Photodestruction of chlorophyll (Chl) inZea mays leaves, after their irradiation with high photon fluence rate (5000 μmol m^-2 s{-1}), was determined in fragments of whole leaves (WL) and also in fraction of mesophyll cells (MC) and bundle sheath cells (BSC) after their mechanical separation. The lag phase and the phase of photooxidation of Chl in MC chloroplasts were shorter than in BSC. Duration of both phases was reduced when the leaves were placed in 0 % CO₂ concentration in the atmosphere, while the increase of CO₂ concentration up to 0.3 % totally protected Chl against photodestruction in BSC within the 9 h experiment. During that period of time Chl was destructed by about 30 % in MC.

Three groups of winter wheat (Triticum aestivum L.) genotypes having spike fertility genes (SFG) were used in field trials: (1) Tetrastichon sessile spikelets (TSS), (2) Normal spikelets (NS), (3) Indeterminate rachilla spikelets (IRS). The capacity of conducting system of the peduncle and the ear sink capacity of the main stem have been measured. There was a highly significant positive correlation (r = 0.899 and higher) between peduncle diameter and parameters quantifying peduncle vascular system. Compared with the control cultivar Hana, the TSS and NSS genotypes had higher both the number of vascular bundles, phloem and bundle cross section area and kernel number per ear. However, the highest kernel number per ear was found in the IRS genotypes although their bundle and phloem area was only equal or even lower then that of the variety Hana. Further studies are needed in developmental anatomy of spikes and stems to elucidate also differences in the relationships between the conducting capacity and kernel number per spikes in the TSS, NS and IRS genotypes.

The rice (Oryza sativa L.) cultivar IET 1444 showed a nonsequential mode of senescence as evident from the decline in chlorophyll and protein of the flag and second leaves at the senescent stage. Removal of 50,75 and 100 % spikelets from the panicle of rice plant or emasculation of the panicle by hot water treatment induced the development of secondary branch from the axil of second leaf but 25 % removal had no effect. Similarly, removal of 75 and 100 per cent spikelets from the panicle of secondary branch induced tertiary branch development, while 25 and 50 per cent removal had no such effect. Similar treatments on tertiary branch had no effect on further branch production. The pattern of leaf senescence of the untreated (control) main tiller, secondary and tertiary branches was identical, i. e. nonsequential, which could be changed into the sequential type only by the development of additional sinks (i. e. side branch). The leaf area and the seed number of secondary and tertiary branches were gradually reduced and reached a critical value in the tertiary branch. The removal of spikelets or emasculation delayed leaf senescence of the main tiller and the secondary and tertiary branches. Also the longevity of the whole plant could be increased by 40 d i. e., up to the senescence of the tertiary branch. Both leaves and reproductive parts control side branch production, which, in turn, controls the longevity of the whole rice plant.

The copy number of genes encoding 5S ribosomal RNA has been found to be constant in Petunia hybrida plants regenerated from protoplast and leaf disc-derived callus cultures. However, in one somaclone a heritable change in the length of the major 5S rDNA repeat has arisen. Despite the constant copy number of 5S rRNA genes, that of the 18S-25S rRNA genes is found to very by at least ten-fold. The relevance of these findings to ribosomal RNA gene variability and to somaclonal variation is discussed.

The activity of acetylcholinesterase (AChE) isolated from coleoptiles of etiolated oat seedlings is strongly inhibited by neostigmine and less so by eserine. The optimum of the enzyme activity occurs at pH 7.2 and a temperature of + 36 °C. The enzyme Michaelis constant is 280 μM. Choline within the range of concentration from 0.001 to 10 mM does not affect the enzyme activity. Calcium ions at 5 mM concentration cause inhibition, while magnesium and manganese ions do not affect the enzyme activity.
AChE isolated from oat seedlings differs in a number of properties from AChE occurring in the tissues of other plants.

Genomic instability of protoplast-derived tobacco plants was studied by means of phenotypic evaluation, karyological analysis, and Southern blot experiments. Of the total number of 91 regenerants belonging to 35 different protoclones 57 plants displayed various morphological and/or functional aberrations, some of them being inherited into the progeny. A karyological study of 20 randomly chosen plants revealed 15 tetraploid and 5 diploid chromosome sets. A Southern blot hybridization analysis of three regenerants displayed some DNA polymorphism (RFLP) and thus confirmed that in such plants alterations in the genome structure could be found and that genotypes of protoplast-derived plants frequently differ from the parental genotype.

