The occurrence of browning in protoplast cultures ofCyamopsis tetragonoloba completely inhibited the growth of protoplast derived colonies. Of the various additives employed to counteract the problem of browning and subsequent necrosis, polyvinylpolypyrrolidone (PVPP) was found most effective. Simultaneous addition of polyvinylpyrrolidone (PVP) to the protoplast culture medium accentuated the effect of PVPP and also improved the frequency of protoplast division.

Growth regulators participate in the differentiation of floral parts, determining the developmental path of the respective type of inflorescence. The effect depends on the expression of the peculiarities of floral part differentiation, the recognition of the character of endogenous substances in certain stages and the choice of the suitable regulator for application. In the primitive flower ofPapaver petals and stamens are formed from the peripheral meristem with a lower content of auxins and a higher level of gibberellic substances. The pistil arises later from central tissues with a higher level of auxins and inhibitory substances. The stamens are more sensitive to the higher level of auxin substances, and by a suitable application of GA₃ and BAP they can be transformed into petals; in this way double flower forms arise. In the differentiation of floral parts ofCampanula, Rosa andMelandrium similar regularities assert themselves in time successions, but in another spatial arrangement. Sex differentiation of diclinous flowers ofMelandrium is based on differences in heterochromosomes XY and XX. The rise of the zygomorphic flower ofVeronica is accompanied by a different distribution of endogenous substances which affect the development of petals, stamens and the pistil.
The differentiation of flowers in the racemose inflorescence occurs in the acropetal succession, and lateral primordia inCampanula develop into actinomorphic regular flowers, whereas inDigitalis they are zygomorphic and only the terminal flower is peloric. In the initial phases the staminate tassel and the pistillate ear in maize are identical. Earlier differentiation of the terminal pistillate tassel is connected with a higher level of gibberellins and the later development of the lateral pistillate ear is accompanied by the increase in auxin-like substances and inhibitions. Similar correlations were found in the development of staminate catkins and the differentiation of pistillate flowers in terminal buds ofJuglans regia. By the application of auxin-like substances it is possible to achieve the transformation of primordia of the staminate tassel into the pistillate ear in maize or to regulate the number of staminate catkins and pistillate flowers on twigs of the walnut tree. In the capitulum of the sunflower differences arise between peripheral pistillate ray flowers and hermaphrodite tubular ones. By applying GA₃ and BAP the number of ray flowers is increased. If the normal course of inflorescence differentiation is affected with a suitable type of regulator, a range of floral abnormalities appears which permit to assess the intervention in different developmental stages and the reaction of the primordium to the applied type of regulator. Abnormalities also suggest some phylogenetic correlations.

Growth of soybean was not altered, whatever the inorganic N-source (NO₃, NH₄ or a NO₃/NH₄ mixture); conversely, growth of Erica x darleyensis plants in vitro decreased more in. NH₄ medium than in a NO₃ medium, compared to a NO₃/NH₄ medium. The GS/GOGAT pathway (in NH₄ medium), the nitrate and nitrite reductase activities (in NO₃ medium), as the contents in free nitrogenous forms and total nitrogen (in NO₃ and NH₄ media) were not more altered in Erica than in soybean, compared to a NO₃/NH₄ medium. PEPCase activity was the highest in soybean irrespective of the N-treatments; the involvement of PEPCase in N-metabolism could be explained by its function in ionic and osmotic balances rather than its function in supplying carboxylates as acceptors for NH₄-assimilation.

The influence of increasing concentrations of copper, zinc, lead, nickel, chromium and cadmium on 14-day-old seedlings of wheat (Triticum aestivum L. cv. Vergina) was studied. Plants were grown in 1/10 strength Rorison's nutrient solution with increasing concentrations of each of the metals added separately. The toxicity of metals depressed shoot growth but the most evident symptoms were on roots. The concentration of each metal which caused inhibition of root growth was chosen to study the influence of metals on isoperoxidases of wheat shoots. The concentrations employed did not alter the number of peroxidase bands but almost in all cases enhanced the intensities of bands of pH 4.0-4.2 and 5.0-5.4, while they decreased the intensities of bands of pH 4.2-4.6 and 5.4-6.5.
The similar effects of the different heavy metals employed may suggest similarity in metal action on wheat isoperoxidases. The increased intensities of peroxidase bands may be considered as an indication of enhanced senescence caused by the heavy metal treatments.
Generally, our results suggest that the heavy metals employed have caused complex changes on the multiple forms of peroxidases.

