Callus culture was derived from haploid barley embryos after crossing withHordeum bulbosum. The callus tissue is cytologically heterogeneous, containing haploid, diploid and polyploid cells. Aneuploidy and karyokinetic irregularities were also observed. Some problems of chromosomal instabilities in plant tissue cultures are discussed.

Seeds of mung bean (Phaseolus aureus Roxb.) cv. Pusa Baisakhi were surface sterilized and sown both in Petri dishes and sand culture containing aqueous solutions of four different saltsviz. NaCl, KC1, Na₂SO₄ and K₂SO₄ each at 5 and 10 m ώ^-1 cm^-1. Malate dehydrogenase (MDH) isoenzymes were studied in different plant parts of mung bean at suitable intervals during germination under four different salts. In cotyledons, 96 h after sowing only one isoenzyme was left in control as compared to three under salt treatment. In the embryo axis, 96 h after sowing, sulphate salts resulted in the disappearance of isoenzymes with R₁ 0.43 and 0.62, whereas isoenzyme with R₁ 0.62 was missing only at a higher concentration of chloride salts. Chloride salts also resulted in the disappearance of band with R₁ 0.15, both in the embryo axis and leaves. However, in the roots the isoenzymic pattern remains the same with all the salt treatments.

The growth changes of cotyledons, leaves, hypocotyls and roots due to photoperiodic induction in short day plantChenopodium rubrum were investigated in relation to flowering. Six-day old plants were induced by photoperiods with a different number of dark hours. We found that the degree of inhibition which occurred during induction in the growth of leaves, cotyledons and roots similarly as the stimulation of hypocotyl is proportional to the length of dark period. The photoperiods with 12, 16 and 20 dark hours bring about marked inhibition of growth and at the same time induce flowering in terminal and axillary meristems. The inhibitory effect of critical period for flowering,i.e. 8 dark hours, is not apparent in all criteria used and even the flower differentiation is retarded. The photoperiods of 4 and 6 dark hours did not affect growth and were ineffective in inducing flowering even if their number has been increased. The experiments with inductive photoperiod interrupted by light break have clearly shown that growth pattern characteristic for induced plants can be evoked in purely vegetative ones. Such statement did not exclude the possible importance of growth inhibition as a modifying factor of flower differentiation. We demonstrated that the early events of flower bud differentiation are accompanied by stimulation of leaf growth. The evaluation of growth and development of axillary buds at different nodes of insertion enabled us to quantify the photoperiodic effect and to detect the effects due to differences in dark period length not exceeding 2 hours.

The variation in stomatal activity within the crowns ofAcer campestre, Carpinus betulus andQuercus cerris was measured by vapour exchange porometer on several summer days in an oak-hornbeam forest, in SW Slovakia, Czechoslovakia. Variation resulted from crown position in the forest stand and from leaf position within the canopy. The highest stomatal conductance was in sunlit sun leaves in the upper part of the canopy. Stomatal conductance decreased with increasing depth in the canopy. The steepest decrease was in the upper canopy, in the intermediate zone between fully sunlit and fully shaded leaves, and was caused by the decline in leaf irradiance and in stomatal density. In codominant trees, the conductance in shade leaves at the base of the crown was significantly lower than in the sun leaves at the top of the crown. In a dominant tree,Q. cerris, the differences in stomatal conductance were small and most frequently insignificant. Variation in incident light also determined the diurnal variation of stomatal conductance with respect to crown aspect. Differences between sun leaves on the east and west facing aspects of the overstory crown ofQ. cerris were demonstrated for several days.

The plants of two herbaceous species, namelyPulmonaria officinalis L. andSymphytum tuberosum L., growing in two deciduous forests in SW. Slovakia, were used for analysis of anatomicphysiological gradients along the insertion level of individual leaves. The gradients were established for six leaf characteristics. Specific leaf area and development of leaf area increased, while leaf tissue hydration, degrees of succulence and consistency decreased with height of insertion of leaves upon the stems. The gradients indicate the decreasing of the leaf water content and dry mass with height of the leaf on the stem. Stomatal resistance was usually the lowest in basal leaves and the highest in apical leaves of the plant. The anatomic-physiological heterogeneity of leaves of a plant is large and cannot be neglected in any anatomical or physiological investigations.

Among different populations of monogerm sugarbeet fruits, those characterized by the lowest percentages of germination exhibited the lowest percentages of mechanical deoperculation (removal of the fruit cap under the sole imbitition pressure). X-ray radiography of dry fruits allowed a classification based on the space occupied by seeds inside the fruit cavity and further established a correlation between the fruit type (filled, semi-filled, empty), passive deoperculation and germination. The degree of correlation depended on the amount of bedding water which further conditioned the fruit surrounding water film.

During high altitude acclimatization both the number of stomata and their pore width decreased. The number of open stomata per unit leaf area in the morning and evening hours was higher as compared to that in plants grown at a lower altitude. Thickness of leaves also decreased at high altitudes but the effect on the size of epidermal, mesophyll and spongy parenchymatous cells varied from species to species. Adaptational significance of these changes are discussed.

