I have always believed that plants were immortal. That given the right conditions and absence of disease, they will live forever. A few months back, someone expressed amazement at the fact that our tomato plant has survived for so long. Since the seeds were the type you can get commercially for under RM2, it is believed that they have a limited life span.
Initially I found it hard to believe. Then suddenly one by one the branches started drying up for no apparent reason. Adding more organic soil or fertilizers did not help at all. Eventually it was no more. So I guess there may be some truth to it (either that or I messed up somewhere... its easier to blame plant genetics in this case).