I started looking for the photoreceptor for phototropism in 1957  (believe it or not), and have been searching on and off every since.  We were only successful when we could apply the powerful tools of  molecular genetics to the problem.

Frankly I am surprised that it is one of the most cited recent papers! I suspect that the paper is highly cited because it describes biophysical properties of an entirely new photoreceptor module with unique photochemical properties within the new class of plant photoreceptors we recently characterized, namely the phototropins. It has attracted the attention of a fairly large number of spectroscopists all of whom have wonderful instruments and are ever searching for a new system to exploit (something that they are doing really elegantly).

It really only elaborates on a new discovery we made a year earlier (that the protein domain that bound the light-absorbing flavin mononucleotide as chromophore carries out unique photochemistry). What the paper does do is indicate that this chromophore module and the photoreceptor protein in which it is found occurs outside of higher plants and is found in the unicellular alga Chlamydomonas reinhardtii—the ~110-amino acid chromophore-binding domain module. There are now several papers showing that this same chromophore module is found in many different proteins in a number of different micro-organisms, and at least in the mold Neurospora crassa it serves as the chromophore module for two otherwise entirely different photoreceptors responsible for responses of that fungus to blue light.

I guess the best way to summarize the finding in layman's terms is to point out that plants have photoreceptors that allow them to detect light intensity, light color, light duration (daylength) and light direction. Our discovery of the phototropins arose from our desire to characterize the photoreceptor (it had to be blue light-absorbing) that was responsible for detecting light direction and directing the plant growth in the direction of the light source. This ultimately led to our being able to characterize the chromophore module.

I started looking for the photoreceptor for phototropism in 1957 (believe it or not), and have been searching on and off every since. We were only successful when we could apply the powerful tools of molecular genetics to the problem. Again, the paper really describes some careful biophysical studies that were in themselves extensions of previous work, but the timing was such that people discovering similar chromophore domains in other proteins would likely cite this paper.