Consequences of accelerated aging for DNA integrity and seed germination of cowpea
Deterioration and loss of seed germination in the germplasm are related to the aging that occurs during the conservation process. The mechanisms related to the aging and death of seeds are not yet fully understood, but it is known that longevity can be affected by moisture content and temperature. We examined the effects of accelerated aging (A.A.) on the DNA of seeds of three different cultivars of cowpea (Vigna unguiculata) and compared the data to data from vigor and germination tests. The DNA of A.A.-seeds of BR 17 Gurgueia, BRS-Marataoã and BRS-Guariba cowpea cultivars were extracted and subjected to agarose gel electrophoresis. The increase in temperature, relative humidity and time used in A.A. culminated in a progressive and increasing degradation of seed DNA, which was expressed by continuous bands of DNA molecules with different lengths in the electrophoresis gel under all but the most extreme conditions (combinations 45°C/72 h and 45°C/96 h at 100% relative humidity) under which total disintegration of the DNA band was observed. This, in turn, was reflected in a progressive decrease in seed vigor. The combination of 35ºC/48 h was the most efficient for evaluating vigor in cowpea. The BR 17 Gurgueia and BRS-Guariba cultivars showed the highest values of vigor. A lack of DNA degradation in the laddering pattern on an electrophoresis gel is an indicator that DNA degradation and cell death in cowpea seeds did not occur by apoptosis but by non-programmed processes, such as Maillard reactions, lipid peroxidation and hydrolysis of sugars.