Invloed van rusverbreking deur suurstof op sekere aspekte van die respiratoriese metabolisme van saad van Strelitzia Juncea

Abstract

Sterlitzia juncea seeds are released from dormancy by incubation of the seeds in 100% oxygen at 25°C; germination commences on the fifth day of incubation. After incubation of the seeds for various periods, embryos were removed from the seeds and used for the preparation of crude extracts for the determination of the activity of specific respiratory enzymes and metabolite concentrations. Results were compared with similar determinations made on extracts of the embryos of seeds which were airincubated at 25°C. Comparisons led to the conclusion that embryos of the oxygen treated seeds have a higher respiratory activity than those of air-treated seeds. The glycolytic enzymes phosphofructokinase (PFK) and inorganic pyrophosphate:D-fructose-6-phosphate:1-phosphotransferase (PFP), exhibited only slightly higher activity in response to oxygen treatment of the seeds. Although aldolase and pyruvate kinase (PK) activity could be demonstrated, the activity was not influenced by oxygen treatment. A similar conclusion was drawn as regards the activity of alcohol dehydrogenase (ADH) and cytosolic malate dehydrogenase (MDHcyt). The D-glucose, D-fructose, ethanol and pyruvate content of embryos of oxygen treated seeds was slightly lower than that of air-treated seeds. On the first day of incubation however, there was a definite decline in the content of glucose, fructose and ethanol as a result of oxygen incubation. Within each treatment, the glucose and fructose contents were remarkably similar. The conclusion drawn from the above observations is that glycolytic activity of the embryos was only slightly enhanced following oxygen incubation of the seeds. Fermentative activity appears to be similar for the two incubation treatments. The activity of the two pentose phosphate pathway enzymes D-glucose-6-phosphate-dehydrogenase (G6PDH) and 6-phosphogluconatedehydrogenase (6PGDH) extracted from embryos, showed a definite increase in activity over the first four days of seed incubation in oxygen. The ratio of 6PGDH/G6PDH was ca 3 for both treatments. The results are in accordance with the hypothesis for the mechanism of dormancy release put forward by Roberts. Succinate dehydrogenase (SDH), malate dehydrogenase (MDHmit) and cytochrome oxidase (cyt ox) activity were found in the mitochondrial fraction. Oxygen treatment of the seeds led to a significant increase in cyt ox activity of the embryos, and the increase was linear with respect to incubation time. Cyt ox activity was associated with the non-mitochondrial fraction as well, which can be ascribed to the occurrence of in vivo extramitochondrial activity in imbibing seeds, or to mitochondrial breakage during extraction. The total cyt ox activity increased with incubation time, but only in the case of oxygen treated seeds. Both the mitochondrial and non-mitochondrial fractions contained a pseudo-SDH reaction which complicated the determination of true SDH-activity. The SDH-enzyme of embryos from oxygen treated seeds was deactivated to a larger extent than that of air-treated seeds. Activation may be accomplished by "high" temperature incubation of the extracts in the presence of succinate. The linear increase in the adenosine triphosphate (ATP) content and the total adenylate pool of the embryos with incubation time, led to a twofold increase in the value of these parameters, and is the most prominent consequence of oxygen incubation of the seeds. Oxygen incubation led to AEC values ≥0,8, while AEC values for air treated seeds were ≤ 0,7.