The excretion of cytokinins into the cultivating medium, which are produced by the phytopathogenic fungiMonilia sp. andCytospora sp. has been investigated. All the isolates of the fungi used in the experiments (Monilia fructicola, Monilia fructigena, isolate 2 and 4,Monilia laxa isolate 3 andCytospora sp. isolate CPL and C₁) have been found to produce cytokinins. The production is increased during the formation of the fructification organs. Among the isolates investigatedMonilia fructigena isolate 4 andCytospora sp. isolate CPL showed the highest production of cytokinins. After chromatographic separation, cytokinin activity was found at R_F 0.7-0.8 values by the biological test as well as by identification according to UV spectra. Application of purified cytokinins produced by the fungi evoked the formation of "green islands" on isolated barley leaves underin vitro conditions.

The investigation of the hormonal nature of plant flowering in connection with their photoperiodic reaction has shown that flowering depends on a bicomponental system of hormones, gibberellins regulating stem formation and growth and substances of the anthesin type regulating flower formation. In agreement with the division of the photoperiodic reaction into a leaf and a stem phase the study of the internal factors acting on plant flowering was carried out by means of leaf and stem (apex, bud and callus) models. The results obtained from work with leaf models proved the presence of two groups of hormones of flowering in plants. The data obtained from the application of stem models pointed to the localization of the action of gibberellin and anthesin in different zones of the shoot apices and characterized the potential capacity for flower formation of isolated callus tissue of neutral and photoperiodically sensitive species.

The time course of the changes in the level of endogenous growth regulators was followed during the stratification at 5 °C of the seeds of 'Panenské české' apples. An increase in the endogenous gibberellin activity was found already during the first and the second week of stratification which is according to it decisive for the release of dormancy in the seeds, as it precedes with the anticipation of approximately two weeks the curve of the release of dormancy in the seeds. The rise in the level of endogenous cytokinins in the seeds is belated one to two weeks behind the rise in gibberellin activity in them and thus approximately coincides with the release of dormancy. The rise in auxin level occurs approximately 4 weeks after the increase in cytokinin level. The increase in auxin level, which is accompanied by an increase in inhibitions, is apparently not connected with the release of dormancy in the seeds during the stratification.

Arabidopsis thaliana was susceptible to eight out of ten investigated viruses with six of which it did not show any symptoms of local infection; this appeared only in two cases.A. thaliana was a symptomless carrier for three viruses. The considerably distinct systemic symptoms after the infection with turnip yellow mosaic, tomato black ring, cucumber mosaic and cabbage black ring viruses make possible a very reliable and specific distinction of the causal agens.A. thaliana could be used for these viruses as a differential host.

Besides IAA, other compounds with auxin activity (of both indole and non-indole nature) can also cause an increase in glutamate dehydrogenase level in excised pea roots. The effect of these substances is probably not mediated by ethylene, depends on proteosynthesis, is independent of the regulatory effect of sugars and need not be influenced by the antagonism between auxins and cytokinins.

The healthy leaves of rice cultivar 'BJ 1' resistant to bacterial leaf streak pathogen (Xanthomonas translucens f. sp.oryzicola) contained higher quantities of total phenolic compounds, reducing and nonreducing sugars than the susceptible cultivar 'IR 8', while the leaves of cultivar 'IR 8' possessed larger concentration of total soluble amino acids than the resistant cultivar 'BJ 1'.
In the leaves of cultivar 'BJ 1', the disease development caused an initial decrease in the concentration of phenols followed by an increase at later stages. As a result of inoculation, soluble carbohydrates and amino acids generally decreased in the leaves of resistant cultivar 'BJ 1', in contrast to an increase in their concentration in the leaves of cultivar 'IR 8'.

