CYTOGHROME OXIDASE IN MYCORRHIZAL AND UNINFEGTED ROOTS OF FAGUS SYLVATICA

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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.

Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Carbohydrate Physiology of Mycorrhizal Roots of Beech

Harley¹

1965

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“…Uninfected, that is, nonmycorrhizal, roots were obtained from beech saplings grown in sand culture essentially according to the method of Harley and ap Rees (1959).…”

Section: Methodsmentioning

confidence: 99%

Carbohydrate Physiology of Mycorrhizal Roots of Beech

Harley¹

1965

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115

SUMMARYThe presence of several classes of reducing substances in mycorrhizal roots of beech is demonstrated, throwing considerable doubt on the values of 'easily soluble reducing substances' which have been used for correlation with degree of mycorrhizal infection by several workers. The soluble sugars of beech mycorrhizas are glucose, fructose, sucrose and trehalose, together with the acyclic polyol, mannitol and two cyclic polyols, myo-inositol and an unidentified inositol. Trehalose and mannitol are absent from uninfected roots showing their presence to be dependent on fungal infection. Methods for the individual assay of the soluble carbohydrates are presented. The main sugars obtained by acid hydrolysis of the insoluble residue of mycorrhizas are galactose, glucose, mannose, arabinose, xylose, fucose, ribose, rhamnose and a deoxypentose provisionally identified as deoxyribose. The mannose and deoxypentose polymers are absent from beech tissue and deoxyhexose polymers from the fungus. Much of the glucose is derived from fungal glycogen. Mycorrhizas accumulate principally trehalose and glycogen from exogenous glucose and trehalose, and mannitol from fructose and mannitol. The pattern of synthesis from exogenous sucrose is intermediate between glucose and fructose. The results are compared with those obtained for other fungi by other workers and a possible ecologically significant role for mannitol is suggested.

“…l-r. and Neurospora crassa Shear and Dodge (Boulter and Hurst i960) and by mycorrhizal roots of Fagus sylvatica L. (Harley et al, 1956) must be through a system other than cytochronie oxidase but such evidence is not conclusive (Darby and Goddard, 1950b;Smith and Chance, 195S). Harley and ap Rees (1959) suggested that the fungal component of beech mycorrhizas contains a cytochrome system wbich, in the presence of inhibitors, diverts electron transfer through a non-phosphorylating by-pass around the inhibited oxidase. Such a system would be similar to cytochrome bj of aroids (Beevers, 1961;Hackett, 1963).…”

Section: Terminal Oxidasesmentioning

confidence: 99%

A Theoretical Study Relating the Concentration and Diffusion of Oxygen to the Biology of Organisms in Soil

Griffin

1968

SUMMARYSome components necessary for the eventual construction of a general model relating the concentration and diffusion of oxygen to the ecology of soil organisms are elaborated from biochemical and physical data and concepts. From the analyses and discussions presented, tentative conclusions can be drawn concerning some of the factors involved in the relationship between oxygen and soil ecology.