When to meet senesce?

什么时候会老？

Chillness intensified the senesce of leaves, enhanced the MDA content and the O2-. produce rate, this was more evident in Shanyou63.

低温处理加剧叶片的老，使得MDA含量和O2-产速率上升，两优培九的升幅较汕优63小。

But hang on -- how do we know that radioactive atoms don't senesce?

但是，听清—们怎么知道放射性原子不老？