Plants of Vigna mungo raised from seeds presoaked in salicylic acid (0.0, 0.01, 0.1 and 1.0 mM) and nodulated with the cowpea strain of Rhizobium leguminosarum were analysed 15 and 30 d after sowing. The foliar nitrate and nitrite contents were varying but soluble protein and total nitrogen contents were lower in treated than control plants. Nitrate reductase activity was increased at the two lower concentrations of 0.01 and 0.1 mM but was inhibited at the highest concentration used (1.0 mM). The number of nodules, their leghemoglobin and protein contents and nitrogenase activity of roots were reduced.

Cytokinin content in xylem sap was higher in plants grown under local supply of fertilizers as compared to those grown under homogenous distribution of nutrients in soil. The separate assay of cytokinins in xylem exudate from split root system showed that roots, which were in contact with fertilizer mainly contributed to cytokinins transported from roots to shoots.

Plants of maize (Zea mays L.) were waterlogged for 7 d and irrigated (root application) or sprayed (foliar application) with 0, 1, 3 and 6 mg dm-3 of boron. The stability of leaf membranes was assessed by determining leakage of electrolytes from leaf discs exposed to heat (51 °C) and dehydration (40 % PEG). Leaf membranes were more stable to heat than to dehydration. The membranes of waterlogged plants were more injured than those of control plants. Waterlogging reduced contents of dry mass, chlorophyll, soluble proteins, total free amino acids and soluble sugars and leaf relative water content (RWC). Application of boron increased the stability of leaf membranes, chlorophyll, soluble sugars, soluble proteins, amino acids contents, leaf RWC and dry mass accumulation. Foliar boron application was more effective. Application of boron alleviated the deleterious effect of waterlogging.

The suitability of the fluorescent dye rhodamine 123 for qualitative and quantitative determinations of the electrical potential difference (ΔΨ) in isolated pea (Pisum sativum L.) stem mitochondria was evaluated. A fluorescence quenching of rhodamine 123, as a consequence of dye uptake, occurred following mitochondria energization by both external and internal substrates. This quenching was associated to the generation of ΔΨ, because it was completely released by uncouplers and respiratory inhibitors. The conversion of the proton gradient (ΔpH) into ΔΨ, induced by nigericin or a permeant weak acid (phosphate), increased the quenching. The uptake of the probe was accompanied by 40 % of unspecific binding in coupled, but not in uncoupled, mitochondria. Rhodamine 123 quenching varied linearly with a K+-diffusion potential. ADP induced a transient and cyclic change of fluorescence which was associated to ATP synthesis. Consequently, rhodamine 123 did not influence oxygen consumption by mitochondria in both state 4 and 3, thus indicating that, at the concentrations assayed, the probe was not toxic. It is concluded that rhodamine 123, followed by fluorescence quenching, is a suitable probe to study the energetics of isolated plant mitochondria.

Light regulation of diurnal variation of sucrose-phosphate synthase (SPS) activity was studied in potato leaves during pre-tuber initiation stage. SPS activity was greatest at 14:00 and coincident with highest irradiance [2 000 µmol(PAR) m-2 s-1], and lowest at 18:00 during lowest irradiance (200 µmol m-2 s-1). In contrast, fructose-1,6-bisphosphatase (FBPase) activity was greatest at 12:00 (irradiance 1 700 µmol m-2 s-1). Inhibition of SPS activity by phosphorylation was least at 14:00 and highest at 18:00. Considerable inhibition was also observed at 10:00. SPS showed hyperbolic saturation kinetics in response to varying UDP-glucose concentrations. Diurnal variation of SPS activity was due to a change of affinity for its substrate (Km), but not due to change of Vmax. Phosphate (Pi) decreased the activation state of SPS. Inhibition by Pi was most severe under limiting UDP-glucose concentration. Sensitivity towards Pi inhibition at limiting substrate concentration was highest at 18:00 and lowest at 14:00. Change of tissue phosphate concentration followed the opposite pattern to that of diurnal variation of SPS activity and irradiance, being highest at 18:00 and lowest at 14:00. A dual mode of regulation is considered to exist for diurnal variation of potato leaf SPS: covalent modification and effector (Pi) regulation. Thus the change of tissue phosphate concentration may play a pivotal role in regulating potato leaf SPS.

