This paper reviews the results obtained in studies of the extracellular polysaccharides, lipopolysaccharide-protein complexes, polysaccharide-lipid complexes, lipopolysaccharides, and O-specific polysaccharides from bacteria of the genus Azospirillum. On the basis of present knowledge, the possible roles of the extracellular polysaccharides and polysaccharide-containing complexes of azospirilla in interaction with the roots of plants are discussed. Some pieces of evidence are considered in light of the lectin hypothesis originally proposed for the legume-Rhizobium symbiosis. In the context of these views of Azospirillumcereal associative pairs, a key process at the early stages of the interaction is the specific reaction of cereal root lectins with the extracellular polysaccharide components, containing N-acetyl-D-glucosamine as part of their structure. z

It was shown that Azospirillum brasilense strains Sp7, Sp107, Sp245, and S17 when cultivated in a liquid synthetic malate medium to the end of the exponential phase of growth, produced at least two complex polysaccharide‐containing components. The components were arbitrarily called lipopolysaccharide‐protein complex and polysaccharide‐lipid complex. These complexes were shown to interact with a wheat germ agglutinin. From polysaccharide‐lipid complexes, acidic polysaccharides were isolated and their specific rotation, molecular masses, affinity for wheat germ agglutinin, and monosaccharide composition were determined. The polysaccharides of all strains contained rhamnose, galacturonic acid, and glucosamine, while the polysaccharides of strains Sp7 and S17 included additional fucose and mannose, respectively, and both had galactose. It is suggested that lipopolysaccharide‐protein complexes, polysaccharide‐lipid complexes, and polysaccharides may be involved in the process of interaction of azospirilla with wheat root surfaces.

The spectra are discussed and many assignments made from considerations of the bond anisotropies. Double resonance provided some checks and gave IJgeml for the a-methylene protons of hexahydropyrrolizine.Over the range -70 to +190" hexahydropyrrolizine exists mainly, if not entirely, in the cis-fused form. The 3-endo-methyl derivative, however, shows rapid nitrogen inversion at room temperature, and only below -60" does it exist predominantly in the cis-fused form. Incidentally, the configurations of the two stereoisomers of 3-methylhexa hydropyrrolizine were confirmed.The shielding of the methyl group in hexahydropyrrolizine methiodide is compared with that in the methiodides of cisand trans-octahydroindolizine and of trans-octahydroquinolizine.MOLECULAR models (of various types) suggest that in simple hexahydropyrrolizines (I) the rings are cis-fused. This configuration is free of strain and rather flexible, allowing interconversion between ' unfolded ' (Ia) and ' folded ' (Ib) conformations, through a ' half-folded ' conformation (not shown). A Courtauld model of (Ia) is sufficiently flexible to suggest that pseudo-rotation occurs in each ring. In contrast, the trans-fused system (Ic) is rigid and perhaps strained. Nevertheless tram-9 R (I) [exo-bonds (x), solid; (IV) R = H (or D) endo (n), dotted] (V) R = Me, X = I (11) 3x-Me (111) 3n-Me (3,5,8 = a-positions; 1,2,6,7 = /3-positions) 1 (Ia) ( I d (Ia) cis-I-Iexahydropyrrolizine system, unfolded ' conform-(Ib) cis-Hexahydropyrrolizine system, ' folded ' conformation * (Ic) trans-Hexahydropyrrolizine * ation * * The dotted line represents the lone electron pair orbital or h-H(9) or h-C(9) bondring juncture is possible, as has been demonstrated in some annelated quaternary derivatives ,l and the models of simple hexahydropyrrolizine do indicate that cis-trans interconversion should be possible through nitrogen inversion. of simple hexahydropyrrolizines has not been verified by any physical method and so we have studied the system by lH n.m.r. over a temperature range.

This paper reviews the results obtained in studies of the extracellular polysaccharides, lipopolysaccharide-protein complexes, polysaccharide-lipid complexes, lipopolysaccharides, and O-specific polysaccharides from bacteria of the genus Azospirillum. On the basis of present knowledge, the possible roles of the extracellular polysaccharides and polysaccharide-containing complexes of azospirilla in interaction with the roots of plants are discussed. Some pieces of evidence are considered in light of the lectin hypothesis originally proposed for the legume-Rhizobium symbiosis. In the context of these views of Azospirillumcereal associative pairs, a key process at the early stages of the interaction is the specific reaction of cereal root lectins with the extracellular polysaccharide components, containing N-acetyl-D-glucosamine as part of their structure.

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