls. TherolAB androlABC transformants were very similar to the control plants in their morphology as well as in most other traits measured.

The barley (Hordeum vulgare L.) seeds were germinated in the non-saline conditions after 12 h imbibition in 2 % of NaCl solution. The results of treatment were: (l) the membrane system in meristematic cells of root tips developed well; (2) many profiles of endoplasmic reticulum and Golgi bodies appeared; and (3) the quantities of amoeboid plastids and amoeboid mitochondria increased. Thus the inhibitory effects of short-term NaCl stress on plants were reversible, and simultaneously NaCl treatment enhanced the metabolic activities in cells. The amoeboid form may be an adaptive form of plastids or mitochondria to an enhanced metabolic activity.

This study examined whether 'Risnod2' and 'Risnod27' non-nodulating mutants of pea (Pisum sativum L.) provided with increasing concentrations of nitrate could achieve a growth and nitrogen accumulation comparable to their parental N₂-fixing cv. Finale. In the cv. Finale, nodule number, nodule dry mass accumulation, total C₂H₂-reducing activity of nodulated roots (TAR) and estimated N₂ fixation were considerably inhibited at 5.0 and 10.0 mM root medium NO₃ ^- concentrations. In contrast a 0.63 mM level stimulated both the nodule dry mass and TAR. The cv. Finale N₂-fixing plants grown on 0 to 2.5 mM NO₃ ^- levels had higher shoot N concentrations than the Nod^- mutants, but within the 5.0 to 10.0 mM levels the Nod^- mutants approached or even overtopped the N concentration of the cv. Finale plants. Compared with a high positive correlation found in the Nod^- mutants, shoot N concentration in the cv. Finale was negatively correlated with the root medium NO₃ ^- concentration. The pattern of nitrogen content in shoot dry mass was very similar to that seen in the shoot dry mass accumulation. The Nod^- mutants grown on the 5.0 and/or 10.0 mM NO₃ ^- level had plant dry mass, shoot nitrogen concentration, shoot nitrogen content, and root/shoot dry mass ratio comparable with those of the nodulating cv. Finale grown on the same nitrate levels.

Interspecific hybrids from the crosses betweenBrassica campestris, B. carinata, B. juncea andB. napus were obtained throughin vitro ovary and ovule culture. F₁ hybrids were studied morphologically and flow cytometry was used to estimate 2C nuclear DNA content both in parentalBrassica species and their hybrids. It was found that in comparison with the A genome, the B and the C genomes ofBrassica contained 26.9 % and 43.9 % more DNA, respectively. This finding may be used to distinguish interspecific hybrids containing various genome combinations. It was concluded that flow cytometric analysis of nuclear DNA content might be useful tool inBrassica breeding.

Several factors influencing reliability of the quantitative fluorimetric β-glucuronidase (GUS) assay in transgenic plant tissue have been investigated. We obtained linear dependence of fluorescence on both the duration of hydrolysis and the extract concentration. The stability of the enzyme in the homogenate was fairly high, the same as the stability of the substrate solution and of the final reaction product. The modification of the extraction/incubation buffer was proposed, resulting in several times higher activity in comparison with original procedure.

The interactive effects of certain phytohormones (GA₃, IAA or kinetin) and drought on plant-water relations and mineral accumulation of the three crop plants; maize, cowpea and broad bean, were studied. Phytohormone applications were capable of counteracting to some extent, the adverse effects of drought on transpiration, stomatal frequency, and leaf area.

C. rubrum plants of different age were treated with methyl jasmonate (JA-Me), in some cases in combination with photoperiodic flower induction. Plants treated with JA-Me (3×10^-4, 3×10^-5 and 5×10^-7M) showed inhibition of growth and flowering. No effect of JA-Me application on ethylene formation was observed.

Between 1986 and 1989 we studied the influence of γ-irradiation (2.5-80 Gy) on growth processes and the content of arbutin glycoside. Bearberry [Arctostaphylos uva-ursi (L.) Sprengel] shows polycyclic characteristics of growth; the vegetation period is divided by summer dormancy (June) into periods of spring and summer growth. As plants age the summer dormancy gets longer and the period of summer growth is shorter. Irradiation with a dose of 80 Gy was lethal and a dose of 60 Gy damaged plants so much that they were not able to grow in the first spring after irradiation. Significant growth stimulation (both in the height of plants and in branching) was shown only in the second year after irradiation (2.5-60 Gy). In the fourth year the growth in all irradiated variants was weaker than in the control. Doses of 2.5 and 5 Gy did not influence the content of arbutin significantly; higher doses of irradiation changed the dynamics of production and decomposition which is connected with growth changes.