The influence of increasing concentrations of copper, zinc, lead, nickel, chromium and cadmium on 14-day-old seedlings of wheat (Triticum aestivum L. cv. Vergina) was studied. Plants were grown in 1/10 strength Rorison's nutrient solution with increasing concentrations of each of the metals added separately. The toxicity of metals depressed shoot growth but the most evident symptoms were on roots. The concentration of each metal which caused inhibition of root growth was chosen to study the influence of metals on isoperoxidases of wheat shoots. The concentrations employed did not alter the number of peroxidase bands but almost in all cases enhanced the intensities of bands of pH 4.0-4.2 and 5.0-5.4, while they decreased the intensities of bands of pH 4.2-4.6 and 5.4-6.5.
The similar effects of the different heavy metals employed may suggest similarity in metal action on wheat isoperoxidases. The increased intensities of peroxidase bands may be considered as an indication of enhanced senescence caused by the heavy metal treatments.
Generally, our results suggest that the heavy metals employed have caused complex changes on the multiple forms of peroxidases.

Aqueous salicylate solutions stimulated ethylene formation only when injurious, or potentially injurious, concentrations were exogenously supplied to soybean cuttings. Stimulation occurred via the biochemical sequence involving ACC as an intermediate, and was attributable to stimulation of ACC synthesis but not of EFE activity. Similar results were obtained by testing wound-induced ethylene, whereas the production of virus-induced ethylene was not affected by salicylate. Prolonged salicylate treatments which did not produce evident injurious effects inhibited soybean growth and rooting, probably through the moderate antiauxinic property attributable to salicylates. These findings are discussed in relation to other results obtained from similar or different plant materials.

Morphogenic callus cultures were obtained from 7-10 days old immature embryo explants on Murashige and Skoog and Gamborg's medium supplemented with 2,4-D. In the initial stages of culture the frequency of shoot formation varied from 28% to 65%. After 5 to 6 months of subculturing, the frequency of shoot formation was reduced to 14%. In the initial stages of culture, growth hormones do not seem to be very important for regeneration. 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/root, changes in isozymes takes place but no specific isozyme(s) could be related to the process of induction of morphogenesis.

21-day old plants ofChenopodium rubrum L. ecotype 374 were used. Organ relationships in the shoots were investigated by³²P distribution, which indicated different organ correlations in plants grown in continuous light and in plants treated with flower-inducing and non-inducing dark periods. Dark periods were associated with a low³²P distribution in young leaves and a high one in axillary buds. In the following light period the high³²P distribution in axillary buds continued whereas the³²P distribution in the leaves on the main axis increased and was similar to that in plants grown in continuous light. The high³²P distribution in axillary buds was brought about by both, flower-inducing and non-inducing dark treatments. Decapitation resulted in a high³²P distribution in buds, in continuous light an increased³²P distribution was also found in leaves. These effects were not fully cancelled by IAA application.
The results are discussed with respect to an assumption that decrease of apical dominance represents a step in a sequence of events leading to flowering.

Twenty six winter wheat cultivars representing early maturing (Em), medium early maturing (Mm), and late maturing (Lm) cultivar groups were grown in the field for two growing seasons. The dates at which plants reached the double ridge (DR) and terminal spikelet (TS) stages were determined using anatomical analysis of shoot apices. Thereafter the dates of anthesis (AN) and full maturity (MA) were recorded. The length of the time spans between subsequent developmental stages was then expressed both chronologically (number of days, d) and in terms of thermal time (degree day, °C d) which was calculated with the basal temperature equalling to zero. The results obtained confirmed the suitability of the utilization of degree days for the description of the time course of plant development, because the great differences in the time between subsequent developmental stages recorded between the two growing seasons when expressed in terms of numbers of days markedly diminished when expressed in terms of degree days. For example the period DR-MA expressed in number of days amounted in the year 1986 only to 87 % when related to the number of days recorded in the year 1985, whereas the corresponding value expressed in terms of degree days amounted to 98 %. The utilization of degree days is especially suitable for the AN-MA period (956 and 937 degree days in the years 1985 and 1986, respectively) within which temperature is the main factor determining the rate of plant development. Further analyses of the effects of basal temperatures, vernalization, and daylength appear to be necessary for a better understanding of the length of the period to the DR stage and differences among groups of cultivars and among different cultivars.

