Uptake of magnesium was studied by continuous flow technique for 82 days old rice plants in nutrient solution over a range of 0.2 to 1 ppm or 8.2 to 41 µM magnesium concentration. Uptake of magnesium followed a Michaelis-Menten kinetics with a Michaelis constant, K_m of 0.2 × 10^-4M and V_m 156 µg g^-1 h^-1. With increasing flow rate, the rate of magnesium absorption was increased.

The treatment of rice seeds with 0.02% proline increased the germination under saline conditions.

Activities of RNasea were studied in cotyledons of dormant and afterripenedAgrostemma githago seeds. Activity of RNase increases during imbibition and germination. This increase in activity cannot be observed in variants which are not able to germinate (dormant seeds and seeds blocked by higher temperature). The development of RNase activities during germination cannot be inhibited by concentrations of cycloheximide or actinomycine D completely preventing phosphatase synthesis. These results may be indicative for the assumption that the increase of RNase during germination is caused by enzyme activation and not by enzyme synthesis. Cytokinins and a combination of cycloheximide and gibberellic acid stimulate the activity of RNase in dormant cotyledons, whereas neither cycloheximide nor gibberellic acid, applicated by themselves, show any effect. Cytokinins and gibberellic acid do not influence the activity of RNase of afterripened cotyledons, abscisic acid inhibits the increase of enzyme activity.
There are characteristic changes in the pattern of RNases during germination revealed by polyacrylamide gel electrophoresis. The increase in RNase activity of dormant cotyledons caused by cytokinins is accompanied by obvious changes in the RNase pattern on polyacrylamide gel. Treating dormant cotyledons with cytokinins dormancy is partially overcome. In consequence of the application of cytokinins the differences in the electrophoretic RNase pattern between dormant and afterripened cotyledons can be nearly balanced.

The activity and localization of alcohol (AD), lactic (LD), malic (MD), isocitric (ICD) and succinic (SD) dehydrogenase, resp. was histochemically determined in shoot apices of plants in the vegetative condition during transition to flowering and at the reproductive state. The enzymes were determined in freehand sections, as well as in shoot apices incubatedin toto according toNachlaset al. (1958) using Nitro-BT. The characteristic localization of the enzymes depending on the ontogenic stage of the shoot apex is described. Different parts, layers and cell groups of the apex showed differences in enzyme activity. SD could not be detected in shoot apices. The histochemical findings are discussed in relation to former results obtained from a biochemical investigation of respiration in the same material.

High accumulation of³²P was observed in the leaves of intact gherkin plants 9 days after their roots had been treated with 0.005% suspension of the systemic fungicide Folcidin 50WP (cypendazole),i.e. 8 days after the roots had been exposed to labelled phosphate. Folcidin also influenced phosphorus metabolism in the plants. High biologic cytokinin-like activity of the fungicide was established when using a callus cytokinin bioassay.

Thes-triazine herbicides studied (atrazine and simazine) inhibited the growth of the seedlings ofTrigonella foenum graecum L.(Viciaceae). These herbicides caused a decrease in the contents of total water soluble carbohydrates and reducing sugars. Pentose sugars increased in the cotyledons. The total protein and free amino acid contents were enhanced. The activity of peroxidase was inhibited in the cotyledons, but was enhanced in the seedling axes.

Water stress in the leaves was induced by gradual decreasing of substrate moisture in five-day cycles.The hydration level of the leaves was characterized by their water potential (ψ_w), osmotic potential (ψ_s), pressure potential ψ_p and water saturation deficit(ΔW _sat ).The activities of Photosystems 1 and 2 were determined polarographically with Pt/Ag(AgOH) electrode as changes in oxygen concentration in chloroplast suspensions. The shape of light curves of Hill reaction was not influenced by leaf (ψ_w), hence both quantum efficiency and dark phase of this process were affected in a similar manner by water deficit. The activities of both photosystems measured at saturating photon flux density declined with the lowering of leaf (ψ_w) (in the range from -5 to -14 x 10⁵ Pa) and the decrease in activity of Photosystem 2 was more rapid than that of Photosystem 1. The ratio of activities of Photosystems 1 and 2 was mildly enhanced by a lowering of (ψ_w), but it decreased with increasing age. The lowering of ψ_winduced lowering in the chlorophyll a/b ratio thus concealing the usual ontogenetic course of this ratio.

In cotyledons ofChenopodium rubrum L. polydisperse RNA is synthesized in the region of the low molecular weight RNAs during photoperiodic induction. After short-time labelling the rate of 4s RNA synthesis was always higher in induced plants than in plants having obtained a light-break in the middle of the dark period. When glucose was added to the nutrient medium during the dark period of a single photoperiodic cycle the rate of nucleic acid (NA) synthesis was higher in non-induced plants than in induced ones at the termination of the dark period. In plants induced by two cycles in the absence of glucose the rate of NA synthesis at the termination of the second dark period was higher in induced than in non-induced plants. This difference is due to the differential kinetics of NA synthesis during darkness. In plants induced in the presence of glucose the peak of the rhythm in NA synthesis was advanced by 4 h relative to that found in plants induced in the absence of sugar. Thus, the termination of the dark period coincided with the negative slope of the oscillation in plants induced in the presence of glucose, while in plants having obtained a light-break NA synthesis decreased only slightly after having attained its peak. In plants induced in the absence of glucose the termination of the dark period coincided with the peak in the rhythm in NA synthesis. The rhythm in NA synthesis of the cotyledons during the dark period of an inductive cycle is out of phase with the rhythm in flower initiation.

The level of RNA in pollen is approximately 20 mg g^-1 and remains constant during 6 h pollen germinationin vitro also in the presence of 2-thiouracil which stimulates pollen tube elongation. The synthesis of RNA in pollen tubes was investigated according to the incorporation of the label from uracil-2-¹⁴C, 2-thiouracil-2-¹⁴C, orotic acid-5-³H, fructose-U-¹⁴C and from³²PO₄^3- into RNA fractions separated by methylated albumine kieselguhr chromatography. The distribution of radioactivity on elution profiles was different according to the radioactivity source, however it was not changed by the presence of 2-thiouracil in cultivation medium. 2-Thiouracil incorporates into pollen tube RNA at about 50% the rate of uracil. It inhibited the incorporation of orotic acid, of fructose and of phosphate into all RNA fractions. It is suggested that the analogue inhibits the enzymes involved in RNA synthesis essentially as 2-thiouridine-5'-phosphate.

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.