István Király

Effect of Light on the Nucleotide Composition of rRNA of Wheat Seedlings

Both qualitative and quantitative differences in the minor nucleotide constituents of rRNA from normally grown and from etiolated wheat plants (Triticum aestivum L.) were established. Using different degradation methods and separation techniques the 18S+26S RNA of 8-day-old wheat seedlings grown in the light was found to contain 5-methylcytidine, 3-methylcytidine, 5-methyluridine, 3-methyluridine, 5-carboxymethyluridine, 1-methyladenine, N-methyladenine, 5-hydroxymethylcytidine, O2′-methyluridine, O2′-methylcytidine, pseudouridine, O2′-methylpseudouridine, N2,N2-dimethylguanine, 1-methylguanine, ribothymidine and some unknown minor constituents. On the other hand, there were only a few minor nucleotides in the rRNA of etiolated wheat seedlings. Cycloheximide, a cytoplasmic protein synthesis inhibitor, simulated etiolation in that it reduced the number of minor nucleotides in rRNA, whereas chloramphenicol, a chloroplast protein synthesis inhibitor, had no significant effect on the minor nucleotide content of rRNA. This finding suggests that illumination may cause de novo synthesis of cytoplasmic modifying enzymes leading to the formation of highly modified rRNAs.

On the mechanism of rejuvenation of ageing detached bean leaves by low-concentration stressors.

The effect of low concentrations of some stress-inducing compounds of different toxicity and chemical nature, such as Cd and Pb salts or DCMU, was investigated on the senescence of chloroplasts in detached primary leaves of bean (Phaseolus vulgaris L.). After 1 week of senescence followed by root development from the petiole, these agents stimulated chlorophyll accumulation and photosynthetic activity ((14)CO(2) fixation) as compared to the control, thus inducing rejuvenation. Low-concentration stressors increased the level of active cytokinins in roots and leaves during the treatment, as monitored by the Amaranthus betacyanin bioassay and high-pressure liquid chromatography. The lithium ion, an inhibitor of the PIP(2)-IP(3)/DAG signal transduction pathway, abolished the stimulating effect of stressors, both in roots (retarding cytokinin synthesis) and consequently also in leaves (reducing cytokinin-dependent chlorophyll accumulation). This suggests the involvement of the PIP(2)-IP(3)/DAG signal transduction pathway in generation of these consecutive organ-specific responses.

Changes in the content of modified nucleotides of total transfer RNA of wheat seedlings during greening.

The contents in minor nucleotides of total transfer RNA (tRNA) of etiolated and light-grown wheat (Triticum aestivum L.) seedlings and of seedlings illuminated for 24 or 48 h were examined. The total tRNA of seedlings illuminated 24 h contained more, and that from seedlings illuminated 48 h still more modified nucleotides than that from etiolated ones. Thus, the appearance of the characteristic minor nucleotides of tRNA of light-grown wheat seedlings needs a rather long greening period, of at least 48 h.

The changes of minor nucleotide content of tRNAPhe of wheat germs (Triticum aestivum) during greening

Abstract The primary structure and minor nucleotide content of tRNA Phe of wheat germs illuminated for 6, 9, 12, 24 and 48 h was investigated. No alterations were found in the primary structure, but three minor nucleotides (cf. m 2 2 G, m 7 G and Cm) were missing when the plants were illuminated for 6, 9 or 12 h, similarly to the case of etiolation. A single minor nucleotide of them, the m 7 G could be shown after a 24-h greening period, while the m 2 2 and Cm appeared only after 48-h illumination.

The effect of light on the nucleotide composition of tRNAPhe of wheat germ (Triticum aestivum)

Abstract The primary structure and minor nucleotide content of normally grown and etiolated wheat germ tRNAPhe were investigated. Etiolation was found to cause no alterations in the primary structure of the tRNAPhe but three minor nucleotides were missing. The minor nucleotides N 2 ,N 2 - dimethylguanine (m22G), 7-methylguanine (m7G) and O 2 ′- methylcytidine (Cm) present in the tRNAPhe of normally grown wheat germs could not be detected in that of etiolated ones. Their absence cannot be due to undermethylation because the same changes were identically located in the tRNAPhe molecule in a number of independent experiments. It is probably the result of a lack of light activation of the synthesis of some modifying enzymes via the phytochrome system.

