Carbon dioxide compensation concentration,Г, net photosynthetic rate,Pn, and photorespiration rate,Rl, were measured in young, adult and old primary leaves ofPhaseolus vulgaris L. over a range of photon flux densities using a closed system with IRGA. Irrespective of leaf age,Г decreased rapidly with rising photon flux density up toca. 260 (μmol m^-2 s^-1. From this valueГ did not change with photon flux density under constant temperature, reaching on the average 178, 118 and 239 mg m^-3 in young, adult and old leaves, respectively. Changes with age in curves relatingPn andRl to photon flux density were found.

Relationships between the CO₂ compensation concentration, the slope of CO₂ curves of P_n and the energy of irradiance were studied in adult leaves ofFagus silvatica L. seedlings. A gazometric method of quantitative analysis of air flow, in a closed system, was applied.
P_n and the slope of CO₂ curve of P_n increased with increasing irradiance at constant temperature of the abaxial leaf surface (19 ± 0.5 °C), however, the CO₂ compensation concentration decreased. This physiological characteristic changed relatively slightly at irradiance close to saturation irradiance (235 Wm^-2).

Nitrogen contents were determined in 20 species of "resurrection plants",i.e. plants with leaves which are able to revive from an air-dry state (viz. Boea hygroscopica, Borya nitida, Cheilanthes sieberi, Coleochloa pallidior, C. setifera, Craterostigma plantagineum, Myrothamnus flabellifolia, Oropetium capense, Pellaea calomelanos, P. falcata, P, viridis, Polypodium polypodioides, Ramondia pyrenaica, Selaginella lepidophylla, Sporobolus stapfianus, Talbotia elegans,Tripogon loliiformis, Xerophyta retinervis, X. villosa, X. viscosa), and in three desiccation sensitive species (Eragrostis tenuifolia, Selaginella kraussiana andSporobolus pyramidalis).
In a preponderance of resurrection plants insoluble nitrogen content fell during dehydration of intact plants and soluble non-protein N rose. Both changes were particularly marked in species which lose chlorophyll and thylakoid structure during drying. These trends were usually only partially reversed after 24 h rehydration. Recovery of¹⁴C-leucine incorporation in rehydrating leaves was slow.
Leaves of desiccation sensitive vascular plants tended on the average to lose soluble protein rather than insoluble N during drying, and tended to have higher soluble non-protein N contents than tolerant plants.
However, similarity in the changes in N-contents inXerophyta villosa leaves killed by airdrying compared to leaves surviving air-drying, opposes the view that death was due to excessive loss of protein.

Significant differences in the net photosynthetic rate (P_N) of sevenHevea brasiliensis clones are found. Though much smaller than the internal resistance to carbon dioxide diffusion (r_i), the stomatal resistance to CO₂ diffusion (r_s') shows larger variation among the clones and might largely explain the differences in P_N.

The frequencies of chlorophyll mutants were investigated in anther cultures derived from mutagen-treated plants ofN. tabacum cv. Samsun (haploid level) and in the seed offspring from the same treated plants (diploid level). Comparison of the induced mutation frequencies at the haploid and diploid levels demonstrated that selection existed against the haploid embryoids with induced chlorophyll deficient mutations. The diploid vegetative stage with phenotypic expression of the chlorophyll mutation was more vital than the haploid one. The suitability of anther cultures for studying induced mutagenesis is discussed.

The effect of different growth substances on the development of normal and abnormal stomata are presented. Anomocytic, paracytic, anisocytic and stoma with a single subsidiary cell are observed. Abnormal developments like persistent stomatal cells, degeneration of guard cells, unusual thickening, unequal guard cells, single guard cells and size and shape of the pore are noticed in various growth substances. The growth substances also affect the stomatal frequency, stomatal index, epidermal frequency and size of guard and epidermal cells in both the plants. The highest meristematic activity is found in MOR 100 ppm in brinjal and in GA 25 ppm in tomato. The largest size of stomata is found in COL 25 ppm in brinjal and in MH 50 ppm in tomato. The same growth substance responds differently in the two plants.

Deficiency in Ca and P in mineral medium reduced the growth and nitrogen content ofAzolla pinnata but increased the content of soluble sugars in the plant; the deficiency in K and Mg was less effective in retarding the growth. The pH of the medium from 5 to 8 encouraged the growth and nitrogen fixation, whereas acidic pH of 4 as well as alkaline pH of 9 inhibited the growth and nitrogen fixation.

The weight of alfalfa plants, especially roots of susceptible strain, decreased when inoculated withCorynebacterium insidiosum. At the 6th week after inoculation the³²P uptake per plant and its translocation into the above-ground organs were considerably decreased in susceptible plants. On the other hand, the³²P uptake was increased and the radiophosphorus was accumulated in above-ground organs in resistant plants.

