Transport of ions in young maize plants was affected by the temperature gradient (gradT). This influence was dependent on the age of plants and the solute concentrations in compartments at the two sides of plants. When gradT was increased, current, volume and heat flows rose during 20 min and then declined. On the other hand, the diffusive flow only declined. The character of the flow changes was given by the changes in permeability and reflection coefficients. In young plants under low solute concentration on both sides of plants, the permeability of the plant tissues shifted from positive to negative values. Under higher solute concentrations on both sides of the plants such phenomenon was not observed. At high gradT the reflection coefficients of the plant tissues were low, but they rose during levelling the temperature in the two compartments.

The influence of salinity, given at germination (stage I) or 75 d after sowing (stage II), on flower production and characteristic features of male reproductive structures was studied in three promising genotypes of chickpea (Cicer arietinum L. cv. ICCV 88102, H 82-2 and C-235). In ICCV 88102 and H 82-2 salinity 20 meq 1^-1 increased the number of flowers when applied at both stages whereas in C-235 only when applied at the later stage. The salinity also delayed flowering; the higher salinity the greater was delay in flowering. In H 82-2 and C-235 salinity treatment given at stage II (when few flower buds appeared) hastened the flowering. The salinity curtailed pollen production; the reduction being minimum in C-235 and maximum in H 82-2. Germination was not significantly affected in C-235 pollen collected from plants grown under salinity conditions upto 60 meq 1^-1 applied at stage I but the tube elongation was inhibited. The inhibition of tube elongation was greatest in C-235. Salinity treatment administered at stage II did not affect significantly pollen germination excepting C-235 in which a consistent decline with increasing salinity was evident. Salinity stimulated tube growth in ICCV 88102. Na₂SO₄ in the germination medium was more detrimental for both pollen germination and tube growth than NaCl.

Lycopersicon esculentum cv. Linia XXIV (L) and cv. Ostravské (O) was infected withAgrobacterium tumefaciens T37 (pTiT37). 37 L tumors and 33 O tumors were isolated. 13.5 % L tumors and 3.0 % O tumors regenerated shoots producing nopaline synthase. The shoots formed roots after transfer on R3B medium without phytohormones. From 10 primary shoots 35 plants cultivated in an unsterile soil were obtained by cutting. 6 selfpollinated plants did not produce any fruits. Fruits obtained through backcrossing had dramatically reduced seed numbers. The same is true of some other transformed plants with nearly normal pollen. Most transformed plants were susceptible to superinfection withA. tumefaciens T37 and B6-806. The incorporation of T-DNA into plant genome seems to cause not only male sterility, but also some kind of female sterility.

The full length cDNA clone of leghemoglobin I gene fromLupinus luteus was placed under dual promoter into the plant expression vector pCB1399 and the resulting vector (pCB1415) was transfered into theAgrobacterium strain LBA4404 (pAL4404). The binary system LBA4404 (pAL4404, pCB1415) was then used for transformation ofNicotiana plumbaginifolia andLotus corniculatus. In both species kanamycin-resistant plants have been selected and regenerated. The synthesis of LbI protein in transformed plants has not been shown.

The efficiency ofAgrobacterium-based transformation technique in oilseed rape and cauliflower was influenced by cultivar specificity, donor plant age and explant type. Marked differences in demands for plant hormone contents in the regeneration medium were recorded already among different types of nontransformed explants. The highest regeneration capacity was recorded with stem and leaf segments isolated from one-month-old aseptically grown plants. The regeneration was markedly species-dependent. Regeneration of transformed plants from stem segments and thin layers isolated from field-grown oilseed rape plants (at the most 2% of regenerating explants) and from oilseed rape hypocotyls (0.8% of regenerating explants) and cauliflower (1.2% of explant regenerated transformed shoots) was achieved after disarmedAgrobacterium treatment. Hypersensitive reaction of explants could be prevented by using prolongedin vitro precultivation and delayed application of the selective agent.

NaCl salinity affected growth, the contents of chlorophyll, carotenoids, saccharides and some minerals (Na, K, Ca, Mg, P) in wheat (Triticum vulgaris L.) plants. Irrigation of soil with CaCl₂ or KCl greatly ameliorated the adverse effects of NaCl salinity. This counteraction was associated with an increase in contents of saccharides, proteins and Ca, Mg and P which might explain their role in osmotic adjustment.

