Uptake mechanisms for neutral amino acids were investigated by expression of mRNA isolated from seedlings of Ricinus communis L. in Xenopus laevis oocytes. After injection of mRNA from root, hypocotyl and cotyledon currents elicited by saccharose and neutral amino acids ranged from 0.3 nA up to 2 nA depending on the respective substrate and the source of mRNA. These currents were due to expression of low affinity uptake mechanisms and the KM values found for amino acid induced charge flow range from 1 to 2 mM. The abundance and/or the specificity of the expressed mechanisms differ in the various tissues. Currents of similar magnitude were recorded for alanine and glutamine with mRNA isolated from root, hypocotyl and cotyledons. Serine and proline induced currents after injection of mRNA from hypocotyl and roots, in case of α-aminoisobutyric acid (AIB) induced currents were generally small with mRNA from all tissues tested. In addition, differential sensitivity of glutamine and AIB uptake in the high affinity range was evident towards the amino acid analogue 2-chloro-aminophenoxybutyric acid which indicated an additional set of carriers operating in the micromolar concentration range. The results suggest that multiple transporters for neutral amino acids exist in various tissues of the plant differing in specificity of charge flow and in sensitivity towards the inhibitor 2-chloro-aminophenoxybutyric acid.

Plants of Calamagrostis villosa were cultivated in nutrient solution alone or in association with a vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum. They were supplied with two levels of inorganic phosphate (Pi; 0.1 or 1 mM) and with or without organic phosphate (dinatriumphenylphosphate, Po; 1 mM). Depression of growth and enhancement of root respiration of mycorrhizal plants in comparison with non-mycorrhizal plants were observed after 12 weeks of cultivation in a growth cabinet. Root colonization was not influenced by the higher phosphorus availability in contrast to the extraradical mycelium (ERM). The lengths of ERM hyphae both attached to the root surface and in the substrate were decreased substantially by higher phosphorus supply, irrespectively of its form.

Alfalfa (Medicago sativa L.) cell suspension cultures of Verticillium albo-atrum resistant and susceptible genotypes were established from leaf callus tissues. Treatment of cultures with conidia and heat-released elicitors of V. albo-atrum induced a large increase in the activity of phenylalanine ammonia-lyase, only in the cells of the resistant genotypes with a maximum after 12 h. In co-cultivation with the fungal conidia and resistant cell lines, the production of spores were inhibited.

The immature zygotic embryos of reciprocal maize hybrids (CHI-31 x GF1 and CHI-31 × GE2) were used as the initial material for induction of somatic embryogenesis in vitro. Histological analysis of somatic embryogenesis revealed high developmental variability. The arising formations were classified into 5 groups: A) somatic embryos phenotypically similar to zygotic embryos, B) polyembryos, C) formations with radicle but without meristematic plumule, D) formations with radicle without differentiated plumule, and E) formations with plumule without radicle. The formatioms A and B regenerated directly into plants. Plant regeneration from formations E required preculture on the rooting medium. Formations C and D failed to develope into plants possibly because of early loss of meristematic cell character during the embryo axis differentiation. The reverse sequence of radicle and plumule differentiation in somatic embryos in comparison with zygotic ones was noted. The epigenetic character of the scutellum, coleoptile, coleorhiza and leaves primordia development was discussed.

Sugar beet was grown in pots and the transport of 6-deoxy-d-glucose (6-dg) and of 2-aminoisobutyric acid (AIB) into leaf and root tissue segments was examined. The uptake of 6-dg into both tissues displayed two kinetic components, one apparently of diffusional nature, the other saturable (half-saturation constant 0.22 mM in leaves, 0.10 mM in roots; limiting rate 0.37 and 0.10 nmol mg-1 (fresh mass) h-1 for leaves and roots, respectively). It was suppressed by d-glucose and inhibited by diethyl-stilbestrol (DES), suloctidil (SUL) and 2,4-dinitrophenol (DNP), but little by D2O and not at all by sodium vanadate. It showed a temperature optimum at 30 °C and a pH optimum at 6.0 - 6.5 in both tissues. The uptake of AIB was also two-componental but even the specific component had an immeasurably high half-saturation constant although it was inhibited by high concentrations of AIB as well as by DES, SUL, DNP and D2O. However, vanadate stimulated the uptake by as much as 40% in both leaves and roots. The temperature optimum in leaves lay at 30 °C while in the roots no maximum was present; its pH optimum was at 5.5 in leaves and again no maximum was observed in roots. Both transport systems were unaffected by 0.1M NaCl or 0.1 M KCl and by the presence of cytokinin in the incubation vessel. However, spraying with the cytokinin N6-(m-hydroxybenzyl) adenosine decreased both the half-saturation constant and the limiting velocity of 6-dg uptake slightly in the leaves and substantially in the roots. Spraying had an insignificant effect on the uptake of AIB.

