Phloridzin level and phloridzin β-glucosidase activity were estimated during apple seed cold stratification and during the culture of apple embryos isolated from seeds after different times of stratification. Both these factors were found to increase parallel to the progress of stratification as well as to the increasing ability of seeds/embryos to germinate. However, in the seed coats phloridzin dissappears during the progress of stratification despite the increasing β-glucosidase activity.
Phloridzin formation in the embryos is postulated to be under light and gibberellin control, when isolated embryos germinate, and under temperature and gibberellin influence during the cold stratification of the seeds. The same factors control β-glucosidase activity development, which is also stimulated by the substrate itself. It is postulated that phloridzin accumulation and its glucosidase activity are indirectly related to the after-ripening process and directly to the germination of the embryos.

InGalanthus nivalis ovules two haploid embryo sacs sometimes occur. One of them originates from the chalazal megaspore, the other from the above-chalazal one. The former is usually fertilized and pushes the latter to the lateral position.

Irradiation of the seeds of radioresistant kohlrabi with gamma-rays causes at doses SO to 300 kR a decrease in growth and a drop in tryptophan (Try) level in seven-day-old plants. The level of glucobrassicin (GLUBR), 3-indolylacetonitrile (IAN) and gibberellic acid (GA3) in these plants increases up to a maximum with a dose of about 150-200 kR, afterwards it decreases. We assume that the specific system of auxin synthesis inBrassicaceae plants takes an important part in the reparation processes and thus in the radioresistance of these plants as well. In contrast to the divergent systems of auxin biosynthesis in other plants which are damaged by lower doses of irradiation, the specific system of auxin formation via GLUBR synthesis, under formation of IAN intermediate, is widely not. attacked by radiation. Thus, these irradiated plants are supplied with auxins and with gibberellins too, the both hormones having a radioprotective effect.

In decapitated pea plants an increased peroxidase activity ocours after the cotyledon excision in cotylars growing in axillas of cotyledons prior to the growth of excised cotylars. It was found that peroxidase plays an important role in this correlation.
Auxin applied on epicotyl stumps inhibited the growth of cotylars and the removal of this inhibition by cytokinin or ethrel was associated with an increased peroxidase activity followed by the growth of cotylars situated in axillas of treated cotyledons.

Following a 24-h exposure to a solution of polyethylene glycol 4 000 of a -12.66 bar osmotic potential the roots of maize ceased growing. The inhibition of growth was conditioned by the inhibition of cell elongation and division. The elongation of cells was substituted by their radial enlargement which took place both in the peripheral and central root parts. The cells either did not divide at all, or sporadic mitoses still occurred in the roots. The meristematic cells treated were highly vacuolized, chromatin condensation being observed in their nuclei. In contrast to growth processes, differentiation was stimulated: the formation of the secondary wall in protoxylem elements occurred at a shorter distance,i.e. 1 500-2 400 µm from the apex, in comparison with 4000-5 000 µm in the control, this evidently being caused not only by the inhibition of growth, but also by the capacity of cells to differentiate more rapidly. The changes induced by a 24-h exposure to water stress were of a reversible nature; however, a 48-h treatment brought about irreversible changes.

The water potential of wheat and barley leaves considerably decreased with the decrease of the soil moisture percentage, with the increase of the eleotrical conductivity of the soil solution and with the increase in the exchangeable sodium percentage level. Also the leaf insertion level affected the values of water potential and the most negative values were found in the top leaves.

Pretreatment with calf thymus DNA decreases the frequency of chromosomal aberrations in metaphases and anaphases induced by X-rays in barley root meristem cella. This effect is manifested in a wide range of concentrations (5% -0.001%) without any great dependence on the concentration. Calf thymus DNA alone does not induce any chromosomal aberrations in barley root meristem cells.

