The absorption of UV light by nucleic acids arises from n!p* and p!p* transitions of the purine (adenine, guanine) and pyrimidine (cytosine, thymine, uracil) bases that occur between 260 nm and 275 nm. 

TLS Online TPP Program

#Id: 9852

#Unit 6. System Physiology – Plant

Blue light depolarizes membrane of hypocotyl cells and inhibits of growth rate.

This membrane depolarization is caused by the activation of anion channels, which facilitates the efflux of anions such as chloride.

TLS Online TPP Program

#Id: 9853

#Unit 6. System Physiology – Plant

an anion channel blocker, NPPB (5-nitro-2-[4-phenylbutylamino]- benzoate), prevents the blue light–dependent membrane depolarization and decreases the inhibitory effect of blue light on hypocotyl elongation.

TLS Online TPP Program

#Id: 9854

#Unit 6. System Physiology – Plant

Phototropins (phots) are involved in directing organ, chloroplast, and nuclear movements, solar tracking, and stomatal opening

TLS Online TPP Program

#Id: 9855

#Unit 6. System Physiology – Plant

In Mougeotia, the photoreceptors regulating chloroplast movement consist of a fusion between phytochrome and a phototropin known as neochrome, and show typical bilin binding as well as red/far-red reversibility.

TLS Online TPP Program

#Id: 9856

#Unit 6. System Physiology – Plant

Mougeotia appears to have evolved the ability to exploit red light as a signal to induce a response (chloroplast movement) that is typically mediated by blue light.

TLS Online TPP Program

#Id: 9857

#Unit 6. System Physiology – Plant

phot1 is the primary phototropic receptor mediates phototropism in response to low and high fluence rates of blue light. 

phot2 mediates phototropism in response to high light intensities