The content of abscisic acid (ABA) in abaxial leaf epidermis of the host (Capsella bursa pastoris) and the unattached hemiparasiteMelampyrum arvense showed diurnal changes. ABA content increased during the light period and declined rapidly upon the darkening of leaves. In an attached hemiparasite the content of ABA in the epidermis was maintained at an almost constant level irrespective of the diurnal cycle. As compared with the maximum level in the host, at the end of the light phase the content of ABA in abaxial epidermis constituted about 70 % and 164 % in the unattached and attached hemiparasite, respectively. No significant changes in ABA content were recorded in adaxial epidermis. In all the samples abaxial/adaxial epidermis ABA content ratio was about 3.6:1 in light phase. In darkness this ratio decreased to about 1.1:1 in the host and the unattached hemiparasite and did not show significant change after attachment. ABA content ratio in mesophyll was 1:0.7:1.5 for the host, the unattached, and attached hemiparasite, respectively. In comparison with the host the concentration of ABA in xylem sap of the hemiparasite constituted about 31 % and 152 % for the unattached and attachedM. arvense, respectively.

Difluoromethylornithine (DFMO) counteracted several processes that are promoted or inhibited by auxins or inhibitors of polar auxin transport: inhibition of asymmetric gene expression in carrot, stimulation of gametic embryogenesis inBrassica, inhibition of root elongation in tobacco, inhibition of the development of lateral roots in pea and adventitious roots in apple, and inhibition of floral bud formation inArabidopsis

We measured PAR-saturated CO₂ exchange rate (CER), and leaf N, P and chlorophyll (Chl) concentrations in 21 plant species, selected to encompass as broad a range in specific leaf area (SLA) as possible, and encompassing non-succulent C3 as well as succulent CAM plants. We worked with plants growing under uniform conditions in the facilities of a biological research station to ensure that any correlations found were due to inherent, genetically controlled, relationships between the measured parameters and not due to variations in resource availability in different habitats. We found CER to be strongly correlated to SLA, leaf N concentration and Chl concentration. CER increased much faster with increasing leaf N concentration (CER ≈ N^3.1) than with increasing SLA (CER ≈ SLA^1.2). CER also increased much faster with leaf N concentration than with increasing Chl concentration (CER ≈ Chl^1.3), indicating the photosynthetic N-use efficiency (NUE) to be higher for plants with high N concentration than for plants with low N concentration (NUE ≈ N^2.1). Analysis of covariance showed that these relationships exist even when comparing plants of widely different growth forms - succulent or non-succulent, and of different photosynthetic pathways, as the C3 and CAM plants compared here. Testing against scaling coefficients calculated using dimensional analysis, showed that the scaling of N, Chl and CER against SLA was not merely a result of diluting N and Chl with carbon in thicker leaves but that SLA, probably through influencing light absorptio and/or CO2 diffusion pathway, played an independent role in controlling CER.

Developing fruits on lower nodes were major reproductive sink for photosynthates in bell pepper (Capsicum annuum L.). The removal of these fruits resulted in faster growth of other fruits on upper nodes. Sink manipulated plants have the higher rate of net photosynthetic rate at the later stages of plant development.

Single treatment of expanding radish leaves with N₁-(2-chloro-4-pyridyl)-N₂-phenylurea (4-PU-30) lead to the stimulation of root cambial tissue activity and root growth. Leaf thickness, the volume of chlorophyll (Chl) containing cells per unit leaf area, starch content in the chloroplasts, and the Chl content increased simultaneously. These alterations were associated with increased leaf net photosynthetic rate and stomatal conductance in treated plants.

A non-destructive method of total vertical projections for estimating the length of rigid root systems, not introduced yet in plant sciences, is described. It is demonstrated on measuring less and more dense root systems of seedlings of Zea mays grown at hypoxic or control conditions. Photographs of six vertical projections (30° apart) of each root system were taken and evaluated. The method being based on proved mathematical formula offers unbiased estimation of the length of a rigid root system, curved in three-dimensional space, by non-destructive means. Thus, it is applicable during ongoing experimentation on plants grown in a solution culture. It was shown that less than 120 intersections between the root projection and test lines in one photograph ensured sufficient precision of the method and that the observer subjectivity could be overcome by presented instructions.