The effects of soaking seed in 2-chloroethylphosphonic acid (CEPA) for 24 or for 48 h on the cumulative 5-day seedling growth ofCucumis sativus L. (cucumber) andPisum sativum L. (peas) were studied. Each cucumber seed absorbed an average of 0.015 ml of CEPA solution, while pea seed absorbed 0.365 ml, over a 24 h period.
In cucumber, 240 mg l^-1 CEPA concentration decreased radicle length by 23%, regardless of soaking duration. The same concentration increased radicle weight in a 24 h soaking duration, but decreased radicle weight when soaking was for 48 h. At 48 h, CEPA concentrations of 0.24 and 2.4 mg l^-1 increased plumule growth by 26%. In peas, the 240 mg l^-1 decreased the length and the weight of both the radicle and the plumule in a 48 h soaking duration, but had no significant effect at a 24 h soaking. At the low concentration of 0.24 mg l^-1, seedling growth was stimulated by over 30%.
Cucumber was 3 times more efficient than peas in the utilization of CEPA for seedling growth, in terms of total fresh weight of seedling per microgram of CEPA absorbed: 1 127 and 274 mg μg^-1 CEPA in cucumber and peas respectively. Extrapolative calculation, using cucumber responses as standard, suggests from this seedling study that about 12 mg l^-1 CEPA is likely to stimulate growth and/or yield in sprayed pea plants.

Treating scooped out bulbs of hyacinths (Hyacinthus orientalis L. cv. 'Lady Derby', cv. 'Pink Pearl', cv. 'Delft Blue') and tulips (Tulipa gesneriana hort. cv. 'Oxford') with cycloheximide stimulated strongly the infection of the tissues of the bulbs byPenicillium sp. The possible mechanism of such an activity of cycloheximide is discussed.

MLO containing invaginations were found in protoplasts of phloem parenchyma cells in symptomless young leaves ofRibes houghtonianumJancz. infected with a yellows disease. The invaginations originate between the cell wall and plasmalemma, usually at plasmodesmata, and change apparently into superficial vesicles in the protoplast; they are entirely or partially limited by host plasmalemma. The formations mentioned occur in parenchyma cells which contain normal organelles. Sometimes they are divided by a smooth membrane system enclosing MLO. Besides MLO the invaginations contain in some cases slimy fibrils resembling the P-protein in sieve tubes. The MLO bodies seen in invaginations have usually a diameter of 50-250 nm and their plasmalemma (unit membrane) is identical with the plasmalemma of MLO bodies occurring in sieve tubes. However, only few MLO bodies in invaginations are electron dense, so that they resemble naturally degenerated forms of MLO. Similar MLO containing invaginations were formerly described from some leafhoppers transmitting MLO.

Preparations of alcohol dehydrogenase (ADH) were prepared from germinating seeds by a procedure including fractionation with ammonium sulphate, desalting on a column of Sephadex G-25 and chromatography on DEAE-cellulose, the specific activity of ADH was in the case ofPhaseolus 31 times,Brassica 43 times,Triticum 47 times, andVicia 212 times higher than that of crude extract. The enzymes were homogeneous when filtrated on Sephadex G-200. Molecular weight of all the four studied ADH was approximately 63 000. Some kinetic properties as K_m for ethanol as substrate, substrate specificity towards different alcohols, and the effect of some intermediates of sugar metabolism and of some inhibitors on the activity of the enzymes were also followed. The results obtained are discussed with respect to possible mechanism of action of the plant ADH.

The relationships between DNA synthesis and germination capacity ofAgrostemma seeds have been studied. Protein synthesis and RNA synthesis are activated at the very beginning of imbibition, whereas DNA synthesis starts in the second part of the imbibition phase.
Agrostemma seeds inhibited by higher temperature (30° C), or aged seeds with a low germination capacity are characterized by a remarkably reduced protein synthesis. DNA synthesis is also reduced. The inhibition of protein-synthesis ofAgrostemma embryos fed with cycloheximid or actinomycin D causes a depression of DNA synthesis. These results indicate that the initiation of DNA synthesis of imbibingAgrostemma seeds depends on the synthesis of special proteins. Abscisic acid inhibits growth as well as DNA synthesis of isolatedAgrostemma embryos. Mitomycin inhibits germination and DNA synthesis to the same extent. Dormant seeds with an undiminished intensity of protein synthesis also show a reduced incorporation of³H-thymidine in DNA. We suggest that DNA synthesis of imbibed seeds, which is a necessary prerequisite for the radicle protrusion, is involved in the mechanism of afterripening of theAgrostemma seeds.

