The main scientific results achieved in individual departments of the Institute of Experimental Botany during 30 years of its existence are briefly summarized. They include methods of studying photosynthesis, ontogenetic changes of photosynthetic characteristics, stress factors affecting photosynthetic activities, photosynthesis of transgenic plants and duringin vitro cultivation, roles of auxins and cytokinins in plant growth and development, development and testing of new plant growth regulators, models of organogenesisin vitro, metabolic and mutagenic activities of phenolic substances, hormonal regulation of flowering, activities of promutagens (nitrosamines, 7,12-dimethylbenzanthracene), model systems of genetic damage, repair synthesis and post-replication repair, developmental pollen biology and biotechnology, extracellular nucleolytic activity of pollen, selection of apple scab immune cultivars of apple tree, chemotaxonomy ofFabaceae andAllium species, selection pressures in embryoids, somatic embryogenesis and nuclear genome changes in plant cell and callus cultures, discoveries of new plant viruses, virus spread and persistence in crops, development of polyclonal and monoclonal antibodies, role of oxidative pentosephosphate cycle in biosynthesis of viral RNA, and virus diseases of forest trees.

The inhibitory effect of 23N-alkyl-4-piperidylesters (alkyl = ethyl-butyl) (APEA) and 8N-ethyl-2-pyrrolidinylmethylesters (EPMEA) of 2- and 3-substituted alkoxyphenylcarbamic acids (alkoxy = butoxy-heptyloxy-) on photosynthetic Hill reaction activity of spinach chloroplasts and on chlorophyll (Chl) synthesis in green algaeChlorella vulgaris was investigated. Inhibitory activities of these compounds were strongly connected with the lipophilicity of the whole molecule. A lower inhibitory activity of 2-alkoxy-substituted derivatives in relation to the corresponding 3-substituted ones was confirmed. Electron spin resonance (ESR) spectra of spinach chloroplasts demonstrated that the studied compounds affected the structure of photosystem (PS) 2 with the release of Mn²⁺ ions into interior of thylakoid membranes.

Germinated tubers of selected cultivars Kera, Resy, Nicola and Oreb were made healthier by heat treatment. They were derived from germ explants on MS media with the addition of BAP 1 mg 1^-1 and IAA 0.2 mg 1^-1. After sufficient multiplication of stems, optimum conditions of the photoperiod were followed for the induction of axillary microtubers on stem segments in media with BAP 10 mg 1^-1 and 8% sucrose. The ability of tuberization is different: the early cvs. Kera and Resy induce earlier tubers at a long photoperiod and late cvs. Nicola and Oreb tuber rather at a short photoperiod. In suitable photoperiods the inhibitory substances accelerate the induction of axillary tubers and limit the formation of adventitious roots. Synthetic inhibitors applied in induction media increase the number of the tubers.
The quality of tubers was affected by the addition of a mixture of amino acids: aspartic, glutamic, lysine and proline in concentrations of 12.5, 25 and 50 mg.1^-1 into the induction media. In the course of cultivation the types which were growing well, formed tubers and increased the volume were selected. The representation of amino acids in the tubers was not significantly affected, there was only an increase in proline. The higher content of amino acids was reflected in the increase of proteins in the tubers. The selected clones are further multiplied.

Plants regenerated from callus cultures derived from leaf discs and mesophyll protoplasts ofPetunia hybrida cv. Rose of Heaven exhibit a high frequency of genetic and chromosomal variation. Of twelve leaf disc-derived plants examined, only three had the normal diploid chromosome number (2n=14) while seven were tetraploid and two were aneuploid (16 and 27 chromosomes). Of seventeen plants derived from two protoplasts, none had the diploid chromosome number. Most had 28 chromosomes, one 29, two 27, one 26 and one had variable numbers (14-28) in different root tip cells. In all cases aneuploidy was associated with developmental abnormality. In addition, heritable differences in growth, morphology and flower pigmentation were observed in callus-derived tetraploids and diploids, including one diploid which differed from parent plants in at least four characters. These results are discussed in terms of the importance ofPetunia in genetics research and for studies of somaclonal variation.

Lemon plants (Citrus limonum L. cv. Verna) were grown in the field under two different flood irrigation treatments. The dry treatment received four irrigations per year (March, July, September and November) and the wet treatment one monthly. The amounts of water applied per year for dry and wet treatments were 340.0 mm and 1020.0 mm, respectively. The effects of the two treatments on certain aspects of the plant water relations during the period between flowering and the end of rapid fruit growth (critical period) were studied. Soil matric potential (ψm) and leaf water potential (ψi) values in the dry treatment revealed development of water stress during the experimental period. The water supply in the wet treatment seems sufficient to achieve the crop water requirements. The g₁ values in July were higher in the wet than dry treatments. Pronounced oscillations in g₁ from sunrise to afternoon were found especially in the dry treatment.