The role of plant antioxidant system in water stress tolerance was studied in three contrasting wheat genotypes. Water stress imposed at different stages after anthesis resulted in a general increase in lipid peroxidation (LPO) and decrease in membrane stability index (MSI), and contents of chlorophylls (Chl) and carotenoids (Car). Antioxidant enzymes like glutathione reductase and ascorbate peroxidase significantly increased under water stress. Genotype C 306, which had highest glutathione reductase and ascorbate peroxidase activity, also showed lowest LPO and highest MSI, and Chl and Car contents under water stress in comparison to susceptible genotype HD 2329, which showed lowest antioxidant enzyme activity as well as MSI, Chl and Car contents and highest LPO. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Thus, the relative tolerance of a genotype to water stress as reflected by its comparatively lower LPO and higher MSI, Chl and Car contents is closely associated with its antioxidant enzyme system.

Recently, evidence has increased for both long- and short-distance transport of polyamines (PAs) in living organisms, but the mechanisms involved and physiological significance of PAs translocation are still not well understood. This review deals with various aspects of polyamine uptake and transport in higher plant tissues.

When distantly related plants are crossed, embryos abort on the mother plant. One of the methods used to rescue the embryo is to cultivate the ovulein vitro. When the ovule is precociously detached from the mother plant, survival rate of the embryo is very low. To increase the chance of survival as well as the growth of the embryo, the medium was supplemented by different extracts of plants after either autoclaving or filtering. Autoclaved tomato extract seemed to have no simulating effect in spite of reports from different authors. Filtered coconut milk increased growth and filtered cucumber extract improved survival. Other new extracts had a stimulating action on both growth and survival and are of interest for further study.

Protocols were developed for plant regeneration from callus induced in mature embryos of rice. Somaclonal variation was scored by genome mutation, chromosome mutation and plasmon mutation in R₀, R₁ and R₂ plant progenies. The frequency of haploids and diploids appeared in the ratio of 20:33. Variation in the chromosome number in callus cells was found to be high and age dependent. Different types of chlorophyll deficient mutants including albinos appeared in R₂ plant progeny where gene mutation frequency was the highest (52.4 %). The results revealed that a high frequency of somaclonal variation is possible to generate by tissue culture techniques.

Mutagenesis provoked by exposure to increased concentration of antibiotics of five indigenous Rhizobium galegae strains resulted in the generation of several antibiotic-resistant mutants. The mutants differed from the wild type and one from another in respect to the nodulation capacity, the nitrogenase activity, the nodule ultrastructure, and the plant growth response. Galega plants inoculated with mutants resistant to streptomycin and rifampicin formed nodules with higher nitrogenase activity and accumulated more shoot dry biomass than plants inoculated with the parent strains. Resistance to kanamycin and nalidixic acid was associated with significant decrease of nitrogenase activity. A correlation between nitrogen-fixing efficiency and nodule infected cell ultrastructure was found. When the bacteroids occupied about 10 times higher area in infected cells of nodule than peribacteroid spaces and host cytosol had electron dense and homogenous structure, the nitrogenase activity was the highest.

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.

Effects of water stress at different stages of plant growth on leaf relative water content (RWC), osmotic potential (Ψos) and changes in contents of chlorophyll, abscisic acid (ABA), zeatin riboside (t-ZR), ethylene and proline in six cultivars of French bean (Phaseolus vulgaris L.) were studied. Under water stress, Ψos and RWC were highest in cv. Contender and lowest in cvs. IIHR-909 and Sel-2. The increase in contents of ABA and proline was marked in cv. Contender followed by cv. UPF-626. Decrease in t-ZR and chlorophyll contents was prominent in cv. IIHR-909. Ethylene production surged in all the cultivars under 4- and 8-d stress and declined under 12-d stress.

