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.

The growth changes of cotyledons, leaves, hypocotyls and roots due to photoperiodic induction in short day plantChenopodium rubrum were investigated in relation to flowering. Six-day old plants were induced by photoperiods with a different number of dark hours. We found that the degree of inhibition which occurred during induction in the growth of leaves, cotyledons and roots similarly as the stimulation of hypocotyl is proportional to the length of dark period. The photoperiods with 12, 16 and 20 dark hours bring about marked inhibition of growth and at the same time induce flowering in terminal and axillary meristems. The inhibitory effect of critical period for flowering,i.e. 8 dark hours, is not apparent in all criteria used and even the flower differentiation is retarded. The photoperiods of 4 and 6 dark hours did not affect growth and were ineffective in inducing flowering even if their number has been increased. The experiments with inductive photoperiod interrupted by light break have clearly shown that growth pattern characteristic for induced plants can be evoked in purely vegetative ones. Such statement did not exclude the possible importance of growth inhibition as a modifying factor of flower differentiation. We demonstrated that the early events of flower bud differentiation are accompanied by stimulation of leaf growth. The evaluation of growth and development of axillary buds at different nodes of insertion enabled us to quantify the photoperiodic effect and to detect the effects due to differences in dark period length not exceeding 2 hours.

In addition to the primary seminal primordium, the so-called secondary seminal root primordia are also initiated in a barley embryo. The primary root primordium is developmentally most advanced. It is formed by root meristem covered with the root cap, and by a histologically determined region with completed cell division. On germination, the restoration of growth processes begins in this non-meristematic region of root primordium by cell elongation, with the exception of the zone adjacent to the scutellar node, the cells of which do not elongate but continue differentiating. In the root primordia initiated later, the zone with completed cell division is relatively shorter, in the youngest primordia the non-meristematic cells may be lacking. The root meristem is reactivated after the primary root primordium has broken through the sheath-like coleorrhiza and emerges from the caryopsis as the primary root. The character of root meristem indicates a reduced water content at the embryonic development of root primordium. With progressing growth the root apex becomes thinner, the meristematic region becomes longer, and the differences in the extent of cell division between individual cell types increase. - The primary root base is formed of cells pre-existing in the seminal root primordium. Upon desiccation of caryopsis in maturation, and subsequent quiescent period, their development was temporarily broken, proceeding with the onset of germination. The length of this postembryonically non-dividing basal zone is different in individual cell types. The column of central metaxylem characteristic of the smallest number of cell cycles, has, under the given conditions, a mean length of about 22 mm, whereas the pericycle, as the tissue with most prolonged cell division, has a mean length of about 6 mm. In the seminal root primordia initiated later the non-dividing areas are relatively shorter. The basal region of seminal roots thus differs in its ontogenesis from the increase which is formed "de novo" by the action of root meristem upon seed germination.

Accumulation of phenolics in barley seedlings was examined in relation to elongation; the seedlings were cultivated at 5 °C or 26 °C in light or in darkness. It was found that a higher accumulation of phenolics (mainly saponarin) was accompanied by slower elongation. This relation was repeatedly observed regardless of whether growth retardation or stimulation was obtained by light and temperature conditions of growth or treatment with CCO orp-fluorophenylalanine (p-FPA), respectively. It is proposed that PAL and peroxidase activities are responsible for maintaining the level of phenolics in seedlings. These enzyme activities are differently influenced by temperature conditions of growth. It is also suggested that accumulation of saponarin may lead to slowing down the growth by stimulating IAA oxidase and lowering the auxin level in the tissues. Thus, phenolics may belong to the factors through which environmental conditions influence elongation of seedlings.