The increase in the measured transpiration rate in tobacco leaves due to the experimentally decreased humidity of the bulk air was found to be significantly lower than the theoretical value calculated from the change of water vapour concentration gradients. Boundary layer and stomatal diffusive resistances remained unchanged under experimental conditions with no change of net photosynthetic CO₂ uptake. This suggests an increase in intercellular diffusive resistance with an increase in water vapour concentration gradient which is the driving force of water vapour diffusive part of transpiration flux.
The increase can be ascribed to the lengthening of intercellular diffusive pathway as steeper water vapour concentration gradient in intercellular spaces results in an increased evaporating surface of intercellular cells thus moving the effective plane of vaporization in leaf mesophyll further inwards. Due to different and independent changes of concentration gradients for water vapour and CO₂, different length of intercellular diffusive pathways for CO₂ and water vapour may be expected.

Application of 1 ppm zeatin raises the respiration rate (measured by the Warburg method) of leaf mesophyll protoplasts ofPetunia hybrida by about 50% after 4 h; afterwards there is a rapid decrease. While the rate of respiration in the controls rises after 5 to 6 h, 1 ppm zeatin has a strong inhibitory effect. When the protoplasts are incubated with 0.1 ppm zeatin the rise in the rate is much slower, and after 7 h the rate is 30% higher than in the controls. Abscisic acid (10 ppm) decreases the respiration rate so that after 5 h it is less than half that of the controls. Later on there is a rise as in the controls, perhaps caused by senescence promoting effects of abscisic acid. The photosynthetic rate of the mesophyll protoplasts measured by¹⁴CO₂ fixation decreases with increasing age of the preparation. The protoplasts previously incubated with zeatin for 1 to 3 h show an increase in photosynthesis: with 0.1 ppm zeatin the¹⁴C-fixation rate is higher the longer the hormone could operate. With 1 ppm zeatin we get a typical optimum curve similar to that for respiration. These optimum curves indicate the inhibitory effect of high concentrations of zeatin on respiration and photosynthesis.

Treatment of two-week-oldBrassica campestris andTrigonella foenum-graecum plants with morphactin andVicia faba, Antirrhinum orontium, andPapaver somniferum with Niagara, induced marked variations in the orientation and ontogeny of stomata and the epiderma cells. Morphactin-chlorflurenol at 12.5, 62.5, 125, 250, and 500 ppm, caused marked damage of the shoot apices and changes in the epidermal tissue, such as divisions of the guard cells, reduction in the size of the stomata, and epidermal cells. Niagara-ethyl-hydrogen-1-propylphosphonate at 100, 500, 1 000 5 000, and 10 000 ppm caused thickenings of the epidermal cell walls and differentiation of new meristemoids from the epidermal cells, contiguous stomata, and incomplete development of the guard cells.

The results presented in this paper indicate an immediate relation between the increased activity of the pentosephosphate cycle and the biosynthesis of the virus. In the period of its maximal reproduction (4 to 8 days after inoculation) also pentosephosphate cycle activity is enhanced what enables an increased biosynthesis of both purine and pyrimidine nucleotides which are necessary for the formation of the viral RNA. As soon as the period of the maximal reproduction of the virus ends, the activity of the pentosephosphate cycle drops deeply under the value of the control. The lowered intensity of respiration at the period of intense reproduction of the virus could be then explained by a decrease in the content of ADP-either on the level of its biosynthesis or by its preferential incorporation into the RNA of the virus-necessary for oxidative phosphorylation connected immediately with respiration. The courses of glucokinase, fructokinase and sucrase activities also correspond to the activity of the pentosephosphate cycle; these enzymes supply a sufficient amount of substrate for Glc-6-P dehydrogenase. The increased glycolysis activity from the 12th day on probably balances the energetic deficit in host metabolism caused by virus reproduction.

