Impact of imbibition on the regulation of antioxidant metabolism in naturally versus artificially aged chickpea seeds

Declined seed nutritional and physiological quality due to long-term storage is known as seed aging. Similar mechanisms of seed aging based on oxidative stress development are proposed during both natural aging (NA) and artificial aging (AA). The similarity of oxidative stress development in NA versus AA and its exacerbation after imbibition were investigated by analyzing the antioxidant metabolism of aged chickpea (Cicer arietinum L.) seeds before and after imbibition phase I. Both NA and AA increased electrolyte leakage, compromised seed viability and germination, as well as embryonic axis superoxide anion production and seedling competency for reserve utilization. Aging increased oxidative stress, and imbibition further exacerbated it. Consequently, imbibed aged seeds displayed greater lipid peroxidation and hydrogen peroxide levels. Both NA and AA were associated with decreased ascorbate content, but in NA proline decreased while in AA it increased, at least at initial stages, implying differential responses of non- enzymatic antioxidants in NA versus AA. Imbibition, however, increased ascorbate and decreased proline regardless of the aging treatment, possibly to combat the rise in oxidative stress. Despite different responses of enzymatic antioxidants to NA and AA, imbibition enhanced their activities regardless of the aging process. Patterns of antioxidant enzyme activity were more consistent with the corresponding gene expression patterns following imbibition of aged seeds. Thus, NA and AA differentially influence the antioxidant metabolism of chickpea seeds. The enhanced and more integrated antioxidant metabolism observed in aged seeds after imbibition may be viewed as a response to the increased oxidative stress they experience.