Further observations on the activity of Y chromosome heterochromatin in Rumex thyrsiflorus

Observation of premeiotic nuclei of plants containing different numbers (from one to five) of Y chromosomes reveal that is such plants prior to meiosis all Y chromosomes are in fuzzy state, while in nuclei of tapetal cells or nuclei from anther stalk the number of big chromocentres is directly correlated with the number of Y chromosomes in given plants. This finding provides a further indication of genetic activity of Y chromosomes in this particular stage of the life cycle (premeiosis). Another indication of genetical activity of Y chromosomes was obtained from analysis of the rate of RNA synthesis in premeiosis. It was found that PMC's in the last premeioitc interphase exhibit a high rate of 3H-uridine incorporation. Thus in PMC's the fuzzy appearance of Y chromosomes coincides with intensive RNA synthesis.

The metabolism of aged seeds. The formation of polyribosomes in germinating field bean ( Vicia faba sp. minor) seeds of different ages

Total dehydrogenase activity and formation of polyribosomes in embryonic axes and cotyledons of field bean seeds from different harvest years were studied. ³H-uridine incorporation experiments showed that seed ageing was accompanied by decreased capability for RNA synthesis and polyribosome formation. The embryonic axes of seeds with reduced vigor contained lower levels of polyribosomes.

Ribonucleic acids and ribosomal proteins synthesis during germination of unripe and aged wheat caryopses

Caryopses collected at milk, wax and full ripeness as well as aged ones stored at air humidity of 30, 60 and 80 per cent were subjected to germination. The more unripe were the caryopses the lower was their germination capacity and dry mass increment of the sprouts, the same was true for fully ripe but aged caryopses. After 48 h of germination in the presence of radioactive precursors the embryos were removed from the caryopses and used for isolation of the total ribosomal fraction and RNA. Distinct synthesis of three basic total RNA fractions and of the polyribosomal fraction was observed in all samples and in embryos from grain which had completely lost its germination capacity. High radioactivity was recorded in preparations of total RNA and polyribosomal ones from 48-h sprouts growing from caryopses collected at milk ripeness and in those of aged caryopses stored under air humidity of 30 and 60 per cent. According to the authors, the depressed amount of latent forms of RNA (preformed mRNA, tRNA and ribosomes) is the cause of intensive ³H-uridine incorporation into RNA in embryos from unripe and aged caryopses. For germination of grains with a reduced amount of latent forms the biosynthesis mechanisms must be based to a much higher extent on newly synthesised molecules of ribonucleic acids.

Autoradiographic analysis of the effect of cytokinin on protein and RNA syntheses in the Ceratodon purpureus protonema

In the protonema of <em>Ceratodon purpureus</em> (Hedw.) Brid., apical parts of the protonemal filaments (apical cells, initials of protonemal side branches and of gametophore buds) proved to be preferential sites of [¹⁴C]-leucine incorporation into proteins. In some filaments, a similar preference for [³H]-uridine incorporation into RNA was observed, whereas in others there was a rather uniform distribution of label over all cells. A short (0.5-2 h) treatment with cytokinin (N⁶-2-isopentenyladenine) enhanced [¹⁴C]-leucine incorporation, without changing the relative distribution of label. No such enhancement, as well as no change in label distribution could be observed in [³H]-uridine incorporation. No direct relationship seems to exist between the early promotion of protein synthesis by cytokinin in the protonema and cytokinin induction of gametophore buds.

Ribonucleic acids in the embryos of germinating wheat grains of different ripeness

During 48 h germination of wheat grains of different ripeness the amount of RNA in the germinating embryos doubles, while the rate of synthesis is to a large extent correlated with the level of ribonucleic acids accumulated during the development and ripening of the grain. The highest RNA content was noted in the germs developing from grain harvested at the stage of full ripeness, the lowest - in germs from grain at milk ripeness. Intensity of ³H-uridine incorporation into the RNA fraction of the germs during 24-h germination also depends on ripeness. Significantly lower RNA synthesis was noted in germinating embryos from wheat grain harvested during milk ripeness as compared to wax or full ripeness.

