The Azolla-Anabaena azollae relationship. XIV. Chemical composition of the association and soluble carbohydrates of the association, endophyte-free Azolla, and the freshly isolated endophyte

Grown under controlled conditions with dinitrogen as the sole N source, the Azolla caroliniana-Anabaena azollae association exhibited a doubling time of 2.3 +/-0.2 days. Dry matter content was 5.2 +/-0.2% of the fr. wt. and contained 41.2 +/-0.3% C and 5.2 +/-0.1% N. Other dry wt. analyses yielded about 32% crude protein (N X 6.25), 17% Lowry protein, 23% total sugars, 14% neutral sugars, and 9% minerals. The water soluble carbohydrate content of the association was determined and compared with that of endophyte-free Azolla. The total sugars/g FW of the endophyte-free plants grown with nitrate or ammonium as the sole nitrogen source were consistently significantly higher than the total sugars/g FW of the association grown on dinitrogen alone or on dinitrogen with nitrate. The water soluble carbohydrates obtained from each of these sources and from the endophyte isolated from the dinitrogen grown association were fractionated into three size groups roughly corresponding to large polysaccharrides, smaller polysaccharides and oligosaccharides other than disaccharrides, and di-/monosaccharrides. Gas-liquid chromatography analysis revealed that the sugars in the individual fractions were qualitatively similar in all cases. In the examples shown, the association grown on dinitrogen alone contained 1 mg total sugars/g FW, the association grown on dinitrogen and nitrate 1.2 mg/g FW, the endophyte-free Azolla grown on nitrate 1.5 mg/g FW and the endophyte-free grown on ammonium 1.9 mg/g FW. The increase in the soluble sugar content of the endophyte-free plants appears to be at least in part attributable to an increase in the mono- and dissacharrides, especially sucrose. Relative to the association, this fraction from the endophyte-free Azolla accounted for a significantly greater proportion of the total sugars. This finding is consistent with a prior study (Kaplan and Peters, 1988) which revealed that the fern provides the endophyte with sucrose in the symbiotic association.