Planteose is a short-term storage carbohydrate in Actinidia leaves

Abstract

The polyol myo-inositol constitutes 10-20% of soluble carbohydrates in mature leaves of Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson var. deliciosa 'Hayward' and A. arguta (Sieb. et Zucc.) Planch. ex Miq. var. arguta. In contrast with other non-structural carbohydrates, myo-inositol concentrations in A. deliciosa leaves increase only slightly during development from sink to source, and are not affected in source leaves by increased sink demand upon fruit set. In mature fruit-bearing leaves myo-inositol concentrations fluctuate diurnally, increasing during the night and declining towards morning, but in plants with less sink demand a diurnal pattern is not observed. In potted A. arguta seedlings subjected to extended dark periods, leaf concentrations of sugars and starch decline rapidly while myo-inositol concentrations are maintained. Labelling studies with 14 CO 2 revealed that myo-inositol in leaves is not a primary photosynthetic product and is turned over more slowly than other soluble carbohydrates. A suggested role of myo-inositol as a precursor in mucilage synthesis was not substantiated, as radioactivity was incorporated into mucilage more rapidly than into free myo-inositol. Planteose, a trisaccharide comprising sucrose and galactose, incorporated substantial amounts of radioactivity and accumulated to high levels, indicating a role in short-term storage of sucrose. Planteose was synthesised during the day and degraded during the night in a manner that was opposite to that of sucrose while starch and myo-inositol levels remained relatively constant. Planteose has been reported in Cyclamen persicum, ash and sesame seed. This is the first report of planteose in Actinidia, and the first time it has been identified as a major short-term storage carbohydrate in Actinidia leaves.

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

“…Radiolabelled carbon was rapidly incorporated into planteose in the A. arguta leaf, showing it is a primary photosynthetic product that accumulates during the day and begins to decline in the evening and night, reaching low concentrations by dawn (Klages et al, 2004). Planteose has previously been reported as a storage carbohydrate in cyclamen leaves and petioles (Rothe et al, 1999) and in sesame seeds (Dey, 1980) but there was no evidence that it was translocated in either species.…”

“…In A. arguta, sucrose and planteose are the major sugars found in the leaves (Klages et al, 2004). Radiolabelled carbon was rapidly incorporated into planteose in the A. arguta leaf, showing it is a primary photosynthetic product that accumulates during the day and begins to decline in the evening and night, reaching low concentrations by dawn (Klages et al, 2004).…”

“…The trisaccharide planteose, found in Actinidia arguta leaves, was described as a putative short-term storage carbohydrate by Klages et al (2004) Planteose (alpha-d-galactopyranosyl-(1-> 6)-beta-d-fructofuranosyl alpha-d-glucopyranoside) like raffinose, is composed of sucrose and galactose, except the galactose moiety is attached to the fructose rather than the glucose of the sucrose molecule. Generally, sucrose found in leaves is either transported to the phloem or converted to short-and long-term storage carbohydrates to avoid feedback inhibition of photosynthesis from high sucrose concentrations (Slewinski and Braun, 2010).…”

Boron dynamics related to fruit growth and seed production in kiwifruit (Actinidia deliciosa, cv. Hayward)

“…The main factor conferring mobility to boron in the phloem is the synthesis of sugar-alcohols and the subsequent transportation of B-poliol complexes. On the other hand, Bieleski et al (1997) mentioned that Actinidia plants contain unusually high levels of inositol, and Klages et al (2004) indicated the possibility that this sugar might be transported by the phloem from the leaves to the fruits, forming B-inositol complexes that may allow boron mobility. Therefore, boron may accrue in the meristematic zones in fruits of A. deliciosa.…”

“…In addition, Klages et al (2004) found that mioinositol represents between 10 and 20% of the soluble carbohydrates in the mature leaves of A. deliciosa, cv. Hayward.…”