Epidermal features of control, 16 treated and 7 mutants ofPhysalis ixocarpa BROT. (tomatillo),Lycopersicon esculentum MILL. (tomato) andL. pimpinellifolium MILL. (currant tomato) are studied. Although the distribution, ontogenesis and mature structure of stomata in control as well as in treated and mutant plants were similar, the mutagens reduced the stomatal abnormalities which were abundant (60%) inP. ixocarpa. Maximum rectification was found after combined treatment of gamma radiation (5.16 C kg^-1 [= 20 kR]) + 1 % dimethyl sulphate. Methyl ethane sulfonate, gamma radiation and gamma radiation + DMS caused an increase in epidermal cell size irrespective of the leaf size but in DMS and diethyl sulphate treated plants, a close negative correlation between leaf size and epidermal coll size was observed. The size and frequency of stomata were also affected, the large leaf usually showed high frequency and small size stomata. The data reveal that mutagens affect the epidermal structures differently.

The sensitization of chlorococcal algae by 5-BdU for the purpose of UV-light mutagenesis was studied. The results obtained were compared with our earlier findings on the sensitization of the same algal strains by 5-BU. No shielding effect of the 5-BdU molecules against UV-light was observed. Probably, the uptake of them from the liquid medium did not result in such excess as compared with the treatment by 5-BU, even if the cells were long enough (24 h) exposed to the concentration of 5-BdU. Likewise, neither stimulating nor inhibiting growth effects on the growing cell colonies were observed after treatment with 5-BdU. The sensitization of the algal cells for UV-light effects was effective in all the experiments. An increased damage of the algal cells by UV-light after sensitization was proved in all the parameters recorded. The frequencies of permanent changes of the cells or their colonies were also increased, but their spectrum did not change significantly. A suitable combination of the 5-BdU sensitization of the cells before their influencing by UV-light and the induction of their repair mechanisms by visible light may decrease the frequencies of the lethal or sublethal damage and increase the frequencies of the useful permanent changes in the characteristics of the chlorococcal algae. The results obtained are discussed from the viewpoint of the regulated mutation process in the breeding of algae.

A decreased germination capacity of the seeds ofChenopodium bonus- henricut collected at high altitude is not due to an embryo dormancy. It is caused by a seed coat inhibition. The seed coats contain large amount of strongly oxidisable phenolic compounds which deprive the embryo of oxygen.

In agreement with the results of biological tests with transmission to herbaoeous indicators and on orientation electron microscopic investigation, alfalfa mosaic virus (AMV) and tomato bushy stunt virus (TBSV) were serologically identified in the leaves of some of 8 samples of hop plants and of 17 bushes of grapevine, showing a complex of symptoms described in this paper. The latter reacted in double gel diffusion tests toPetunia strain but not to artichoke strain. The identification of these two viruses in grapevine is the first finding in Czechoslovakia, whereas in hop it is probably the first finding anywhere.

The role of a globule-like structure in the leaf epidermal cells ofC. auriculata has been studied in relation to stomatal regulation. Water stress and direct sunlight promote the appearance of globules at the same time as the stomata close. Ample water supply and shade inhibit the appearance of globules and the stomata open. The number of stomata is the same on either leaf surface, but their behaviour is different because of different exposure to light.

Indole-³H or tryptophan-³H are applied to tips of sterile grown oat or maize coleoptiles. The produced amounts of IAA and Try are extracted, purified by paper ohromatography, and quantitatively determined by liquid scintillation spectrometry. Admixtures of serine or inhibitors of monoamine oxidase are without effect on the IAA production from indole. The yield of IAA from indole equals the IAA yield from Try. If the amount of free Try-³H in the tissue is used as a reference quantity, indole-³H application yields higher³H-activity in the protein and in the IAA fraction than does Try-³H application, probably as a result of compartmentation effects. There are no results indicating a pathway of IAA biosynthesis from indole without Try as an intermediate.

The effect of short and long term auxin treatments on the elongation of axillary buds and³²P accumulation were studied in 2-leaf decapitated Alaska pea sailings. It was found that (1) auxin delayed the elongation of the lateral buds, (2) none of the auxin concentration applied completely inhibited the elongation of axillary buds, (3) auxin had no retarding effect on the growing buds, (4) strong polarization of 32P occurred in the parts above the treated leaf, when auxin was applied for a short period just after decapitation, (5) long term auxin treatments did not induce any such polarization of 32P to the parts above the treated leaf, (6) the root acted as an alternate accumulating organ for 32P when the apex was removed and the buds were inhibited, and (7) in decapitated plants the growing buds polarized 32P.