Age-induced changes in 1) nocturnal and diurnal acidity fluctuations that coincide with the ongoing environmental conditions, 2) the build up of abscisic acid (ABA) in plant roots and leaves during sunrise, midday, and sunset in all growing stages, 3) the changes in phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities as key enzymes of the photosynthetic pathways of C3 and CAM, 4) leaf water potential (ψ1), and 5) Km and Vmax for PEPC to express its activity and affinity, were studied in Mesembryanthemum nodiflorum during transition from C3 to CAM mode of CO2 fixation. The acidity during sunset in mature stage was higher than in earlier stages and reflected the impact of environmental conditions on physiological and metabolic changes. Moreover, the higher acidity during sunrise and sunset was observed during the senescence than the mature stage; this might be due to CO2 release and oxygen intake during senescence induced ethylene formation that lead to increased malic acid formation. The ABA concentration was high in M. nodiflorum leaves, but stomatal closure was insensitive to elevated ABA concentrations recorded. Vmax of PEPC, Km, and the affinity of PEPC during later stages indicated the ability of PEPC to fix CO2 taking up at night in CAM cycle of M. nodiflorum. Less affinity during sunrise indicated inhibitory effect of malate on PEPC during the release of CO2. The second peak of PEPC activity before sunset caused CO2 fixation. The RuBPCO was inactive at night. Slight increase in ABA during sunset, and night drop in air temperature and increase in relative humidity reduced markedly transpiration rate without decreasing ψ1.

Indoor experiments demonstrated that allelopathic potential of rosette and flowering plants of qort is an important factor explaining the growth reduction of its associated species. Aqueous tissue extracts of flowering plants exhibited strong inhibitory effects on the germination percentage and radicle growth rate of the tested species as compared with those of vegetative plants. Under laboratory conditions, this inhibition was in agreement with toxicity assessments of soil samples collected from the rhizosphere of T. resupinatum L., where shoot and root dry mass of the tested species were significantly reduced. Detoxification of allelochemicals by presence of activated carbon can eliminate the inhibitory effects of the different extracts. This technique clarifies the occurrence of allelopathic interference by qort on seed germination and seedling growth, and hence suspects the allelopathic potential of qort in the growth reduction of associate species under field conditions along with competition.

Changes in photosystem (PS) 2 activity were measured inAnacystis nidulans cells exposed to UV-B irradiation. The decrease in PS 2 activity was biphasic in cells exposed at the surface (0 cm) and at 2 cm depth in the water column, while gradual in those exposed at 10 and 30 cm depth. Addition of supplemental "white light" reduced the extent of UV-B damage. Decrease in photosynthetic activity was primarily due to the loss of energy transfer from phycobilisome to chlorophyll as the former in cyanobacteria acts as the primary light-harvesting complex. This was supported by the absorption and fluorescence excitation and emission spectral studies. All these changes were proportionally reduced by the thickness of the water column that reduced UV-B irradiance.

In leaf discs of maintenance foliage of tea (Camellia sinensis) polyamines (PA_s) and kinetin retarded chlorophyll (Chl) loss, whereas inhibitors of PA biosynthesis [difluoromethyl arginine, difluoromethyl ornithine, methylglyoxal-bis(guanylhydrazone)] and abscisic acid (ABA) promoted senescence. The contents of RNA and protein were significantly higher in PA and kinetin treated leaf discs as compared to those treated with inhibitors and ABA. The contents of total and reducing saccharides declined with the progressive loss of Chl, and the concentration of starch increased in all the PA treated leaf discs. Free amino acid content also increased under all the treatments, but the increase was comparatively larger in case of inhibitors application.

