The Effect of Light upon Development in Potato Tissue Slices

The dramatic changes in oxygen consumption which occur following slicing of dormant tuber tissue have been well documented (6, 7, 9). It has been difficult to interpret the results of various workers because the investigators have frequently employed different methods of slicing, aeration, and illumination, as well as various culture solutions, temperatures, and types of tissue. Lee and Chasson (10) suggested that these different techniques might contribute to the variety of interpretations assigned to the aging phenomenon. The relative contribution to the total respiratory rate by the glycolytic pathway, the pentose phosphate pathway, and the tricarboxylic acid cycle may be influenced by aeration, temperature, and light (11). Ap Rees and Beevers (1), who suggested that pentose phosphate metabolism is largely responsible for the respiratory increase, allowed light from normal laboratory conditions to strike the aging slices. Romberger and Norton (12), on the other hand, indicated that culturing (aging) was carried out in the dark and have interpreted their results to indicate that the tricarboxylic acid cycle becomes enhanced with aging. The latter conclusions were also reached by Laties (8), although light conditions were not reported. It is not unreasonable to suspect that light might influence the activity of respiratory enzymes since it does affect other enzyme systems in potato (14). However, previous attempts in our laboratory have failed to demonstrate any relationship between tissue 02 consumption and either light quality or quantity. Neither was it possible for us to show any influence of light on the malonate or cyanide sensitivity of potato tissue slices following conventional aging treatments. The effects of these two inhibitors on the tricarboxylic acid cycle and terminal oxidation are well known, and their influence upon fresh and aged potato tissue is specific: cyanide greatly suppresses 02 uptake in fresh tissue but has little influence on aged tissue; malonic acid only inhibits the respiration of aged tissue (2, 9). In a further attempt to demonstrate a possible link between light and respiration in tuber slices, we have modified previously applied procedures such that the tissue is aged in the presence of either cyanide or malonate. The results reported here confirm one of the conclusions drawn from our previous experiments referred to above, namely, that red light and far red light yield essentially the same results. Therefore, only the data from the former will be presented here. Cylinders of tissue having a diameter of 8.0 mm were prepared from potato tubers (Solanum tuberosum L., var. Russet) and cut into 1.0-mm slices with a hand microtome. Eight fresh slices weighed approximately 0.5 g. The dry weight of these