Ultrastructure of soybean nodules. II: deterioration of the symbiosis in ineffective nodules

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Abstract
Ineffective nodules, formed on Clark-63 soybeans by Rhizobium japonicum strain 8-0 (Iowa), and effective nodules, formed on Clark-63 soybeans by strain 138 (U.S.D.A.), have been examined by electron microscopy at 10–12, 16, and 21 days after seed inoculation. Though strain 8-0 bacteria are able to infect the host cells in a normal manner, infection is followed closely by a progressive deterioration of the symbiosis involving selective autolysis of host cell contents and degeneration of the intracellular bacteria. The host cells, though disrupted, apparently survive the destruction of the bacteria. The observed ultrastructural changes suggest either a suddenly manifested incompatibility between host and rhizobia, or an acute, localized, nitrogen starvation in the infected cells.