Análisis de la interacción entre radiaciones gamma y mms sobre la plántula de semillas de Triticale pretratadas con ácido ascórbico

The protective effect of the ascorbic acid against the physiological damage induced by gamma irradiation and MMS in Triticale caryopses was rested: caryopses were irradiated in absence of water, with water or in an ascorbic acid solution. No variation was detected in the survival following the different treatments. Germination speed was not affected by the different gamma irradiation doses. MMS concentrations and ascorbic acid were toxic.

The use of transcription inhibitors in the study of the mechanism of abscisic acid action in germinating triticale caryopses

The study was conducted on germinating triticale (var. Grado) caryopses. The purpose of the experiments was to compare the effect of selected inhibitors of transcription with the action of abscisic acid during germination of caryopses. The following inhibitors were used: α-amanitin, cordycepin, cycloheximide and 5-fluorouracil. Studied were the synthesis of total and polyribosomal RNA, the process of polyribosome formation and the synthesis of ribosomal proteins. The effect of exogenous ABA, especially in the early stages of germination, was not similar to any of the four above inhibitors of transcription. After 12 h of imbibition at a lowered temperature and 3 h of germination, ABA caused a relatively low level of inhibition of RNA synthesis, whereas all of the inhibitors used halted RNA synthesis in embryos by about 50-60%. After 6 h of germination, the same proportion of polyribosomes in the total ribosome fraction (46%) was found in both the embryos from the control sample and treated with ABA. The use of inhibitors brought this figure down to below 40%. The conclusion is drawn that in the early stages of germination, regulation of protein synthesis by ABA in triticale caryopses must occur on a level other than transcription.

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.

Role of gibberellins and cytokinins in regulation of germination during development and ripening of Triticale caryopses

The germination of caryopses of M-T3 <em>Triticale</em> generation, which were freshly harvested in different growth and developmental phases has been studied. A significant influence of the abscisic acid (ABA) accumulation on the increment of number of germinating caryopses has been found. Already in the first phase af the embryogenesis considerable stimulating effects of kinetin and gibberellin-A₃ (GA₃) on the germination of embryos which were isolated from freshly collected grains have been shown. When both stimulators were used together marked synergetic reaction occurred. It has been also determined that in the initial period of embryogensis premature germination occurs, to a higher extent, under the action of cytokinins than! Whether in the further phases of the caryopse development, when embryo develop mainly through the cell elongation, mostly gibberellins seem to be responsible for the activation of germination processes. The more mature were seeds the quicker germinated whole caryopses and embryos isolated from them at different ripeness, after 3-month storage. The highest stimulation of germination by phytohormones has been found for the most mature caryopses. The action of gibberellic acid has been particulary strong.

The role of the embryoless parts of triticale caryopses in inhibiting precocious germination and transcription in the embryo during development and maturation of caryopses

The experiments were conducted on developing and ripening triticale cv. Dagro caryopses. Increasing capability for precocious germination of the caryopses was seen as development and maturation progressed. A significant role of the embryoless parts of the caryopses (testa, pericarp and endosperm) in preventing germination processes was found. Isolated embryos (after 8 days of incubation) germinated by 100% from the 32nd day after flowering, while only 10% of whole caryopses from this sample germinated. Removal of the outer pericarp strongly stimulated germination of unripe caryopses. However, incising the caryopses near the embryo only slightly stimulated this process, which indicates that hypoxia of the embryo is not the cause of triticale embryo dormancy. Another very sensitive indicator of release of dormancy in the caryopses was the increased synthesis of embryo polyribosomal RNA induced by germination. The results of investigations on RNA synthesis in embryos - which undergoes extreme intensification when germination processes are initiated in the caryopses - were in agreement with those of biological studies based on observation of the elongation of the radicle. The lowest inhibition of transcription in the embryo was found when it was completely separated from the testa, pericarp and endosperm. A smaller effect was seen upon removal of the outer pericarp from developing and ripening caryopses, and decidedly the smallest effect still of incising the caryopses near the embryo.

The effect of ABA and AMO-1618 on the preharvest sprouting of triticale caryopses

The experiments were conducted on developing triticale var. Grado caryopses. Treatment of freshly gathered, unripe triticale caryopses with abscisic acid (ABA) decreased their precocious germination throughout the entire period of development and ripening. The more mature the embryos that were germinated, the lower the inhibition by ABA. This indicates that the sensitivity of the embryo to ABA decreases during the course of caryopsis development and that the role that this hormone can play in the prevention of spouting in ears during the final stages of maturation, is limited. A known inhibitor of gibberellin synthesis, the retardant AMO-1618, was also tested in these experiments. This compound caused the reduction of germination capability only in the initial stages of development of triticale caryopses. Its most visible effect was noted during the germination of caryopses collected 30 days after flowering. The effect of this compound on the precocious germination of isolated embryos also decreased as the degree of maturity of these embryos increased. In the opinion of this author, this is connected with the fact that intense gibberellin synthesis and accumulation occurs only in the early stages of caryopsis development.

Precocious germination and its regulation in embryos of triticale caryopses

Triticale var. Lasko embryos, isolated from grain gathered at milk ripeness, the beginning of wax ripeness and at full ripeness, were allowed to germinate for 48 h on agar with glucose. The highest incorporation of tritiated adenosine into polyribosomal RNA during germination was found in the ribosome fractions from embryos of grain gathered at full ripeness, lower incorporation was in preparations from embryos of milk ripe grain and the lowest in preparations from embryos of wax ripe grain. Different tendencies were observed in respect to the synthesis of ribosomal proteins. The highest incorporation of ¹⁴C-amino acids into ribosomal proteins was found in preparations of ribosome fractions from embryos of milk ripe grain, lower in preparations of embryos from fully ripe grain, the lowest in preparations of embryos from wax ripe grain. ABA (10^-4 M) completely inhibited the external symptoms of germination of immature embryos, while its inhibition of the synthesis of polyribosomal RNA and ribosomal proteins was greater the more mature the embryos that were germinated. The greatest stimulation of precocious germination by exogenous BA and GA₃ was demonstrated in the least mature embryos isolated from milk ripe grain. Under the influence of both stimulators, an increase of the proportion of polyribosomes in the total ribosome fraction occurred in this sample, as did a rise in the intensity of ribosomal protein synthesis. The incorporation of ³H-adenosine into polyribosomal RNA, however, was lower than in the control sample. The results obtained suggest that the regulation of precocious germination of triticale embryos by phyto-hormones is not directly related to transcription.

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.