1-Amino-2-phenylethylphosphonie acid (PheP) retards growth inSpirodela oligor-rhiza causing morphological malformations, inhibits chlorophyll synthesis in progeny fronds, and markedly stimulates L-phenylalanine ammonia-lyase (PAL) activityin vivo and inhibits itin vitro; in prolonged experiments ribonuclease activity is stimulated. PheP severely inhibits anthocyanin synthesis in seedlings of red cabbage, with moderate inhibition of PAL activityin vivo; chlorophyll synthesis and growth of the seedlings are little affected.

Petunia hybrida plants were inoculated with differentAgrobacterium rhizogenes andA. tumefaciens strains and developed tumors were further cultivatedin vitro. Transformed flowering plants differentiated from tumors induced byA. rhizogenes strains 8196 and TRIOL Transformed but non-rooted plants developed also from tumors incited byA. tumefaciens T37. Cultures of roots transformed byA. rhizogenes strain 15834 did not show increased incidence of chromosomal aberrations in anaphases in comparison with untransformecl control. Permanent growth of isolated untransformedPetunia roots was not induced by addition of IAA into the medium.

Rooting cofactors and proanthocyanidins were studied in cuttings ofCastanea sativa Mill. from a natural mutant Nana and juvenile plants, both of which are easy to root, and from adult plants that do not root. Rooting cofactors and a high amount of proanthocyanidins were found in the easy-to-root cuttings, whereas in the adult plants no rooting cofactors were detected and the amount of proanthocyanidins was very low.

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.

The senescence of detached leaves of the Australian seagrassZostera muelleri Irmisch ex Aschers was associated with decreased levels of chlorophyll, soluble protein, and alkaline pyrophosphatase and catalase activities. Senescence was faster in artificial seawater than in distilled water. Irradiance has a retarding effect on senescence while cycloheximide did not retard senescence appreciably. The action of cycloheximide was studied usingCyperus rotundus L.,Hydrangea macrophylla (Thunb.) Ser.,Solandra maxima (Sesśe & Moc.) P. S. Green, andDatura suaveolens Humb. & Bonpl., and the cycloheximide sensitivity correlated with low chlorophyllase activity of the leaf.

A comparative study of dark respiration and effects of high and low temperature on dark respiration in five greenhouse cultivated tropical and sub-tropical species was made. The respiration rates determined manometrically were low in all species. Respiration rates increased with increasing temperature. Low temperature treatment accelerated the rate of respiration at 25 °G except in two species. An attempt has been made to determine the critical and optimum temperature for these species. The respiratory behaviour of these species has been discussed with respect to their original habitats and prevailing environmental conditions.

With the aim to reduce the period of flowering and of fruit maturation, we investigated the effect of auxins on flower formation. For these experiments we used young decapitated plants with two plagiotropic branches. Both the auxins, indol-3-ylacetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), retarded flower formation in coffee, the latter one being more effective. The effects of 2,4-D if applied on only one of the two plagiotropic branches can be observed only in this treated one. Furthermore, the auxins seem to act in coffee plant directly by affecting flower formation and not indirectly by inducing endogenous ethylene production.

Abscisic acid was analysed in seeds of oak, at. five stages of development in threeweek intervals, starting on the 6th week after anthesis until maturation in the 18th week after anthesis. The physico-chemical methods and bioassays were used for a closer characterization and quantification of the examined compounds. Differentiation of the ABA level depending upon the stages of seed development has been observed in various parts of acorn.

In young needles of the Douglas-fir (Pseudotsuga menziesii) GA₉ has been shown by GC and HPLC to be the main gibberellin. As minor compounds GA₇, GA₃ and GA₈ have been tentatively identified by HPLC. In addition to the free gibberellins small amounts of GA₉ glucosyl ester and a not yet identified ester of GA₂₀ have been isolated.
From the group of endogenous inhibitors ABA has been identified by GC-MS and ABA glucosyl ester by HPLC. After enzymatic hydrolysis of the ester, ABA and glucose have been quantified by GC and GOD-POD reaction giving the ratio 1:1. Another plant growth inhibitor has been identified as the methyl ester of jasmonic acid.

Circumnutation oscillations of hypocotyls were studied in Norway spruce and Scots pine using time-lapse cinematography. It was found that the circumnutations were specific in species. The analysis of hypocotyl ontogeny (100 h) revealed a different duration of the phases I, II and III of nutation oscillations in the first and second taxon. From the quantitative point of view it can be stated that during the phase I of nutation oscillations the Norway spruce hypocotyls exhibited higher frequency activity (corrections in direction of the hypocotyl by an elongation-controlling system corrected by a feedback mechanism), while in the phase III of nutation oscillations higher growth rate and larger amplitudes were observed in the Scots pine hypocotyl when compared with those of Norway spruce. The hypocotyl hook appeared only in Norway spruce.

