The scale of salt tolerance of each plant tissue can be characterized by a "critical" concentration of NaCl. At this concentration the endogenous content of free proline rises. A correlation exists between the endogenous Na⁺-concentration and this increase of proline. Calcium cations can enhance the NaCl-tolerance by inhibiting the Na⁺-permeability. Thus, the rise of the proline concentration in this case is produced only by NaCl concentrations higher than the critical concentration. The calcium pretreatment of caryopses during soaking leads to the enhancement of the tolerance under salt stress, too.

A range of endogenous cytokinins have been identified inDatura crown-gall tissue by GC-MS. Incorporation of [³H]adenine into zeatin riboside, zeatin and its nucleotide(s) is also shown. Metabolism studies usingcis- andtrans-isomers of zeatin riboside indicate that interconversion of the two isomers does not occur in this tissue. Data on the identity of major endogenous cytokinins in a genetic tumour line of tobacco is also provided.

Endogenous concentrations of indol-3-ylacetic acid (IAA) in auxin-autotrophio crown gall tissue cultures are presented in relation to culture growth rate and to tissue IAA levels in auxin-dependent cultures maintained on IAA as auxin source. Cellular levels of synthetic auxins absorbed from culture media were monitored in auxin-dependent cell cultures exhibiting selectivity in growth response to exogenous auxins. The results are used in modelling culture growth patterns and changes in intracellular auxin content.

Two phases of radish ontogenesis (I-when the plant had produced 3 -5 nodes and II-when the plant had produced 8 -10 nodes) were established on the basis of axillary, meristem localization. Flowering of the plants in response to GA treatment depends on the phases in which they were treated and on growth correlations in the apical meristem. The results obtained suggest that the reaction ofRaphanus sativus (LDP) to GA treatment is parallel to that ofChenopodium rubrum (SDP), and that the response of radish plants also depends on changes in growth correlations in the shoot apical meristem at the time of treatment.

Acid-soluble phosphate esters were determined in extracts of plant material after a 24 h exposure of the roots of intact alfalfa plants to nutrient media labelled with³²P_i. Similar phosphate ester patterns were found in 2-, 3-, 8-, and 9-week-old plants with the exception of Gra-P which could be detected only in shoot extracts. However, phosphate ester levels differed in the shoots and roots. Whereas Fru-P₂, Glc-6-P, Fru-6-P, and adenine nucleotides were more abundant in the shoots, Grn-P and P-choline levels were higher in the roots. Certain differences in the levels of P-esters were also recorded between plants susceptible and resistant to bacterial wilt.

In an embryo shoot apex more different mutations may be induced after the mutagenic treatment of seeds. These mutations may be distributed among the apical initial cells in different ways. According to the proposed mathematical model it is possible to estimate the proportion of initial cells with 0, 1, 2, …,x mutations in the apioes with a given number of initials,k, which is characteristic for each plant object, and under a certain number of induced mutations per apex,n, determined by the conditions of the mutagenio treatment. Owing to the disadvantage of multimutations in plant breeding it is possible according to the formula P(X > 1) = 1 -e^-n/k(l + n/k). to use, at a knownk, suchn's which secure minimum multimutations.

Exogenous³H-thymidine is absorbed by the primary root of young plants ofDatura stramonium L. and gradually translocated into shoots: following a 3 to 72-h application of³H-thymidine the radioactivity was revealed, using the autoradiographic technique, especially in the region of primary and secondary meristems and in proximity to vascular bundles of the primary root, stem, hypocotyl and leaves. These regions may be considered as the sites of active DNA synthesis. The intensity of incorporation was dependent on the time of plant incubation in labelled thymidine.

Plant tissue connected in a d.c. circuit behaves as a capacitor, short-circuited through a resistor. Using a saw-tooth voltage (T = 2 ma, U_max = + 13 V), structural and physiological conditions in a plant tissue can be analyzed on the basis of changes in the current character.

Seedlings ofVicia faba L. were cultured on diluted Knop's solution containing one of the tested substances: 9-(2,3-dihydroxypropyl)adenine (DHPA), 3-0-phosphonylmethyl DHPA (DHPA phosphonate), 3-(adenin-9-yl)-2-hydroxypropanoic acid and its esters, (2R,3R)-4-(adenin-9-yl)-2,3-dihydroxybutanoic acid (D-eritadenine) and its methyl ester. The development of main and side roots was checked. Most of the substances tested were more powerful inhibitors than DHPA. The results are discussed in connection with the role of S-adenosyl-L-methionine in plant objects.

Acid phosphatase isolated from low altitude grown plants of two high altitude plant species,Selinum vaginatum Clarke andAcer caesium Wall, displayed higher thermostability than that from plants of the same species grown at high altitude. The isozyme composition, however, remained unchanged inSelinum vaginatum. InA. caesium, one of four isozymes, was thermolabile in the samples from high altitude and was lost after 10 min heating of the extracts at 60 °c. In the samples from low altitude, this isozyme was not detected and a band with slightly lower Rf value was present which was thermostable. The described changes in the thermal properties of acid phosphatase reflect an adaptive step towards high temperature acclimation at low altitude.