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 glycollate metabolism of wheat (Triticum vulgare Vill. cv. Sonalika) and rice (Oryza sativa L. ev. Jaya) leaves was studied during senescence by estimating the endogenous levels of glycollate and hydrogen peroxide (H₂O₂) and the activities of glycollate oxidase and catalase. In comparison with light incubation the incubation of excised leaves in the dark caused a decline in the glycollate content and in the activities of glycollate oxidase and catalase, and an increase in the H₂O₂ content, more marked in the leaves of rice than in the leaves of wheat. Glycollate oxidase activity gradually decreased with incubation time, and glycollate metabolism decreased during senescence. The glycollate oxidase in particular and glycollate metabolism of rice were more sensitive to incubation time than those of wheat. Kinetin increased the glycollate oxidase activity and glycollate metabolism during senescence, while ethrel (2-chloroethylpho-sphonic acid) and ABA (abscisic acid) reduced these activities in both plant species.

Young seedlings ofGmelina arborea Roxb. were subjected to 2 weeks of drought. Despite the gradual reduction in stomatal conductance, leaf and root growth was not affected until the later part of the stress period. This was attributed to solute adjustment in the roots of the plants. As the severity of water stress increased, root growth was prolific in all the soil segments. As a result, water in the lowest soil segment was used to maintain plant turgor, which in turn sustains the leaf and root growth during the water-stress treatment. The influence of soil water content and soil water potential upon soil water uptake rate was also evaluated on soil profile basis. Rates of extraction began to decline in all soil segments as soon as soil water potential fell below -0.06 MPa, presumably as a result of vapour gaps between the root and soil (root: soil interface resistance). It is suggested that the growth of roots ofGmelina plants away from drying soil will minimize the resistance to water uptake.

Allelopathic interactions between plants and other organisms have been recognized by scientists worldwide because they offer alternative uses in agriculture, such as decreasing our reliance on synthetic herbicides, insecticides, and nematicides for disease and insect control. The recognition of the role that allelopathy can have in producing optimum crop yields is of fundamental importance. Despite much optimism and some progress in unravelling the complexities of biochemical interactions between species, a firm foundation for the scientific rationale of the existence and function of the allelopathic phenomenon has not been developed. Allelopathic chemicals are primarily secondary products of plant metabolism which have been an enigma to plant scientists; however, they undergo a variety of reactions with plant, insect and animal species that inhibit or stimulate their growth and development. Examples of some allelochemicals and their basis of molecular and biological action are shown: interaction between the unicorn plant (Proboscidea louisianica L.) and cotton (Gossypium hirsutum L.); diterpenoid alkaloids (fromDelphinium ajacis L.) as allelochemicals; substances that occur in wheat (Tritcum aestivum) and wheat soil that cause autotoxic effects; alfalfa (Medicago sativa L.) root saponins as allelochemicals; humic acids from wheat soil as allelochemicals; and structure-function of flavonols serving as allelochemicals in chloroplast-mediated electron transport and phosphorylation. This paper concludes with a discussion of some frontier areas of research in allelopathy.

The pRi T-DNA markers were followed in the first generation of the progeny ofAgrobacterium tumefaciens strain C58Cl(pRiA4b) transformed tobacco regenerant. Two categories segregating probably in the ratio 15: 1 can be distinguished: those showing a complex of pRi T-DNA transformation markers and those showing no transformation markers. The presence of both T_L and T_R-DNA was demonstrated by Southern blotting. The most prominent of the transformation markers observedIn vitro was rapid growth of detached plagiotropic roots on media without phytohormones. Most of the progeny plants of the transformant showed irregularities of leaf morphology and inflorescence and flower morphology. The last resulted in sterility in most progeny plants.

The rates of maintenance and growth components of leaf dark respiration of a C₃ plant (Phaseolus vulgaris L.) and C₄ plant (Zea mays L.) as affected by temperature were studied using the McCree concept. Respiration rates were measured by means of infrared gas analysis in a closed gas exchange system. In both C₃ and C₄ species R_D and R_m increased with temperature in the temperature range (15-62 °C) studied. R_G depended on temperature with an optimum near the temperature optimum of gross photosynthetic rate, P_g. Significant correlation between R_D and R_M and between R_G and P_G was found.