The rates of canopy apparent photosynthesis (P_C) and canopy respiration (R_c) were studied during vegetation season in two erectophile and two planophile hybrids of maize (Zea mays L.) grown at two canopy densities [7.5 plants m^-2 (HD) and 4.5 plants m^-2 (LD)]. Large differences in P_C, R_c, R_C/P_C, leaf area index (LAI), dry matter accumulation and grain yield were found among hybrids and plant densities. Variations in P_C and R_C were associated mainly with changes in LAI. There was also found change in P_C per unit LAI with time. The average R_C/P_C was 28.9 % for all treatments throughout the vegetation season. P_C and R_C per unit dry matter were higher in LD than in HD and decreased throughout the measurement period. The HD stand had higher P_C and yield in hybrids with erectophile foliage, whereas LD stand had higher P_C after male tetrad and got higher yield in hybrids with planophile foliage. Only R_C in hybrids of the two foliage types was higher under HD than under LD throughout the vegetation period.

Haploid and dihaploid female and rare dihaploid male plants were produced inMelandrium album throughin vitro induced androgenesis. In the seed progeny obtained from cross-hybridization between dihaploid androgenic males (supermales) and standard females only male plants were observed. The microspores containing Y chromosome gave rise to supermales.

The protein coding region of theE. coli DNA repair geneada combined with the CaMV 35S promoter has been transferred to tobacco by means ofAgrobacterium tumefaciens Ti plasmid. In transgenic plants having theada gene in a sense orientation, detectable amounts of O⁶-alkylguanine-DNA-alkyltransferase has been found whereas in non-transformed plants this activity is absent. Cell suspension cultures derived from the former plants showed lower sensitivity to the toxic (growth inhibiting) effects of the bifunctional alkylating agent 1-(2-chloroethyl)-1-nitroso-3-(aminomethyl-1,3-diazinylo)-methylurea compared with cell cultures derived from a control non-transformed plant or from transgenic plants harbouring theada gene in an opposite, non-sense orientation.

Salinity inhibited growth, and affected the contents of chlorophylls, carotenoids, saccharides, amino acids, proteins, DNA and RNA in broad bean plants. Foliar application of NaH₂PO₄ and NaNO₃ greatly ameliorated the adverse effects of NaCI. This counteraction was associated with an increase in contents of saccharides, proteins, DNA and RNA.

Total nonstructural saccharides (TNS) content in young plant ofAlopecurus pratensis was always above 4% of dry matter even at several types of stress treatment (nitrogen deficiency, low irradiance). TNS content was in negative correlation with concentration of total nitrogen in all cases. Positive correlation was found between the TNS content in plants and relative increase in their root growth rate.

A disease of spiraea(Spiraea xvanhouttei) manifested in leaves by very mild, mostly hardly perceptible mosaic, was found to be caused by cucumber mosaic virus (CMV) infection. The proof was given on the basis of responce of differential plants after virus transmission, by immunosorbent electron microscopy and ELISA.

DNA methylation of two repetitive sequences in tobacco nuclear genome was studied in the course ofin vitro dedifferentiation and differentiation. Using 5-mC sensitivè restriction enzymes and DNA/DNA hybridization with 25S-rDNA probe it has been shown that during the early phase of callus induction prominent changes in the methylation pattern occur which are stably maintained during subsequent callus growth. The following protoplast recovery and plant regeneration have again displayed some more modifications of the methylation status. Comparing the patterns of R₀ plants with the original plant material and the calli it can be assumed that both share in the resulting methylation status. The experiments analyzing the HRS60 family of non-transcribed highly repetitive sequences have displayed a quite monotonous methylation status thus indicating no random methylation perturbations in silent DNA sequences.

The transaminations of L-tryptophan (L-trp) and of L-phenylalanine (L-phe) are catalysedin vitro by the same non-specific aminotransferase. The transaminations procceed at the same pH (pH 8.5) and temperature (45 °C) optima, have parallel increases in activity with addition of the coenzyme pyridoxal phosphate (PRP) and have identical elution characteristics in gel chromatography. The enzyme from pea seedlings has a relatively weak affinity for both amino acids (K_m L-trp = 4.16 × 10^-1 mmol 1^-1; K_m L-phe = 2.10 × 10^-1 mmol 1^-1). Differences in affinity for a series of keto acids in the pea enzyme were observed, with pyruvate having the strongest and glyoxylate the weakest affinity. Transamination of L-trp and L-phe was demonstrated by enzyme extracts from pea, maize and tomato, but was not detected in kohlrabi. The amino acids L-asparagine (L-asn), L-phe, L-lysine (L-lys), L-methionine (L-met) have distinct inhibitory effects on the transamination of L-trp. Indolylacetylaspartate and tryptophol were shown to be competitive inhibitors. The regulation at the molecular level of L-trp transaminase activity is discussed.

