ABA is transported by both the xylem and the phloem, but it is normally much more abundant in the phloem sap

TLS Online TPP Program

#Id: 4947

#Unit 6. System Physiology – Plant

Expression of the other phytochrome types (B to E in angiosperms) is independent of light and both Pr and Pfr forms are stable.

TLS Online TPP Program

#Id: 4948

#Unit 6. System Physiology – Plant

Phytochrome B (PhyB) is probably the photoreceptor involved in shade detection and avoidance. This response allows many species to greatly increase their stem extension rate when they become shaded by competitors.

TLS Online TPP Program

#Id: 4949

#Unit 6. System Physiology – Plant

PHY genes encode two types of phytochrome

TLS Online TPP Program

#Id: 4950

#Unit 6. System Physiology – Plant

PHYA is the only gene that encodes a Type I phytochrome. Phytochrome A predominantly perceives far-red light.

TLS Online TPP Program

#Id: 4951

#Unit 6. System Physiology – Plant

Phytochrome B predominantly perceives red light, both phyD and phyE help mediate the shade avoidance response—a response mediated primarily by phyB.

TLS Online TPP Program

#Id: 4952

#Unit 6. System Physiology – Plant

phyB, phyD plays a role in regulating leaf petiole elongation, as well as in flowering time.