Studies on the mechanism which prevents germination of unripe Triticale caryopses

<em>Triticale</em> (MT-3) caryopses were collected at three developmental stages (milk, milk-wax, and full ripeness i.e. 25, 39, 53 days after flowering) and germinated for 72 hours. The highest polyribosome contribution to the sum total of ribosomes, as well as, the highest ³H-uridine incorporation into the total ribosomal fraction of embryos (seedlings) were found at full ripeness, lower - at milk ripeness, and the lowest at milk-wax ripeness. Treatment of caryopses with gibberellin-A₃ (GA₃) and benzyloadenine (BA) caused an increase in the percentage of embryonic polyribosomes in caryopses which were collected at milk and full ripeness. Whereas the significant increase in ³H-uridine incorporation intothe total ribosomal fractions of embryos (seedlings) was observed only during the germination of the least ripe caryopses. This was characteristic of samples with caryopses at milk ripeness treated with BA, or BA and GA₃ together. The studies proved that the mechanism which prevents the germination of unripe Triticale cyryopses and the formation of polyribosomes which were germination-induced, originated at the final stage of grain development, before its full ripeness.

The role of zeatin and gibberellic acid in breaking of the abscisic acid-induced dormancy in Triticale caryopses

The investigations were conducted on the germinating embryos and the whole caryopses of <em>Triticale</em>. During preimbibition and 24 hours germination caryopses were treated with abscisic acid (ABA), which produced 63% inhibition of embryo growth. Gibberellin-A₃ (GA₃) reversed the ABA effect in 18%, while zeatin in 22%. The clear synergic reaction was observed (36%) when both stimulators acted together. There was no significant effect of ABA, ABA and GA₃, as well as ABA and zeatin on the synthesis of polyribosomal RNA in the initial period of germination of excised embryos. However, during 24 hours germination of whole caryopses ABA caused a twofold decrease in ³H-uridine incorporation into the total fraction of embryonic ribosomes. While the incorporation of ¹⁴C-aminoacid mixture into ribosomal proteins was even three-fold lower. Effect of GA₃ and zeatin on breaking of the ABA-induced "dormancy" was studied. It was confirmed that the higher polyribosome contribution to the sum total of ribosomes the more intensive synthesis of ribosomal proteins. No higher ³H-uridine incorporation into polyribosomal fraction was observed. From the results it may be inferred that in the initial period of germination of <em>Triticale</em> caryopses regulation of protein biosynthesis occurs rather at the translation than transcription level.

Effect of short- and long-lasting chilling on pre-rRNA synthesis and transport in root meristematic cells of three soybean cultivars

<p>Autoradiographic studies of ³H-uridine incorporation (20-min incubation) and dynamics of radioactive particle translocation from nucleolus into cytoplasm (following 80-min postincubation in non-radioactive medium) in root meristematic cells of soybean have been carried out. The experiment was performed with plants subjected to 4-day acclimation in chilling or subjected to 2-hour cold stress and control plants. Three cultivars of soybean: Mazowia, Polan and Progres (cultivated in Poland) were used in the experiment.</p><p>It has been shown that in control conditions the greatest number of RNA precursor is incorporated into nucleoli after 20-min incubation. Following 80-min postincubation cytoplasm is the most radioactive area of the cell - this mainly testifies to dynamic translocation of radioactive ribosome subunits from nucleolus into cytoplasm.</p><p>In chilling conditions the reduction of ³H-uridine incorporation into cells occurs, as compared to control conditions. Plants subjected to a 4-day acclimation incorporate the radioactive precursor more intensively than plants subjected to cold stress.</p><p>Following 80-min postincubation - in the case of acclimated plants - the nucleolus is the most radioactive area of the cell, which testifies to accumulation of pre-rRNA in it. After the cold stress cytoplasm is more radioactive than the nucleolus. In all three cultivars the processes of synthesis and transport of pre-rRNA particles are similar, only their intensity is different.</p><p>Morphometric measurements of nucleoli in all cultivars subjected to 4-day chilling have shown that root cell nucleoli are larger than those in control. This phenomenon can be connected with stronger inhibition of rRNA transport than its synthesis.</p>