myo-Inositol is the major sugar in Actinidia arguta during early fruit development

Actinidia arguta (Sieb. et Zucc.) Planch. ex Mig. is a cold tolerant and heavy cropping species from the kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev.) C.F. Liang et A.R.Ferguson] family that has potential for commercialisation, As fruit developed, glucose was the major sugar (74%) in A. deliciosa during the first 40 days after anthesis, whereas myo-inositol was the major sugar (60-65%) in A. arguta. myo-Inositol accumulated rapidly in A. arguta during the first 20-30 daa then more slowly as fruit grew to reach a steady state level, between 15 and 50 mg fruit(-1) for different selections. Peak levels were 55-60 mg g(-1) dry wt. In contrast, maximum myo-inositol concentrations in A. deliciosa were only 18 mg g(-1) dry wt. As fruit of A. arguta ripened, sucrose became the dominant sugar. In contrast to the fruit, myo-inositol concentrations were lower in leaves of A. arguta (similar to 5 mg g(-1) dry wt; similar to 10% of major sugars) than in leaves of A. deliciosa (15 mg g(-1) dry wt; similar to 20% of major sugars). To ascertain whether myo-inositol was transported from the leaves to the fruit in the phloem stream, exudates were also analysed. In both species, sucrose was the predominant sugar (>95%) in the phloem. Therefore we suggest that an unusual accumulation of myo-inositol in A. arguta during early stages of fruit development, may be due to synthesis in the fruit.