In five-day-old etiolated pea seedlings an increase in IAA content and in L-tryptophan aminotransferase (TAT) and L-tryptophan dehydrogenase (TDH) activities in the apical part of the epicotyl was found 12 h after root excision, which was followed by a decrease up to 48 h. In ten-day-old seedlings a continuous decrease in IAA, TAT and TDH levels in the apical part of the epicotyl was recorded up to 48 h after root excision. This indicates a growth-correlative effect of the root becoming evident in dependence on plant ontogenesis in changes of IAA content and activities of the above enzymes catalysing IAA synthesis.

Biochemical characteristics (enzyme activities, contents of vitamins, phytohormones, nucleic acids, proteins, saccharides, etc. ) in germinating seeds and developing seedlings are summarized, and the inhibitory and stimulatory actions of these compounds on plant growth and development are discussed.

There exist two main mechanisms of allelopathy: 1) direct transfer of metabolites between neighbouring plants during their life and 2) accumulation and transformation of bioactive substances in the environment with their subsequent influence on higher plants. The latter mechanism is similar to that causing soil sickness or soil toxicity. Allelochemicals affect all functions of the living system: photosynthesis, respiration, mineral nutrition, transpiration, immunity, and growth. The initial biochemical effect of allelochemicals seems to be on the synthesis of protein mediated by RNA/DNA. Knowledge of the mechanisms of concrete signals during realization of hereditary codes would serve as a powerful tool for the improvement of crop plant development and productivity.

The ultrastructural aspects of the cell division in the grapevine(Vitis riparia × V.labrusca) calli were studied. A large central vacuole plays a noticeable part in this process. Before its division the nucleus with some encircling cytosol moves into the central vacuole where the small, round-shaped portion of cytosol (phragmosome) originates. In this central mass of cytosol connected with the peripheral one by thin cytosolic strands karyokinesis is carried out and the cell plate formation starts. Before karyokinesis the phragmosome, however, does not exhibit the form of the cytosolic layer completely traversing the cell. No preprophase band of microtubules has been observed in the cells either. The polarity of the mitotic spindle designating the orientation of the new cell wall is random then and it is not determined by the position of the preprophase band of microtubules or by the orientation of phragmosome. The unorganized growth of the grapevine callus reflects this fact.

Studies on exogenous application of phenolic compoundsviz: p-hydroxybenzoic acid, resorcinol and chlorogenic acid each with concentration of 10^-4 M are done on the legume (Cajanus cajan (L.)Millsp.) AL-15. The effect of applied phenolic compounds as well as of structural differences in phenols indicate a marked influence of phenolic compounds in regulating growth processes in plants. Fresh and dry mass of various plant parts increased after foliar spray with phenols resulting in an improved harvest index. It is seen that phenols also play an important role in the initiation and development of nodules.

Allelopathic compounds, including fatty acids, phenolics, flavonoids, terpenoids, and alkaloids, have been found in various plants and soils of different habitats in Taiwan since 1972. For example, in a monoculture of rice plants, phytotoxins were produced during the decomposition of rice residues in soil, suppressed the growth of rice seedlings, and reduced the numbers of tillers and panicles, leading to yield reduction. The allelopathic metabolites are also affected by environmental factors, such as oxygen, temperature, soil moisture, microbial activity, and levels of fertilizers in soil, and allelopathy was pronounced in areas where environmental stresses were severe. Substantial amounts of phytotoxic mimosine and phenolics were released into soil by plant parts of Leucaenaleucocephala, and these suppressed the growth of many understory species except that of L.leucocephala itself. A unique pattern of absence of understory plants was ubiquitous beneathPhyllostachys edulis, due primarily to an allelopathic effect. In a forest pasture intercropping, an aggressive kikuyu grass was planted in a deforested land where Chinese fir grew previously, to help in understanding the mechanism of biological interactions between plants. Aqueous soil leachate and extracts of the grass significantly, retarded the growth of local weeds but not that of the Chinese fir. Allelopathy thus plays an appreciable role in natural vegetation and plantations in Taiwan.

