Planteose is a major sugar translocated in Actinidia arguta ‘Hortgem Tahi’

• Planteose is a trisaccharide found in similar concentrations to sucrose in Actinidia arguta ‘Hortgem Tahi’ leaves.
• Planteose was found in phloem exudates from Actinidia arguta ‘Hortgem Tahi’ leaves and fruit peduncles.
• Export of labelled carbohydrate from leaves was highest in the late afternoon and evening coinciding with peak movement of planteose and sucrose from leaves.
• Planteose was rapidly metabolised in the fruit.
• This is the first plant where planteose has been found in phloem exudates and transported to sink tissues.

Planteose, an unusual trisaccharide with galactose attached to the fructose moiety of sucrose, is a major carbohydrate present in Actinidia arguta ‘Hortgem Tahi’ leaves. The aim of this study was to investigate whether planteose was transported in the phloem of ‘Hortgem Tahi’ vines by 14C labelling of recently fixed photosynthate in leaves and measuring the soluble carbohydrate content of phloem exudates. 14C movement was monitored within the vine either non-invasively, detecting Bremsstrahlung radiation or by destructive sampling. Phloem soluble carbohydrate content was examined by EDTA-facilitated exudation from mature leaf petioles and developing fruit peduncles. Bremsstrahlung radiation detection showed that export from the radiolabelled leaf to the peduncle of the subtending fruit or to roots increased rapidly in the late afternoon and evening. During this period of peak export, planteose was present in the phloem exudate from both leaf petioles and fruit peduncles in equal or greater quantities than sucrose. Radiolabelled planteose and sucrose were also both found moving along the shoot away from a radiolabelled leaf. By contrast, in the fruit planteose represented only 2% of the soluble carbohydrate compared with 14% for sucrose. However, the specific activity of 14C was five times higher for planteose than for sucrose, indicating that planteose is quickly metabolised in the fruit. This is the first reported finding of planteose in phloem exudates from the leaf petioles or fruit peduncles in any plant species and indicates planteose is transported in ‘Hortgem Tahi’ vines.