Expression of MtGS2 in effective and ineffective root nodules. A, Total RNA (15 μg lane−1) isolated from nodules inoculated with S. meliloti, wild-type (WT), fixJ, and nifH mutants, and from noninoculated roots was fractionated on formaldehyde-agarose gels followed by RNA-blot hybridization using a 32P-labeled GS2 fragment (MtGS2) and an rRNA gene fragment (rRNA). B, Total soluble protein extracted from roots and nodules produced by S. meliloti, wild-type (WT), fixJ, and nifH mutants (30 μg lane−1) was fractionated by SDS-PAGE and transferred to nitrocellulose, and the membrane was probed with a GS antibody. GS1, GS2, and preGS2 refer to the cytosolic, plastid, and plastid precursor GS, respectively. Molecular masses are indicated.