The action of two anticytokinins, 3-methyl-7-n-pentyl-aminopyrazolo[4,3-d] pyrimidine and 4-cyclopentylamino-2-methylthiopyrrolo [2,3-d] pyrimidine on the zeatin and 6-benzylaminopurine induced lateral bud growth ofLycopersicon esculentum Mill. cv. Fireball seedlings was studied. Bud growth stimulation by 0.1 mM zeatin was not overcome by application of anticytokinin at concentrations of 0.01 to 1.0 μ 24-h after zeatin application. However, application of 0.1 μM of anticytokinin 24-h before 0.1 mM zeatin caused a significant enhancement of bud growth. A simultaneous application of 1 mM anticytokinin and 6-benzylaminopurine or concurrent with young leaves excision significantly reduced bud growth.

Morphogenic callus cultures were obtained from 7-10 days old immature embryo explants on Murashige and Skoog and Gamborg's medium supplemented with 2,4-D. In the initial stages of culture the frequency of shoot formation varied from 28% to 65%. After 5 to 6 months of subculturing, the frequency of shoot formation was reduced to 14%. In the initial stages of culture, growth hormones do not seem to be very important for regeneration. Cultures from young and old non-differentiating calli, and calli with shoot and/or root formation at different intervals were analysed for isozymes of esterase, peroxidase and acid phosphatase for studying the morphogenic capacity. With the development of shoot/root, changes in isozymes takes place but no specific isozyme(s) could be related to the process of induction of morphogenesis.

Abscisic acid, a potent growth inhibitor inhibits hypocotyl growth ofRaphanus sativus seedlings. Phenolic compounds,viz., trans-cinnamic acid, chlorogenic acid, ferulic acid, salicylic acid, tannic acid and quercetin when applied with ABA, antagonize ABA action and restore normal seedling growth.
Gibberellic acid promotes hypocotyl growth and on combined application with ABA, the ratio of their concentrations determines the course of the resultant growth. This interaction can be modulated by phenolic compounds. Phenolic compounds in low concentrations when present together with GA and ABA, favour GA-induced growth by antagonizing the inhibitory influence of ABA.
The inhibitory action of abscisic acid on a wide range of growth processes is so far known to be reversed only by growth promoting hormones,viz., IAA, GA and cytokinins. Antagonistic action of phenolic compounds towards ABA, and increasing the action of GA when present together with GA and ABA, establishes a dual role to this class of compounds; balancing the effect of both growth promoting and growth inhibiting hormones.

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.

Plants regenerated from callus cultures derived from leaf discs and mesophyll protoplasts ofPetunia hybrida cv. Rose of Heaven exhibit a high frequency of genetic and chromosomal variation. Of twelve leaf disc-derived plants examined, only three had the normal diploid chromosome number (2n=14) while seven were tetraploid and two were aneuploid (16 and 27 chromosomes). Of seventeen plants derived from two protoplasts, none had the diploid chromosome number. Most had 28 chromosomes, one 29, two 27, one 26 and one had variable numbers (14-28) in different root tip cells. In all cases aneuploidy was associated with developmental abnormality. In addition, heritable differences in growth, morphology and flower pigmentation were observed in callus-derived tetraploids and diploids, including one diploid which differed from parent plants in at least four characters. These results are discussed in terms of the importance ofPetunia in genetics research and for studies of somaclonal variation.

Embryogenic callus which has maintained its embryogenic ability on media without growth regulators for three years has been induced at the base of shoots of a genotype with CMS propagated for a long timein vitro by transferring the shoots onto media richer in inorganic and organic components. The effect of two basal media (MS and PG₀) on the intensity and completeness of the proliferation of somatic embryos was examined with different combinations of growth regulators. Pollen fertility was evaluated in 87 plants regenerated from somatic embryos. Cytoplasmic male sterility was conserved in all of them.