The partitioning of¹⁴C-assimilates was studied in pigeonpea(Cajanus cajan L.) at vegetative and flowering stages (40 and 70 d after sowing, respectively) exposed to moderate and severe drought induced by withholding the irrigation. At vegetative stage, the ethanol soluble fraction in shoot decreased from 99 to 43.16 % between 0 and 120 h, whereas in underground part it increased from 1% to 56.84 % with maximum amount in nodules (35.51 %). Similar trend was observed in ethanol insoluble fraction. At moderate drought, a significant increase in soluble fraction (11.31 %) in nodules was observed. Stem showed significant reduction of assimilates (13.09 %). After flowering, the assimilates produced in leaves were exported to reproductive parts, especially under drought. In plants recovering from severe drought, 14C in soluble and insoluble fractions in reproductive parts was reduced to 85 % and 43 %, respectively, whereas leaf and nodules showed a significant increase. Thus the assimilate partitioning to different plant parts was dependent on growth stage and affected by drought.

Cytological and cytophotometric analysis of root tips of regenerated plants, derived from rhizome expiant ofKniphofia nelsonii andKniphofia uvaria, revealed marked difference in behaviour of chromosomes and level of 4C nuclear DNA content. Karyotypic stability could be retained in all 52 regenerants of K. nelsonii whereas inK. uvaria out of 75 regenerants analysed, 12 plants were exclusively diploid and the rest 63 plants were predominantly diploid comprising variable amount of aneuploid and tetraploid cells. Cytological data was further confirmed by nuclear DNA content estimation. Alteration in the structure of chromosomes could also be noted in 57 regenerants ofK. uvaria giving rise to two new karyotypes. The use of polysomatic tissue for securing variantsin vitro inK. uvaria has been suggested.

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.

Strawberry plants have been regenerated from petioles and flower buds Petiole segments derived from strawberry plants(Fragaria vesca L. andFragaria xananassa Duch. cvs. Gorella and Redgauntlet) maintainedin vitro have been cultured on the Gambobg's. agar medium supplemented with 2,4-D (2 mg 1-¹) either alone or with kinetin or BAP (0.1 mg I-¹ or 1 mg I-¹). The calli thus obtained have been transferred to media differing from the first ones only by the nature and the concentration of the growth regulators used. One or two months later, shoots appeared on these calli. The influence of the media hormonal content on plant regeneration has been observed. Moreover, genotypic variations have also been investigated: the wild strawberry exhibited the greatest organogenic capacity.
Shoots have also been obtained from flower buds(Fragaria xananassa Duch. cvs. Fern, Hummi Gento, Gorella and Redgauntlet). In this case, shoots appeared directly on small calli derived from the peduncular base of the flower buds. These regenerations have been observed, without changes of media, on the Lee and de Fossabd's agar medium.

A comparative study of the isoenzyme patterns of esterase and peroxidase and overall peroxidase activity in stamens of male-sterile (MS) lines of Pearson ms-35 and P ms-35aa and of the respective male-fertile (MF) tomato plants have been conducted. The study has been made at two stages of stamens development - tetrad and pollen. Higher activities of the esterase isoenzymes in the MF stamens than that of MS in both ontogeny stages have been found. The slow moving esterase isoenzymes both of the MF and the MS stamens are the major isoenzymes in the early stage and are connected with tapetum development while the fast moving esterase isoenzymes are connected with pollen formation in the later ontogeny stage. Overall peroxidase levels in the MS stamens were higher than those of MF. The peroxidase patterns of the MS lines are also characterized by the greater number of isoenzymes and also the presence of specific isoenzymes, the contrast between the MF and the MS stamens being more strongly expressed at the later stage of development. A strong similitude between esterase and peroxidase patterns behaviour in both MS lines has been found.