An analysis of flows through primary root and first node root tissues of plants grown under conditions of salinity and nutrient deficiency induced by temperature gradients was carried out using. a mathematical model. The results obtained show that high KNO₃ concentration in Knop's nutrient solution (salinity) causes an inhibition of volume and heat flows and that the omission of KNO₃ from Knop's nutrient solution (deficiency) stimulates these flows. The causes of the inhibition lay in the fact that salinity reduced hydraulic, electric, and osmotic conductivity when compared with the control (Knop's solution), but relative to nutrient deficiency, it increased osmotic conductivity, electrodiffusion, diffusion, and filtration of heat flow induced by the electric and heat power. The causes of the stimulation were that deficiency partially decreased conductivities, similarly as salinity when compared with the control, and also decreased osmotic abilities of the system. By contrast, it increased heat conductivity and corresponding filtrations (diffusion-thermal, thermoosmotic). In first node root tissues, it increased all conductivities with the exception of electric conductivity, then osmotic, electroosmotic, diffusion, electrodiffusion, and filtration of heat flow and current flow, that is the number of possible ways of solution transport through root tissues increased.

The responses of seedlings of three fast growing tree species,Eucalyptus hybrid(E. camaldulensis × E. teriticornis), Casuarina equisetifolia andMelia azedarach, to different levels of soil moisture in controlled glasshouse conditions were compared. The survival percentage, height of plants, number of leaves per plant, number of branches, fresh mass and dry mass of roots, stems, branches and leaves decreased in the three species with increasing water stress. Stomatal frequency and length of stomata inEucalyptus andMelia also decreased with increasing water stress. However, no significant difference was obtained in the width of stomata and the ratio of number of open stomata to total number of stomata per unit area. The leaf thickness decreased, but the thickness of palisade parenchyma increased with increasing water stress inEucalyptus hybrid andCasuarina. Leaf thickness ofMelia did not show any significant variation due to water stress.

This report presents, results of a feasibility study of use of allelopathic aquatic plants for aquatic weed management. In order to establish a list of potential allelopathic plants, we selected 16 aquatic plants native to the southeastern United States and subjected them to two bioassays - one involving lettuce seedlings and one involving the aquatic plantLemna minor as the target species. The lettuce seedling bioassay was selected because it is a widely used, experimentally simple assay to determine allelopathic activity. However, it uses lettuce, a terrestrial plant, as the target species, and thus may be less appropriate for use with aquatic plants. TheL. minor assay involves an aquatic plant as the target species and so is more appropriate for our goals, but it is experimentally much more complex and time-consuming. The plants selected for study wereBrasenia schreberi, Cabomba caroliniana, Ceratophyllum demersum, Eleocharis acicuiaris, Eleocharis obf usa, Hydrilla verticillata, Juncus repens, Limnobium spongia, Myriophyllum aquaticum, Myriophyllum spicatum, Najas guadalupensis, Nymphaea odorata, Nymphoides cordata, Potamogeton foliosus, Sparganium americanum, and Val/isneria americana.Nymphaea odorata (leaves and petioles) inhibited 78 % of lettuce seedling radicle growth and 98 % ofL. minor frond production. Brasenia schreberi inhibited 82 % of lettuce seedling radicle growth and 68 % of L. minor frond production. These results suggest thatN. odorata andB. schreberi are both highly inhibitory and are therefore candidates for use in aquatic weed management. Results also suggest that the simple lettuce seedling assay is a reasonable first "easy" one to use in an attempt to determine allelopathic potential of aquatic plants.

