Studies on the Carbon Dioxide Promotion and Ethylene Inhibition of Tuberization in Potato Explants Cultured in Vitro

Abstract

the C2H4 inhibition of tuberization in vitro. The earlier work on potato stolons has been further extended to the study of the actions of CO2 and C2H4 on tuberization of sprout sections cultured in vitro. MATERIALS AND METHODSPlant Material and in Vitro Culture. Tubers of Solanum tuberosum L. var. Red La Soda which had been grown for seed were used in all experiments. On one occasion, var. White Rose was also tested. Sprout sections or stolons were obtained according to the technique described previously (16) with a few modifications. Excised stolons grown from axillary buds of sprout sections were surface-sterilized by immersion in a Purex bleach solution (diluted 1:10), for 2 to 3 min, before being transferred to culture flasks or test tubes. Where indicated, kinetin was used at a concentration of 5 mg/i. Tuberization of sprout sections was studied by culture in medium 2 using the methodology described by . When used, CO2 and C2H4 were injected in amounts which would produce initial concentrations in the flasks of 10% (v/v) of CO2 and 5 Al/1 of C2H4. Filter paper was inserted in small (16 x 41 mm) test tubes before autoclaving the flasks containing the culture medium. Trapping solutions (16) for CO2 and/or C2H4 were dispensed later in the small test tubes.Time Course Experiments of CO2 Action. The following changes were made in relation to the methodology described previously (16). Sprouts were excised when they were 6 to 8 cm long. Two ml of sterile H20 were added to culture flasks on top of the solidified culture medium 2 to prevent desiccation of the internal atmosphere in the flasks produced by absorption of H20 by a 20% (w/v) KOH solution (CO2 trapping solution).One-third of the available stolons was cultured in medium 2 with 10% (v/v) CO2 in the absence of C2H4 for 30 days. Another third was cultured in the same conditions for 1, 2, 3, or 5 days and then transferred (designated as tr) to medium 2 in a flask covered with a Morton stainless steel closure which allowed exchange with external air (open control), or the flasks were purged (designated as p) under vacuum in the sterile transfer hood for 3 min and then covered with a Morton closure. After purging, the CO2 concentration in the flasks was less than 0.2%. The small test tube containing mercuric perchlorate solution was removed from the flask at this time. The final third of the stolons was cultured in medium 2 in an atmosphere in equilibrium with the exterior (open control).Extraction and assay of starch synthetase from potato tubers were based on the procedure described by Hawker et al. (10).

Shoot, Stolon, and Tuber Formation on Potato (Solanum tuberosum L.) Cuttings in Response to Photoperiod

“…He also showed that tuber formation was promoted by darkness and moisture. Recent evidence (16,17) suggests that elevated CO2 levels may also favor tuberization at below ground rather than above ground buds. However, tubers do not always develop even from underground buds of cuttings.…”

Effect of Calcium on Tuberization in Potato (Solanum tuberosum L.)

“…Although ABA has been shown to promote tuberization in Solanum andigena (22), it inhibited cytokinin-mediated tuberization of Solanum tuberosum (7). Ethylene inhibited tuberization (11) and the role of auxin in this process has not been studied in detail (9).…”

Effect of Ethylene on the Endogenous Cytokinin and Gibberellin Levels in Tuberizing Potatoes

“…3) on treated potatoes. As the endogenous level of cytokinins did not change in the Ethrel-treated tubers, ethylene could also have prevented these compounds from acting at the subapical meristem, particularly as kinetin-induced tuberization (17,19) can be reversed by this hormone (12,13). This reversal could have been the result of an inhibition of cell division and/or starch synthesis.…”

“…They do, however, promote stolon elongation (15). Natural tuberization (12) as well as the kinetin-stimulated accumulation of starch in stolons (13) are inhibited by ethylene. Ethylene also inhibits stolon elongation and causes the development of abnormal subapical swellings (13) devoid of any appreciable starch (6).…”