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.

A new method of simultaneous measurement of membrane (E_m) and transorgan (E_tr)electric potential in intactChenopodium rubrum plants and changes in E_m and E_tr under various experimental conditions are described. E_m was measured in mesophyll leaf cells, and E_tr in the same plant as a potential difference between a first pair leaf, tip and roots. The two potentials differed distinctly, E_m averaging-156mV and E_tr -5mV. But the,-changes in E_m and E_tr had approximately the same magnitude and time-course after changing light and darkness or KCl concentration in solution flowing around the leaf or during the photoperiodic induetive cycle. In relation to the same electrode connection they had an opposite polarity. The nature of E_tr and its relation to E_m are discussed.
The measurement of E_tr is much more stable and simpler than that of E_m. The similarity of E_m and E_tr time-courses justifies the use of E_tr measurement in electrophysiological studies as a replacement for E_m measurements especially in intact plants.

The uptake of cadmium and its effect on the growth of potato shoot tips grownin vitro were followed in dependence on cadmium concentration in nutrient medium.
Concentration of 10^-6M Cd²⁺did not substantially affect potato plantlet growth dynamics; but the concentration of 10^-3 M Cd²⁺ showed a strong growth inhibitory effect accompanied with increased cadmium accumulation in both root and shoot tissues.

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.

Pollen embryos of Brassica juncea (L.) Czern., obtained through anther culture, were examined histologically and histochemically to find explanation for their inability to germinate normally like a zygotic embryo. Most of the embryos lacked a distinct plumule or both plumule and radicle. Anotherabnormal feature of these embryos was the degeneration of cells in the hypocotyl and radicle, whichoccurred either through lysis or cell shrinkage. Reserve food material was mainly in the form of proteinbodies and starch grains. Unlike the zygotic embryos, the pollen embryos lacked lipids. It is concluded thatthe inability of the pollen embryos to germinate normally is due to their structural abnormalities andphysiological immaturity.

A method of cultivation and effectiveness of different light sources and light regimes in photoperiodic induction of flowering in non-rosette long-day plantChenopodium murale L. ecotype 197 are described. Under the described conditions of cultivation 5 days, of continuous light produced by incandescent bulbs (TESLA 74 3x40 W, red 4.9 μWcm-²nn-¹, far-red 7.4 μWcn-2nm-¹, blue 0.25 μW cm-²nn-¹) induced flowering in the majority of plants.

From nine different plant species grown at 1500 cm³ m^-3 CO₂ five responded with a significant increase in stomatal numbers per mm² as compared with plants grown under normal air conditions. Within a collection of twelve french bean cultivars remarkable cultivar differences with regard to the CO₂ enhancement effect on stomatal numbers was found.

In triticale and its parental species, the application of a root osmotic stress induced either a transient increase or an immediate decrease in transpiration rate. The response of wheat (Trticum dicoccum farrum) proved to depend on relative humidity of air. In rye (Secale cerealecv. Petkus) and triticale (T. 300) the effect of NaCl stress was less expressive, than the effect of PEG.

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.

Germinated seeds ofVicia faba were continuously irradiated at low dose rate of gamma rays (0.05 Gy h-¹) up to a total accumulated dose of 2 Gy. The FPG (fluorescence plus Giemsa) technique of differential chromatid staining was used to monitor the frequency of sister chromatid exchanges (SCEs) in irradiated root tip meristem cells. The results of the experiments have demonstrated that SCE frequency is raised by continuous gamma irradiation only in plant cells containing BrdU in the chromosomal DNA. No effect concerning SCE formation was recorded at continuous irradiation of meristematic cells of Vicia faba with native, i. e. BrdU-nonsubstituted, DNA. In contrast to SCEs, a significant increase was found in the yield of chromosomal aberrations in all variants of irradiation.

Electrophysiological processes were investigated in the reception organ of photoperiodism, cotyledons and first leaves, in a model short-day plantChenopodium rubrum L. (selection 374) within the dark inductive cycle for flowering. Membrane potential (E_m) was measured in cotyledon and first leaf mesophyll of intact plants. The E_m time-course was fairly similar during inductive dark or postinductive light period or in non-inductive continuous light and had a character of irregular oscillations. The most distinct oscillations were found during the postinductive light period. Changes in light régime at the beginning (light off) and the end of inductive dark period (light on) triggered marked transient E_m changes having a character of damped oscillations. Cortical root cells in intact plants did not react to switching light and darkness. Changes in E_m in reception organs during the inductive cycle could not be correlated with the formation and transport of floral stimulus or with reaching the induced state. Thus, the electrophysiological nature of floral stimulus has not been confirmed.

Different NaCl concentrations in a nutrient medium ofGossypium hirsutum L. induced a different decrease in the rates of photosynthesis and photorespiration in two cultivars.

Cultures of isolated mesophyll protoplasts ofBrassica napus L.have shown a positive reaction with the acidic phloroglucinol test for lignin (Wiesner reagent) 30 h after the beginning of the culture period. The reaction was observed in protoplasts and in a very early stage connected with divisions, in which acidic phloroglucinol positive material was primarily deposited like a girdle surrounding the division plane. Brown exudates, which are a serious problem even in young cultures derived from isolated protoplasts, have been secreted into the medium by cells, and also showed a positive reaction. The same staining pattern has been found with toluidine blue 0.

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.

