Under strictly non-inductive photoperiods (24-h photoperiods) floral buds were initiated on plants receiving 25 treatments with Reso (resorcinol) or 8 treatments with GA₃ (gibberellic acid) or GA₃ + Reso, while water treated control plants did not flower at all. Although a single treatment of plants with GA₃ or GA₃ + Reso is not adequate to cause induction under LD conditions, its effect is added to the sub-threshold induction caused by one SD (short day: 8-h photoperiod) cycle. The initiation of floral buds was hastened with an increasing number of SD cycles accompanying respective number of treatments, the effect of GA₃ alone or together with Reso being more pronounced than that of Reso alone. GA₃ increased the number of floral buds more than Reso, the number being the highest in plants receiving the respective number of treatments with the combination GA₃ + Reso under both inductive as well as non-inductive photoperiods.

The effects of salicylate on stomatal resistance (a measure of stomatal opening) were compared with those produced by 2,4-dinitrophenol and abscisic acid. Salicylate and dinitrophenol had the same minimum effective concentration and comparable kinetics, and induced stomatal closure persisting for a long time in the absence of further supply. However, a K and Ca solution prevented the salicylate-induced, but not dinitrophenol-induced, stomatal closure. The effects of salicylate and abscisic acid had very different characteristics. Cytokinins had no relevant effects on the stomatal closure induced by the three compounds. A close correlation was found between stomatal closure and K⁺ leakage from the treated leaves, suggesting that damage to the cell membrane may be involved.

A rapid method is presented for the determination of ribonuclease activity in coloured extracts from citrus leaves. At the same time, the influence exercised by several precipitating reagents and the storage time at 4 °c on the activity of the enzymatic system are studied. In addition the enzyme stability against heat is studied.

As the dynamics of changes in phytohormones may be involved in photoperiodic regulation of the rates of growth and flowering, fluctuation of cytokinins was followed in long-day and short-day tobacco. Zeatin (Z) and zeatin riboside (ZR) were identified in leaves and roots using a GC-MSC system. In plants of the long-day tobaccoNicotiana silvestris increasing the number of long-day inductive for flowering (10, 20, 30, 40 LD) resulted in a rise in ZR activity. Half the plants reached a reproductive stage on the 40th day of induction. In short-day Mam moth tobacco plants, short-day floral induction (10, 20, 30, 40 SD) caused similar but less marked changes in ZR.

An attempt is made to characterize the functional activity of the protein moleculo possessing both peroxidase and IAA oxidase activity by comparing the kinetic parameters for the two types of enzyme activity with regard to the following substrates: H₂O₂, benzidine, guaiacol and IAA. The curves expressing the dependence of the enzyme reaction velocity on the concentration of the enzyme or the substrate are different depending on the enzyme extract origin and the type of the substrate. It is established that the K_m of peroxidase for IAA decreases while its K_m for H₂O₂ increases during cell development. Both types of enzyme activity show similar pH and temperature dependence. The presented data show that IAA oxidase activity of the peroxidase develops as extension and differentiation of the root cells proceed. This is one of the possible mechanisms through which peroxidase may participate in the regulation of growth and differentiation of the primary root cells of maize (Zea mays L.)

The clone SJ ofSpirodela polyrhiza (L.) Schleiden forms turions under various nutritive conditions. As compared to 1500 μmol 1^-1 phosphate (P+), growth and frond yield of mixotropic cultures decreased, when 60 μol 1^-1 phosphate (P-) were available. By contrast, P-conditions increased the number, individual size, dry matter content, and total turion yield (mg turions per ml of the nutrient medium) of P-turions as compared to P+ ones. Germination behaviour of P-turions is characterized by fairly low zero levels in the controls, and by low heterogeneity in individual size as well as in the response patterns concerning the influence of light and/or phytoactive substances. P-turions from youngSpirodela cultures are extremely dormant. However, they undergo an after-ripening process if kept inside ageing cultures.

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.

Some general data on the genetic control and the possibilities of regulation of developmental paths inDrosophila are furnished. The insights to be gained from this insect will surely have implications that extend far beyond the fruit-fly. For example, in plants, developmental programs for floral organs, implying specific proteins are known. Developmental mutants in which mutate alleles control developmental programs for flowering were also selected in several species (Zea, Pisum, Sorghum, Cucumis, Mercurialis). Chemicals, especially phytohormones interfering with these programs are discussed. The case of sexual differentiation ofMercurialis is discussed in more detail. In this species, sex organs are controlled by sex determination genes and by auxins (male) and cytokinins (female). Flowers of each sex can be characterized by specific mRNA populations. They were evidenced by translationin vitro in a cell-free system of the various kinds of mRNAs [poly(A), non poly(A), polysomes]. The feminisation of genetic males by cytokinins induces the mRNA population of female type. Evidence concerning the implications of cytokinins in protein synthesis before translation level is presented. This is also probably true for auxins, although direct evidence is lacking.

The phenotype appearance ofArabidopsis thaliana hairy roots and crown galls their teratomas and regenerated plants were compared. Several differences were found, which correlate with T-DNA differences between Ti and Ri plasmids.