In a study on the phenolic distribution of rice husk (lemma, palea, rachilla and sterile lemmas), seven phenolic acids were detected in the alkali and alcoholie extracts. The total quantity of phenolic compounds in the husk differed with cultivars; however, no qualitative difference was noticed.

Chemotropic effects exerted by metal cations have been investigated simultaneously with their influence on the increments ofSinapis alba roots cultivated in dark and light. The effects of Na-EDTA and Na-humate and its fractions, as well as the interaction of these substances with cations have also been studied. Chemotropics have been administered in agar-agar to the ends of roots growing on glass plates. Chemotropic and growth effects were exerted by Cu²⁺, Fe²⁺, Fe³⁺ and Ca²⁺ cations. The light strongly changed the effects of all but Cu²⁺ cations. Both Na-EDTA and humante appeared to be active chemotropically and generally abolished the effects of cations, although in some cases Na-EDTA made this influence more intense. Of the humate fractions, only those characterized by the ability to form complex compounds appeared to be active. No correlation has been found between chemotropic effects and the influence on the growth of roots, except for the Cu²⁺ cations, which always caused positive chemotropism and inhibited the growth of roots.

The changes of content and some chromatographic characteristics and biological activities of natural free cytokinins were studied during the vegetation season in the growing apices of apple tree shoots. Biological cytokinin activity was discovered in two groups of compounds differing in the time of their biological actions. Rf values and in the time of their maximal content in the growing apices. The time of maximal content was in accordance with their biological activity.

The occurrence of beet mild yellowing virus (BMYV) on feeding- and sugar-beet in Czechoslovakia has been proved. The virus was transmitted by aphidMyzus persicae (Sulz.) on indicator plantsSinapis alba L.,Capsella bursa-pastorisMedik, andClaytonia perfoliataDonn and from these plants back to sugar-beet cv. 'Dobrovická A.' A weed plantRaphanus raphanistrum L. was identified as a new natural host plant of BMYV. The virus was identified in ten of twelve biologically examined samples of beet with BMYV-like symptoms, which were collected at various places in Czechoslovakia

A modified procedure for the extraction of betacyanin fromAmaranthus seedlings is described. Application of this modification increased the absorbance of cytokinin-treatedAmaranthus explants in most cases. The modifiedAmaranthus test is compared with the soybean callus test in the bioassay of kinetin, 6-benzylaminopurine, and 6(δ,δ-dimethylallyl) aminopurine.

In 7 species (Eleocharis palustrisR. Br.,Juncus bufonius L.,Gypsophila muralis L.,Trifolium repens L.,Agrostis stolonifera L.,Potentilla anserina L. andAchillea millefolium L.) growing in a gradient of habitats from aquatic to terrestrial, on a sandy fishpond shore in Southern Bohemia, Czechoslovakia, the daily course of transpiration rate and water content was assessed gravimetrically in their cut-off transpiring parts on two typical summer days. Transpiration rate was largely controlled by microclimate but depressions occurred inJuncus and in some species growing in the drier habitats. The highest instantaneous transpiration rate and total daily transpiration per unit dry weight, about 100 mg g^-1 min^-1 and 50 g g^-1 d^-1, respectively, were recorded inAchillea andTrifolium. The water turnover rate ranged from 16.1 g g^-1 (H₂O) d^-1 inJuncus to 10.7 inGypsophila. The estimated daily maximum water saturation deficit was highest inEleocharis (45.7%) and lowest inAchillea (15.0%). The adaptational significance of the observed phenomena is discussed.

Salicylic,p-coumaric, and ferulic acids were detected in the acetone-insoluble cell fraction, presumably protein, extracted from the brown discoloured tissues of rice (Oryza sativa L.) leaves infected withPyricularia oryzaeCav. but not from healthy leaves. It is proposed that these phenolic acids are oxidizedin vivo in blast diseased rice leaves, and forms a protein-quinone complex.