Responses of the photosynthetic system and peroxidase activity to the rooting conditions of oak micropropagation

The effects of indole butyric acid (IBA) concentration and the duration of the plant growth regulator (PGR) treatment on the rooting ability, peroxidase level and photosynthetic activity of young Quercus robur L. plants were studied. Four-week-old oak shoots were transplanted to rooting media supplemented with 10 or 20 μM IBA. After 2, 3, 4, 5 or 7 days the shoots were transplanted again to a fresh, PGR-free medium. On the tenth day after transfer to rooting medium, the CO2 fixation capacity, pigment content and peroxidase activity were measured. The photosynthetic parameters varied as a function of the time spent on medium containing PGR, showing maximum values in plants transplanted on the third to fourth day to PGR-free medium. The rooting percentage of these plants reached its maximum within two weeks. However, peroxidase activity was the highest in plants transferred later to PGR-free medium. The most pronounced stimulating effect on rooting was achieved with the higher initial IBA concentration followed by a transfer to PGR-free medium on the third to fourth day. These plants showed the highest vitality and the best rooting ability.

Effect of light on the activity of the protein synthesising system in wheat seedling

Abstract Light, an important regulatory factor in the growth and development of plant, influences not only the quantity and composition of the RNAs, but also the modified nucleotide composition of the tRNAs and rRNAs, since under-modified RNAs are formed due to the lack of light, gradually returning to the modification level characteristics of the RNAs in green plants in the course of illumination. The current experiments were aimed at investigating how tRNAs obtained from etiolated plants, or from plants greened for various lengths of time, influenced the activity of cell-free protein synthesising systems, and what changes in activity were brought about by changes occurring in other components of the protein synthesising system due to the effect of greening. It was found that under-modified tRNAs caused a substantial reduction in the intensity of protein synthesis, i.e. in the incorporation into the proteins of the labelled amino acids, and the activity characteristic of green plants could only be restored with tRNA obtained from plant greened for 48 h. At the same time, changes induced by etiolation in other components of the protein systhesising system (e.g. rRNA under-modification) reduced the intensity of protein systhesis to a lesser extent.

Effect of combined stress on the O2 scavenging enzyme activities in bean and poplar leaves

Wounding, Drought, Elicitation, Catalase, Peroxidase The activity of O2-scavenging enzymes in bean leaves in different positions and poplar leaves in different leaf storeys was investigated. The effects of wounding, elicitation and drought and the combination of these treatments at various levels were studied. Distal bean leaves showed higher responsiveness than those opposite the treated leaves. Poplar leaves above the treated ones proved to be more active than those in lower storeys. A comparison of the interaction of different stress treatments revealed both synergistic and antagonistic effects on the oxidant-generating rate and anti-oxidant synthesis of damaged and non-damaged plant tissues

Effect of Cd and Pb on Photosynthesis in Cucumber

Heavy metal pollution strongly affects plant metabolism including photosynthesis. The effects of Cd and Pb (10 δM) on photosynthetic apparatus were investigated at different leaf storeys of hydroponically cultured (4 δM Fe chelated with either EDTA or citrate) cucumber plants. Cd given from the fourth-leaf stage of plants retarded their growth, particularly that of roots and reduced the amount of all pigment containing complexes in thylakoids, the PSII core being a little more resistant. The organization of treated thylakoids seemed to be very similar to that of iron deficient plants. Pb caused similar but moderate changes. EDTA exerted a protective effect. Fluorescence induction parameter Fv/Fm showed a slight change. However, severe inhibition of CO2 fixation was observed at all leaf storeys.