Hello. I can answer the part of seeds. If you are working with longevity of seeds I strongly recommend the ISTA procedures (type that on Google). ISTA is an Agency who works on ageing and conservation of seeds for different purposes and brings procedures so as to minimise the lab effects and so on for companies and researchers. You can find almost all the crop species and even a lot of forestry species there.

If you want to know further about longevity and deterioration, there is a bibliographic paper called Seed deterioration: physiology, repair and assessment from MB McDonald (1999) published in Seed Science Technology 27, 177–237.

I can not give to you a real backed answer for the buds, but interpreting the stems produced from an in-vitro essay could give you a possible overview of the state of the meristems (for example, were you to find some kind of mutations it would indicate deterioration of the primary meristem). Good luck!

@Yang Li,  Alberto  gave you detailed answer, I just can add that if you need to compare longevity of seeds for 2 or > genotypes, you can try artificial aging of seeds.

Thank you very much@Alberto Arnal Olivares@Alex Ignatov.  your's anwers help me a lot.   

Dear Sir

Attached to this e-mail there is a document that may interest you.

Best regards.

Walter

Dear sir,

Don't forget to associate to seed longevity with the management of temperature and relative humidity. They are closely linked to the viability of the seeds.

Regards,

Roland

Ec of extract 

or determine the prevailed chemical compound in any given seeds

Tetrazolum Formazan  test Respiration