Growth, dark transpiration rate (DTR) as well as water saturation deficit (WSD) of 30 single plants of 8 alfalfa genotypes growing in experimental field of 50 × 10 cm spacing, in four cuts at early bud stage, were studied. The growth and WSD of genotypes examined were significantly different, the differences in DTR were not significant. The growth of alfalfa plants was in negative correlation with both DTR which reflects non-effective water loss and WSD. Significant negative correlation established between plant growth and its variability shows that fodder productivity in alfalfa genotypes was dependent on growth variability of individual plants. Positive correlations established between WSD or DTR and the growth variability show some of the causes of growth variability.

Cholinesterase activity was studied in 2 to 10-week-old pea plants cultivated under artificial illumination. Free and membrane-bound forms of the enzyme were separated by extracting the enzyme from pea shoots with buffers differing in ionic strength. The ratio of the free cholinesterase to the membrane-bound one fluctuated between 1 : 1 and 1 : 2.5. The free cholinesterase was inhibited by neostigmine (0.1mmoll^-1) by 50%, the membrane-bound enzyme by 90%. The pH optimum of cholinesterase activity was 8.5, the temperature optimum 37 °C. The enzyme activity was increased by some cations in this order: Mg²⁺ < < K⁺. The K^m value for the substrate S-acetylthiocholine iodide was 250 μmoll^-1, the enzyme activity being inhibited by concentrations higher than 3 mmoll^-1 of this substrate.
The activity of the membrane-bound enzyme was demonstrated in the roots, leaves, stems, fruits, seeds and carpels, but could not be reliably detected in the blossoms. The highest activity expressed per fresh matter was found in older leaves and in the fruits, the lowest in the roots and stems. Cholinesterase activity in plant parts markedly varied during the investigated growth period.

The hypothesis that allelochemicals released from members of the Florida scrub community deter the invasion of fire-prone sandhill grasses was investigated. Constituents of the endemic scrub members, Ceratiola ericoides, Conradina canescens and Calamintha ashei, were examined for their phytotoxic activity. Effects of the plant natural products on the germination and radicle growth of lettuce (Lactuca sativa), as well as little bluestem (Schizachyrium scoparium) and green sprangletop (Leptochloa dubia), two native grasses of the Florida sandhill community, were tested.
The data suggest that ursolic acid and other natural detergents which are released from a source plant enhance the solubilization of allelopathic lipids via micellization. In general, natural surfactants seem to play a significant role in the water transport of lipophilic phytotoxins to target seeds or seedlings.

The effect of plant tissue culture medium with different concentrations and combinations of growth regulators (kinetin, indol-3-ylacetic acid, 2,4-dichlorophenoxyacetic acid) was evaluated on mitosis ofAllium sativum meristem root tip cells. Different combinations of growth regulators at low concentrations had no effect on induction of mitotic aberrations or inhibition of mitotic activity. Inhibition of mitotic activity, a tendency to chromosome stickiness and clumping and a slight increase in the frequency of mitotic aberrations were observed at higher concentrations. It may be proposed that plant tissue culture media have no direct effect on induction of mitotic aberrations in plant tissue culturesin vitro.

Crown galls induced onArabidopsis thaliana plants by octopine or nopaline strains ofAgrobacterium tumefaciens were grownin vitro on different media. Dark growth of all tumor tissues was strictly hormone-dependent. In contrast, hormonal autonomy was observed in the light where crown gall calli readily differentiated into teratomas and (sometimes fertile) plants. Differentiating tissues always grew more vigorously than subtended calli. The growth of transformed calli was stimulated by vitamins and partly inhibited by growth regulators in concentrations used for the maintenance of untransformed calli. Crown gall calli, teratomas and sometimes regenerated plants were shown to express lysopine or nopaline dehydrogenase activities.

