Gibberellic Acid Content of Spinach in Relation to Photoperiod, Temperature, and Flower Induction

Abstract

The hypothesis that gibberellic acid is involved in the regulation of spinach flowering was tested. The two-fold objectives of the present study were, first, to isolate and identify gibberellic acid present in induced and non-induced spinach (Spinacia oleracea L., cv. Bloomsdale) tissues and, second, to quantify levels of this compound during the ontogeny of flower induction. Plants were initially grown in a growth chamber under short photoperiod conditions (8 h of light at 25°C and 16 h of darkness at 18°C) for 7 weeks and then half of the plants were transferred to a long photoperiod growth chamber (16 h of light at 30°C and 8 h of darkness at 20°C). Harvest of plants began 48 hours later and over a period of 12 days with 2-day intervals. Plants were subjected to a purification procedure involving preparatory solvent partitioning and reversed-phase high-performance liquid chromatography. The purified gibberellic acid was then identified and quantified using combined gas chromatography-mass spectrometry. When plants were transferred from floral non-inducing to inducing conditions, the gibberellic acid content increased progressively 2- to 6-fold during the 12-day sampling period. Two additional and independent experiments were performed in which the above photoperiodic regime was employed and temperature was kept constant at 30°C and 20°C throughout each experiment. These two experiments showed similar trends of decreasing gibberellic acid content under non-inducing conditions and, conversely, increasing under flower inducing conditions. Our study establishes a correlation between increased gibberellic acid level and flowering of spinach.