Trehalose becomes the most abundant non-structural carbohydrate during senescence of soybean nodules

Carbohydrate metabolism and symbiont survival were studied in nodules of so ybean (G, max [L.] Merr. cv. Maple Arrow infected with Bradyrhizobium japon icum 61-A-101), induced to senesce simultaneously by application of the pho tosynthesis inhibitor dichloromethyl urea (DCMU). The plant-borne carbohydr ates sucrose and starch started to decline after 2 d and reached background levels after 8 d, in parallel with the decline of nitrogenase. However, th e microsymbiont-borne disaccharide trehalose declined only by about 40% and subsequently remained at a constant level of c. 6 mg g(-1) dry weight up t o 14 d, when nodules softened and decayed. The number of re-isolated viable bacteria was not significantly decreased in senescent nodules as compared to control nodules. These results indicate that during terminal senescence of nodules an appreciable part of the bacteria conserve their trehalose poo ls and survive.