Plants of teak (Tectona grandis L.f.) growing after transplantation to fertile soil for 5 - 6 months were subjected to water stress by withholding watering continuously for 3 weeks. The growth rates of both plants in height and developing leaves in length were unaffected during the first week after withholding watering, but they were decreased by about 50 % during the second week and became negligible during the third week of water stress treatment. The rate of leaf production and internodal elongation were also decreased in plants experienced 2 weeks of water stress. However, after rewatering, these plants regained growth potential and exhibited high rates of leaf expansion and plant growth comparable to those of well-watered plants. Diurnal course of net photosynthetic rate (PN) of plants subjected to water stress for 2 weeks was similar as that of well-watered plants. However, PN of plants subjected to water stress for 3 weeks was reduced in the afternoon. Similarly, stomatal conductance (gs) and transpiration rate (E) of plants experiencing 3-week water stress were decreased in the afternoon. Soon after rewatering, PN, gs and E reached similar values to those of well-watered plants.

Chenopodium rubrum L. ecotype 184 is a qualitative short-day plant with critical length of the night of eight hours that must be exceeded in order to flower: Five days after sowing, the plants were exposed to a various number of inductive cycles (14/10 h of däy/night cycle) to test the optimal photoperiodic conditions for flowering. In our experimental conditions the plants flowered with high percentage after more than four received inductive cycles, but there was no flowering below that. The plants grown on the herbicide Norflurazon (photobleached plants) showed different photoperiodic characteristics. There was negligible flowering of photobleached plants in the same experimental conditions as for the green ones.

Zygotic embryos of Karwinskia parvifolia, isolated from seeds obtained from different regions of Mexico, were cultured on Woody Plant Medium (WPM) supplemented with 0.06 µM indole-3-acetic acid, 0.03 µM gibberellic acid, and 2 µM 6-benzylaminopurine. The growth of embryos and multiplication of shoots from stem segments were achieved. Rooting of excised shoots could be initiated on basal WPM medium with prolonged subculture period to 2 months, or on WPM medium supplemented with 10 µM 1-naphthaleneacetic acid. Multiplication capacity of shoots and rooting of K. parvifolia differed in dependence on the origin of explant material. The shoot multiplication was much lower than that of Karwinskia humboldtiana. The rooting depended on the origin of K. parvifolia seeds. The regenerated plants were successfully transferred to glasshouse.

Eichhornia crassipes plants brought from the River Nile were cultured in jars containing river water supplemented with various concentrations of Cd, Pb, and Sr (0 to 100 μg cm-3), added simultaneously. Treatment continued for 20 d during which each cultivation solution was being replaced with fresh one every 3 d. The growth of Eichhornia was drastically retarded at heavy metal concentrations higher than 15 μg cm-3. At concentrations 15 or 25 μg cm-3, the accumulation of Cd and Pb to levels several times higher than those in control plants was found. More than 50 % of the uptaken metals were retained by roots alone. Leaves and leaf petiols received around 30 and 20 % of the accumulated metals, respectively. X-ray microanalysis indicated the presence of the three heavy metals in Ca oxalate crystals. Content of metals in the crystals increased progressively over time of exposure in a way similar to those in whole plant tissues. These results suggest a possible role for Ca oxalate crystalization in toxic heavy metal deposition and thus tolerance by Eichhornia.

The chlorophyll and protein contents of the flag, second and third leaves gradually decreased during the reproductive development of rice (Oryza sativa L. cv. Rasi) and wheat (Triticum aestivum L. cv. Sonalika) plants, whereas proline accumulation increased up to the grain maturation stage and slightly decreased thereafter. In rice plant, the rate of decrease in chlorophyll and protein and increase in proline level were higher in the flag leaf than in the second leaf. It was opposite in wheat plant. The export of [³²P]-phosphate from leaves to grains gradually increased reaching a maximal stage at the grain development stage, and then declined. The export of this radioisotope was greater in rice than in wheat. Removal of panicle at the anthesis and grainfilling stages delayed leaf senescence of rice plant, while in wheat the ponicle removal at any stage did not have a marked effect on delaying leaf senescence. The contents of chlorophyll and protein of glumes were higher in wheat than in rice. The variation of such source-sink relationship might be one of the possible reasons for the above effect on leaf senescence.