The three plant types ofAmaranthus namely,A. caudatus f.albiflorus, A. caudatus f.caudatus andA. tricolor var.tristis are qualitative short day plants with critical photoperiods 16.0, 15.5 and 15.0 h, respectively. Gibberellins A₃, A₄₊₇ and A₁₃ affect extension growth, leaf differentiation and floral induction differently. Thus, in all the three plant types ofAmaranthus, whereas, GA₃ and G₄₊₇ enhanced extension growth, GA₁₃ was completely ineffective under both, 24- and 8-h photoperiods. None of the three gibberellins could affect the leaf differentiation. In all the three plant types, flowering was promoted by GA₁₃ and not by other gibberellins tried. GA₁₃ caused promotion was manifested in two manners, firstly by lowering the critical dark period requirement in each inductive cycle, and secondly by shortening the total period taken for the initiation of inflorescence primordia under inductive photoperiods. The floral induction by gibberellins inAmaranthus is contrary to the gibberellin-anthesin concept of Chailakhyan. It is suggested that gibberellins other than GA₃ may be playing an important role in floral morphogenesis of short day plants.

Virus isolates resembling the dandelion yellow mosaic virus (synonym: lettuce necrosis virus) were obtained from dandelion plants in twenty five localities of Bohemia and also of Norway, Sweden and Finland. All isolates were sap transmissible merely to lettuce, but some of them also toChenopodium quinoa; other test plants could not be infected. Attempted serological and biological identification of the isolates with some viruses presumed to be able to infect spontaneously dandelion plants have failed.

A simple maceration procedure for cell suspension preparation from white poplar tissue culture has been devised which makes it possible to count cell number from microphotographs reliably. The results obtained are suitable for quantitative evaluation of cell proliferation tissue growth.

Studies performed on seeds of several cultivars of spring wheat (Triticum aestivum L. var.lutescens) revealed differences in the studied seed dehydration tolerance affecting seed germination and seedling emergence. Among the cultivars studied, seeds of Kolibri showed capability to maintain both high germination energy and high emergence rate at diminished water potential of the environment. Seed dehydration tolerance was increased when the parent plants were subjected to drought.

Nitrate reductase (NR) induction is enhanced by exogenously supplied sucrose in excised pea roots exposed to both exogenous nitrate and exogenous nitrite. NR synthesis is preferentially supported by sugars transported to the cells at the moment, however NR induction can take place for some time without exogenous sugar influx if roots are saturated with sugars during precultivation. Steady high NR levels are dependent on steady sugar and nitrate influxes. NR induction is low in roots precultivated for 20 h without sucrose although sugar content is still high in them. This suggests that compartmentation of sugars in the cells is of major importance during NR induction. Total nitrate content in roots exposed to nitrate is not influenced by sucrose supplied together with nitrate. Some nitrite is oxidized to nitrate in roots exposed to exogenous nitrite ; we assume that this nitrate is responsible for NR induction. Our results indicate that sugars, besides many indirect effects on NR induction, may also directly influence NR synthesis either as coinducers or as derepressors of NR synthesis. Our results further show that NR is not a product-inducible enzyme.

Phosphate is an effective inhibitor of the phosphohydrolases of wheat embryos (Triticum aestivum L.).In vitro the inhibition was competitive with K₁ = 4.48 × 10^-3 M (1.6 × 10^-3 M P₁, applied as KH₂PO₄).In vivo the inhibition with KH₂PO₄ was relatively low during germination (48 h), but inhibition increased when other P₁-compounds were used. In ungerminated embryos the phosphatase activity comprised three isozymes; the pattern of iaozymes changes during germination, but there was no influence of P₁ in comparison with the control.
Concluding we may state that the activity of phosphohydrolases is regulated by an inhibition mechanism caused by P_i-concentration.

Poly(A)⁺RNA is synthesized during the first hours of pollen germination and is rapidly incorporated into polysomal structures. After a 2-h pulse with uracil-¹⁴C, 42% of the transcribed fraction of polysomal RNA is polyadenylated. Following 4 h of germination the amount of the newly-made poly(A)⁺RNA decreases steadily at the rate of about 14% per h, whereas that of rapidly-labelled poly(A)^-RNA continues to grow. Beginning 1 h of cultivation the ratio of poly(A)^-/poly(A)⁺RNA increases exponentially. Similarly as in non-polyadenylated mRNA the main portion of the synthesized polysomal poly(A)⁺RNA sediments at a rate of 4 to 14 S and its mean size decreases slightly with the time of labelling. RNA isolated from nuclei and cell wall containing pollen tube fraction differed from the polysomal one in higher apeoific radioactivity and the polyadenylated RNA exhibited higher size distribution. The comparison of the results with earlier observations suggests the involvement of poly(A)in mRNA translation in pollen tubes.

The formation of adventitious buds under the influence of 6BAP has been observed on various aerial organs of culturedPinus silvestris seedlings. The inductive power of this cytokinin was found to depend on the concentration and the physiological age of the explant.