The ribulose 1,5-bisphosphate activity and its relative content in pea (Pisum sativum L., cv. Bordi) seedlings grown either under white or red light were investigated. Plants grown under red light had a lower ribulose 1,5- bisphosphate carboxylase (RuBPCO) activity as compared to plants grown under white light, if expressed on a fresh mass. These activities were very similar under both lights, as calculated on protein basis, although the relative content of RuBPCO was higher in the red one. The activity of RuBPCO under red light corresponds to the lower rate of net photosynthesis. The results are discussed in respect to possible presence of RuBPCO inhibitor in pea plants growth under red light.

Decrease in leaf irradiance to 50 % due to shading of plants in glasshouse only during clear summer days did not induce significant changes in growth parameters, characteristics of water relations and epidermal conductance of two cyclamen cultivars. Thus the possibility of acclimation of plants to non-stable changes in environmental conditions was not proved.

Leaves of drought-resistant and drought-sensitive genotypes of maize (Zea mays L.) were sprayed with ethephon to determine its effect on water and osmotic potentials. With both sufficient and limited water supplies, ethephon decreased the water potential, but not the osmotic potential, of the drought-sensitive maize. It had no effect on the water and osmotic potentials of the drought-resistant maize under either water regime. The results showed that the response of a genotype of maize to ethephon depends upon its susceptibility to drought.

Cotyledons ofXanthium strumarium, organs with low sensitivity to photoperiodic treatment show a higher free indol-3-ylacetic acid level (by about 35 %) than the first pair leaves, organs with high sensitivity to photoperiodic treatment. This was seen in plants of three different age groups : A. with the first pair of leaves of 15-20 mm in length; B. with the first pair of leaves having finished their growth and C. with the third leaf of 30-40 mm in length.
Changes in free IAA level during the inductive dark period were similar in both cotyledons and leaves of the first pair. The level of IAA rose in the first half of the dark period, began to decrease in the latter half, reaching nearly initial level at its end.
Application of IAA (10^-4 - 10^-2M) to the cotyledons reduced their already low photoperiodic sensitivity resulting in inhibition of flowering (almost 70 % using 10^-4M IAA).
Elevated free IAA level is assumed to be one of the causal factors of low photoperiodic sensitivity of cotyledons.

The contet of phenols, o-dihydroxyphenols and peroxidase activity in healthy andCurvularia andropogonis (Zimm.) Boedijn infected leaves ofJava citronella were determined. As a result of infection, the content of phenols and peroxidase increased two- and four-fold, respectively in necrotic lesions compared to healthy leaves. In surrounding tissue of lesions, their increase was one-and half fold only. The peroxidase activity decreased with the maturity of the necrotic lesions. Necrotic lesions produced in response to infection appear to be the consequence of higher accumulation of phenols and their oxidation by peroxidase.

Potassium (K⁺) and nitrogen (N) supply affect stomatal apertures within the daylength conditions. There is a negative proportion between potassium supply and stomatal pore area: the smallest pores were to be found in the plants with K⁺ surplus, whereas the plants in K⁺ shortage had the largest pores. This is interpreted as a reaction of the plant to get more ions by an increased transpiration stream. With different nitrogen concentrations in the supply solution a similar proportion could be found, with the exception of the condition "N shortage in shortday", and further testing is necessary. The ionic supply has a parallel effect in both daylengths.

Arabidopsis thaliana tumors were induced by octopine strain ofAgrobacterium tumefaciens B6S3 and its derivatives with modified T-DNA. Flowering shoots appeared sponta-neously onin vitro cultivated tumors and set seeds. R₁ and R₂ progeny of octopine synthesizing plants segregated in opine synthesis activities 3:1 and 15:1. Octopine synthase activity showed absolute linkage with agropine synthesis in most lines. In R₃ and R₄ progenies, the fraction of octopine synthase and agropine synthesis positive plants was lower than expected, but Mendelian segregation was restored if plants were cultivated on medium with 5-azacytidine. The most probable mechanism of disapearance of opine synthesis is cytosine methylation. The effect of 5-azacytidine lasted for at least next two generations.

