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SUMMARYLeek plants (Allium porrum) were grown on partially sterilized soil either inoculated (M) or not (NM) with the vesicular-arbuscular mycorrhizal fungus, Glomus mosseae. They were pulse-fed with ^"COj in an apparatus which allowed CO^ subsequently respired either by the shoots or by the roots plus soil to be separately monitored. There were three experiments. In two, plants were harvested 48 h after labelling and in the third after 214 h. At harvest, the distribution of^C between shoot,, root, soil organic matter and root washings was measured. Similar growth curves for M and NM plants were obtained by supplying extra phosphorus to the latter, so that C distributions for both treatments could be compared directly. In all three experiments, about 7 % more of the total fixed C was translocated from shoot to root in M plants compared to NM plants. In the third experiment, this extra translocate could be accounted for by increased root respiration plus increased loss of C to the soil but, despite this drain, M and NM plants had equal rates of C assimilation per unit of leaf area. However, shoots of M plants had a lower content of dry matter and hence higher assimilation rates expressed on a dry matter basis.Increased hydration is suggested as a mechanism whereby leaf area and hence C assimilation increases in mycorrhizal plants and which offsets the effects of the drain imposed by the mycorrhizas.

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fSixtio ar. Experiments were designed to determiine the signlificanlce of dark CO.. fixatioii in excised mlaize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate-14C was used to determiine the pathway anld aniounlits of CO., fixation, while leucine-'4C was uised to estimate protein synthesis in tissues aerated with various levels of CO..Organic acids were labeled fromi bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were laleled in the aminlo acid fraction and these 2 alilino aci(ls comilprised over 90 % of the 14C label in the ethanol-water insoluble residue.Studies with leuciine-14C as an indicator of protein synltlhesis in carrot slices and tomato roots showed that those tissues aerated with air iincorporated 33 % more leucine-14C into protein than those aerated with CO.)-free air. Growth BaCO:,(12).At predetermined times, the tissues were removed, rinsed with deionized water, transferred into 75 ml of boiling 100 % ethanol and boiled for 3 minutes.The ethanol was decanted and the tissues were ground 755 www.plantphysiol.org on April 27, 2019 -Published by Downloaded from