Responses of a salt tolerant and a normal population of an oilseed crop,Eruca sativa Mill. were assessed after four weeks growth in sand culture salinized with 0 (control), 100, 200, or 300 mol m^-3 NaCl. The salt tolerant plants produced significantly greater dry biomass than the normal population. The populations did not differ significantly in leaf osmotic potential, relative water content and leaf soluble proteins. However, the tolerant population accumulated significantly greater amounts of soluble sugars, proline and free amino acids in the leaves compared with the non-tolerant population. It is established that leaf soluble sugars, proline, and free amino acids are important components of salt tolerance inEruca sativa.

Plasma membrane H⁺ATPase extracted from leaves of spinach plants induced to flower by gibberellic acid treatments or by a transfer to a photoperiod of 24 h had a lower Km_app than that from vegetative plants grown in short days. The Km_app obtained after inhibition by vanadate was decreased in vegetative plants and increased in induced ones showing a differential effect of this inhibitor on the kinetic properties of the enzyme between vegetative and induced plants. The phospholipid fatty acid analysis of the purified plasma membrane showed an increase of C18:1/C18:2 fatty acid ratio upon induction by light or by gibberellic acid treatments, whereas the saturated to unsaturated fatty acid ratio was kept constant. The decrease in the Km_app observed after induction may be thus interpreted in terms of the observed changes in lipid environment.

The accumulation of nitrogen and potassium by plant cells at undesirable concentrations manifests itself in changes in the osmotic phenomenon and finally in the transport process. Temperature gradient is another factor influencing the transport phenomenon. We have followed the changes in the electric diffusion potential and the heat transfer under the influence of these two factors on transport properties of roots of plants grown under conditions of either salinity or nutrient deficiency on the transport of KG solution through segments of the first node roots and of the primary root. Physical causes of the accumulation of the above mentioned ions were then studied by means of a mathematical model. The results obtained showed that high KNO₃ concentration in nutrient solution caused an inhibition of volume and heat flows, stimulated osmotic flow, and reduced electrical polarization of root cells. Cell polarization was slowed down when temperature gradient was increasing and enhanced when temperature gradient was decreasing. This indicates that the pressure difference between the exterior and the interior of root cells was levelled off by osmotic water flow but not by potassium ion flow.

Parameters of water relations were measured throughout the season in phenologically identical leaves of rose plants grown in a heated greenhouse. The increase in osmotic potential observed from spring to early autumn seems to result from the decrease in the non-osmotic water fraction, and, conversely, its decrease from early autumn to winter seems to be due to an increase in the non-osmotic water fraction. These observations support the hypothesis that the non-osmotic water fraction may be correlated to starch concentration in rose leaves.

The slot-immunobinding assay (SIBA) was adapted for detection of plum pox virus (PPV) and compared with DAS-ELISA. SIBA was easy to perform and as sensitive as DAS-ELISA in detection of various PPV isolates in herbaceous and woody plants, but not in aphids (Myzus persicae).

There exist two main mechanisms of allelopathy: 1) direct transfer of metabolites between neighbouring plants during their life and 2) accumulation and transformation of bioactive substances in the environment with their subsequent influence on higher plants. The latter mechanism is similar to that causing soil sickness or soil toxicity. Allelochemicals affect all functions of the living system: photosynthesis, respiration, mineral nutrition, transpiration, immunity, and growth. The initial biochemical effect of allelochemicals seems to be on the synthesis of protein mediated by RNA/DNA. Knowledge of the mechanisms of concrete signals during realization of hereditary codes would serve as a powerful tool for the improvement of crop plant development and productivity.

The influence of N, P, K supply on the contents of dry mass, chlorophyll (a+b), vitamin C, saccharides and the activities of peroxidase (E.C. 1.11.1.7), catalase (E.C. 1.11.1.6), and acid phosphatase (E.C.3.1.3.2) in leaves of celery plants during their growth stages was investigated. A correlation between the amount of N, P, K and the chemical composition and catalytic activities of enzymes was found.

A low activity of peroxidase (POD, EC 1.11.1.7) was found in crude extracts fromin vitro plants ofSyngonium podophyllum cv. Butterfly sealed in the multiplication vessels. Removal of the lids from the vessels increased the POD activity. A greater increase in the POD activity was measured whenin vitro plants were transplanted into a weaning growth medium. The POD activity was further promoted by removal of the phenolic substances from the extracts by polyvinyl-polypyrrolidone (PVPP).