A polyspecific antiserum against protein extracted from PSTV-infected tomato leaves was prepared and the IgGs were separated by affinity chromatography on a beaded cellulose adsorbent with an immobilized "healthy" antigen. The antibody not adsorbed entered into a preferential reaction with the antigen from PSTV-infected leaves as estimated by an enzyme-linked immunosorbent assay. The immunochemical reactions did not significantly exceed the control background, if antigens from tomato leaves infected with potato viruses X, Y and M were analyzed. By immunoblot technique we revealed, however, that several antigens not detected in healthy leaves appeared in the leaves infected either with PSTV or with viruses X and M. An accumulation of a major antigen having a molecular mass of about 70 kDa was observed in viroid-infected leaves only, suggesting the specificity for viroid infection. The antigen was found not to be an alkaline endoproteinase - the pathogenesis-related protein P-69.
Some antigens with molecular masses approximately 38.0, 23.7 and 22 kDa, which occurred in PSTV-infected leaves and in healthy calluses, were not detectable in PSTV-infected calluses.
No reaction exceeding the control level was observed using enzyme-linked immunosorbent assay for antigens from silver nitrate-treated tomato leaves, although such leaves showed symptoms similar to that caused by viroids.

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.

Variations in water content, relative water content (RWC), pressure potential and intracellular pH (pH) had been studied as factors of bud growth in rose plantlets grown in vitro for micropropagation. During the phase of healing, pressure potential and pH, were high enough to allow bud growth. During the following growth phase only buds of the lower part of the stem were able to grow. The growth ability of these buds and the growth inhibition of the others, associated with ΔpH, were retained during the last three days of culture, when dry matter content and RWC were the lowest. The results also showed a tight link between pH, and pressure potential. This may enable to distinguish different stages of plantlet development in vitro.

This study was carried out to investigate the effects of water stress on cell division, relative frequency of different phases of mitosis and mitotic index in root tips of two cultivars of Eragrostis curvula (Schrad. Nees) (weeping lovegrass). The water stress treatment affected both cultivars by increasing mitotic index as a result of changes in the relative frequency of cells in interphase and prophase with marked increases in the prophase index. These increases were more evident in the less resistant cultivar. Changes in the relative frequency of other phases were also observed. The presence of cells with persistent nucleoli was detected, and the number of these cells increased with the lowest medium water potentials.

Germination and seedling growth of pea (Pisum sativum L. cv. Rachna) was studied in salts and PEG-6000 solution having osmotic potentials -0.1, -0.2, -0.3, -0.4 and -0.5 MPa. At equivalent level of stress, NaCl proved more harmful to germination, seedling growth, vigour index, as well as initial mobilizing efficiency of food material from seed to the growing seedling, while PEG-6000 was more harmful to imbibition rate and mobilization efficiency in further days.

Shoot multiplication of hornbeam was stimulated onWPM, QL andDKW medium supplemented with a low concentration of BAP or BPA (0.1-0.2 mg I -1) andIBA (0.1 mg I -1). Low concentration of thidiazuron promoted axillary bud formation, higher concentration inhibited shoot elongation. Microshoots were rooted onWPM supplemented with a low auxin concentration (IBA or NAA 0.2-0.5 mg I -1). High rooting percentages were obtained. Shoot proliferation of ash was stimulated on MS andDKW medium supplemented withBAP orBPA (2.0-5.0 mg I -1) andIBA (0.1 mg I -1). Root formation was promoted onWPM containing a low auxin concentration. Rooted plantlets were transplanted into soil and after hardening off the micropropagated trees were planted in the field. The planted trees grew normally without showing signs of abnormality.

Red-light-induced (via phytochrome) germination decreased with increasing numbers of turions per germination flask (overcrowding). Three hypotheses concerning the mechanism of this germination inhibition were tested, related to abscisic acid, ethylene, and oxygen deficiency: (i) Although abscisic acid is a powerful inhibitor of turion germination it had to be excluded as a cause, because abscisic acid was not secreted from turions into the nutrient solution, (ii) Ethylene (ethrel) strongly inhibited growth of newly formed sprouts, but germination response itself was not inhibited, (iii) Germination inhibition did not appear if short light pulses were substituted by continuous irradiation. It reappeared in the presence of the photosynthesis inhibitor 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea, but it was not observed in aerated nutrient solutions, or when Petri dishes instead of Erlenmeyer flasks were used. Decreased oxygen concentrations in the nutrient solution were produced by turion respiration. Consequently, anaerobiosis within the nutrient solution caused by turion respiration was the reason for germination inhibition by overcrowding.

Two classes of phosphonopeptides, those containing P-terminal 9-aminofluoren-9-ylphos-phonic acid and those of dialkyl 9-aminofluoren-9-ylphosphine oxides, influence plant growth according to different mechanisms. The effect of these compounds on the growth of several bacterial species, including the photosynthetic bacteriumRhodospirillum rubrum, as well as on the activity of photosystems 1 and 2 in isolatedPisum sativum andSpirodela oligorrhiza chloroplasts was studied. The peptides of free, unblocked 9-aminofluoren-9-ylphosphonic acid acted in a morphactin-like manner, whereas those of dialkyl 9-aminofluoren-9-ylphosphine oxides influenced photosynthesis indirectly.

