Evaluation of DNA integrity as a potential marker to detect aging in soybean (Glycine max) seeds
Seed aging is a complex process that includes degradation of macromolecules, such as DNA. Evaluation of DNA deterioration in asymptomatic stages of seed aging may help the development of improved methods for monitoring long-term conserved seeds. We examined DNA integrity in artificially aged soybean (Glycine max) seed lots using cytogenetics, quantitative polymerase chain reaction (qPCR), and random amplified polymorphic DNA (RAPD). Freshly harvested soybean cultivar BRS 7980 seeds were dried and kept at 10oC in a dry room until the analyses. Six lots of 450 seeds were artificially aged (42°C, 100% relative humidity) for 6, 12, 24, 48, 72 or 96 h to obtain lots with different germination capacities. One unaged seed lot (0 h) was used as a control. Germination of aged lots varied from 12 to 86% at 96 and 6 h of aging, respectively. Cytogenetic data did not characterized aged seed. DNA integrity among seed lots was also evaluated based on the comparison of frequencies of three fragments amplified using an anchored variable-length primer set. Fragments of 86 and 193 bp had similar frequencies, while the largest one (491 bp) showed greater variation among samples. Data suggested different fragment frequencies were due to variation in the number of intact templates among lots, which might have been caused due to the fact that shorter DNA sequences have a smaller probability of developing random breaks than larger ones. RAPDs confirmed the differences in template amount detected using qPCR and variation in DNA repair capacity among aged lots. Though some seed lots were characterized using physiological parameters, most of them could not be characterized based on cytogenetic and molecular data, suggesting that these tests might not be ideal to detect aging in soybean seeds.