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

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.