Life span of the second leaf of wheat(Triticum aestivum L., cv. Grana) plants was studied from day 8 to day 50 of plant age in a variant with nitrogen (+N) and in a variant in which plant senescence was induced by the omission of nitrogen from the nutrient solution (-N). Seed protein was the sole source of nitrogen for these plants. Specific leaf mass (SLM) in the -N variant, and specific leaf area (SLA), the mass of fresh leaf, soluble protein content and total nitrogen content in the +N variant peaked by day 22 of plant age (that is by day 19 of leaf age). Dry matter content, leaf length and leaf area, and SLM in the +N variant peaked by day 29 of plant age (that is by day 26 of leaf age). The ontogeny of the second leaf in the variant with enhanced senescence was shorter by at least 14 days. Plants from this variant showed typical symptoms of N deficiency, that is yellowing of leaves, tip burn, and lack of tillering. However, the growth and biochemical characters studied did not indicate an earlier onset of the senescence of the second leaf of -N plants. Both +N and -N variants reached their peaks (with the exception of an earlier peak by day 12 in case of total nitrogen content in the -N variant) on the same day of leaf age. Thus the first part of the leaf life span from leaf growth initiation to full expansion was of the same length in both the control and N-def icient plants. The stage of the proper senescence of the second leaf of -N plants was very short; the leaf completely died away within 7 days after senescence onset.

Various regimes of predominantly chloride and sulphate salinity reduced chlorophyll (Chl) (a +b) content and net photosynthetic rate (Pn) in two cultivars ofCicer arietinum L. However, the rate of respiration (Rd) was stimulated up to 6 dS m^-1 of salinity and thereafter it declined with increase in salinity levels. Chloride salinity was more detrimental than the sulphate one as far as Chl (a +b) and Pn were concerned, but R_D was reduced more under sulphate salinity in cv. H-75-35 especially in 110 d-old plants. The cultivar L-144 was relatively more salt sensitive than the cv. H-75-35.

NaCl (0 to 274 mM) was added to the culture media of normal and habituated (auxin and cytokinin independent) sugarbeet calli and its effect on growth (estimated by the increase of dry and organic matters), water content and osmotic potential was tested. Growth of normal callus was stimulated by 68 mM NaCl after a lag period of two weeks. This callus tolerated up to 137 mM NaCl without growth reduction and maintained its hydric status by readjustment of its osmotic potential in 24 h. NaCl quantities under 34 mM stimulated growth of the habituated callus from the 3rd day on; higher NaCl concentrations (68 to 274 mM) inhibited growth or were lethal. NaCl sensitivity of this habituated callus was not due to its inability to adjust its osmotic potential: this adjustment occurred from the 4th h of culture whatever the media. From the 3rd day on, however, this callus presented a water deficit which depended on NaCl concentration. It is suggested that the lowering of osmotic potential corresponds to an important water loss in relation to changes in membrane permeability. This study finally shows that mechanisms of salt tolerance may have developed at the cellular level. Lower growth and lower salt tolerance of the habituated callus need further investigation in relation to cell structure and hormone autonomy.

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.

α-Glucan phosphorylase was extracted fromDioscorea rotundata tubers and purified 55 fold with specific activity of 360 nmol min^-1 mg^-1 protein and a yield of 41.5 %. By electrophoresis of purified enzyme on polyacrylamide gel a single band of phosphorylase activity appeared. The enzyme showed normal Michaelis-Menten kinetics and was activated by AMP. ATP, ADP, ADP-glucose, calcium and magnesium inhibited the enzyme. It is active in the presence and absence of primer. No effects were observed on the addition of glycolytic intermediates or amino acids. Using gel filtration molecular mass of the enzyme determined is 188 000 and the extract seems to contain one form. Properties of the enzyme indicate that phosphorylase from white yam tuber functions primarily as a starch degrading enzyme. The possible role of the enzyme during yam tuber storage is dicussed.

The changes in the content of free and esterified phenolic acids extracted with methanol and the phenolic acids nonextractable with this solvent were studied during a long term cultivation (4 subcultures, 27 weeks total) of alfalfa callus in darkness and light. The total content of phenolic acids in the callus grown in darkness was lower as compared to their content in callus cultivated under 10/14 h light/darkness regime. It was decreasing during cultivation differently in the two treatments being in light-grown callus dependent on the length of cultivation and decreasing by each subcultivation in darkness. The portion of benzoic acid derivatives related to the total phenolic acids changed with the age of the culture reaching 90 % after the fourth subcultivation in darkness while only 45 % in light. Considerable decrease of the content of esterified form of phenolic acids accompanied by relatively stable content of free and firmly bound phenolic acids caused significant decrease of esters as related to total phenolic acids (from 87 % to 25 %).