Aminopeptidase, carboxypeptidase and proteinase activities were measured in endosperms from unripe and ripe seeds of ×Haynaldoticum sardoum. Aminopeptidase and proteinase activities were high during the early maturation stages and then decreased. In contrast, carboxypeptidase activity increased with maturation.
Localization studies demonstrated that aminopeptidase and carboxypeptidase activities were present in the three tissues examined (pericarp, green layer plus aleurone, and starchy endosperm). Proteinase activity against gliadin was located in the pericarp and in the green layer plus aleurone, but was absent in the starchy endosperm.
The presence of proteolytic activities in the outer kernel layers might be correlated to the hydrolysis of transitory protein reserves during the senescence of the seed coatś.
Aminopeptidase and carboxypeptidase activities located in the starchy endosperm could participate in the breakdown of protein reserves during the early phases of seed germination.

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.

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.

The influence of light of different spectral composition and levels of irradiance (2-40 Wm-²) on adventitious root formation (ARF) in birch shoot segments was investigated. Spontaneous rooting of shoot segments occurred in segments with intact apical or axillary meristems. Concerning ARF shoot meristems could be substituted by application of auxin. The very low rooting percentage of shoot segments in darkness was improved considerably by auxin application. Irradiation of cuttings was a requirement for a high percentage of spontaneous rooting. The promoting effect of light was dependent on its spectral composition and was the highest under red followed by white and blue light. The low rooting response under blue light was enhanced almost to the red light level by shielding the root-forming cutting base from light.

Soil drenches containing 250 μg of paclobutrazol or uniconazol (50 ml of a 17 μM solution) reduced the height of both corn (Zea mays L. cv. How.Sweet It Is) and soybean (Glycine max (L.) Merr. cv. A2) seedlings. With corn, uniconazol was considerably more active than paclobutrazol in reducing height whereas with soybean both compounds had similar dwarfing effects. The compounds increased foliar chlorophyll content and leaf thickness in soybean but had no effect on these parameters in corn. The increase in leaf thickness with soybean was due primarily to an increase in the thickness of the palisade cell layer. Chloroplast size and ultrastructure of both species were unaffected by the compounds. The growth regulators increased root diameter in both corn and soybean because of increased size of cortical parenchyma cells and particularly in soybean because of radial rather than longitudinal growth of the first few layers of the cortical parenchyma.

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.

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.

The cotyledons ofXanthium strumarium plants are of low sensitivity to photoperiodic treatment and contain only trace amounts of ABA under long-day conditions. The first pair of leaves, very sensitive to photoperiodic treatment, contains a higher level ofABA, decreasing with age of the plant. Prolonged short-day photoperiodic treatment increases the ABA level in the cotyledons but this is still 10times lower than in the first two leaves. Exogenous 10^-4M ABA increases the ABA level in the cotyledons to the level corresponding to that in the first leaves, and enhances the photoperiodic sensitivity of cotyledons. In contrast to cotyledons, the photoperiodic treatment affects the ABA level in the first pair of leaves only slightly. The authors propose that a high ABA level supports the transition of plants to flowering, while a low ABA level may be responsible for a low photoperiodic sensitivity of cotyledons inXanthium plants.

Electrophysiological processes were investigated in reception organs of photoperiodism in a model short-day plant,Chenopodium rubrum L. (selection 374), within the inductive cycle for flowering. Transorgan (surface) electric potential (E_tr) was measured as a potential difference between the first leaf surface and the roots of an intact plant, and between the surface of an excised leaf and the petiole base. The time-course of E_tr in intact plants showed irregular, or partially regular, oscillations within both phases of the inductive cycle and under continuous light. The highest amplitudes were during the postinductive light period. E_tr in excised leaves behaved practically in the same way as in intact plants. The E_tr oscillations were localized in leaves. In general, no electrophysiological changes were found in the reception organs within the inductive cycle which could be correlated with the formation and transport of floral stimulus, or with the attainment of an induced state. The results indirectly support the idea that the floral stimulus is chemical in nature.

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.

Immature embryo and root meristem expiants of wheat were cultured on modified medium of Murashige and Skoog and Gamborg's medium supplemented with 2,4-dichlorophenoxy acetic acid. Morphogeriic callus cultures were obtained from both the expiants. The frequency of shoot formation varied from 22% to 48% from callus obtained from embryos while only root formation could be induced from root meristem expiants. 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 and/or root from callus, some conspicuous isozymes appeared which indicates the involvement of these isozymes in root/shoot development rather than in the induction of morphogenesis in callus. Basic isozyme pattern of each enzyme for the callus was retained in all the callus stages.

