The relation between Einstein theory of relativity and photosynthesis
E = MC^2
The speed of light determines the number of photons incident up on the dorsal surface of a green leaf in unit time.
If the speed of light were ten percent of it's current value a plant would not get enough sunlight ( i.e. photons per unit time and it would not be able to perform photosynthesis ).
So the speed of light is coupled with process of photosynthesis in green plants.
agree or disagree ?
This is wrong.
First, E=mc² is irrelevant, as it does not apply to light, for which m = 0 . The full expression is E²= (mc²)² +p²c². For massless photons the first term is zero and we are left with E=pc, which by de Broglie's relation is equivalent to E=hν, Planck's relation between the energy of a photon and its frequency.
Second, the energy per unit time depends on the intensity of the light, i.e. number of photons arriving per unit time. This has nothing to do with their speed, only with the number emitted per unit time in the direction of the object in question. (If light travelled more slowly there would just be more in transit - it would not affect the intensity.)
What you could argue is that if light travelled more slowly the energy per photon would be less and therefore it would not be absorbed by chlorophyll and for that reason would be able to support photosynthesis.