Germination of two rice (Oryza sativa L.) cultivars (Ratna and IR 36) in the presence of 10 µM PbCl2 and 10 µM HgCl2 decreased germination percentage, germination index, shoot/root length, tolerance index and dry mass of shoots and roots. Mercury was more toxic than lead. Reduced glutathione (GSH), cysteine (Cys), ascorbic acid, and α-tocopherol alleviated the adverse effects of these metals on plants in the order GSH > Cys > ascorbic acid > α-tocopherol. The effects were more pronounced in tolerant cultivar IR 36 than in the relatively susceptible cultivar Ratna.

In vitro response of six tomato genotypes to different copper concentrations was studied. Cu was toxic to tomato explants at a relatively high concentration (100 µM), which reduced callus growth and shoot regeneration. Peto-86 followed by UC-97-3 were more tolerant to copper than the other genotypes. Cu (100 µM) induced the synthesis of eight new proteins (70.86 - 14.78 kD) in Peto-86 and six in Western Improve (46.43 - 14.78 kD) and UC-97-3 (77.69 - 14.78 kD). Cu-stress reduced the expression of some enzymatic bands of alcohol dehydrogenase and esterase, meanwhile, one peroxidase band at the locus Prx-1 was newly expressed under Cu-treatment.

The effects of cadmium and copper on in vitro growth of Bacopa monniera (L.) Wettst. was monitored. Cadmium (25 and 50 µM CdCl₂) inhibited plantlet growth and addition of 50 or 100 µm CuSO₄ partially alleviated this negative effect. Cadmium increased both protein and proline contents, but to a lesser extent with the additional supply of CuSO₄.

Hypocotyls, cotyledons and true leaves of in vitro seedlings of 10 cucumber and melon genotypes resistant to downy and powdery mildew were cultured on several combinations of initiation and multiplication media to produce callus and subsequently cell suspensions as suitable sources for isolation and culture of protoplasts. Cotyledons of both species were shown to be the most responsive to variation in culture media. However, calli and cell suspensions derived from hypocotyls generally provided higher number of protoplasts by treatment with several enzymatic solutions. The protoplasts formed new cell walls after 12 h of culture in liquid culture medium and first cell division was observed 2 d later with more frequent divisions after one week of culture.

The activities of nitrate reductase and glutamine synthetase in leaves of greenhouse grown rose plants (Rosa hybrida cvs. Ilseta and Mercedes) grafted on various rootstocks were compared with those in leaves of non-grafted, own-root plants of these cultivars. The results obtained showed that the enzymatic activities as well as nitrate content in the leaves were altered by the grafting and by type of the rootstock used. These rootstock-imposed alterations differed between the two cultivars used in the study.

Direct differentiation of shoot buds from hypocotyl segments of 12-d-old seedlings of Tamarindus indica was obtained on Murashige and Skoog (MS) medium with or without growth regulators. The highest regeneration (66 %) and the maximum number of shoots (3 - 4) per explant were obtained from the explants on MS medium containing 6-benzylaminopurine (5 × 10-6 M). A maximum roots per shoot were produced on medium containing 3-indole butyric acid (5 × 10-6 M). The resulting plantlets were hardened and transferred to soil in pots where 75 % of them survived and resumed growth. Histological examination of explants suggests that the shoots were of de novo origin which would make this system suitable for transformation experiments.

It is a matter of controversy whether secondary wall deposition is dependent on lignification during the development of tracheary elements. To understand this, tracheary element differentiation was studied in the homogeneous calli obtained from the cotyledonary explants of Cucumis sativus subsequent to treatment with plant growth regulators, such as naphthalene acetic acid (NAA) and benzylamino purine (BAP), which are necessary for the induction of tracheary elements, along with metabolic blockers such as 2-aminoindan-2-phosphonic acid (AIP), 2,3,5-triiodobenzoic acid (TIBA) and nifedipine. Calli treated with AIP, a potential inhibitor of L-phenylalanine ammonia-lyase (PAL), have no PAL activity at any time during the culture period. There was a complete inhibition of lignification although secondary wall deposition was unaltered. Similar results were obtained using TIBA, an inhibitor of auxin transport, and nifedipine, a known calcium channel blocker. Thus the present study suggests that secondary wall deposition in the course of tracheary element differentiation need not to be dependent on lignification.

