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

Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. 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 (60Ð65%) in A. arguta. myo-Inositol accumulated rapidly in A. arguta during the first 20Ð30 daa then more slowly as fruit grew to reach a steady state level, between 15 and 50 mg fruit Ð1 for different selections. Peak levels were 55-60 mg g Ð1 dry wt. In contrast, maximum myo-inositol concentrations in A. deliciosa were only 18 mg g Ð1 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 (~5 mg g Ð1 dry wt; ~10% of major sugars) than in leaves of A. deliciosa (15 mg g Ð1 dry wt; ~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.