<Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> bacteroid appendages expressed in senescing and argon-treated soybean nodules

Bradyrhizobium japonicum bacteroids in soybean nodules expressed fibrillar appendages during senescence. In both scanning and transmission electron microscopy (SEM and TEM), these structures were observed to connect adjacent bacteroids, and bacteroids to symbiotic membranes. They were 20–25 nm in diameter, 100–2,500 nm in length and were linear, branched, or part of a web-like matrix. Bacteroids expressing appendages were not uniformly distributed, but were abundant within localized regions in the senescing nodule. The root systems of nodulated greenhouse-grown plants flushed with argon induced the appendages at earlier plant ages, and they were more prolific and wide spread than those in untreated nodules. Bradyrhizobium japonicum symbiotic appendages appear to be a response to an environmental niche within senescing nodules.