RNases and nucleases in embryos and endosperms from naturally aged wheat seeds stored in different conditions.

Temperature and moisture content are particularly important factors influencing the longevity of seeds, and therefore the ageing of seeds is closely tied to storage conditions. The ageing process is characterised by many physiological and biochemical changes: membranes tend to leak, enzymes lose catalytic activity, and chromosomes accumulate mutations. Since viability loss is also associated with the breakdown of nucleic acids, the aim of the study was to determine whether the damage induced by ageing could be associated with changes in the activity of RNases and nucleases in embryos and endosperms of differently stored wheat seeds. In order to better characterise seed conditions, the damage to membranes during seed ageing was evaluated by measuring the conductivity of the soaking solution during imbibition, and by using the Evans Blue colorant; lipid peroxidation was also recorded. RNases and nucleases were studied by SDS-PAGE and activity staining. Ageing of seeds stored in a dry state involved a progressive loss of membrane integrity, which increased with the degree of ageing, while lipid peroxidation remained unchanged. Changes in nucleolytic enzyme activity were recorded in embryos: a decrease in RNases and an increase in nucleases. In the endosperm compartment there were no significant differences in ribonuclease and nuclease patterns during seed ageing. Moreover, neutral RNases were absent in endosperms of dry seeds and were activated following imbibition. Present studies reveal that embryos and endosperms have different enzymatic patterns, thus highlighting that the two seed compartments age independently. A different nucleolytic pattern was present in seeds of comparable viability and membrane damage, which were stored differently, and nuclease metabolism was subject to regulation according to both ageing and the length of the storage period.