The effect of cytokinins (CKs) and K+ on stomatal behaviour in darkness were studied in the root hemiparasite Melampyrum arvense before (the preparasitic stage) and after attachment to the host (Capsella bursa pastoris L. Med.). The solutes were applied with xylem stream. The stomatal apparatus of the attached hemiparasite was insensitive to externally supplied CKs and K+. Contrary to this finding, the stomatal aperture of hemiparasite in the preparasitic stage increased to about 25, 40 and 69% of the value obtained in light, respectively, after treatment with 200 mM KCl and 10-5 M zeatin riboside ([9R]Z), applied separately or together. CKs influenced K+ transport. The treatment with KCl and [9R]Z,separately or together, increased the content of K+ in guard cell pairs to about 32, 46 and 79 % of the value obtained in light, respectively. Other CKs had a smaller effect (45 - 16 %) in comparison with that of [9R]Z; isopentyladenine was nearly inactive.

We have examined the toxicity of ethanol in tissue culture of the apple rootstock 'Jork 9'. During proliferation through axillary branching, 0.2% (v/v) ethanol slightly stimulated proliferation whereas significant inhibition occurred at concentrations of 0.4 % or higher. In adventitious root formation, significant inhibition occurred at concentrations of 0.1 % or higher. The effect of ethanol was stage-dependent: during the induction period (i.e. from 24 to 72 h after the start of the rooting treatment), there was little or no inhibition. During autoclaving, ethanol evaporated to ca. 50 %.

Standard methods of isolation of chromatin histones from Arabidopsis thaliana yield strongly degraded proteins when applied to plants grown from seeds in axenic liquid media. For isolation of undegraded histones from Arabidopsis grown in liquid media we used extraction with guanidine hydrochloride followed by selective binding of histones on BioRex 70 resin in the batch system. The quality of obtained proteins is confirmed by SDS polyacrylamide gel electrophoresis.

The mechanisms of saccharose and sorbitol transport in Prunus persica leaves were investigated in plasma membrane vesicles purified by aqueous 2-phase partitioning and equilibrated in pH 7.5 buffer containing K+. The imposition of an artificial proton motive force energized an active uptake of both saccharose and sorbitol. The maximum uptake rate of saccharose was 2.5 times higher than that of sorbitol. Saccharose and sorbitol uptake exhibited saturation kinetics suggesting they were carrier-mediated. Apparent Km for the saccharose and the sorbitol uptake were 0.36 and 0.67 mM, respectively. Active absorption of saccharose was completely inhibited by a non-permeant thiol reagent, PCMBS, contrary to sorbitol absorption. These results suggested that saccharose and sorbitol were transported at least by two different carriers.

Suspension-cultured rice cells growth was markedly inhibited and ammonium content increased when rice cells were deprived of phosphate. When rice cells were cultured at increasing concentrations of ammonium chloride, ammonium content increased, however, no significant inhibition of cell growth was observed. Addition of D-arginine, an inhibitor of putrescine biosynthesis, resulted in a complete recovery of growth in rice cells under phosphate deprivation, but did not decrease the content of ammonium. Our results indicate that the growth inhibition induced by phosphate deprivation is not associated with ammonium accumulation.

Triazine (0.6 mM) quenched the chlorophyll fluorescence emission at 686nm, selectively reduced the biosynthesis of linolenic acid (C18:3), lowered the ratio of unsaturated/saturated fatty acids in thylakoid membranes and percentage of total glycerides in the extracted oils, and extremely enhanced ethylene production by seedlings. These effects were partly reversed by the addition of 100 g m-3 of vitamins (thiamine > nicotinic acid >pyridoxine).

In order to clarify the role of endogenous growth inhibitors A-2α and A-2β in a dwarf pea plant, red light (emission peak 657 nm) treated, 9-d-old seedlings of dwarf pea (Pisum sativum L. cv. Progress No. 9) were transferred to darkness, and the resulting changes in growth rate and concentrations of A-2α and A-2β were monitored. The growth rate of the epicotyls increased, and the concentration of the inhibitors in the epicotyls decreased, according to sigmoidal time courses. The relationship between the logarithms of the concentration of the inhibitors and the corresponding growth rate was linear. These results suggest that A-2α and A-2β, may play an important role in the growth recovery process of the dwarf pea cultivar after termination of red light irradiation.

The response of Brassica carinata hybrids and their parents to moisture stress at different growth stages was studied. B. carinata 226 was found to be susceptible to stress at pre-flowering and post-flowering stages while B. carinata 241 at flowering stage. Neither the changes in stomatal conductance nor in chlorophyll content could fully explain the reduction in net photosynthetic rate (P_N) induced by stress. B. carinata 241 had higher leaf water potential (ψ_w) although, it had lower P_N compared to B. carinata 226. Both the parents had lower P_N as well as leaf ψ_w. The stress response of PN in hybrids followed that in their respective female parents.