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.

An analysis of axillary meristem (axillary bud) localization of radish (Raphanus sativus L. cv. Tetra-Iłówiecka) was undertaken on vernalized (flowering) and unvernalized (vegetative) plants. It has been shown that the localization of these meristems can be different on successive nodes of the same plant and is connected with the development stages of the plants. The axillary meristems can arise on the stem as well as in the leaf axil or on the base of the subtending leaf. The localization of axillary meristems has been discussed in relation to growth directions and growth correlations inside the meristematic region of the shoot apex.

Growth behaviour, proline changes and water saturation deficit (WSD) changes were studied in two maize cultivars, Agati-76, a drought resistant oultivar, and cv. Vijay, a susceptible one after stress conditions were removed. Plants of both the cultivars showed a tendency to recover during rehydration. Phenotypically the plants appeared just normal on 7th day of rehydration, although recovery was never complete. Significant positive correlation existed between free proline content and concomitant change in water saturation deficit. Significantly higher proline content in cv. Agati-76 was reoorded in cv. Vijay, immediately after the stress was released, thereafter continuous decline was observed up to 7th day of rehydration in both the cultivars. Proline changes in relation to recovery of plants from stress conditions are discussed.

GA₃ as well as SA increase the protein content of the stem and the leaves at 1 day under both 8- and 24-h photoperiods. A new protein band with Rm 0.47 seems to be associated with floral bud initiation as it develops within 1-3 days in the stem as well as in the leaves of plants exposed to inductive treatments regardless of whether the induction is caused by 8-h photoperiods or by treatment with GA₃ of SA under 24-h photoperiods. Another band with Rm 0.23 developed only in the stem of water-as well as GA₃- or SA-treated plants under 8-h photoperiods. It may possibly be associated with extension growth.

Two phases of radish ontogenesis (I-when the plant had produced 3 -5 nodes and II-when the plant had produced 8 -10 nodes) were established on the basis of axillary, meristem localization. Flowering of the plants in response to GA treatment depends on the phases in which they were treated and on growth correlations in the apical meristem. The results obtained suggest that the reaction ofRaphanus sativus (LDP) to GA treatment is parallel to that ofChenopodium rubrum (SDP), and that the response of radish plants also depends on changes in growth correlations in the shoot apical meristem at the time of treatment.

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.

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.

Certain cultivars ofMalus growing at Geneva, New York, USA, begin growth and bloom 2 -3 weeks later than commercial cultivars of apple. Our research suggests that these late bloomers bloom late because they have a very high chilling requirement for bud burst. The chilling requirement interacts with the heat requirement for bud burst in such a way as to result in delayed bud burst and bloom. Abscisic acid (ABA) decreases in the terminal buds of both early and late bloomers during the chilling period, but it decreases more rapidly in the early bloomers. It has not been determined if ABA plays a role in controlling bloom date.

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.

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.

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.

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.

Pigeon pea cultivars AL 15 (early-) and T₂₁ (late-maturing) were compared for dry matter accumulation in fruit parts pod wall (PW), seed coats (SC) and seed at various seed developmental stages. Significant water loss and dry matter accumulation in the fruit parts commenced much earlier in cv. AL 15 as compared with cv. T₂₁. The pod wall accumulated starch, reducing sugars and N-substances up to 21 and 28 days after anthesis (DAA) in cultivars AL 15 and T₂₁, respectively, which was later distributed to the seed. Growth of pod wall and seed was sequential, not concurrent, as the pod wall lost significant dry matter when the seeds within them reached their maximum dry matter. The fruit parts of cv. AL 15 accumulated more photosynthates than cv. T₂₁ at all comparable stages.

Abscisic acid (ABA) was applied in a concentration of 1. 10^-3 M and 1. 10^-4 M to the quantitative SD plantChenopodium rubrum under various light regimes. ABA did not influence flowering in plants under continuous illumination, enhanced flowering in plants subjected to long days and inhibited it in plants induced by short days. It was concluded that ABA can not substitute for inductive treatment but its action may be additive to initial stages of reproductive morphogenesis (enhanced growth rate and branching of the apical meristem) as evoked by long days.

