Occurrence of natural auxin and accumulation of calcium during early fruit development in kiwifruit

This note tracks for the first time the natural occurrence and metabolism of the plant hormone free indole-3-acetic acid (IAA) in young kiwifruit (Actinidia deliciosa var. deliciosa, C.F. Liang et A. R. Ferguson). Simultaneous measurements of IAA and fruit calcium (Ca) levels were examined to discover possible correlations. The IAA was detected using gas chromatography-mass spectrometry and Ca was assessed spectrophotometrically. Both determinations were carried out on fruits sampled from field-grown mature vines 6, 13, 19, 27, 35, 45, 55 and 67 days after pollination (DAP). The hormone level was greatest at 6 DAP (55 ±5 ng g-1 fresh weight, FW, ±SD) but declined markedly thereafter to a minimum of 5.32 ±0.5 ng g-1 FW by 45 DAP (about 6 weeks later). Modulation of free IAA concentration did not appear to depend on conjugation of the hormone. Results show that the IAA (ng g-1 FW) and Ca (mg g-1 FW) concentrations were closely correlated (R2=0.92) with a linear regression slope value of 0.061. Although further research is required to identify possible causality, this relationship‟s possible significance in determining fruit storage quality is discussed.