CCG and CGG are the rarest trinucleotides in most A+T-rich bacterial genomes and CTAG is the rarest tetranucleotide in G+C-rich bacterial genomes.

TLS Online TPP Program

#Id: 4985

#Unit 6. System Physiology – Plant

The ratio of red light (R) to far-red light (FR) varies remarkably in different environments. This ratio can be defined as follows:

TLS Online TPP Program

#Id: 4986

#Unit 6. System Physiology – Plant

Phytochrome is that it enables plants to sense shading by other plants. Plants that increase stem extension in response to shading are said to exhibit a shade avoidance response.

TLS Online TPP Program

#Id: 4988

#Unit 6. System Physiology – Plant

As shading increases, the R:FR ratio decreases.

TLS Online TPP Program

#Id: 4989

#Unit 6. System Physiology – Plant

The greater proportion of far-red light converts more Pfr to Pr, and the ratio of Pfr to total phytochrome (Pfr/Ptotal) decreases.

TLS Online TPP Program

#Id: 4991

#Unit 6. System Physiology – Plant

When stimulated natural radiation was used to vary the far-red content, it was found that for so-called sun plants, the higher the far-red content (i.e., the lower the Pfr:Ptotal ratio), the higher the rate of stem extension.

TLS Online TPP Program

#Id: 4992

#Unit 6. System Physiology – Plant

For a “sun plant” or “shade-avoiding plant” there is a clear adaptive value in allocating its resources toward more rapid extension growth when it is shaded by another plant.