Using the enzyme-linked immunosorbent assay (ELISA) beet yellows virus (BYV) could be detected reliably in the leaves of sugar beet andTetragonia expansa Pall. and in the roots of sugar beet. Specifio γ-globulin of BYV antiserum was coupled to horse radish peroxidase by periodate oxidation. Optimum dilutions of antigen (extract from infected leaves) were1: 50 to 1: 200 for BYV detection in sugar beet andT. expansa leaves and1: 2 to 1: 5 for detection in sugar beet roots. Extracts from beet roots are not to be purified by ultracentrifugation, however, by the described method virus can be demonstrated only in 80-90% of naturally infected sugar beet roots. The method is specific, no increase of extinction values was found in healthy or beet western yellows virus infected plants. Presence of virus can be demonstrated by visual as well as photometric evaluation. Results confirmed the suitability of peroxidase application for detection of plant viruses by ELISA.

Cell division contributing to longitudinal growth of the shoot apex was investigated inChenopodium rubrum in segments marked by the axils of leaf primordia. Plants treated with two short days (16h of darkness and 8h of light) were compared with two non-induced controls (cultivated in continuous light or treated by alternations of 8 h of darkness and 4 h of light for two days). During the short-day treatments the rate of cell division contributing to the longitudinal growth decreases in all segments of the shoot apex irrespective of whether the darkness was given in inductive or non-inductive photoperiods. The rate of cell division contributing to longitudinal growth increases in the upper internodes of the shoot apex after the termination of the photoperiodic treatment and transfer of the plants to continuous light. However, cell division remains inhibited in the lowest segment of the shoot apex. This inhibition in the differentiating parts of the shoot apical meristem is a direct consequence of photoperiodic induction. It is supposed that this inhibition is related to evocation similarly as the well-known phenomenon of stimulation of cell division in the apical dome.

Four tree, five shrub, and ten herbaceous species growing naturally in an oak-hornbeam forest were used for simultaneous study of the leaf diffusive resistances in the course of several summer days. Absolute minima of the stomatal resistance in the sun tree, the shrub, and the herbaceous species leaves were 1.7 to 6.2 s cm^-1, 6.1 to 10.8 s cm^-1, and 4.8 to 9.7 (17.3 inConvallaria majalis leaves) s cm^-1, respectively. Minimum daily leaf resistances in the course of a day were noted earlier in the morning in sun leaves of large trees than in shade leaves of other species. Stomata were fully opened later in the morning and they began to close sooner in the afternoon in usual shade leaves of the plants in the interior of the forest canopy than those in sun leaves in active surfaces of the canopy (tops of tree crowns). The relatively large differences in leaf resistances found among investigated species may be explained by differences in leaf anatomy (stomata frequency and size) and in ambient leaf or plant environment caused by leaf (plant) position in different vertical layers.

A time course study of changes in the pattern of peroxidase isoenzymes shows that two new isoenzymesa andb appeared in hypocotyl cuttings cultured either in indolyl-3 acetic acid (IAA) + sucrose or in water but not in maleic hydrazide (MH). Roots were also initiated in the former two cases but not in the last case. That these isoenzymes may be associated with root initiation is also evident from the fact that these appeared when hypocotyl cuttings were transferred from MH to IAA + sucrose. The time of appearance of these isoenzymes in different cultures also synchronized with the time of microscopic root initiation. While the isoenzymea disappeared,b persisted in cuttings transferred from IAA + sucrose to MH. The number of roots produced on cuttings transferred to MH was very low, though their development was normal. It is suggested that isoenzymesa andb may be associated with root initiation andc andd with root development.

Protoplasts isolated from cell suspension cultures of potato were cultured as far as the level of regeneration of substrains. The influence of various factors (age of the cell culture, mode of precultivation, composition of the enzymatic mixture, incubation period) on the efficiency of isolation as well as the viability of protoplasts, has been studied. Various cultivation procedures have been screened and the effect of especially the hormonal composition of the medium on different phases of the regeneration of cell colonies (regeneration of the cell wall, growth and elongation, cell division) evaluated.

The reaction: Chlorophyll + Enzyme → Chlorophyllide + Phytol follows a first order kinetics with regard to the quantity of enzyme, when it is saturated by substrate. K_m and V_m were determined from the average reaction rates for the substrates: Chlorophylla andb, pheophytina andb, methylchlorophyllidea and methylpheophorbide a: The lowest K_m corresponded to chlorophylla and the highest V_m to methylpheophorbidea. For a substrate of chlorophyll (a + b), K_m and V_m were determined also using the initial reaction rates. "Enzyme efficiency" was calculated using both methods of determination. The reaction products partially inhibit the hydrolytic process.

