how plants know when autumn is? Or how they know know when to do seasonal things?

Question

how plants know when autumn is? Or how they know know when to do seasonal things?

In: Biology

Answer 1

Plants measure the duration of uninterrupted hours of darkness using phytochromes. Plants that flour in the summer (long day plants) need short nights and long days to trigger flowering. Plants that flower in winter/autumn need long nights and short days to flower.

There are 2 different phytochromes, Pr and Pfr. Pr, absorbs red light (r=red) and Pfr absorbs far red light (fr= far red). During day light Pr is converted into Pfr quickly and at night Pfr is converted back into Pr at a slowly.

Short day plants need consistently low levels of Pfr which is brought about by long nights. On the other hand long day plants need high levels of Pfr which is brought about with long days and short nights.

I hope this is a good explanation