Phosphoenolpyruvate carboxylase (PEPC) was isolated from maize seeds which were germinated for 20 h, using a procedure which included extraction of seed homogenate with Tris-HCl or sodium phosphate buffer, precipitation of the extract with ammonium sulphate, chromatography on DEAE cellulose, and gel filtration on Sephadex G-200. Phosphate buffer was found to be less suitable than Tris-HCl buffer both for maize seed extraction and for further PEPC purification steps. The enzyme preparation obtained was electrophretically homogenous. PEPC activity was inhibited by both phosphate and malate. It values obtained at pH 8.1 which is the pH optimum of the reaction equelled to 42 mmoll^-1 for phosphate and to 13 mmoll^-1 for malate. PEPC isolated from germinating maize seeds was activated by glucose-6-phosphate, glucose-1-phosphate, ribulose-l,5-bisphosphate, fructose-1,6-bisphosphate, and fructose-2,6-bisphosphate. The authors intend to elucidate the mechanism of PEPC activation by sugars by means of the application of a number of derivatives of the sugar phosphates, among which for example 2-deoxy-2-fluoro glucosephosphate also activated PEPC. Sugar phosphates activated PEPC isolated from germinating maize seeds in this order, with increasing effect: fructose-l,6-bisphosphate, glucose-1-phosphate, glucose-6-phosphate, 2-deoxy-2-fluoro glucosephosphate, ribulose-l,5-bisphos-phate, fructose-2-6-bisphosphate.

Amphistomatous C₃ (Nicotiana tabacum L., Datura stramonium L.) and C₄ (Sorghum saccharatum Pers. and Zea mays L.) species were examined to find how (if at all) their inherent differences in water-use economy are reflected in apparent cuticular transpiration or vice versa. Transpiration efficiency (TE) was calculated from steady state photosynthesis (A) and transpiration (E) rates estimated for the upper side of the leaf after light induction of stomata opening. Apparent cuticular transpiration ('E_c) was measured as the part of transpiration which was not eliminated by convective counteraction of the air stream passing across the amphistomatous leaf: total pressure difference (AP) across the leaf was increased and the minimal value of E_ΔPτ0 was taken as the apparent cuticular transpiration rate ('E_c). 'E_c was treated relative to E at AP equal to zero (E_GDP=0), E'_cr. Measurements were carried out under two leaf-air vapour pressure differences (VPD).
E_r (i.e. E_GDPτ0/E_GDP=0) versus GDP patterns differed qualitatively between the investigated C₃ and C₄ plants. TE increased and 'E_cr decreased from tobacco, stramony, maize to sorghum for both VPD of air. 'E_cr and TE were approximately linearly related, the slope being dependent on VPD. The increase in VPD resulted in larger E and slightly smaller epidermal conductance (g) at GDP equal to zero. Both E'_cr and E'_cr decreased markedly at the same time especially, for species with high TE. The results were considered as an indirect confirmation that E'_c values estimated by the technique used reflect species-specific differences in external peristomatal and cuticular vapour loss, at least in a relative sense.

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.

A NADH-ferricyanide reductase activity found in radish microsomes isolated from germinated seeds has been shown to be stimulated by pCMB and pCMBS which are both strong nactivators of many plant proteolytic enzymes. In the same preparation a leucine aminopeptidase was found while endoprotease and carboxypeptidase activities were not detected using exogenous substrates. The aminopeptidase, highly active at the same optimal pH-condition of FeCN reductase, was stimulated by CoCl₂ and non-polar detergents (Triton X-100 and Brij 35). It was inhibited by sulphydryl reagents. By gel filtration of microsomal detergent extract two peaks of activity were separated: red I coeluted with LeuAPase and red II, free of aminopeptidase. Red I, a protein, was inhibited by sulphydral reagents and stimulated by duroquinone. Red II, stimulated by pCMB, is not a protein because of the small size and the noninfluence of heating treatment on catalytic activity.