The translocation of¹⁴C-ABA from roots into other parts of the plant was followed in intact and decapitated pea seedlings. In intact plants ABA from roots was translocated above all into the apical part of epicotyl. In decapitated plants the regulative ability of intact apex can be partly simulated by exogenous IAA. The growth of lateral buds occurring after decapitation was associated with an intensive flow of¹⁴C-ABA from roots into released lateral buds as late as 72 h after decapitation,i.e. in the stage of intensive elongation growth of buds.

Barium chloride at 0.1 mM concentration inhibited elongation of mungbean (Phaseolus aureus) roots more strongly than elongation of hypocotyls. Root growth was completely inhibited at 80 mM and there was no germination at 100 mM. Respiration rates which were directly proportional to seedling vigour declined at varying degrees at the growth-inhibitory concentrations of BaCl₂. Barium retarded senescence in isolated leaf discs ofCephalandra indica by maintaining the chlorophyll level in darkness. The carotenes were similarly protected from degradation by Ba in darkness whereas xanthophylls were retained both in darkness and light. Ba also protected anthocyanin pigments in the staminode discs ofCanna indica flowers and reduced to a variable extent the leakage of betacyanin pigment fromBeta vulgaris root discs caused by various membrane active chemicals. Applied either alone or in combination with IAA, Ba inhibited cell enlargement in wheat (Triticum aestivum) coleoptile sections. Barium-induced inhibition of lettuce (Lactuca sativa) hypocotyl elongation was largely overcome by GA₃.

Using polyacryl amide gel electrophoresis isoenzyme patterns were studied of α- and β-glucosidase, α- and β-galactosidase, α-fucosidase, β-glucosaminidase, β-glucuronidase, α-man-nosidase and β-xylosidase in whole root tips, in particular growth zones and in the cortex and central cylinder of broad bean and maize. Though considerable differences even in number and position of isoenzymes were found in particular cases in both objects, no general conclusion could be reached. The mentioned differences are not obligatory and have been observed both between zones of division and elongation and between zones of elongation and maturation. This fact is hard to understand on the basis of proteosynthetic processes involved in proliferative and postproliferative cell growth.

Field trials on the effect of chlorocholinechloride (CCC) on rye plants of the cultivar Danae and of a selected population "WRS" proved that rye principally shows as reaction analogous to wheat. The CCC-induced decrease of stalk length is due to the reduction of elongation growth of the 4th internode. This shortening effect is mainly the result of decreased cell extension and, in the middle internode, additionally of inhibited cell division in longitudinal direction. The shape of internodes is changed under the influence of CCC. Walls of parenchyma cells of CCC-treated plants are thinner and those of sclerenchyma cells are thicker compared with cell walls of control plants.

Two selected strains ofSilene armeria L. were used: S_1-2 (GA-line, not induced to flowering by GA₃ in SD of 8 h) and S_2-1 (GA+ line which reacts to GA₃ with flowering in non-inductive photoperiod). Moreover S_1-2 and S_2-1 differ in their critical daylength 14.5 and 8.0 h, respectively. Changes in the mitotic index and DNA content of cells in the various zones of the apical meristem during GA₃ treatment were described. At the start of the experiment, the functioning of the apex was characterized by a predominance of G₁ phase in the two strains. Therefore S_2-1 differed by a higher mitotic activity specially in the central zone. In S_1-2, GA₃ acted mainly on the rib-meristem cells, which resulted in stem elongation. Lack of response in the cells of the central zone explains why GA₃ fails to induce flowering in this strain. In S_2-1, GA₃ acted mainly on the central zone where a gradual increase in mitotic acitivity and in the percentages of nuclei at the (S + G₂) level was recorded. This stimulation brought the meristems into the prefloral stage. The differences between the two strains are discussed according to the status of control meristems. The reactions induced by GA₃ were compared with the pattern of changes during induction, in LD.

Agrobacterium tumefaciens C58M (a nopaline strain) was used for induction of crown gall tumors inCentaurium umbellatum Gilib. The formation of tumors is very rare. After elimination of bacteria the tumor tissues grow in the light on R3B medium without growth regulators. They are positive in nopaline synthase.