The main sites of lead entering the protonemata were spores with broken cell walls and apical cells of protonemata. The lead ions could enter the symplast probably by endocytosis but we can not exclude diffusion as the way of entering. Lead deposits inside a protoplast were observed after 2 h of lead application. After 12 h, Pb deposits were commonly present in all cell structures surrounded by a membrane. Some disturbances in ultrastructure of organelles were found after 8 h. The most frequent were: change of endoplasmatic reticulum configuration from linear to concentric one in many cases surrounding other organelles (e.g. mitochondria) and large and numerous plastoglobuli in chloroplasts. Longer treatment of protonemata with lead (24 h or 48 h) caused degeneration of organelles and even death of the cell.

Morphology of pollen grains collected from healthy and virus infected plants ofChenopodium quinoa L.,Chenopodium album L. andNicotiana tabacum L. cv. Samsun was investigated using scanning electron microscopy (SEM). Pollen grains from tobacco plans infected with tobacco mosaic virus (TMV) were smaller, with rounded shape and conspicuous deformation of aperture unlike oval and smooth pollen grains from healthy plants. No morphological alterations were observed inC. quinoa andC. album plants infected with TMV and cucumber mosaic virus (CMV). Polyacrylamide gel electrophoresis of pollen proteins revealed substantial quantitative and qualitative differences in protein components of pollen grains collected from healthy and virus infected plants

Callus cultures ofArachis hypogaea L. cv. JL-24 adapted to 200 mM NaCl (otherwise lethal to cells) were used for the study. Calli grew slowly when transferred to 250 mM NaCl, but the growth was enhanced when ABA was included in the medium. ABA induced increase in growth of callus was not accompanied by corresponding increase in internal free proline levels. 0.5 mM of CaCl₂ ameliorated the negative effect of NaCl indicating that cells require a specific Ca²⁺/Na⁺ ratio for their growth. Proline content also increased at this ratio thereby suggesting that increase in growth at 0.5 mM Ca²⁺ may be due to an increase in proline content. However, exogenous proline did not increase the growth of callus (adapted to 200 mM), and higher concentrations even inhibited the growth. This shows that proline is not required for growth or adaptation of cells to salt stress, but is produced as a consequence of stress.

The effect of salinity on contents of water, soluble saccharides, phenols, minerals and on respiration rate in bulbs of five garlic (Allium sativum L.) cultivars differing in salinity tolerance was determined. Cultivar HG-6 was found to be the most tolerant followed by cvs. G-l and G-42, and cv. Aru the least tolerant to salinity. The cultivars which were tolerant showed lesser reduction in water content of the bulbs by salinity. Initial contents of phenolic compounds and sulphur were comparatively low in salinity tolerant cultivars but they increased under high salinity levels whereas reverse was found in salt sensitive cultivars. The fatty acids profile did not show significant changes under saline conditions. Contents of K and Ca were reduced, content of Na was increased and there were no changes in the contents of N, Mn, Cu, Zn and Fe. The changes in soluble saccharides content and respiration rate were not found to be associated with the salinity tolerance.

The thickening that appeared on maize roots under the influence of 6-benzylaminopurine and α-naphthylacetic acid (concentration 10^-5, 10^-6, 10^-7 and 10^-8 M) were analysed. The changes in length and width of maize roots at the edge of elongation zone after 24,48 and 72 h of treatment were studied. The growth in length of cells at the edge of elongation zone stopped abruptly but the growth in width slowly continued. So, the growth of cells in length and width under the influence of growth regulators was not simultaneous. They had distinct time limits.

Erythrina variegata Lam. seedlings were grown under low (100 mM NaCl) and high (250 mM NaCl) salinity. Seedlings exposed to high salinity for 10 d showed significant reduction in growth rate and biomass production while the root/shoot ratio increased. In contrast to pigment and protein contents, starch and saccharide contents increased in salt stressed seedlings. When the seedlings were subsequently sprayed with triacontanol (1 mg kg^-1) the salinity effect was partially ameliorated and growth, biomass, chlorophyll and carotenoid contents increased.