On the basis of proportionality between flow and its conjugated force a mathematical model for volume, current and osmotic flows was designed and a method for the experimental measurement of flows, the transbarrier (trans-segmental) potential and the rate of flow was devised.
The results obtained experimentally as well as using the mathematical model indicate that the plant root is differentiated not only according to localization, but also according to the conductivity, permeability and selectivity of these tissues.

In young needles of the Douglas-fir (Pseudotsuga menziesii) GA₉ has been shown by GC and HPLC to be the main gibberellin. As minor compounds GA₇, GA₃ and GA₈ have been tentatively identified by HPLC. In addition to the free gibberellins small amounts of GA₉ glucosyl ester and a not yet identified ester of GA₂₀ have been isolated.
From the group of endogenous inhibitors ABA has been identified by GC-MS and ABA glucosyl ester by HPLC. After enzymatic hydrolysis of the ester, ABA and glucose have been quantified by GC and GOD-POD reaction giving the ratio 1:1. Another plant growth inhibitor has been identified as the methyl ester of jasmonic acid.

Gibberellins A₃ and A₁₃ cause floral induction inImpatiens balsamina, a qualitative short day plant, under non-inductive 24-h photoperiods (continuous illumination). However, the influence of the two inductive factors,i.e. gibberellins and short days (8-h photoperiods) on the peroxidase enzyme system is different. The total peroxidase activity decreases under both inductive and non-inductive photoperiods, with or without gibberellin treatment. The electrophoretic pattern of isoperoxidases changes only in response to gibberellin treatment. Under 24-h photoperiods, treatment with gibberellins A₃ and A₁₃ causes the appearance in the stem of three additional isoenzymes of peroxidase (Rm 0.50, 0.71 and 0.76). These bands do not appear in the leaves, which are non-essential for gibberellin-caused floral induction in this plant. Under 8-h photoperiods also, gibberellins induce the appearance of new isoenzyme bandsi.e. two in the stem (Rm 0.50 and 0.76) and one in the leaves (Rm 0.05). These may be correlated with the synergistic increase in the number of floral buds in these plants in response to simultaneous exposure to two inductive factors.

An analysis of axillary meristem (axillary bud) localization of radish (Raphanus sativus L. cv. Tetra-Iłówiecka) was undertaken on vernalized (flowering) and unvernalized (vegetative) plants. It has been shown that the localization of these meristems can be different on successive nodes of the same plant and is connected with the development stages of the plants. The axillary meristems can arise on the stem as well as in the leaf axil or on the base of the subtending leaf. The localization of axillary meristems has been discussed in relation to growth directions and growth correlations inside the meristematic region of the shoot apex.

With the aim to reduce the period of flowering and of fruit maturation, we investigated the effect of auxins on flower formation. For these experiments we used young decapitated plants with two plagiotropic branches. Both the auxins, indol-3-ylacetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), retarded flower formation in coffee, the latter one being more effective. The effects of 2,4-D if applied on only one of the two plagiotropic branches can be observed only in this treated one. Furthermore, the auxins seem to act in coffee plant directly by affecting flower formation and not indirectly by inducing endogenous ethylene production.

Cotyledons of gourd (Cucurbita maxima Duchesne) and bean (Phaseolus vulgaris L.) were used to study the changes in the activities of catalase, peroxidase, acid inorganic pyrophosphatase and alkaline inorganic pyrophosphatase during ageing and the diversion in such changes that occur when cotyledon senescence was retarded by detopping the seedlings above the cotyledons. Catalase, acid inorganic pyrophosphatase and alkaline inorganic pyrophosphatase activities declined during the senescence of the cotyledons. When cotyledon senescence was retarded by detopping as marked by the increase in the levels of chlorophyll and protein, there was also an increase in the activities of these enzymes. Peroxidase activity, on the other hand, increased during the senescence of the cotyledons and detopping the seedlings resulted in a further increase in the peroxidase activity. It can be suggested that some root factor(s) probably cytokinin(s) is (are) mobilised into the cotyledons of the detopped seedlings which otherwise would have been mobilised into the shoot apices, and help retard or even reverse the senescence of the cotyledons.

The rice is important in plant science for its ability to germinate and grow with restricted or without oxygen availability. In this work we have investigated the variation of growth substances when anoxia was imposed to rice seedlings previously grown in air. An increase, in all the organs of a seedling and in particular in the fraction released in the medium, was observed for ABA (abscisic acid), PA (phaseic acid) and DPA (dihydrophaseic acid) quantities.Vice versa a reduction of total IAA (indol-3-ylacetic acid) was observed in seedlings. This was accompanied by its accumulation in roots. IAA was poorly released in aerobic conditions and anoxia has not changed this pattern.

