Stimulation of benzyladenine-induced in vitro shoot organogenesis and endogenous proline in melon (Cucumis melo L.) by fish protein hydrolysates in combination with proline analogues

A previous study demonstrated that proline is beneficial for improving melo n in vitro shoot organogenesis. A natural source of proline and proline pre cursors can be obtained from fish protein hydrolysates (FPH), a byproduct o f the fishery industry. Proline analogues azetidine-2-carboxylate and hydro xyproline in combination with standardized FPH were used to stimulate proli ne synthesis and benzyladenine-induced shoot organogenesis by exploiting th e proposed proline-linked pentose phosphate pathway (PPP). In the presence of elevated levels of endogenous proline, potential stimulation of cytokini ns and auxin may occur via the PPP and shikimate pathways, respectively. Tr eatments with FPH singly and in combination with the above proline analogue s significantly increased the endogenous proline content and the extent of differentiation, suggesting that in vitro organogenesis is closely linked t o proline synthesis, strengthening the hypothesis that purine metabolism vi a the proline-linked PPP may be important for organogenesis. Thioproline ad dition resulted in increased proline levels but without corresponding stimu lation of organogenesis. This study also provides potential use of fishery waste for value-added application in plant micropropagation industry.