Wheat seedlings were cultivated in nutrient solutions containing 10^-3 M CCC, 10^-3 M CEPA or 5 × 10^-4 M CCO and CEPA, respectively. CCC applied alone or mixed with CEPA increased chlorophyll content per unit fresh matter but had no influence on the epinastio response of the primary leaf. In contrast, CEPA had no influence on chlorophyll content but greatly increased the epinastic response. The different response to the application of these substances with regard to chlorophyll content ha been claimed in a previous paper to be due to their different effect on cell extension and cell division. The epinastic response of the primary leaf suggests that ethylene participates in the reaction chain of CEPA effect on plant tissues.

The investigation of the substrate specificity of the anionic peroxidase isoenzymes, isolated from the zone of differentiation of the primary roots ofZea mays, for some representatives of phenolic compounds and aromatic amines, as hydrogen donors, is reported. The investigation was carried out electrophoretically with peroxidase isoenzymes partially purified by a combination of gel filtration by Sephadex G-25 and Sephadex G-100. A difference in the substrate specificity of the individual isoenzymes is observed. It was established that the anionic peroxidase isoenzymes showed a similarity in total number and relative activity on staining with bivalent phenols and difference on staining with trivalent phenols, as hydrogen donors. A greater number of isoenzymes was stained with benzidine ando-dianisidine and a lesser number witho- andp-phenylendiamine. The substrate specificity of the peroxidase isoenzymes was compared for guaiacol and benzidine. The substrate specificity of peroxidase soenzymes was discussed as regards their diverse role in the plant metabolism.

Conductance of abaxial epidermis was measured in leaves ofAcer campeatre, Carpinus betulus, Quercus cerris andQ. petraea sample trees growing in an oak-hornbeam forest. Measurements were performed on several summer days during morning and midday hours. Stomata tended to oscillations only inQ. cerris. The occurrence of stomatal oscillations was controlled by environmental conditions,e.g. weather.

Inoubation of thin slioes ofTaraxacum root segments in 3-indoleaoetic acid solutions enhanced the level of total proteins, RNA, DNA and a number of enzymes reaching an optimum at 0.01 mg 1^-1. It has been shown that the auxin promotes the synthesis of DNA, again with an optimum promotion at 0.01 mg 1^-1 IAA.

The influence of phenolic and humic acids on the activity of glucose-6-phosphate-dehydrogenase in the roots of pea under aseptic conditions has been investigated. It seems clear that vanillic and protocatechuic acids inhibit the enzyme activity in the excised roots of pea, but their dry weight increases in relation to the control. Gallic acid stimulates the G-6-PD activity in the roots of whole plants. The humic acids influence neither the enzyme activity nor the dry weight of pea seedlings after short-term treatment.

The effect of 2,4-dinitrophenol (2,4-DNP), NaN₃, and iodoacetic acid (IDA) on glutamine synthetase (GS) and the effect of arsenate on GS, glutamate dehydrogenase (GDH) and nitrate reductase (NR) was studied in isolated pea roots. In sucrose supplied roots, GS level is depressed by higher concentrations of all the inhibitors tested and increased by lower (2 × and 3 × 10^- M) concentrations of 2,4-DNP; the decrease in GS level caused by sugar starvation is enhanced by all but IDA. GDH is enhanced by arsenate in a wider range of concentrations in sucrose-supplied roots than in roots cultivated without sucrose. NR is affected by arsenate similarly as GS.

Germination inPhaseolus trilobus is controlled by different moisture levels of seeds. The hard seed coatedness which develops secondarily can be removed by pretreatment with oonc. H₂SO₄. This also enhanced the onset of seed germination.

Carbohydrate changea in drought resistant and susceptible cultivars ofZea mays L. were studied at two different stages under imposed water stress in water culture experiments. The gradual decline in total carbohydrates with increasing stress levels was observed. At the 1st leaf stage starch content of the resistant cv. Agati-76 was lower than that of susceptible cv. Vijay but the reducing and non-reducing sugar content was much higher. At the 3rd leaf stage starch content was similar in two cultivars but sugar content was higher in the resistant cv. Agati-76. Differential changes in root and shoot carbohydrates as affected by increasing levels of stress were noticed. Carbohydrate changes have been discussed in relation to drought resistance.

³H-thymidine incorporation and DNA-polymerase activity during early hours of wheat embryo germination at two viability levels have been studied. The patterns of two biosynthetic activities, as well as the dependence of DNA synthesis on protein synthesis, indicated the presence of a delay in the early phase of imbibition of the aged embryos with respect to viable germs.

When flax seedlings are decapitated above cotyledons and three days later one of the two cotyledons is removed then the remaining cotyledon stimulates in four to five days growth of its axillary bud. It has been found that content of endogenous cytokinins was higher in the stimulated bud as compared with the other one already 12 h after the cotyledon removal.
Flax seedlings decapitated under cotyledons regenerate adventitious buds on thy hypocotyl stump during 5-6 days. The endogenous fytohormonal preparation of this regeneration was investigated in the 20 mm apical part of the hypocotyl stump. Decrease in auxin and increase in gibberellins was already found during the first day after decapitation while the level of cytokinins increased as late as three days after the apex removal.