MORPHOGENESIS OF ROOT-NODULES IN WHITE CLOVER - II - THE EFFECT OF MUTATION IN GENES NOD IJ OF THE MICROSYMBIONT UPON THE NODULE STRUCTURE

Morphogenesis of ineffective root nodules initiated on the roots of wh ite clover 'Astra' by the Rhizobium leguminosarum biovar. trifolii str ains ANU261 (Tn5 insertion in nod I gene) and ANU262 (Tn5 insertion in nod J gene) was investigated. Following changes were observed, as com pared to the wild-type nodulation: the exaggerated, not delayed reacti on of root hairs; the delay in nodulation with the number of nodules t he same as in plants inoculated with a wild strain; the formation and organization of the nodule primordium not changed in comparison with t he wild-type nodules; infection threads abnormally branched and diffus ing with bacteria deprived of light zone and enriched with storage mat erial; infected cells of bacteroidal tissue abnormally strongly osmiop hilic and only slightly vacuolated; symbiosomes with very narrowed per ibacteroidal space, subject to premature degradation; abnormal accumul ation of starch in the nodule tissues; nodule development blocked at t he stage of laterally situated meristem and single nodule bundle; inhi bition of divisions in the meristem and vacuolation of its cells; the appearance of single cells with colonies of saprophytic rhizobia embed ded in the fibrillar matrix in the old, degraded regions of the bacter oidal tissue.