Plant proteases rapidly destroy virus architecture in sap ofSolanum laciniatumAit., with yellow mosaic symptoms but even under these conditions the partially digested amorphous nucleoproteins retain their immunospecificity and infectivity for a limited time. Homogenization with phenylmethylsulfonylfluoride inhibits efficiently host serine proteases and fully stabilizes the virus particles in plant sap and in partial purificates. During the electronmicroscopic examination of stabilized infectious saps in 12 out of 14 isolates of yellow mosaic ofS. laciniatum besides alfalfa mosaic virus a poty-virus was disclosed. This was identified serologically and by transmission tests as a weakly virulent type of bean yellow mosaic virus.

Gladiolus "grassy top" disease was recorded in Czechoslovakia. Electron micrographs of ultrathin sections prepared from dwarfed leaves sprouting in spring from corms of affected gladiolus plant showed a very high accumulation of mycoplasma-like organisms (MLO) in sieve tubes. These corms were stored during the winter period in a cold glasshouse and their overground plant parts were removed only before planting in spring.
In autumn, when the corms were dug up in the field, those of affected plants were mostly infected withFusarium sp. while those of apparently healthy ones were intact. This observation may indicate a conspicuously increased susceptibility of affected corms to the fungus.

The objective of this study was to determine if the two surfaces of a leaf had different, or the same, water potentials. Maize (Zea mays L. cv. Cargill 805) was the test plant. During an 11 day period, the water potentials of the upper and lower surfaces of the maize leaves were measured daily with anin situ thermocouple psychrometer under growth-room conditions. Plants were grown in pots with a well-watered, commercial greenhouse soil. Stomatal resistance also was measured. The water potential of the upper surface was less negative (more wet) than that of the lower surface. The overall average of the water potential of the upper and lower surfaces was -1.48 and -2.07 MPa, respectively. The stomatal resistance of the upper surface was greater than that of the lower surface. The average stomatal resistance during the experiment was 780 and 600 s m^-1 for the upper and lower surfaces, respectively. Since the upper and lower surfaces were not at the same water potential, the results indicated that the parallel-resistance equation, used to combine resistances on the two surfaces of a leaf, was not strictly valid when applied to the maize leaves, as the law assumes equal potentials on the two surfaces.

Flours prepared from seeds of two non-agglutinating and one agglutinating cultivar ofPhaseolus vulgaris ssp.vulgaris (tested against human A, B, O, and rabbit erythrocytes) were stored in a refrigerator for eight months. Extracts from aliquot portions of these flours were prepared in one-month intervals, their agglutinating activity was tested against rabbit erythrocytes, and their immunoelectrophoretic patterns and protein contents were determined. Agglutinating activity occurred during storage in ageing flours of originally non-agglutinating cultivars and a typical lectin zone which was absent in extracts of freshly prepared flours appeared in their immunoelectrophoretic patterns. This newly formed agglutinating activity in some cases again disappeared during further storage.

N-malonyl-D-tryptophan (MT) and D-tryptophan added to the medium instead of auxin stimulated growth of soybean and tomato cell and tissue cultures. Effects of 50-100 μmol 1^-1 MT and 100 -300 μmol 1^-1 D-tryptophan were equal to the effect of 3-10 μmol 1^-1 IAA. Soybean cells grown in the presence of 100 μmol 1^-1 MT contained 125-170 ng IAA per 1 g fresh mass (as determined by spectrofluorimetric indole-α-pyrone method), whereas the cells grown in the presence of NAA 10. 7 μmol 1^-1 contained 50 -60 ng IAA and the cells grown in the absence of auxin failed to show endogenous IAA. MT as proposed can be hydrolyzed by plant cells with liberation of D-tryptophan, which in turn can be used in IAA synthesis. It is proposed that MT is a possible source of endogenous auxin in plants.

Amaranthus viridis is a quantitative SD plant in which inflorescence primordia are initiated under both 24- and 8-h photoperiods after 12 and 10 days, when 8 and 7 leaves are differentiated, respectively. Photoperiod plays a non-determinate role, whereas the maturity of plants linked with the attainment of minimum leaf number is significant and of primary importance in floral induction. This is further confirmed by the more or less identical nature of changes in the total enzyme activity and isoenzyme patterns of peroxidase, esterase and alkaline and acid phosphatase under the two photoperiods. These changes occur once the minimum vegetative growth has been achieved prior to the reproductive transformation, irrespective of the photoperiod, pointing to the activation of a general common pathway of events leading to floral induction.

The percentage of sucrose in sugar beet storage root fresh and dry matter is closely related to root structure. It has been suggested that the sucrose content might be increased by using plant growth regulators to modify storage root structure through control of cambial development, cell division and cell expansion. During storage root development correlations were found between the changing phytohormone profiles and the formation of secondary cambia and their subsequent cell division and expansion. Sugar beet root derived cell suspension cultures were used for detailed studies of the roles of endogenous phytohormones. The gibberellin synthesis inhibitor paclobutrazol was tested in cell cultures and whole plants. The observations provide a basis for development of plant growth regulator regimes to optimise sucrose yield from sugar beet.