Dry matter production of shoots and roots and the diurnal fluctuation of titratable acidity of single leaves were investigated in the CAM plant Agave attenuata during the first 70 d after germination. The plants were grown either in vermiculite sub-irrigated with a nutrient solution or in in vitro cultures on an inorganic nutrient agar. Two types of culture tube covers were used: either airtight closures or polypropylene caps with membranes permeable to air.
In the earliest ontogenetic phases of development (cotyledon and primary leaf stage), the plants were already able to carry out considerable nocturnal organic acid accumulation. In vitro cultivated plants, from the beginning of their development, were also capable of diurnal acid fluctuation, though of distinctly weaker activity than the pot plants. The mean relative growth rates (RGR) of pot culture plantlets approached a third of perennial herbaceous plants. Plantlets grown in in vitro culture reached only half to the one quarter of the RGR of pot plants. The reduced yield could be attributed to the low CO2 supply in the culture tubes and the less than optimal water and nutrient supply in the agar medium.

The physiological responses of alfalfa (Medicago sativa L. cv. Gilboa) to salinity (100 mM NaCl) and some inorganic nutrients (K+, Ca2+ and N as NO3-) were investigated. Salinity caused a substantial reduction in biomass, carbon assimilation rate, stomatal conductance, water use efficiency, leaf area, relative growth rate, NO3- content and nitrate reductase activity, whereas, transpiration rate was slightly affected. Inclusion of K+, Ca2+ and N as NO3- in plant nutrient medium in combination or alone brought about a marked stimulation in control plants and moderated the salinity caused reductions in NaCl treated plants. In addition, plants also exhibited differences in these parameters at two growth stages.

Nine sugar beet lines were grown in a glasshouse on chernozem soil watered to 35, 50 and 65 % of maximal soil water capacity. After 12 d, plant water potential, net photosynthetic rate, contents of soluble proteins, DNA and RNA, proportion of ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) protein, and carbonic anhydrase activity were measured. As soil moisture decreased, the leaf water potential and net photosynthetic rate decreased. DNA and RNA content and carbonic anhydrase activity decreased under moderate drought, and increased with severe drought. RUBISCO protein proportion did not change significantly under decreased soil moisture, while the total soluble protein content decreased.

Tissue specific plant lectins were searched in the seeds of 44 tropical trees of Kerala, India. Seeds of only 12 plant species showed lectin activity. N-acetyl-D-galactosamine was the best inhibitor of lectin activity for the majority of the seeds. Lectin activity in the seeds of 4 species were not inhibited by any of the mono- or polysaccharides used.

The role of proline in imparting tolerance to salinity was investigated in Hydrilla verticillata, Najas indica and Najas gramenia. The plants were exposed to different concentrations of NaCl and artificial sea water (SWS) separately. The chlorophyll (Chl) a/b ratio decreased significantly in all the three plant species in both NaCl and SWS treatments, comparatively more in former than the latter. NaCl resulted in drastic decrease in this ratio in salt sensitive H. verticillata and N. indica, but in somewhat lesser decrease in salt resistant N. gramenia. Proline content increased at both NaCl and SWS treatments, especially at the latter. However, in H. verticillata proline content at 1.5 and 2.5 % NaCl decreased. It was concluded that proline cannot be used as a biochemical marker of salt tolerance in aquatic plants, however, the decrease in Chl a/b ratio in response to NaCl may be used as an index of salt sensitivity in this ecological group of plants.

The effect of growth in saline medium on the activity of two ATP utilizing enzymes was studied. Hexokinase in carrot (Daucus carota L.) cells grown in suspension culture either in the absence or presence of 150 ml NaCl, and tonoplast H⁺-ATPase in tobacco (Nicotiana tabacum L. cv. Wisconsin 38) cells grown in suspension culture either in the absence of presence of 428 mM NaCl. There was no difference in the pH profiles, NaCl sensitivity and kinetic parameters towards glucose of hexokinase activities from carrot cells grown in the presence or the absence of NaCl, but the activity from cells grown in the presence of NaCl was more resistant to inhibition by N-ethylmaleimide and to inactivation by heat. Two separate apparent Km values toward ATP were delineated in the extract from cells grown in presence of NaCl while extracts from cells grown in the absence of NaCl had only one apparent Km value. The tonoplast H⁺-ATPase from NaCl grown tobacco cells showed changed kinetic compared to this activity from cells grown in the absence of NaCl. These data may indicate that growth in NaCl results in the appearance of isozymic activity that enhances the ability of plant cells to utilize metabolic energy more efficiently.

