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Fructan metabolism in leaves of Lolium rigidum Gaudin
Author(s) -
SMOUTER HENK,
SIMPSON RICHARD J.
Publication year - 1991
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1991.tb01042.x
Subject(s) - fructan , sucrose , shoot , fructose , monosaccharide , lolium rigidum , botany , biology , lolium , chemistry , poaceae , food science , biochemistry , weed , herbicide resistance
summary Accumulation of water‐soluble carbohydrates (WSC) in leaves of intact seedlings of annual ryegrass ( Lolium rigidum Gaudin cv. Wimmera) was studied using a novel model system. The roots and leaf bases of intact seedlings, grown in nutrient solution, were cooled to 5°C to reduce sink activity and the production of photosynthates was enhanced by continuous illumination of the plants. This resulted in accumulation of WSC in the shoots. Thin‐layer chromatography showed the presence of a complex series of fructans, distinct from those found in tubers of Helianthus tuberosus. Two trisaccharides, 1‐kestose and neokestose, were present in various proportions, but no 6‐kestose was detected in the shoots. After feeding 14 CO 2 to the seedlings in a pulse‐chase experiment, high specific radioactivity was measured in monosaccharides, sucrose and fructan oligosaccharide fractions to DP 5 within 1 hr. These fructan pools were rapidly turned over without significant accumulation of fructans during the first 16 h of the accumulation phase. Neokestose and 1‐kestose contained equally high specific radioactivity, 1 h after feeding. These results indicated that neokestose was possibly as important as 1‐kestose as a possible precursor for synthesis of fructan. Concentrations of WSC increased linearly from 2 to 14 mg g −1 f. Wt of the leaves after 16 h and reached a concentration of 30 mg g −1 f. wt after 64 h. Sucrose, glucose and fructose were the first sugars to be accumulated and reached concentrations of 10, 3.5 and 2.5 mg g −1 f. wt, respectively. Tri‐ and tetrasaccharide accumulated to measurable concentrations after approximately 16 h of treatment and reached concentrations of 2.5 and 2.0 mg g −1 f. wt, respectively. The appearance of these oligosaccharides occurred when sucrose and monosaccharides reached stable concentrations in the leaves, The WSC concentration declined at a rate of about 0.8 mg g −1 f. wt h −1 , when the root temperature was raised to 24°C after 64 h and plants were darkened. The decline in WSC concentration was accompanied by a 70% decline in sucrose concentration and a decline in all other fructan concentrations, white the concentration of fructose increased 2‐fold.