Glucosinolate variation among organs, growth stages and seasons suggests its dominant accumulation in sexual over asexual-reproductive organs in white radish

Abstract

Radish (Raphanus sativus L.), a root vegetable crop, contains a large amount of glucosinolate but information on its changes in field condition among different organs, growth stages and seasons is very limited. The glucosinolate composition, concentration (mmol∙kilogram−1) and content (μmol∙organ−1) of radish were analyzed among shoots, roots, inflorescences and siliques in vegetative and/or reproductive growth stages during autumn and spring to estimate sink/source relation and proper harvest time for high glucosinolate. Glucosinolates were measured weekly during autumn and spring using two autumn and one spring cultivars. All cultivars did not flower in autumn while only autumn cultivars had inflorescences in spring. Among three glucosinolates detected, glucoraphasatin was predominant, and glucobrassicin and gluconasturtiin varied in ratio among organs, growth stages and seasons. Root and shoot glucosinolate concentrations decreased as plants grow during autumn. Glucosinolate concentration in roots tended to decrease but that in shoots continuously increased during spring. Glucosinolate concentration was higher in roots than shoots during autumn and early spring but higher in shoots during late spring. Total glucosinolate content was also significantly higher in roots than shoots during autumn. However, it was higher in shoots at vegetative stage but in roots shortly at flower initiation, and then sharply increased in shoots at developmental stage during spring. The sharp increase in shoot glucosinolate content never happened in a spring cultivar without inflorescences. Glucosinolate concentration in the tenth week was significantly higher in inflorescences than other organs. These results suggest that when they co-exist, glucosinolate accumulates more in inflorescences than roots, which act as organs for sexual and asexual reproduction, respectively. Proper harvest time for leaves and roots were suggested based on the glucosinolate content and growth of radish plants.