Effects of auxin on growth and ripening of mesocarp discs of peach fruit

A bio-assay system using the mesocarp discs of peach fruit (Prunus persica L. cv. Akatsuki) was developed, and the effects of auxin on the physiology of fruit tissues were investigated at different stages of development (FWI: initial period of exponential growth, FWII: period of slow growth, and FWIII: second period of exponential growth). Auxin promoted both the enlargement of discs as well as ripening processes such as softening and anthocyanin formation. In particular, discs at FWI and FWII enlarged remarkably after four weeks of incubation with NAA. The highest value of the weight of FWI discs was observed at 10 mu M of NAA; that of FWII discs was at 1 mu M Weights were compared between discs that were incubated with and without NAA. NAA-incubated discs reached to 3.1-fold in the FWI stage and 2.7-fold in the FWII stage. Discs at each stage of development lost their firmness with increasing concentrations of NAA up to 100 mu M. There was a significant difference in anthocyanin formation between light- and dark-incubated discs. Anthocyanin formation at the surface of the discs was enhanced by high concentrations of NAA and light, whereas that inside of the discs was enhanced by darkness and low concentrations of NAA. These multiple effects of auxin on growth and the ripening process of fruit tissue may be caused by multiple mechanisms of auxin action as influenced by the stage of fruit tissue growth and environmental conditions. (C) 2000 Elsevier Science B.V. All rights reserved.