IAA synthesis proceeding by indol-3-ylpyruvate (IPyA) pathway seems to be regulated in two steps. In the first the L-trp conversion into IPyA is reduced by a low affinity of L-trp to the unspecific aminotransferase, by competition of L-trp with some aminoacids (e.g. L-asp) and indoles (e.g. indol-3-ylacetylaspartate). Simultaneously, a specific L-trp-dehydrogenase in dependence on the NAD(P)/NAD(P)H ratio regulates by its reversible effect the level of IPyA, connecting photosynthesis with growth. A second more "delicate" regulation of IAA level is carried out by the indol-3-ylacetaldehyde system. In pea plants two indol-3-ylacetaldehyde oxidases with pH optima 4.5 and 7.0 were found. The oxidases are differentially inhibited by an excess of IAA, different indoles as indol-3-ylacetylaspartate and aminoacids as L-asp. GA₃ and kinetin stimulate the conversion of indol-3-ylacetaldehyde to IAA.

Both N,N-diethyl-N-(2-hydroxyethyl)glycine (DEHEG) and N,N-diethyl-2-oxomorpholinium chloride (DEOMC) in an optimal dosage of 4 × l0 μmoles per seedling initially accelerated then retarded leaf growth in onion, and doubled the yield of bulbs in field conditions. Gibberellin and auxin nullified the latter effect. It is concluded that DEHEG represents a physiologically active form of DEOMC.

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.

The objectives and methodology of metabolic studies of the gibberellins are discussed with particular reference to the rôle of gibberellins in the promotion of stem elongation in gibberellin-responding dwarf mutants of pea.

Height growth ofMentha piperita L. is better at 44% than 100% daylight. At 14% daylight, growth is limited, probably by lack of photosynthate, and no flowering occurs. Specific leaf area and protein content increase significantly with the decrease of irradiance. Shade leaves contain more chlorophyll and potassium than sun leaves. Sun leaves show higher levels of calcium because of their more xeromorphic structure. Transfer experiments between light and shade indicate thatM. piperita responds very effectively to irradiance also in a late stage of the life cycle with changes of specific leaf area and chlorophyll content.

Pharbitis nil, strain Kidachi and Violet, were grown at 20° C under continuous light in various cases of different sizes, containing the nutrient solution or tap water. Kidachi initiated flowers when seedlings were cultured in small cases containing nutrient solution but did not flower in large cases. The application of NAA, kinetin, ABA or 5-chlorobenzoiec acidvia roots in large cases caused flowering, Floral initiation was always accompanied by the suppression of root elongation. The promotion of root elongation by aeration inhibited flowering. Root cutting inhibited flowering. On the other hand, Kidachi did not flower in tap water irrespective of vessel size. Violet did not flower in the nutrient solution even in small vessels, but initiated floral buds in tap water irrespective of vessel size, though the plants grown in large cases developed very long roots. In both types of flowering, cotyledons are necessary to induce flowering and the removal of cotyledons before the 16th day after the start of culture in Kidachi and before the 12th day in Violet completely inhibited flowering. GA₃ promoted stem elongation without preventing flowering of Kidachi.

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.

The influence of growth regulators (GA and IAA) on the genetic effects of sodium azide was studied. Treatments with growth regulators were administered either prior to or after the mutagen. Post-treatments were found to be more effective against mutagen-induced plant growth injury and gave a slightly higher frequency of mutations. M₁ spike sterility however showed a rise following treatments with growth regulators.

The specificity of IAA-binding site from the wheat shoots was investigated in an attempt to confirm its receptor function. Several monofluoro-, monochloro-, dichloro- and monobromo-substituted indol-3-ylacetic acids were allowed to displace¹⁴C-IAA from the binding site. Displacement abilities of these halogenated IAAs were closely related to there activities in wheat coleoptile straight growth biotest. This finding indirectly confirms thephysiological significance of this binding site.

Inhibition of root growth was observed inChenopodium rubrum under photoperiodic conditions inducing flowering. That this inhibition is mediated by the cotyledons was shown directly by the effect of their excision, which changes the responsiveness of the roots to photoperiodic treatment. On the other hand, decapitation did not lead to such an effect. Some evidence is put forward suggesting that changes in IAA may be involved in these correlations. The existence of two different mechanisms of photoperiodic action in flowering and in root growth is proposed to explain these differences.