The rooting capacity of leaves isolated from a vegetative clone ofAnagallis arvensis L. exposed to 9 hours of light (75 W m^-2) at 22 °C and 15 hours of dark at 12 °C a day is significant only in F₁ young leaves and not in adult ones. The rooting capacity of the young leaves and of the vegetative shoots is greater in longer photoperiods. The leaves make roots even under weak (14 W m^-2) irradiance. The rooting capacity of the leaves is diminished and even suppressed by exogenous sucrose (14,60 ×10^-3M). This inhibition may be counteracted by IAA (10^-6M). When leaves and shoots are taken from clones under long (16 h) photoperiods, or in constant irradiance, they progressively lose their rooting capacity during the treatment. Rooting capaoity is regained if the clones are returned again to "short day" (9 h) condition.

Globular embryoids were continually produced in anther cultures of tobacco (Nicotiana tabacum L. cv. Samsun) from the pool of resting microspores if the iron-free medium was used. The supplement of iron stopped the development of fresh early embryoids still inducing continual conversion of the resting globular embryoids into torpedo-shaped embryoids, and into haploid plants. Globular embryoids in the anthers responded to the iron supply even after eight months' cultivation on iron-free media. Isolated embryoids showed the same response. Haploid plants were regenerated from the anthers on the minimal medium consisting of agar, sucrose, iron and distilled water. Iron requirements of preglobular, globular and postglobular embryoids are discussed.

The analysis of growth and movements of seedling organs of kidney bean (Phaseolus vulgaris L.) provides a pattern of periodic phases of activity and relaxation. The existence of a central organ which would control the phase relationships, is not anticipated in the integrity of the plant. The cyclic activity of individual organs shows itself by growth associated with oscillation movements. One and the same organ may simultaneously accomplish oscillatory movements with a diurnal and ultradiurnal frequency. These rhythms originate during the organ development; the first pair of kidney bean leaves at first executes oscillation movements with a diurnal frequency and only after it is fully developed it exhibits a diurnal cycle with the photophil phase upwards and the scotophil downwards, the oscillations with an ultradiurnal oycle being maintained. The movements of the two leaves are synchronous, but there occur short sections with a desynchronous cycle. Simultaneously with these oscillations, in which the leaf petiole takes part, the adult leaf performs oscillatory movements perpendicular to the longitudinal leaf axis, the so-called side swings, controlled by periodical changes of the joint attaching the leaf blade. Their frequency is practically identical with that of the ultradiurnal cycle. Thus the periodic growth activity of the kidney bean results in growth oscillations passing in the diurnal cycle with a frequency of 0.043 rev.h^-1, their ascending and descending phases consisting of periodical ultradiurnal oscillations in cycles of 0.73-0.59 rev.h^-1. The epicotyl growth shows a similar pattern: into the basic diurnal nutation cycle with a frequency of 0.042 rev.h^-1 ultradiurnal oscillation cycles are incorporated having a similar frequency to that revealed in leaves (0.69-0.64 rev.h^-1). The diurnal oscillatory cycles belong to a system established on the basis of periodicity of day and night and other geophysical cycles. The ultradiurnal rhythmic oscillations are presumed to be an expression of the geocontrol system of root and shoot growth direction and orientation of the organ in space. The shape of their trajectories in bean leaves is contradictory to this; they are not spatial helices, as the kybernetic model would presuppose, but have a vertical, upwards and downwards course in one plane. Since these oscillatory movements with an ultradiurnal cycle cease after petiole excision from the stem and after shoot apex amputation, one may presume that they are coupled with the low-frequency oscillatory system of the epicotyl.

Radioactive phosphate was applied to the roots of intact alfalfa plants (Medicago sativa L.) on the 49th day after inoculation withCorynebacterium insidiosum (Me Culloch) Jensen and the³²P contents in different fractions of phosphoric compounds were determined. In inoculated plants, susceptible to bacterial wilt, the inorganio phosphate contents (³²Pinorg) was increased markedly and the³²P bound in organic compounds soluble in acids (³²Porg) decreased as compared with control. In roots of the same plants the³²P contents in phospholipid fraction and DNA were decreased. In tolerant inoculated plants the³²Pinorg increase and³²Porg decrease as compared with those changes in susceptible plants were less expressive. No expressive changes in determined³²P fractions have been proved in resistant plants without any visible disease symptoms.

Net photosynthetic (P_N) and dark respiration (R_D) rate, stomatal (rs') and internal (ri') resistances to carbon dioxide were measured by gas exchange methods on leaves of different ages, expressed in leaf plastochron index units (LPI) for a fast growing poplar cultivar Unal 2. Although the optimal leaf age differs slightly for the different gas exchange parameters, leaf ontogeny is reflected in the same way in these different parameters. MaximalP_N and minimalrs' and ri' values were found at LPI between 6 and 10. Chlorophyll concentrations were lowest at LPI lower than 10 although an increase in two steps was found, when leaf age increases up to maturity.