The equilibrium density of chloroplasts from barley (Hordeum vulgare L. cv. Hassan) was analyzed by sucrose gradient centrifugation. Natural and detachment-induced leaf senescence were associated with a decrease in density and an increase in heterogeneity of the chloroplast population. Treatments (with growth regulators and light) which retarded or accelerated senescence, respectively, retarded or accelerated chloroplast density decrease. Accelerators as well as retardants of senescence decreased the heterogeneity of the chloroplast population.

Evidence for the existence of a neutral inhibitor specific for auxin has been in the literature for 45 years. The inhibitor is demonstrable by its effect in causing positive curvature of theAvena coleoptile. The growth of the mesocotyl of oat and corn seedlings in darkness and its inhibition by light are determined by the neutral inhibitor as is the phototropic response of the sunflower stem. Production of the inhibitor is promoted by red and fluorescent light. Irradiance at 730 nm promotes auxin production while irradiance at 660 nm promotes production of the inhibitor. The positive curvature induced by 2,3,5-triiodobenzoic acid can be used to quantify the neutral inhibitor. Since the benzoic acid is more effective than iodoacetate in reacting with the sulfhydryl of cysteine, a sulfhydryl group is indicated to bo one reaction site for auxin and to be the basis of polar transport.

The mechanisms by which exogenously applied plant growth regulators act to express those genes that are selectively involved in cell and tissue differentiation are not at all well comprehended. However, the ontogenetic sequences of events that enable receptor or target cells to be activated and to undergo dedifferentiation and redifferentiation, can often be followed experimentally and can lead to a better understanding of the causal relations and control mechanisms in coordinated cell growth and development.
Cytokinins, applied either in an agar medium or as high-concentration, short-duration pulses to expiants or as high-concentration, intermittent sprays to intact plants, induce switches in the normal developmental pattern of cells of certain explanted tissues. Examples of cells that are particularly receptive are the subsidiary cells of stomatal complexes and the differentiating cells of very young presumptive leaf primordia, that is before the latter have become irreversibly determined as leaves.

NaCl (0 to 274 mM) was added to the culture media of normal and habituated (auxin and cytokinin independent) sugarbeet calli and its effect on growth (estimated by the increase of dry and organic matters), water content and osmotic potential was tested. Growth of normal callus was stimulated by 68 mM NaCl after a lag period of two weeks. This callus tolerated up to 137 mM NaCl without growth reduction and maintained its hydric status by readjustment of its osmotic potential in 24 h. NaCl quantities under 34 mM stimulated growth of the habituated callus from the 3rd day on; higher NaCl concentrations (68 to 274 mM) inhibited growth or were lethal. NaCl sensitivity of this habituated callus was not due to its inability to adjust its osmotic potential: this adjustment occurred from the 4th h of culture whatever the media. From the 3rd day on, however, this callus presented a water deficit which depended on NaCl concentration. It is suggested that the lowering of osmotic potential corresponds to an important water loss in relation to changes in membrane permeability. This study finally shows that mechanisms of salt tolerance may have developed at the cellular level. Lower growth and lower salt tolerance of the habituated callus need further investigation in relation to cell structure and hormone autonomy.

Red-light-induced (via phytochrome) germination decreased with increasing numbers of turions per germination flask (overcrowding). Three hypotheses concerning the mechanism of this germination inhibition were tested, related to abscisic acid, ethylene, and oxygen deficiency: (i) Although abscisic acid is a powerful inhibitor of turion germination it had to be excluded as a cause, because abscisic acid was not secreted from turions into the nutrient solution, (ii) Ethylene (ethrel) strongly inhibited growth of newly formed sprouts, but germination response itself was not inhibited, (iii) Germination inhibition did not appear if short light pulses were substituted by continuous irradiation. It reappeared in the presence of the photosynthesis inhibitor 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea, but it was not observed in aerated nutrient solutions, or when Petri dishes instead of Erlenmeyer flasks were used. Decreased oxygen concentrations in the nutrient solution were produced by turion respiration. Consequently, anaerobiosis within the nutrient solution caused by turion respiration was the reason for germination inhibition by overcrowding.

