The thick ascending limb of the loop of Henle is the site of action of the powerful “loop” diuretics.

TLS Online TPP Program

#Id: 4955

#Unit 6. System Physiology – Plant

Phytochrome is most heavily concentrated in the regions where dramatic developmental changes are occurring: the apical meristems of the epicotyl and root.

TLS Online TPP Program

#Id: 4957

#Unit 6. System Physiology – Plant

very-low-fluence responses (VLFRs), low-fluence responses (LFRs), and high-irradiance responses (HIRs).

TLS Online TPP Program

#Id: 4958

#Unit 6. System Physiology – Plant

Phytochrome responses can be distinguished by the amount of light required to induce them. The amount of light is referred to as the fluence, which is defined as the number of photons impinging on a unit surface area. 

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#Id: 4959

#Unit 6. System Physiology – Plant

In addition to the fluence, some phytochrome responses are sensitive to the irradiance, 2 or fluence rate, of light. The units of irradiance in terms of photons are moles of quanta per square meter per second (mol m–2 s–1).

TLS Online TPP Program

#Id: 4960

#Unit 6. System Physiology – Plant

Phytochrome responses fall into three major categories based on the amount of light required; very-low-fluence responses (VLFRs), low-fluence responses (LFRs), and high-irradiance responses (HIRs).

TLS Online TPP Program

#Id: 4962

#Unit 6. System Physiology – Plant

Induction-Reversion Responses or, Low Fluence (LF) Responses

Examples include:

Light-sensitive seed germination;

Many seeds require light for germination (like lettuce), whereas others are inhibited by light (wild oats, Phacelia, Royal Paulownia). Phytochrome presumably stimulates GA synthesis/release which in turn, stimulates the mobilization of stored reserves