Tobacco and carnation plantlets were grown in vitro on Murashige and Skoog's medium with 2 % saccharose. Carnation plantlets were also grown fully photoautotrophically on a medium without saccharose. The ambient CO2 concentration was increased from 0.6 to 10 or 40 g m-3 during the last 3 weeks of in vitro cultivation or during the first 3 weeks of acclimation to ex vitro condition (plantlets transplanted to pots with sand and nutrient solution) or during both growth phases. CO2 enrichment during in vitro cultivation markedly stimulated growth of tobacco plantlets, and also of carnation plantlets, both with and without saccharose. CO2 enrichment during the acclimation period promoted plant growth more effectively in plantlets grown in vitro at a CO2 concentration of 0.6 g m-3 than in plantlets grown in either growth phase at higher CO2 concentrations.

Source-sink relationship, which was influenced by both genotype and environmental factors, contributed to the variation in photosynthesis and photosynthate partitioning of wheat. Source reduction by partial defoliation increased leaf net photosynthetic rate (PN), and sink reduction decreased PN of irrigated wheat. However, the change in PN varied among genotypes. Source reduction enhanced photosynthate translocation into grain in irrigated wheat. However, the enhancement was more evident in cv. Lumai 215953 than incv. Lumai 15. Sink reduction had little effect on the translocation of photosynthate into grain in cv. Lumai 15, but decreased the translocation of photosynthate into grain and increased it into stem in cv. Lumai 215953. In rainfed, non-irrigated wheat, the source or sink manipulation influenced PN only slightly. The source reduction decreased the partitioning of photosynthates into the upper parts (including grains) of plant. However, very little effects of sink reduction on the production of photosynthates occurred in rainfed wheat. This showed that grain sink size was not a factor limiting the production of photosynthates, but controlled the partitioning of photosynthates. Sink reduction decreased photosynthate translocation into grains, and increased it into upper parts of rainfed wheat plant.

Comparative analysis of the electrolyte efflux, as a screening test of the membrane tolerance to water stress, was carried out in poikilohydric plants Ramonda serbica Panč. and Ramonda nathaliae Panč. & Petrov. and homoiohydric plant Saintpaulia ionantha Wendl. from the same family Gesneriaceae. Water stress was induced by PEG 600. The high degree of solute leakage in the East-African drought-intolerant Saintpaulia ionantha points to the loss of membrane integrity. In contrast, Balkan endemites Ramonda serbica and R. nathaliae show high resistance to water stress due to the specific constitutional drought tolerance mechanisms.

An efficient protocol was developed for in vitro plant regeneration via somatic embryogenesis from cell suspension cultures of metal tolerant grass Echinochloa colona (L.) Link. Callus was obtained by culturing leaf base on MS medium supplemented with 0.5 mg dm^-3 of 6-benzylaminopurine (BAP) and 2.0 mg dm^-3 of 1-naphthaleneacetic acid (NAA). Cell suspensions were initiated and established in MS liquid medium containing 0.5 mg dm^-3 BAP, 1.0 mg dm^-3 NAA and 2.0 mg dm^-3 2,4-dichlorophenoxyacetic acid (2,4-D). A reduction in the concentration of 2,4-D to 0.5 mg dm^-3 induced formation of somatic embryos. The embryos developed and grew into normal plants in the presence of half strength MS medium without growth regulators. The regenerated plants were hardened in the greenhouse and subsequently grown in the open. This system may be also used for isolation and culture of protoplasts as a first step in somatic hybridization.

Pre-submergence reserve saccharides was found adequate to substantiate the survival of tolerant cultivar under flooding. Survival percentage declined in both tolerant and susceptible cultivars with less saccharide content. However, it was more apparent in susceptible cultivar. Plant height, fresh and dry mass of shoots, leaf mass/area ratio and starch content per plant before flooding showed significant positive association with submergence tolerance. Hence, the improved seedling vigour could be used to increase submergence tolerance.