Carbohydrate Physiology of Mycorrhizal Roots of Beech

Abstract

SUMMARYMycorrhizal roots of beech absorb [i'*C]glucose, fructose and sucrose at rates some two and a half times faster than uninfected roots. In the latter, sucrose is synthesized from all three sugars despite the presence of an active surface invertase, clearly suggesting that uptake from sucrose involves prior hydrolysis. There is only a small incorporation into polysaccharides by uninfected roots, this being into structural polymers. In contrast, mycorrhizal roots synthesize principally trehalose and glycogen from glucose, and mannitol from fructose. Sucrose feeding results in synthesis of all three storage carbohydrates. Whatever sugar is supplied to mycorrhizas, host sugars incorporate little radioactivity and dissection shows that 70% of the activity, following long term glucose feeding, remains in the sheath and, of the 30% in the core, most is in fungal metabolites of the Hartig net. When fed separately, core tissue more closely resembles the behaviour of uninfected roots.From the totally different destinations of the two hexoses in mycorrhizas, it is concluded that the fungus, unlike host tissue, has a restricted ability to interconvert hexoses. From experiments with high specific activity [^^cjglucose supplied to mycorrhizas in tracer quantities, it appears that alternative pathways of carbohydrate breakdown such as the pentose phosphate cycle and Entner-Doudoroff scheme may possibly be operative in addition to glycolysis and so supplement the breakdown of sugars to the level of pyruvate.

Fungal Polyol Metabolites in the Control of Carbohydrate Metabolism of Mycorrhizal Roots of Beech

“…4 is possibly confirmed by the observations of Lewis and Harley (1965b) where [^'^CJsucrose was supplied to excised mycorrhizal roots under two conditions. In one group, the sheath and core remained intact during sucrose uptake and were then separated and analysed separately.…”

“…In the studies of Lewis and Harley (1965b), uninfected roots tended to incorporate a lower proportion of sucrose supplied into 'insoluble' forms than did mycorrhizal roots. Interpretation of this fact is complicated by the synthesis of glycogen and protein by the fungus, and no direct evidence on the effect of mannitol on starch synthesis in uninfected beech roots is available.…”

Trehalose synthesis in mycorrhiza of Norway spruce: an indicator of vitality

“…Excised mycorrhizae of beech have been shown to convert glucose and fructose into the fungus specific metabolites trehalose and mannitol, respectively (LEWIS and HARLEY 1965;HARLEY and SMITH 1983;MARTIN et al 1985;MARTIN et al 1988). We are testing here if these activities can be used to develop a vitality test for ectomycorrhizae of Norway Spruce.…”

Observations on the Mycorrhizas of Forest Trees. II. The Rhizosphere of Pinus Radiata D. Don

“…It is apparent that a close nutritional relationship exists between the two organisms. Mannitol is one of the carbohydrates used by bacteria, and Lewis and Harley (1965a, 1965b, 1965c showed that beech mycorrhiza secrete this substrate. Hassouma and Wareing (1964) found that in the presence of mannitol rhizosphere bacteria could fix nitrogen.…”