The kinetics of ageing in dry-stored seeds: a comparison of viability loss and RNA degradation in unique legacy seed collections

Abstract

Background and Aims Determining seed longevity by identifying chemical changes that precede, and may be linked to, seed mortality, is an important but difficult task. The standard assessment, germination proportion, reveals seed longevity by showing that germination proportion declines, but cannot be used to predict when germination will be significantly compromised. Assessment of molecular integrity, such as RNA integrity, may be more informative about changes in seed health that precede viability loss, and has been shown to be useful in soybean. Methods A collection of seeds stored at 5 °C and 35–50 % relative humidity for 1–30 years was used to test how germination proportion and RNA integrity are affected by storage time. Similarly, a collection of seeds stored at temperatures from −12 to +32 °C for 59 years was used to manipulate ageing rate. RNA integrity was calculated using total RNA extracted from one to five seeds per sample, analysed on an Agilent Bioanalyzer. Results Decreased RNA integrity was usually observed before viability loss. Correlation of RNA integrity with storage time or storage temperature was negative and significant for most species tested. Exceptions were watermelon, for which germination proportion and storage time were poorly correlated, and tomato, which showed electropherogram anomalies that affected RNA integrity number calculation. Temperature dependencies of ageing reactions were not significantly different across species or mode of detection. The overall correlation between germination proportion and RNA integrity, across all experiments, was positive and significant. Conclusions Changes in RNA integrity when ageing is asymptomatic can be used to predict onset of viability decline. RNA integrity appears to be a metric of seed ageing that is broadly applicable across species. Time and molecular mobility of the substrate affect both the progress of seed ageing and loss of RNA integrity.

Arabidopsis Seed Stored mRNAs are Degraded Constantly over Aging Time, as Revealed by New Quantification Methods

“…Using soybean seeds stored up to 27 years, a high correlation between the RIN of RNA isolated from cotyledons and the percentage of germination was observed, but the correlation was lower between the RIN of the RNAs from the embryonic axis and percentage of germination (Fleming et al, 2017). The authors also extended this analysis to several other plant species and observed similarly that the RNA integrity decreased during seed aging (Fleming et al, 2018a).…”

Lost in Translation: Physiological Roles of Stored mRNAs in Seed Germination

“…The RIN is an index with a value in the range one to 10 (fully degraded RNA to intact RNA) and RNA-Seq protocols typically require total RNA with a value of at least eight [82]. Analyses of seed longevity carried out using the RIN as an index in pea [83,84], soybean [85,86], carrot, crimson clover, lettuce, onion, safflower, sesame, sorghum, tomato, and watermelon [84], revealed a positive and significant correlation between seed viabilities and RIN values in most species. Moreover, the RIN decreased prior to the loss of seed viability.…”

“…Additionally, it is not easy to judge whether the seeds used are alive or dead in the dry state, since dried seeds are in a quiescent state where almost all their vital activities have been stopped. Prominent signs of seed aging appear during water-uptake for germination, but it can be costly for the seed industry and seed banks to monitor viability [84]. Degradation of stored mRNA holds the promise of being a useful indicator for predicting the loss of seed life and vigor, even though the molecular mechanisms involved in the protection and repair of damaged mRNAs remain to be elucidated.…”

Application of the MSAP Technique to Evaluate Epigenetic Changes in Plant Conservation

“…Several physiological and biochemical changes have been associated with seed ageing: reactive oxygen species (ROS) accumulation, lipid peroxidation, membrane phospholipids loss, decrease in the activity of antioxidant enzymes [ 50 , 51 ], impaired protein synthesis, protein inactivation, changes in enzyme activities, protein hydrolysis, and post-translational modifications [ 48 , 52 ], among others. ROS interact with cellular biomolecules, and can cause serious oxidative damage to proteins, nucleic acids and lipids [ 53 , 54 ]. Furthermore, some of the by-products of lipid peroxidation, such as the aldehydes malondialdehyde (MDA) and 4-hydroxy-2-nonenal (4-HNE), are highly reactive [ 55 ].…”