Nodule Structure and Functioning in Chickpea (Cicer Arietinum) as Affected by Salt Stress

Cicer arietinum L. plants raised in sand culture under natural light were subjected to salinity stress induced by mixture of NaCl, CaCl₂, MgCl₂ and MgSO₄ (40, 60 or 80 meq dm^-3). Acetylene reduction activity (ARA) of nodules, leghemoglobin content and nodule structure were followed 55, 75 and 85 d after sowing. ARA declined significantly under salt treatments and the lowest ARA was observed at day 85 after sowing. Decrease in ARA was consistent with decreased nodule leghemoglobin content. The leghemoglobin content of control plants decreased by 50 % at day 85 indicating senescence of nodules. This senescence was further accelerated by salt treatment after which the leghemoglobin content fell to negligible levels. The structural changes associated with salt stress were mainly reduction in size of the nodules, decreased meristematic zone, reduced number and degradation of symbiosomes, reduced intercellalar spaces and deposition of electron dense material in the intercellular spaces in the cortex of nodules.