Buckwheat cotyledons were induced to form callus tissuein vitro, in which shoots or roots could be regenerated, by changing the hormonal composition of the medium. The effect of gibberellic acid (GA₃) was studied in these processes. Addition of GA₃ to cell division medium during the first 5 days after inoculation did not interfere either with the induction of cell division, or with the subsequent organogenesis. However, GA₃ had a very pronounced effect on organogenesis when added immediately upon the transfer of expiants to organ induction medium. While root initiation was accelerated and root number increased, bud induction was inhibited. An initial GA₃ treatment had a long-lasting effect on bud induction and the tissue recovered from inhibition only in the fifth subculture.

Chromosomal variability in callus culture ofAsparagus racemosus was comparatively higher in the presence of 2,4-D than of NAA. The frequency of polyploid cells was enhanced with the increase in the concentration of 2,4-D or with the addition of coconut water. Gradual polyploidization with increasing age of the callus has been recorded.

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.

Germination and seedling growth of rice was studied in NaCl and PEG 6000 solutions having osmotic potentials -0.2, -0.4, -0.6 and -0.8 MPa.
At isoosmotic concentrations, the NaCl proved more harmful to germination, seedling growth, per cent moisture content of seedling organs as well as mobilization of food matter from seed to the growing seedlings. This fact suggested that in rice, at least in the early stage, a specific ion effect rather than osmotic effect is the prime cause of salt injury. Compared to susceptible cultivar, the tolerant one was less inhibited by salinity.

Treatment of etiolated and excisedCucurbita cotyledons with exogenous cytokinin (benzyladenine) in darkness or light results in a marked stimulation of Rubisco activity, content of enzyme protein, and incorporation of labelled precursors into it, indicating cytokinin-stimulatedde novo synthesis of the enzyme. Cell-free translations of RNA in the wheat germ andE. coli systems show an increase in both large and small subunit mRNA amounts relative to the increase of total RNA under the influence of the phytohormone and light. This increase in the level of translatable RNA is confirmed by RNA hybridization with the Rubisco large subunit gene of spinach. In addition, our results demonstrating additive effects of benzyladenine and light in cotyledon and chloroplast development suggest that the two factors co-act independently in the causal sequence of Rubisco gene expression. The data are discussed in a general view of cytokinin action in gene expression steps.

The auxin transport inhibitor TIBA strongly influences meristem structure and activity in the unistratose gemmaling ofRiella. The gradient of cell cycle duration, essential for normal morphogenesis, is abolished and the cell cycle is reversibly arrested during exposure to light. At the same time starch accumulation in the light is inhibited. Possibly, these effects are the consequencc of the inactivation of sulfhydryl-containing proteins by TIBA.

Leaf expiants from vegetative plants of the short-day plantStreptocarpus nobilis (C. B. Clarke) developed flower budsin vitro when cultured in 8 h photoperiods. Tn non-inductive photoperiods only vegetative buds were formed.In vitro photoinduction was demonstrated by giving the expiants short-day (SD) cycles and then transferring them to non-inductive photoperiods for expression of flowering. On medium containing 6-benzylaminopurine (BAP) organogenesis was initiated during the photoinductive treatments. Photoinduction of leaf tissue without adventitious bud development was obtained on medium without BAP. The photoinductive state of the leaf tissue was fairly stable, being expressed after 2-3 weeks in non-inductive photoperiods when adventitious buds were formed. The quantitativein vitro flowering response to the endogenous floral stimuli, resulting from photoinduction, could provide the basis of a bioassay for presumptive flower inducing chemicals.

A specific, high affinity, IAA binding site was demonstrated in both a cytosolic fraction, and in isolated nuclei, fromNicotiana tabacum cv. Wisconsin No. 38 cells grown in suspension culture. The amount of the binding site detected in both these fractions changed during the culture cycle according to a strict pattern. The molecular mass of the binding site was estimated by gel filtration to be approximately 175 000 and it appears to be a protein. When partially purified by affinity chromatography and allowed to pre-incubate with IAA, the site had a significant stimulatory effect on total RNA synthesis, as measured by a cell-free assay system. Unpurified extracts had no such effects. The system behaves rather like the steroid hormone-receptor system in animals.

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.

The influence of different organs on flowering of photoperiod- or temperature-dependent plants and of neutral plants is described. Special attention is given to the influence of roots which generally inhibit flowering. High or low temperatures applied to the roots ofChenopodium polyspermum, a quantitative short day plant, induce flowering. Vernalizing treatment of roots ofCichorium intybus suppresses the inhibition of flowering arising from the tissues immediately underlying the terminal bud. Other plants such as coniferous trees can flower more intensively if the growth of their roots is reduced. After a short presentation of the very complex situation concerning the regulation of floweringvia the presently known hormones, the methodological limitations of our understanding of the precise hormone mechanism of flowering will be discussed. One example of an immunologica 1 approach to localize endogenous hormones inside tissues is given, using abscisic acid.

Experiments were conducted (a) to identify optimum media pH for nitrate uptake by intact corn (Zed ways L. cv. XL-81) plants grown under solution culture conditions, (b) to understand the effect of media pH on growth, nitrate uptake, water use and nitrogen accumulation. pH was maintained using carboxy cation exchange resin IRC-50. Plantswere grown in 15mM NO₃-N per litre and nitrate depleted from nutrient solution over a period of time was measured. Dry matter accumulation by the plants decreased progressively with increased pH. However, the decrease was significant only at pH 7.0 and 8.0. Data on water use showed results similar to dry matter accumulation. Correlation coefficients (r values) among nitrate uptake, dry matter production, water use, nitrate -N accumulation and reduced -N accumulation was observed to be high (above 0.99). All effects of media pH are significant only at pH range 7.0 to 8.0. Despite adequate supply of iron, the plants at pH 7.0 and 8.0 showed symptoms of iron deficiency. Thus, iron and possibly micro-nutrient deficiency could have resulted in poor plant growth. These experimental results indicate optimum pH range for nitrate uptake is 4.0-6.0. Plant growth and dry matter accumulation were directly affected by media pH. The differences in nitrate uptake, water use and total nitrogen accumulation appeared to have resulted as a consequence of differential dry matter production. Whether these differences are due to altered metabolic uptake characteristics of the loots is not known.

