Is there any significant difference between -20°C and -80°C stored biological samples (i.e. Plant tissues for proteins, mRNA and metabolite extraction)?
I think there is no significant difference in the short term (three months) for RNA and protein extraction. May be have differences for metabolite extraction.
Metabolites start being altered after a month at −20 C° (based on urine metabolites, there must be similar impact on plants metabolites). −80 °C is usually considered as the most convenient for the long-term storage condition. Therefore, i suggest store the samples at -80 °C for metabolome anlaysis.
Yes of course, you need to store your biological samples in different temperature, for the extraction of total ARNm or DNA (-80°) and -20° for the extraction of proteins for exemple.