Ears of uniculm wheat (Triticum aestivum L. cv. Gigas) grown in liquid medium for 11d absorbed more solution when the saccharose concentration was 2 % than when it was 10 %. When the ears were grown in 6 % saccharose solution, the rate of uptake from the solution was between that from the 2 and 10 % saccharose medium. Dry mass per grain increased with the saccharose concentration in the medium and the reduced uptake of solution did not decrease the moisture percentage of the grain. The culture of ears decreased pH of the solution with 2 % saccharose more than with 10 %. Addition of 0.5% chloramphenicol to the culture solution had no adverse effect on grain mass; it prevented contamination of the solution and maintained a higher pH

Citrinin lowered contents of chlorophyll, carotenoids, proteins and nucleic acids during seed germination of maize cv. Suwan composite. The inhibitory effect was concentration dependent.

The effects of fusaric acid, a phytotoxin produced byFusarium pathogens, on the metabolism of isolated maize root mitochondria and on maize seed germination and seedling growth were investigated. The phytotoxin inhibited basal and coupled respiration when succinate and α-ketoglutarate were the substrates. Coupled respiration dependent on NADH was inhibited, but basal respiration was not. Consistently, succinate cytochromec oxidoreductase activity was decreased whereas NADH cytochromec oxidoreductase was not affected. The ATPase activities of carbonyl cyanide p-trifluoro-methoxyphenyl hydrazone stimulated mitochondria and of freeze-thawing disrupted mitochondria were inhibited. These results indicate that the phytotoxin impairs the respiratory activity of maize mitochondria by at least three mechanisms: (1) it inhibits the flow of electrons between succinate dehydrogenase and coenzyme Q, (2) it inhibits ATPase/ATP-synthase activity and (3) it possibly inhibits α-ketoglutarate dehydrogenase. Seed germination and seedling growth were also affected by fusaric acid with the most pronounced effect on root development. These effects can possibly contribute to the diseases ofFusarium- infected plants

The after-effects of 24 h high temperature (35 or 45 °C) treatment on the photochemical activities and photooxidative lipid peroxidation, subsequent to their irradiation were studied in 7-d-old etiolated rice (Oryza sativa) seedlings. Photosystem (PS) 1 and PS 2 mediated photoreactions of thylakoids isolated from the seedlings exposed to high temperature did not differ significantly from the thylakoids isolated from control seedlings (25 °C). Hence, all kinds of tested thylakoids were equally efficient in capturing and utilizing radiant energy. The high irradiance induced loss in PS 2 activity and lipid peroxidation measured in terms of malondialdehyde production was more rapid in thylakoids isolated from stressed seedlings as compared to that of control seedlings. Thus the thylakoids isolated from the stressed seedlings were more prone to photodamage than those from the control seedlings.

One-year-old seeds of chickpea (Cicer arietinum L. cv. C-235) lost about 23 % germinability and leaked larger quantities of N, P, K, saccharides and proteins into the soaking medium in the first 48 h, as compared with fresh seeds. The protein content in stored seeds decreased more than in fresh seeds, as the soaking progressed.

Gas exchange characteristics of a hemiparasiteMelampyrum arvense L. before and after attachment to the hostCapsella bursa pastoris (L.) Med. were compared. The net photosynthetic rates (P_N) on a leaf area basis were extremely low and in comparison to the value obtained for the host were about 15 % and 23 % for the unattached and attached hemiparasite, respectively. Also the concentration of photosynthetic pigments was low (as compared with the host the content of chlorophylls was about 33 % and 49 % and of carotenoids about 38 % and 36 % in the unattached and attached hemiparasite, respectively). On the other hand the rates of respiration were high (about 1.8 and 2.6 times higher in the unattached and attached hemiparasite, respectively, than in the host). In darkness stomatal conductance (g_S) of the host and the unattached hemiparasite was rapidly reduced to 10 % of the value obtained in light, g_S of the attached hemiparasite was decreased only by about 30%. A total reduction of g_S occurred at relative water content (RWC) of 85 %, 75% and 45 % for the unattached hemiparasite, the host, and the attached hemiparasite, respectively. The transpiration (E) rate in the preparasitic stage was very low, being 2.6 and 4.5 times smaller than in the host and the attached hemiparasite, respectively. In the attached hemiparasite WUE was 7.5 and 3 times poorer than in the host and in the preparasitic stage, respectively.