Bacteria of the speciesPseudomonas putida andPseudomonas fluorescens isolated from the rhizosphere of maize and bean plants produce indol-3-ylacetic acid and some other auxins when grown in suspension cultures. IAM and ILA were also found besides IAA and its degradation product IAH by means of HPLC and MS methods. This finding indicates the involvement of two different metabolic pathways in IAA synthesis in bacteria. The amounts found varied between 1.6 and 3.3 μg IAA per ml of media which corresponded to 100-200 μg per gram of bacterial dry mass. The effect of IAA production by rhizosphere bacteria on IAA level in the plant is discussed.

In the protonema ofFunaria hygrometrica, predetermined cells run through a period of sensitivity to cytokinins, as part of the morphogenetic system with respect to bud formation. The cytokinin sensitivity is highest immediately after the formation of cells in question. The cells can react if enough hormone is present during the sensitive phase. Kinetin is cleaved very rapidly and at an increasing rate. Most probably the concerned enzyme ("kinetin oxidase") is induced by kinetin. Therefore, cells formed after the beginning of the treatment do not respond by forming buds.

The vegetative apex grows in an indeterminate, iterative mode. When flowers are formed it changes to determinate, sequential growth. The essential change in growth at the transition to flowering seems to be the decrease in primordium size at initiation, relative to the size of the apex. In the formation of the flower itself there may be a further requirement, that primordia undergo a decrease in absolute size at initiation. Where measured, this decrease is parallelled by a decrease in the size of the stem frustum at initiation. While in the case of the stem frustum this decrease in size has a predictable consequence, the reduced size of internodes in the mature flower, it is not clear how the reduction in size of the primordium is related to the subsequent development of flower parts. Reduction in primordium size seems to be fundamental to the changes in primordium arrangement and divergence angle that typically occur on flower formation, but not sufficient to cause the subsequent differentiation of floral parts. This presumably occurs as a consequence of the interactions between the developing primordia and substances present in the flowering apex.
Recent models of flowering show that a realistic simulation of apical growth on the transition to flowering can be made using the equations of catastrophe theory. To account for the growth and development of a flower meristem models must also account for changes in divergence angle and the new developmental pathways followed by the floral organs.
The data on the role of growth substances in the transition to flowering at the apex are at present insufficient. What is needed particularly is information on the identity of the putative inhibitor of primordium initiation that may operate within the apex, and its role in the growth changes that occur during and after the floral transition.

L-tryptophan dehydrogenase (TDH) is a newly found enzyme involved in the metabolism of indole compounds in plants. The substrate specificity of TDH was investigated in extracts prepared fromPisum sativum andProsopis juliflora. The enzyme activity was detected in both plants either in the oxidative or the reductive direction. The occurrence of other dehydrogenases specific to amino acids was also investigated in the experimental plants:e. g. glutamate dehydrogenase was found to be 1.7 to 5.0 times more active than TDH, whereas no activity for phenylalanine dehydrogenase was detected. In pea plants activity of alanine dehydrogenase could be shown as well. In addition to pea and mesquite TDH was also found in wheat, maize, and tomato seedlings, whereas no activity was detected in brassicaceous plants.

The contents of chlorophylls, carotenoids, flavonoids and phytohormones (IAA, ABA and other inhibitors) were determined in green and albino seedlings of cotton (Gossypium hirsutum L.) and pea (Pisum sativum L.) The growth of green and albino seedlings during 1 -2 weeks was similar. The green and albino seedlings do not differ remarkably in phytohormonal content and in the flavonoid concentration. In the etiolated seedlings of green and albino forms the content of flavonoids was rather decreased.

Effects of 2,3,5-triiodobenzoic acid (TIBA) and age of etiolated pea epicotyl segments on the indol-3-ylacetic acid (IAA) stimulated transport of¹⁴C-abscisic acid (ABA) was studied. In spite of a slight decrease of IAA transport after the application of TIBA, the IAA stimulation of¹⁴C-ABA transport did not change. In segments excised from epicotyls of different age,³H-IAA transport was identical and the induction of prolongation growth by IAA in segments from the upper part of the epicotyl was observed. The IAA ap{ie226-01}ation to the growing segments was connected with intensive attraction of¹⁴C-ABA to the site {ie226-02}AA application, while the application of IAA to the older segments was growth ineffective ana no stimulation of¹⁴C-ABA transport by IAA was observed.

Flower initiation takes place during a rise of peroxidase activity following a peak of minimum activity which marked the completion of the flowering inductive phase. Since basic isoperoxidases underwent an inverse variation of activity in the course of successive inductive and initiative phases, it was hypothesized that the induction of flowering led to a temporary peak of maximum auxin level in the leaves. Our analyses and available literature data support the view. They also show the different capacity of non-induced and induced material to respond to external auxin application. Since some aspects of the physiological state characterizing induced plants can be simultaneously obtained in all plant parts as a result of rapid interorgan communication, the classical florigen theory is seriously challenged.