Variations in water content, relative water content (RWC), pressure potential and intracellular pH (pH) had been studied as factors of bud growth in rose plantlets grown in vitro for micropropagation. During the phase of healing, pressure potential and pH, were high enough to allow bud growth. During the following growth phase only buds of the lower part of the stem were able to grow. The growth ability of these buds and the growth inhibition of the others, associated with ΔpH, were retained during the last three days of culture, when dry matter content and RWC were the lowest. The results also showed a tight link between pH, and pressure potential. This may enable to distinguish different stages of plantlet development in vitro.

Shoot multiplication of hornbeam was stimulated onWPM, QL andDKW medium supplemented with a low concentration of BAP or BPA (0.1-0.2 mg I -1) andIBA (0.1 mg I -1). Low concentration of thidiazuron promoted axillary bud formation, higher concentration inhibited shoot elongation. Microshoots were rooted onWPM supplemented with a low auxin concentration (IBA or NAA 0.2-0.5 mg I -1). High rooting percentages were obtained. Shoot proliferation of ash was stimulated on MS andDKW medium supplemented withBAP orBPA (2.0-5.0 mg I -1) andIBA (0.1 mg I -1). Root formation was promoted onWPM containing a low auxin concentration. Rooted plantlets were transplanted into soil and after hardening off the micropropagated trees were planted in the field. The planted trees grew normally without showing signs of abnormality.

It is generally accepted that plant growth and development are regulated by the known plant hormones. Some objections to the functions of auxins and cytokinins in the induction of shoot and root primordia are reported. Instead of them oligopeptides of special amino acid sequences could be the endogenous signals. There exist structure relationships between auxins and parts of the α-helical oligopeptides of defined amino acid sequences. The same is true for cytokinins.
The most difficult part of this hypothesis is its verification. Using protonemata ofFunaria hygrometrica bud induction by various oligopeptides was investigated. The most active peptide tested is leucine-tryptophan. On the other hand endogenous oligopeptides containing [¹⁴C]-leucine in the moss protonemata during endogenous bud initiation were looked for. Three to four different oligopeptide spots seem to be related to bud induction.

Anin vitro procedure for micropropagation ofPinus strobus L., consisting of the following four steps has been established: shoot induction, shoot growth, root induction, and root growth. Influence of certain selected factors on each of these steps was determined. Shoot induction was found to be influenced by the age of the explant as well as the concentration of 6-benzyladenine in the medium. Best shoot growth was obtained on the medium of Litvayet al. without any growth regulators. Addition of activated charcoal to shoot growth medium resulted in fewer shoots. Root induction on several media was compared. Best root induction occurred when shoots were put on a half strength Gresshoff and Doy's medium supplemented with 0.5 to 1.0 mg r1^-1 α-naphthylacetic acid (NAA) for two weeks. Shorter exposure of shoots to higher concentrations of NAA or indol-3-ylbutyric acid (IBA) was not as effective. Low temperature seemed to be a requirement for root growth.

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.

In the long-term cultivated callus cultures ofMatricaria recutita L. the identical concentration changes in the biosynthesis of glutathione, glutamate, aspartate, total thiols and proteins were detected within the subculture. The level of oxidized glutathione during the growth of callus culture was low with the highest value 10.66 nmol g^-1 on the 13th day of subculture. The ratio GSH/GSSG which significantly influences the redox processes in a cell, and the activity of glutathione reductase increased from the 8th day. Ascorbate formation was detected on the 17th day, although no relation between the ascorbate synthesis and the concentration of glutathione and glutathione reductase was found.

The content of auxin-, inhibitors-and gibberellin-like substances in freeze-dried humic acids was studied. The results indicate the existence of growth-promoting substances in humic acids, possibly corresponding to IAA or its precursors. Inhibitory activity is more marked during germination than during the growth process. The inhibitory effect caused by high concentration of humic acids could be due to an auxin-like action rather than an input per se of growth inhibitors. A significant amount of both free and conjugated gibberellin-like substances were observed.

