Alexios Alexopoulos

Effect of plant growth regulators on the tuberisation and physiological age of potato (Solanum tuberosum L.) tubers grown from true potato seed

The effects of plant growth regulators [6-benzyl amino purine (BA), indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), gibberellic acid (GA3), chlormequat chloride (CCC), daminozide] and their time of application on tuberisation and physiological age of cv. Chacasina F1 grown from true potato seed (TPS) were studied in four experiments conducted in spring or autumn in Greece. BA, IAA and 2,4-D did not affect plant development, tuberisation or the physiological age of the tubers produced. Daminozide and CCC reduced plant height when applied 30 but not 60 d after transplanting (DAT) in both spring and autumn. Neither substance affected tuberisation or the physiological age of the tubers formed. Application of GA3 30 DAT significantly increased plant height and the number, but not the weight, of tubers formed per plant. Tubers from GA3-treated plants tended to be elongated with a low dry matter content. When GA3 was applied at 60 DAT, plant height was increased, but tuber number, weight and ...

Bromoethane-induced changes in respiration rate, ethylene synthesis, and enzyme activities in potato tubers in relation to dormancy breakage

Summary This paper describes the effect of bromoethane, which promotes the breakage of dormancy of potato tuber buds, on the metabolic activity of tubers, up to the stage of visible sprouting. The respiratory activity of treated tubers increased to a maximum 2 d after treatment, which, despite a subsequent decline, remained at a higher level than that of untreated controls for a further 8 d. Similarly, bromoethane induced a higher level of ethylene release from tubers over 10 d from its application compared to the controls. With the exception of invertases (acid and alkaline), all the other enzymes studied (i.e., hexokinase, fructokinase, glucose-6-phosphate dehydrogenase, uridine-5-diphosphoglucose pyrophosphorylase, adenosine-5-diphosphoglucose pyrophosphorylase and -glucosidase) exhibited higher rates of activity in bromoethane-treated tubers than in the controls. From the results of this study, it appears that the application of bromoethane increased the metabolic activity of potato tubers prior to the first visible sign of bud sprouting, which occurred approx. 10 d after treatment.

Effect of foliar applications of gibberellic acid or daminozide on plant growth, tuberisation, and carbohydrate accumulation in tubers grown from true potato seed

Summary Foliar application of gibberellic acid (GA3) increased vegetative growth (fresh and dry weights) and the number of tubers per plant grown from true potato seed (TPS). Tubers from plants that had been treated with GA3 were smaller in size and had lower sucrose, but higher glucose and fructose contents. Microscopic examination of starch grains indicated that the changes in sugar content coincided with the breakdown of starch and an increase in αglucosidase activity. In contrast, the activities of UDP-glucose pyrophosphorylase and ADP-glucose pyrophosphorylase were apparently not affected by GA3. Although daminozide (an inhibitor of endogenous gibberellin biosynthesis) inhibited the vegetative growth of plants, it did not affect tuberisation, carbohydrate composition, or the activity of enzymes associated with carbohydrate metabolism. It is apparent, therefore, that tuber formation and carbohydrate composition can be affected by exogenously applied GA3, but not by a possible reduction in endogenous gibberellin levels due to daminozide. Moreover, since the foliar application of GA3 induces tuber elongation as well as the formation of stolons and ‘chain tubers’, it is likely that these processes have a high demand for sugars, thus leading to a decrease in the specific weight of tubers, increased breakdown of starch, and higher glucose and fructose levels in the tuber.