European Journal of Scientific Research - EuroJournals

European Journal of Scientific Research
ISSN 1450-216X Vol.14 No.3 (2006), pp. 407-416
© EuroJournals Publishing, Inc. 2006
http://www.eurojournals.com/ejsr.htm
A Comparative Analysis of Gibberellic Acid Content with
Respect to Tuber Induction in Potato Plants Grown Under
Differential Photoperiod and Temperature
Ahmed Malkawi
Department of Chemistry and Physics
Northwest Missouri State University
Maryville, MO 64468, USA
E-mail: amalkaw@nwmissouri.edu
Abstract
A time-course experiment was performed to determine the effect of photoperiod
and temperature on endogenous gibberellic acid (GA3) levels in vegetative tissues of potato
(Solanum tuberosum cultivar “Russet Burbank”) in search of an unequivocal role for GA3
in tuber induction. Plants were initially grown in tuber non-inducing climatic conditions
(30ºC day and 26ºC night with an 18-hour photoperiod) until they reached a height of 55 to
60 cm after which half of the plants were transferred to inducing climatic conditions (24ºC
day and 12ºC night with a 10-hour photoperiod). Harvest of each plant type began 48 hours
later and over a period of 10 days with 2-day intervals. Plants were divided into aerial and
underground tissues, freeze-dried, ground, and then subjected to a purification procedure
involving solvent extraction and high performance liquid chromatography. The purified
GA3 extract was then quantified by using combined gas chromatography-mass
spectrometry. Levels of GA3 declined progressively during the ten-day tuber induction
period while it slightly increased under non-inducing conditions progressively. Our study
establishes a strong correlation between decreased GA3 level and tuber induction.
Keywords: chromatography, gibberellic acid, plant hormone, potato, Solanum tuberosum
Introduction
Potato tuberization is the physiological process whereby a stem section of a plant undergoes
morphological changes to become a special storage organ for reserve food such as carbohydrates and
proteins (Melis and van Staden 1984; Ewing and Struik 1992). Under optimum environmental
conditions for potato plants to switch from vegetative development to reproductive growth, a signal
formed in the leaves is transmitted through the phloem to the underground stems, called stolons
(Jackson 1999; Suarez-Lopez 2005 Rodriguez-Falcon et al. 2006). The synthesis of such signal and its
translocation is referred to as the induction of tuberization and signal is known as the “tuberization
stimulus”. The leaf-derived signal can be transmitted across a graft union, as demonstrated in
experiments involving ordinary plants (Gregory 1956; Chapman 1958; Kumar and Wareing 1973) as
well as transgenic plants (Jackson et al. 1998). The induction of tubers is considered a key
developmental stage in the potato crop’s life cycle, with “profound implications for subsequent growth
and development” (O’Brian et al. 1998).