The presence of the seed coat delays the early stages of germination of soybean embryos. This retardation seems to be due to the seed coat acting as a mechanical barrier to seedling. Although entire soybean seeds are insensitive to light, removal of the seed coat induces a light requiring condition. The early germination of naked seeds or isolated embryonic axes is enhanced by darkness. Red light produced a similar effect as white, providing evidence for the effective wavelength of the photo-inhibition. Far-red light acted similarly to darkness in promoting the early germination of the embryos. It is suggested that possibly light may act through phytochrome by the high irradiance system.

Manipulations of production systems in rubber tree which were intended to improve sucrose translocation in tapped bark resulted in an increase of latex sucrose and of latex production and reduced the incidence of nonyielding laticiferous tissue. This was achieved by shortening the tapping cut from full to half spiral, by changing the descending direction into an ascending mode of tapping or by annual change-over of tapping panel allowing for a longer time the regeneration of bark removed above the location of the cut. The increase of latex yield did not result in a significant decrease in the growth of trees over a period of three years.
Clonal differences in nonyielding bark appeared to be related to differences in sucrose depletion by tapping. In clone PB 235 which exhibited low latex sucrose, a reduction of tapping frequency resulted in an increase in sucrose level and in a decrease of bark "dryness" tending to an increase in total yield.
The tapping manipulations examined did not affect latex flow characteristics such as the plugging index of latex vessels and the bursting index of lutoids. The results stress the importance of photosynthate allocation for the physiology of laticiferous system productivity and indicate the possibilities of improving assimilate economy in rubber trees.

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.

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.

Tomato fruits on stems immersed in phosphate solution 0.2 M K₂HPO₄ produced less ethylene than control fruits on stems immersed in water. Phosphate mediated inhibition of ethylene production was found to be the highest in fruits in the pink stage of maturity, which produced ethylene at the highest rate. Phosphate also inhibited ethylene production in slices prepared from maturing fruits, both apple and tomato. We suggest that phosphate is an inhibitor of ethylene biosynthesis in sufficiently mature tomato and apple fruits in which the rise of ethylene production is already very rapid.

With increasing altitude, the concentrations of chlorophyll (chl), carotenoids and phenolics decreased but the chla :b ratio increased in the fourArtemisia species grown at four altitudes. The increase in chla : b ratio was due to a reduction in chlb content. The changes in anthocyanin content were irregular. Thus phenolics and anthocyanin pools may be differently regulated along an altitudinal gradient.

The effect of phosphorus deficiency on the activity of acid phosphatase of the first, second and third leaves of maize plants was followed. The supernatant obtained by centrifuging the homogenate of plant tissue at 1500 ×g was further centrifuged at 18 000 ×g, the sediment marked as fraction II and the supernatant as fraction III. Acid phosphatase activity of fraction II of the first to third leaves was for the whole period of culture higher in plants grown in the nutrient solution without phosphate. In fraction III this relation was established in the first leaf, after 3 days of culture in the second leaf and after 5 days in the third leaf. In all leaves higher enzyme activity was unambiguously determined in fraction III when compared with fraction II. Higher acid phosphatase activity was established in those leaves which were younger in their development, particularly in the first days of culture. With the ageing of leaves the enzyme activity decreased.

2-chloroethylphosphonic acid, unlike chlorocholinechloride, does not suppress gibberellin biosynthesis inGibberella fujikuroi cultures, and nullifies the effect of applied gibberellin A₃ on wheat seedling growth.

The mobilization of protein nitrogen reserves in apple shoot bark is subject to abscisic acid (ABA)-mediated regulation. At the biochemical level proteolytic activities in the shoot bark are suppressed in the autumn. As endogenous ABA levels decline during the autumn and winter tissue protease levels increase in parallel with the rate of inducible breakdown of reserve protein; metabolic demandper se plays no significant role. This process is used as a model system to explore the possibilities for chemical regulation ("bioregulation") of ABA-determined dormancy phenomena by: manipulation of tissue ABA concentrations, substitution of synthetic growth regulators and direct interference at the site of action.

Two photooxidation products of indol-3-ylacetic acid (IAA), 3-hydroxymethyl oxindole (HMO) and 3-methylene oxindole (Meox) were almost as effective as IAA in stimulation of growth of oat (Avena saliva cv. Kent) coleoptile sections. The IAA failed to give stimulation of growth after pretreatment of the coleoptiles with chemicals inhibiting oxidation of IAA, but the growth promoting effects of HMO or Meox remained unaffected by such pretreatment. After pretreatment with the chemicals which can form an adduct with Meox, the growth promoting activities of IAA, HMO or Meox were lost showing the involvement of the oxindole pathway of IAA metabolism in IAA action. Time-course experiments also showed that the stimulatory effects of HMO and Meox were the same as IAA.