The pattern of the activity of arginine decarboxylase (ADC) and omithine decarboxylase (ODC) involved in polyamine synthesis in ripening wheat seeds was examined. The aim was to study the polyamines and the activity of the two enzymes in correlation with the growth processes occurring in the developing wheat seeds. The results obtained showed a very different pattern of polyamine content in the two organs of caryopsis, and that the two enzymes in the embryos have a higher activity than in the endosperms. Moreover, while in the embryos the ADC exhibits higher activity than the ODC, in the endosperms the activity of ODC is about similar to that of ADC. This pattern is discussed in relation to the different histological characteristics of embryo and endosperm tissues during seed development.

This report presents, results of a feasibility study of use of allelopathic aquatic plants for aquatic weed management. In order to establish a list of potential allelopathic plants, we selected 16 aquatic plants native to the southeastern United States and subjected them to two bioassays - one involving lettuce seedlings and one involving the aquatic plantLemna minor as the target species. The lettuce seedling bioassay was selected because it is a widely used, experimentally simple assay to determine allelopathic activity. However, it uses lettuce, a terrestrial plant, as the target species, and thus may be less appropriate for use with aquatic plants. TheL. minor assay involves an aquatic plant as the target species and so is more appropriate for our goals, but it is experimentally much more complex and time-consuming. The plants selected for study wereBrasenia schreberi, Cabomba caroliniana, Ceratophyllum demersum, Eleocharis acicuiaris, Eleocharis obf usa, Hydrilla verticillata, Juncus repens, Limnobium spongia, Myriophyllum aquaticum, Myriophyllum spicatum, Najas guadalupensis, Nymphaea odorata, Nymphoides cordata, Potamogeton foliosus, Sparganium americanum, and Val/isneria americana.Nymphaea odorata (leaves and petioles) inhibited 78 % of lettuce seedling radicle growth and 98 % ofL. minor frond production. Brasenia schreberi inhibited 82 % of lettuce seedling radicle growth and 68 % of L. minor frond production. These results suggest thatN. odorata andB. schreberi are both highly inhibitory and are therefore candidates for use in aquatic weed management. Results also suggest that the simple lettuce seedling assay is a reasonable first "easy" one to use in an attempt to determine allelopathic potential of aquatic plants.

In rice (Oryza saliva L. ev. Java), the first (younger) leaf senesced later than the second (older) leaf as shown by the decline in chlorophyll and protein contents. Kinetin treatment significantly retarded senescence of leaves, while abscisic acid (ABA) treatment promoted it. The second leaf exported more³²P to the newly emerged growing leaf at the early stages than the first leaf, which always showed higher retention of³²P than the second one. Kinetin treatment lengthened the duration of³²P export and also increased the retention capacity of both leaves, while ABA had the opposite effect. The second leaf showed a higher depletion of nitrogen and phosphorus but à lower depletion of potassium than the first leaf. Kinetin treatment retarded the decline in nutrient content (N and P) while ABA treatment hastened it. Neither growth substance had any effect on potassium content. The content(s) of endogenous eytokinin-like substance(s) decreased while ABA-like substance(s) increased in the two leaves with senescence: these changes in the second leaf took place earlier than in the first leaf.

The effect of short chain fatty acids on the cellular permeability of embryonic axis inGcer arietinum seeds was studied. Octanoic (OCT) and nonanoic (NON) adds, which reduce both germination and growth of the embryonic axis and raise the inhibitor effects of the supraoptimal temperatures (30‡C), induce a greater ionic efflux into the medium (conductivity). NON reduces glucose (3-0-MG) and K⁺ (⁸⁶Rb) uptake during the germinative process, this action being counteracted by fusicoccin (FC) at optimal (25‡C) and supraoptimal temperatures (30 ‡C). Tonoplast and plasmalemma increase their permeability to the K⁺ efflux when NON is present. Addition of NON+FC gives rise to higher values in the efflux rate, the vacuolar compartment being the most affected. Temperatures around zero (2 ‡C) notably reduce the isotope efflux from cytosol and vacuole. NON acid does not significantly affect the efflux of³H-ABA, suggesting that it does not cause any important changes in the phytohormone compartmentation.