An analysis of flows through primary root and first node root tissues of plants grown under conditions of salinity and nutrient deficiency induced by temperature gradients was carried out using. a mathematical model. The results obtained show that high KNO₃ concentration in Knop's nutrient solution (salinity) causes an inhibition of volume and heat flows and that the omission of KNO₃ from Knop's nutrient solution (deficiency) stimulates these flows. The causes of the inhibition lay in the fact that salinity reduced hydraulic, electric, and osmotic conductivity when compared with the control (Knop's solution), but relative to nutrient deficiency, it increased osmotic conductivity, electrodiffusion, diffusion, and filtration of heat flow induced by the electric and heat power. The causes of the stimulation were that deficiency partially decreased conductivities, similarly as salinity when compared with the control, and also decreased osmotic abilities of the system. By contrast, it increased heat conductivity and corresponding filtrations (diffusion-thermal, thermoosmotic). In first node root tissues, it increased all conductivities with the exception of electric conductivity, then osmotic, electroosmotic, diffusion, electrodiffusion, and filtration of heat flow and current flow, that is the number of possible ways of solution transport through root tissues increased.

Shoot multiplication of Larixdecidua was achieved using axillary and adventitious buds. The formation of axillary buds was stimulated on shoot tips soaked in a cytokinin solution (BAP 10-50 mg 1^-1 for 2-4 h. Adventitious buds were induced on cotyledons, needles and vegetative buds cultured on WPM or QL medium supplemented with cytokinin (BAP 1-3 mg 1^-1). The shoot formation from induced axillary and adventitious buds was promoted on WPM or QL medium containing a low concentration of auxin (IBA 0.1 mg 1^-1). Shoot multiplication of Pinussylvestris was stimulated on WPM, MS, and QL media supplemented with a low concentration of cytokinin (BAP 0.2 mg 1^-1) and auxin (IBA 0.1 mg 1^-1). Shoot segments produced 2-5 new axillary shoots within 4-5 weeks. Root initiation was stimulated on larch and pine shoots cultured first on WPM supplemented with auxins (NAA and IBA) and later transferred to auxin-free medium.

The effect of several nitrogen compounds on the germination of the first seed of each spikelet ofAvena sterilis spp.macrocarpa Mo. was studied on Petri dishes placed in germination chamber. The compounds assayed were ammonium sulphate, ammonium nitrate, urea and calcium nitrate, generally used as fertilizer for cereal crops, as well as a control supplied with water only
The concentration of the assayed compounds were 100, 1000, 2500 and 5000 ppm either at a constant temperature of 15 ° C or at alternated temperatures 5°C and 15 °C, for 16 and 8 h, respectively
Significant increase in the germination percentages occurred when nitrate compounds were used in relation to other compounds and no significant differences were found between the urea, and ammonium sulphate. This increase became significant at 1000 ppm, and therefrom until 5000 ppm germination stabilized. In the case of urea, very high abnormal germination percentages were obtained at 2500 ppm, while the effect turned noxious from 5000 ppm
The use of alternating temperatures significantly increased the germination capacity of the wild oat seeds in the case of urea, ammonium sulphate and ammonium nitrate.
It is found that nitrates are capable of breaking the dormancy ofAvena sterilis spp.macrocarpa Mo. seeds, which according to various authors, is due to an increase of the respiratory activity of the seeds

Axillary meristems of short day plantChenopodium rubrum are localized as caulinar, foliar or axillar. The localization of axillary meristems and axillary buds of 14 day old plants varied in similar pattern as in other plant species so far investigated: after several nodes with foliar axillary meristems the caulinar ones were produced. However, unlike in other species, in C.rubrum a very high percentage of caulinar meristem is produced also on the first node. In this case, like in the case of its later differentiation at higher nodes, the formation of caulinar meristem is confined also to the vegetative state. It was found that the caulinary position coincides with higher responsiveness to photoperiodic induction. The developmental significance of such behaviour is discussed.

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.

Exogenous supply of Spd and Spin stimulated ethylone production in detached tobacco leaves kept in the light. Stimulation, that was first detected after 9 but not 6 h of treatment, linearly increased with concentration and was maintained for several h after returning treated leaves to deionized water. Stimulation of ethylene production was prevented by AVG and Co²⁺ and was accompanied by increased activity of ACC synthase and ethylene-forming enzyme. Put, and other diamines, did not give any stimulatory effect. Stimulation was not accompanied by apparent damage of plasmalomina nor was it reversed by Ca⁺ or Put, suggesting that the cationic properties of polyamines are probably not involved. Stimulation might be due to endogenous polyamine accumulation high enough to inhibit the activity of S-adenosylmethionine decarboxylase, so that all S-adenosyhnethionine might be committed to the ethylene pathway. The stimulatory effect of poly a nines acquires particular interest considering that they have so fur been doscribod to inhibit ethylone production in darkened plant tissues. This finding suggests that polyamines may play a regulatory role in plant development by modulating ethylene bio-synthesis under the control of light.

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.

Divisional activity, intrusive growth of the cell wall and loss of fusiform initials have been studied in Holoptelea integrifolia. The dimensional changes in relation to mean length, length frequency, mean width and length variation in relation to fibre length have also been analysed.

Potato root cultures transformed by_pRiA4 T-DNA do not regenerate plants in vitro spontaneously, but regeneration can be induced by a sequence of callogenesis and regeneration media. Both T_l and T_r-DNA were found by Southern blotting. Regenerated transformants showed characteristic morphological deviations in the in_vitro cultures. Plants in the soil showed differences in the inflorescence and tuber development.