A field experiment was conducted to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in different levels of salinity (33 or 66 mM) and in growth regulators (indolyl-3-acetic acid, IAA at SO g m^-3, gibberellic acid, GA₃ at 100 g m^-3, or kinetin at 100 g m_-3) on the shoot growth and pigment content of the developing wheat flag leaf. Salinity at 33 or 66 mM led to an insignificant increase in the fresh and dry masses as well as in the shoot diameter and shoot length, but it attenuated the flag leaf area. In the majority of cases, salinity increased the chlorophyll (Chla, Chlb) and carotenoid contents as well as the number of chloroplasts per a mesophyll cell. The growth in the wheat shoot of the saline-treated plants was, in general, stimulated in response to presoaking the grains in kinetin or GA₃. On the other hand, IAA + salinity led to a negligible effect on the growth in the wheat plants particularly at the early stages of growth. The presoaking of grains in NaCl at 33 mM + IAA or 66 mM + kinetin induced a marked increase in the pigment content of the wheat flag leaf particularly at the early stages of growth. The interaction between salinity and phytohormones increased the number of chloroplasts; kinetin was the most effective.

Embryogenic callus was initiated from immature zygotic embryos of black pine on medium DCR supplemented with 2 mg 1^-1 2,4-D and 0.5 mg 1^-1 BAP. The diploid number of chromosomes confirmed the origin of callus from zygotic embryos. The callus was white, glossy, mucilaginous and contained somatic embryos consisted of an embryonic region with densely cytoplasmic cells and suspensor region with long vacuolated cells. Although somatic embryos with green cotyledons were recognisable after ABA treatment and subsequent transfer to growth-regulator free media whole plants have not yet been obtained.

Somatic embryogenesis was induced in immature zygotic embryos of pea (Pisum sativum L.), synthetic auxins α-naphthalene acetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram, PIC) being used. Only one (line HM-6) of 46 genotypes tested exhibited good potential for somatic embryogenesis. 2,4-D was found as the best somatic embryo inductor. Three different ways of somatic embryo conversion have been described. Plantlets from individual somatic embryos were micropropagated as somaclones and subsequently rooted. A sterile morphological mutant has been found within a group of fertile plants of T₀-generation. Sufficient amount of T₁-seeds is available for somaclonal variation studies.

The herbicide terbutryn induced up to 11.3 % chromosomal abnormalities in cells undergoing meiosis inVicia faba. The mean number of pods/plant and the mean number of seeds/pod were considerably reduced, but the average seed dry mass was not or was only slightly affected by this herbicide. In C₂ plants chromosomal abnormalities were observed in few but significant numbers of cells.

Chenopodium rubrum L. ecotype 184 is a qualitative short-day plant with critical length of the night of eight hours that must be exceeded in order to flower: Five days after sowing, the plants were exposed to a various number of inductive cycles (14/10 h of däy/night cycle) to test the optimal photoperiodic conditions for flowering. In our experimental conditions the plants flowered with high percentage after more than four received inductive cycles, but there was no flowering below that. The plants grown on the herbicide Norflurazon (photobleached plants) showed different photoperiodic characteristics. There was negligible flowering of photobleached plants in the same experimental conditions as for the green ones.

In a glasshouse experiment, an increase of the number of wheat plants per pot caused the plants to became taller, have more ears and a greater grain yield per pot, while the number of tillers decreased and the straw mass did not change. The N and P contents in straw and N in grain also trended to decrease, while the translocation of these nutrients to the grain increased.
The increase of wild oat plants (Avena sterilis spp.macrocarpa Mo.) per pot, produced a decrease of the growth attributes, grain yield and N accumulation in grain of wheat per pot. Wild oat competition with wheat was higher than the wheat competition with itself. Such competition affected the height, number of tillers and ears, the fertility index of the shoots, the straw and grain mass, and the total accumulation of N, P and K nutrients per wheat plant.

Diurnal variations in endogenous IAA levels inFatsia japonica leaves, maintaining constant other external factors such as temperature and relative humidity, were studied. Plants were cultivated in a growth chamber (20 °C, 75 % RH, 16 h photoperiod, 400 µmol m^-2 s^-1 PAR). IAA analyses were carried out by analytical IP-HPLC with on-line spectrofluorimetry. Rhythmic variation of endogenous IAA levels was found. At the onset of the light period the IAA concentration dropped very rapidly from 1070 pmol g^-1 (fr.m.) to 144 pmol g^-1 (fr.m.). This concentration was nearly constant throughout the entire light period. During the subsequent dark period the IAA levels increased again to about 1000 pmol g^-1 (fr.m.) at the end of the dark phase. These results were not confirmed in open field conditions where many other external factors probably influence the endogenous IAA content.