CAM-like photosynthesis was found in the isoetid aquatic plantsLittorella uniflora andIsoetes lacustris, but not in the isoetid speciesLobelia dortmanna or in the elodeidElodea canadensis. Of the taxa studied, the first three are known to utilize sediment-borne CO₂, whereasElodea is dependent on bicarbonate.

The analysis of the kinetic behaviour of pea L-tryptophan aminotransferase isolated from mitochondrial and cytosolic fraction unambiguously showed the preference of some of its keto acid substrates demonstrated by statistical criteria (R2, SSQ, AIC). An attempt is made to evaluate this result in connection with the availability of the keto acid substrates in different cell compartments.

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.

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.

The effect of anaerobiosis of wheat seedling roots during 6 consecutive days on contents of ethanol, lactate and glucose in roots and shoots and on the exudation of ethanol from roots to the medium was examined. Activities of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) were determined. After 36 h of anaerobiosis the concentration of ethanol in roots increased temporarily about 6 times and after 6 days it decreased to the level of control plants. The exudation of ethanol from roots to the medium showed similar pattern. The content of lactate was unaffected by anaerobiosis. In contrast, the content of glucose in roots of seedlings increased already after 1 day of anaerobiosis about 2 times and this higher level of glucose was noticed during consecutive 5 days. Anaerobiosis of roots caused an increase in the activity of ADH in both roots and shoots but the increase was not related to the content of ethanol in tissues, or exudated to the medium. The activity of LDH was unaffected by this factor. The results are discussed in relation to the limitation of energy supply of plants grown under root anaerobiosis.

Like wet stigmas, the stigmatic secretions of dry stigmas ofEichhornia also have proteins, sugars, amino acids, phenols and fatty acids. No significant difference could be observed in the composition of stigmatic secretions of long and medium styled flowers except that the components were marginally higher in concentration in the former than the latter. The UV absorption profiles of the stigmatic secretions also showed no difference. Stigma surface esterases could be detected in both the stigmas from a very early stage of development.

The salt tolerance was studied according to both fresh and dry matter increases of callus cultivated on the media supplemented with various sodium chloride concentrations as well as a high amount of K⁺, Na⁺, Ca²⁺, and Mg²⁺ ions as found in the East Slovakia salt soil lowland. The cells tolerate salinity at least up to 85 mM. According to statistical evaluation the salt concentrations used did not inhibit growth rate and development of tissue cultures.

Seven day- and six week-old alfalfa (Medicago sativa L.) plants, susceptible and resistant to bacterial wilt, were inoculated withCorynebacterium michiganense pv.insidiosum (McCulloch) Dye & Kemp. Leakage of solutes absorbing UV light from leaf discs into distilled water was investigated. The bacterial infection did not affect solute leakage rate from unifoliate and trifoliate leaves of either susceptible or resistant plants at an early stage of the disease. This may indicate that cell membrane integrity in alfalfa leaf tissues was not impaired.

In maize leaves nitrogen (N)-deprivation induced a significant decline of chlorophyl and total N contents. On the contrary, sulphur (S) content increased with N-deprivation. The activities of ATP-sulphurylase and O-acetylserine sulphydrylase also decreased with N-deprivation, but ATP-sulphurylase activity was more sensitive than O-acetylserine sulphydrylase activity to N-deficiency both in whole leaf extracts and in isolated leaf cells. Finally, N-deprivation induced higher changes in activity of the two enzymes in mesophyll protoplasts than in bundle sheath strands.

The pyruvic acid thiosemicarbazone was found to inhibitin vitro the soluble ornithine carbamoyl transferase as well as the enzyme in a mitochondria-rich cell fraction. For proving the inhibition of ornithine carbamoyl transferase in mitochondria-rich fraction a new method for DEAE-thin-layer chromatography of radiocarbon labelled citrulline and ornithine was used. The mitochondria prepared by discontinuous sucrose density gradient centrifugation are physiologically active and oxidized succinate under state 3 conditions. The respiratory control ratio was determined to 3.3. The results obtained show that this analogue of pyruvic acid is an inhibitor of ornithine carbamoyl transferase.

Proline accumulation in coleoptiles of wheat seedlings or in excised coleoptile segments incubated under shaking for a 24 h period was studied. There was no increase of proline content of coleoptiles after incubation of the seedlings in 5 mM citric acid (a relatively strong and slowly penetrating organic acid) in a pH range from 4.5 to 7.0 and only a slight increase of proline content after incubation in phosphate buffer at pH 7.0 to 7.5 duo to the higher osmotic concentration of phosphate buffer in this pH range. Quite different results were obtained with seedlings incubated in 10 mM acetic acid, a weak and easily penetrating organic acid. With increasing proton concentrations, proline accumulation increased. Application of 400 mM mannitol or higher concentrations of IAA (more than 10^-5M) additionally increased proline accumulation in the presence of 10 mM acetic acid in the pH range from 6.0 to 7.5 in which acetic acid alone was loss effective. It is suggested that a decrease of cytosolic pH causes stress-induced proline accumulation.