aa motif / Coiled-coils

Two helices are wound around each other

Alpha-helices are packed together through the hydrophobic interactions

These two helices are found to be stable in solution

They are generally found in transcription factors and intermediate filaments

They have heptad (7 amino acid) repeated sequences


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#Unit 6. System Physiology – Plant

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

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#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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#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).

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#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).

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#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

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#Unit 6. System Physiology – Plant

Light-sensitive seed germination;

This provides energy for the germinating seed and also decreases the solute potential for water uptake necessary for providing the force for the radicle to push its way through the seed.