Ethylene production and growth of callus cultures of lavandin (Lavandula offidnalis Cham x Lavandula latifolia Villars) cv. Grosso were examined. Callus lines, derived from various kinds of primary expiants (shoot tip, leaf and calyx), exhibited differences in ethylene production patterns independent of callus growth. Moreover these differences could not be ascribed to the expiant source. Within a line, ethylene pattern paralleled callus growth curve. Variations in ethylene evolution were induced in shoot tip callus by means of ACC, AVG and varied amounts of 2,4-D in the culture medium. Following all these treatments callus growth was not altered. Hie decrease in 2,4-D concentration caused changes in Chl a and water content of the tissues.

Effects of phorate (Thimet-10 G) on the activities of enzymes of nitrogen metabolism,viz., glutamine synthetase (GS), glutamate dehydrogenase (GDH), and glutamate synthase (GOGAT) in the primary leaves, nitrogenase (N₂-ase) in detached root nodules, and protein concentration in the primary leaves ofVigna mungo (L.) Hepper have been studied. Phorate stimulated the activities of these enzymes and protein concentration in primary leaves at lower concentrations (50 to 200 mg per pot), but inhibited at higher concentrations (400 to 600 mg per pot). Although, the V_max for each enzyme with different treatments varied, the K_m value of each enzyme in the control and the treated plants remained unaltered.

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.

Protein and RNA contents and synthesis were evaluated in the course of wheat grain (T. durum cv. Cappelli) development. Embryos and endosperms were considered separately during five phases from the 20th day after anthests until full ripenes was reached. No clean-cut changes were observed in the pattern of soluble proteins of the embryos. In the endosperms protein synthesis continues till the later phases and appears to be due to the albumin + globulin component. Screening of bands of endosperm proteins from electrophoresis indicates that the gliadins are synthesized early, with the exception of a Ω - gliadin. Glutelins with high relative molecular mass also appear to be synthesized when the grain approaches full ripeness.
The RNA content of the embryo and the endosperm is high in the early stages, when high cell proliferation occurs, and declines later on. The synthesis of RNA during in vitro imbibition is, however, higher in the later phases of ripening. Most of RNA synthesized in the embryos was ribosomal.

We have studied the effect of glucose on different enzyme activities in callus cultures of N.plumbaginifolia. We provided evidence that the increase in glucose concentration represses the synthesis of GDH, AcPh and MDH whereas ADH and LDH are unaffected. When glucose repressed cultures were transferred to the low glucose concentration medium the activity of GDH and AcPh resumed to the level shown by non repressed cultures. Sucrose and fructose were as effective as glucose in repressing GDH activity. These results support the hypothesis of the existence of a catabolite dependent regulation of enzyme synthesis in higher plants.

The accumulation of nitrogen and potassium by plant cells at undesirable concentrations manifests itself in changes in the osmotic phenomenon and finally in the transport process. Temperature gradient is another factor influencing the transport phenomenon. We have followed the changes in the electric diffusion potential and the heat transfer under the influence of these two factors on transport properties of roots of plants grown under conditions of either salinity or nutrient deficiency on the transport of KG solution through segments of the first node roots and of the primary root. Physical causes of the accumulation of the above mentioned ions were then studied by means of a mathematical model. The results obtained showed that high KNO₃ concentration in nutrient solution caused an inhibition of volume and heat flows, stimulated osmotic flow, and reduced electrical polarization of root cells. Cell polarization was slowed down when temperature gradient was increasing and enhanced when temperature gradient was decreasing. This indicates that the pressure difference between the exterior and the interior of root cells was levelled off by osmotic water flow but not by potassium ion flow.

Eight to nine months old seedlings of the Cactaceae Gereus validus HAWORTH grown in soil culture were chosen to study day-night cycles of net CO₂ exchange, indicating the stomatal rhythm of crassulacean acid metabolism, CAM, in relation to day-night changes of abscisic-acid levels. Drought stress was imposed by repotting the seedlings in dry sand and keeping them without watering for up to 37-39 days while control plants were watered regularly. Abscisicacid levels were higher in the stressed plants than in the controls and higher in the light period aa compared to the dark period. In the stressed plants abscisic-acid levels increased throughout the light period. Abscisic acid reached particularly high levels in the late afternoon in plants stressed for 37 days. It is conceivable that stomatal closure during the first part of the light period of CAM is elicited by high internal partial pressures of CO₂ built up by decarboxylation of nocturnally stored malic acid. However, the elimination of late-afternoon stomatal opening and the reduction of stomatal opening during the dark period of CAM observed under conditions of drought stress must have other reasons. The analyses of abscisic acid presented allow the conclusion that this stress hormone is involved in stomatal regulation of CAM under such conditions.

The size of the spring barley root system was studied on the basis of its electric capacity in plants grown in nutrient solutions either lacking or containing nitrogen in the form of nitrate or ammonium.
Root electric capacity changed in dependence on nutrition from Day 12 after emergence, when F values increased in the root systems of plants exposed to nitrate and ammonium salts. In plants grown in H₂O, the values of electric capacity statistically significantly decreased on Days 15 to 17, in plants grown in PK solution lacking nitrogen on Day 20.
Root electric capacity of plants grown in full nutrient solution gradually increased on Day 18 after emergence. Then a marked increase in root electric capacity values followed with no statistically significant differences between NH₄ ⁺ and NO₃ ^- nutrition. Nitrate nutrition of barley plants only resulted in an increased root to shoot mass ratio.