Life span of the second leaf of wheat(Triticum aestivum L., cv. Grana) plants was studied from day 8 to day 50 of plant age in a variant with nitrogen (+N) and in a variant in which plant senescence was induced by the omission of nitrogen from the nutrient solution (-N). Seed protein was the sole source of nitrogen for these plants. Specific leaf mass (SLM) in the -N variant, and specific leaf area (SLA), the mass of fresh leaf, soluble protein content and total nitrogen content in the +N variant peaked by day 22 of plant age (that is by day 19 of leaf age). Dry matter content, leaf length and leaf area, and SLM in the +N variant peaked by day 29 of plant age (that is by day 26 of leaf age). The ontogeny of the second leaf in the variant with enhanced senescence was shorter by at least 14 days. Plants from this variant showed typical symptoms of N deficiency, that is yellowing of leaves, tip burn, and lack of tillering. However, the growth and biochemical characters studied did not indicate an earlier onset of the senescence of the second leaf of -N plants. Both +N and -N variants reached their peaks (with the exception of an earlier peak by day 12 in case of total nitrogen content in the -N variant) on the same day of leaf age. Thus the first part of the leaf life span from leaf growth initiation to full expansion was of the same length in both the control and N-def icient plants. The stage of the proper senescence of the second leaf of -N plants was very short; the leaf completely died away within 7 days after senescence onset.

Reorganization of growth in the shoot apex ofChenopodium rubrum during transition to flowering is described. Growth and morphogenic changes - a rise in cell division rate, changes in leaf and bud formation and changes in directions of cellular growth - are viewed from the aspect of a possible role of growth hormones in controlling these changes. Growth and morphogenic effects of exogenous growth regulators in the shoot apex ofChenopodium are summarized and their floral effects explained in terms of changing apical growth correlations. New evidence concerning the timing of increased cell division rate and showing the limited requirement of axillary cell division and a shift to more vertical direction of growth in the apex in the floral developmental pathway was obtained in experiments with kinetin application and by surgical treatments.

Transpiration rate, stomatal frequency, growth, contents of pigments, saccharides, total nitrogen, proteins and some nutritive elements (K, Ca, Mg, P) of radish plants were significantly lowere dwith the rise in salinization levels using NaCl. Spraying radish shoots with proline solution (200 g m-³) counteracted the above adverse effects, especially at low and moderate salinity.

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.

Two classes of phosphonopeptides, those containing P-terminal 9-aminofluoren-9-ylphos-phonic acid and those of dialkyl 9-aminofluoren-9-ylphosphine oxides, influence plant growth according to different mechanisms. The effect of these compounds on the growth of several bacterial species, including the photosynthetic bacteriumRhodospirillum rubrum, as well as on the activity of photosystems 1 and 2 in isolatedPisum sativum andSpirodela oligorrhiza chloroplasts was studied. The peptides of free, unblocked 9-aminofluoren-9-ylphosphonic acid acted in a morphactin-like manner, whereas those of dialkyl 9-aminofluoren-9-ylphosphine oxides influenced photosynthesis indirectly.

Glucose, fructose, sucrose, maltose, and lactose stimulated photoheterotrophic growth ofNostoc linckia (Roth.)Born. as well as its heterocyst frequency, chlorophyll and protein contents, ammoniacal nitrogen uptake and nitrogenase activities. Glucose, fructose and sucrose also supported slow chemoheterotrophic growth. α-ketoglutarate, pyruvate, ribose, succinate, acetate, sorbose and formate were inhibitory.

A simple equipment was developed to cultivate young cereal plants under enhanced CO₂ concentration. Cultivation system permits growing of about 40 barley seedlings for about 2 to 3 weeks. The system consists of two identical growth chambers (volume about 30 dm³), gas conditioning circuit and measuring circuit with an infra-red CO₂ analyser. Capabilities of the whole equipment were tested by growing barley plants under 330 and 1000 cm³ (CO₂)m^-3 and in combination with high or low nitrate level.

Low molecular mass humic acid fractions caused a decrease in the germination rate. Only the highest concentration of humic acid solution decreases the soaking of fruits. Neither sodium content nor water and osmotic potential can account for that decrease.
Seed respiration was increased in the presence of humic acids and their medium molecular mass fraction. This increase did not produce an increment in embryonic growth possibly as a result of interference in the respiration chain or decoupling in the oxidative phosphorylation.