Inter-nucleosomal DNA fragmentation and loss of RNA integrity during seed ageing

The germination of viable seeds is the basis for new plant growth and development. Seeds lose viability during storage, but the biochemical mechanisms of seed death are not fully understood. This study aimed to investigate degradation patterns of nucleic acids during seed ageing and subsequent water uptake. Seeds of Pisum sativum L. were artificially aged at 50 C and 12 % seed water content (WC). Nucleic acids degradation was studied during ageing and during imbibition of four seed lots with differential viability from highly viable to dead. As seeds lost viability during ageing, DNA was gradually degraded into internucleosomal fragments, resulting in DNA laddering, in conjunction with disintegration of 18S and 28S rRNA bands. During imbibition, non-aged controls had high levels of DNA and RNA integrity through to radicle protrusion. In an aged seed lot with 85 % total germination (TG) DNA fragmentation decreased upon imbibition probably due to nucleosome degradation, while rRNA integrity did not improve. In an aged seed lot with 44 % TG, neither DNA nor rRNA integrity improved upon imbibition. Dead seeds showed DNA degradation as laddering throughout imbibition along with extensive degradation of rRNA. We present a model in which interlinked programmed and non-programmed events contribute to seed ageing, and suggest that protection of nucleic acids during ageing is key to seed longevity

Mathematically combined half-cell reduction potentials of low-molecular-weight thiols as markers of seed ageing

The half-cell reduction potential of the glutathione disulphide (GSSG) / glutathione (GSH) redox couple appears to correlate with cell viability and has been proposed to be a marker of seed viability and ageing. We investigated the relationship between seed viability and the individual half-cell reduction potentials (Eis) of four low-molecular11 weight (LMW) thiols in Lathyrus pratensis seeds subjected to artificial ageing: GSH, cysteine (Cys), cysteinyl-glycine (Cys-Gly) and -glutamyl-cysteine (-Glu-Cys). The standard redox potential of -Glu-Cys was previously unknown and was experimentally determined. The Eis were mathematically combined to define a LMW thiol-disulphide based redox environment (Ethiol-disulphide). Loss of seed viability correlated with a shift in Ethiol-disulphide towards more positive values, with a LD50 value of -0.90 0.093 mV M (mean SD). The mathematical definition of Ethiol-disulphide is envisaged as a step towards the definition of the overall cellular redox environment, which will need to include all known redox-couple