The virus replication capacity (determined by density gradient centrifugation and spectrophotometric virus assay) and severity of symptoms were compared in ten cucumber(Cucumis sativus L.) cultivars infected by cucumber virus 4. Except the expected resistant susceptible and symptomless virus carrier plants a new paradoxial group of cultivars was found. This group is characterized by low virus reproduction rate but simultaneously associated with severe symptoms and is responsible for difficulties in the virus transmission and purification. It is concluded that the critical evaluation of the resistance against viruses of TMV-group must include symptomatic and quantitative virus assays, as there need not be a direct relationship between virus symptoms and the virus increase.

Changes in respiration, activity of cytochrome oxidase and ascorbic oxidase and in BSMV content were investigated on winter wheat plants cv. 'Kaštická osinatka' after application of growth stimulating and growth inhibiting concentrations of 2,4-D. It has been found that the rate of respiration is almost exclusively dependent on the activity of both these terminal oxidases. Consumption of oxygen was regularly increasing with decreasing herbicide concentration and at concentration 10^-7 M was even higher than the control value. Healthy and BSMV inoculated plants treated with 2,4-D differed in ascorbic oxidase activity while activity of cytochrome oxidase was almost the same. In contrast to healthy plants the BSMV inoculated ones were seriously damaged after 2,4-D application. Plants inoculated with BSMV and treated with 2,4-D contained in contrast to those inoculated and not treated with 2,4-D a higher content of virus (124 to 150 %) which was not proportional to herbicide concentration. These results, which were obtained from experiments with plants grown in nutrient solutions supplemented with 2,4-D, indicate that BSMV inoculation induces metabolic changes which cause a loss of selectivity of 2,4-D.

During their short preparasitic stage, dodder seedlings are able to absorb phosphates, by means of their rudimentary root. The absorbed phosphorus is translocated into the stem of the young parasite and metabolized.

Cytochrome oxidase and ascorbic acid oxidase activities were investigated in rye, wheat, barley and oat plants. The variations in the activity of both enzymes was followed in the course of the initial 28 days of growth, as well as at the phase of milk ripeness, namely in the cytoplasmic and mitochondrial cell fractions of roots, leaves and spikes.
Both enzymes were active in all measurements. Cytochrome oxidase mostly exhibited a higher activity than ascorbio acid oxidase. The activity of the former enzyme was substantially higher in the mitochondrial fraction of leaves, roots and spikes of the four experimental plants in comparison with the cytoplasmic fraction. On the contrary, the ascorbic acid oxidase activity varied in both cell fractions according to the plant species, organ and growth phase.
The variations in the activity of both enzymes exhibited on the whole a course similar to that of the respiration rate. During the first 14 to 21 days of growth the enzyme activities increased up to the maximum. This was thon followed at first by a rapid, later on by a slow decrease. The course of variations in the enzyme activities was, with certain exceptions, alike in all the four plant species investigated.

Pea plants grown in nutrient solution in which K⁺ ions were equimolarly replaced with Na⁺, NH₄⁺ or Rb⁺ did not show morphological symptoms of potassium-deficiency. The activity of diamine oxidase in these plants was higher than in controls. Similarly higher diamine oxidase activity was found in plants grown in a complete nutrient solution supplemented with putrescine.

In the investigated barley cultivar resistant toErysiphe graminis f. sp.hordei Marchal a temporary decrease in water uptake may be observed during the first days following infection in light. No marked differences could be detected in darkness. Starting from the stage of formation of fructification organs the ratio between water uptake in light and in darkness in the resistant cultivar is similar to that of the control, while the opposite is true in the susceptible cultivar where the ratio markedly decreases with the development of powdery mildew. The resistant cultivar responds more rapidly to the pathogen by changes in water uptake than the susceptible one.

Gamma radiation in doses 0.13 to 0.77 C kg^-1 (0.5 to 3.0 kR) significantly (P ≥ 0.01) stimulated seed germination, seedling height, and length of primary leaves of French bean cv. 'Blue Lake'; these doses did not affect chlorophyll content per leaf area unit. Doses of 1.16 to 1.93 C kg^-1 (4.5 to 7.5 kR) induced inhibition of the four parameters studied.