Abstract
D.Sc. (Botany)
Senescence of Petunia hybrida petals is characterized by a typical climacteric
respiration pattern. Pollination enhanced the rate of senescence and the start of the
climacteric rise in respiration of the, corolla. Treatment with ethylene for a period of 6 hours had no effect on the rate of senescence, but increased the respiration rate. A ten hour treatment with ethylene increased the rates of both senescence and respiration. Initiation of the climacteric rise in respiration was also advanced. The cytochrome electron transport path was active throughout normal senescence and was the most important contributor to the total oxygen consumption by the petals during the pre- climacteric phase, while the contribution of the alternative pathway was minor. The contribution of the alternative pathway to oxygen consumption during the climacteric rise in respiration increased considerably, while the contribution of the cytochrome pathway decreased correspondingly. This suggests that the climacteric rise in respiration is due to an increase in the activity of the alternative pathway. Treatment with ethylene increased the contribution of the cytochrome pathway during the climacteric phase. Ethylene did not cause any significant increase in the activities of the processes of respiration preceding electron transport nor did it affect the availability of respiratory substrates. The results of this study suggest that the influence of ethylene on the electron transport system may be due to the effects of this hormone on the physical properties of the mitochondrial membranes.