Regeneration of complete plants is possible from free-cell derived colonies ofIndigofera enneaphylla. In addition to factors such as plating density and composition of the nutrient medium, carbon dioxide is essential for the growth of free-cells whereas changing the light intensity had no effect. Cell colonies were obtained at a plating density of 2.5 × 10³ cells/ml on medium containing benzylaminopurine, 2,4-dichlorophenoxyacetic acid and casein hydrolysate and plantlets were obtained on medium containing only BAP.

Actinomycetes were isolated from the upper 1 - 3 cm of the soil layer in a well-developed forest and in an adjacent clearcut area where Douglas-fir [Pseudotsuga menziesii (MIRB.) Franco] regeneration had been impaired for two decades. The population density in the clearcut area was two times as high as that in the forested area. The percentage of actinomycetes that inhibited seed germination of the test plants was significantly higher in isolates obtained from the clearcut area than in those obtained from the forested area, and isolates from the clearcut showed five times the phytotoxic effect of those from the forest. Some actinomycete isolates, 4 % from the clearcut and 2.6 % from the forest, significantly reduced in vitro growth of two common ectomycorrhizal fungi of Douglas-fir,Laccaria laccata andHebeloma ovstuliniforme. Two actinomycete isolates from the clearcut reduced fungal growth by 40 % and 73 %. Reduction of the nutrient in the growth medium did not affect the antifungal activity of the actinomycetes. The data support the idea that, along with other factors, phytotoxic and antifungal actinomycetes may suppress natural regeneration or establishment of planted seedlings - either directly or. indirectly - through inhibition of seed germination or of mycorrhizal fungi.

In the absence of cations, the release of proteins from pollen tubes ofNicotiana tabacum in culture is greatly dependent on boron concentration and inversely related to growth stimulation. The minimum of proteins in the medium occurs at 100 mg 1^- of boric acid, which is the optimum concentration for growth. The shift of boron level to this optimum further increases the proportion of proteins bound to the insoluble pollen tube fraction; on the other hand the amount of soluble proteins is not affected inside pollen tubes, but greatly decreased in the medium.
The loss of proteins into the medium is considerably reduced by oalcium and also at the optimal boron concentration and in the presence of K⁺ and Mg²⁺ ions. The rate of tube elongation, however, is slightly decreased and the duration of pollen growth activity is not extended. The release of proteins is not affected by potassium and is slightly reduced by magnesium.
The possible mechanism of calcium and boron action on protein release is discussed in relation to the exocytotic function of secretory vesicles and it is suggested that boron supports the incorporation of proteins transported to the growing tip into the pollen tube wall structures.

With the aim to increase citrus fllowering under tropical conditions, two formulations of 2-chloroethyl phosphonic acid (Ethrel and Flordimex), Alar (succinic acid-2, 2-dimethyl hydrazide) and Cycocel (2-chloroethyl-trimethyl ammonium chloride) were applied during the flower induction period (December) to young "Valencia" orange trees at concentrations of 1000, 2500 and 5000 mg l^-1. These treatments effectively increased flowering, mainly at lower concentrations. Treatment using Flordimex at 500 and 1000 mg l^-1 concentrations resulted in flowering increase which is analyzed in this paper.

D,L-indol-3-yllactie acid was applied at concentrations 0.2 - 20 mg 1^-1 (10^-6-10^-4M) to the roots of 3-d-old intact maize seedlings grown in the dark and in the light. By day 3 after application, ILA at lower concentrations (0.2-1 mg l^-1) caused slight increase in the mass of etiolated plants, mainly roots. Shoot and root length was not increased. ILA at concentrations equal to, or greater than, 2 mg 1^-1 reduced the length of the main roots and from 10 mg 1^-1 on also the length of the shoots. In contrast, root mass was decreased by higher ILA concentrations to a lesser extent than shoot mass. The response to ILA application of etiolated seedlings differed from that of the seedlings grown in the light only at 20 mg 1^-1. The inhibitory effect was more pronounced in the case of quickly growing etiolated plants.