Reproduction

sexual reproduction-  by fusion of two gametes

Isogamous (Spirogyra), Anisogamous (Chlamydomonas) or Oogamous (Volvox).

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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.

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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

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Phototropin receptors are associated with the plasma membrane, where they function as light-activated serine/threonine kinases.

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Phototropin contains two light-sensing LIGHT-OXYGEN-VOLTAGE (LOV) domains, LOV1 and LOV2, each binding a chromophore flavin mononucleotide (FMN).

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In the dark, the maximum absorption of the FMN chromophore is around 450 nm. 

Blue light induces the formation of a covalent bond between FMN and a cysteine residue, shifting the absorption maximum to 390 nm via a LOV660 intermediate form. The reaction is reversible in darkness.

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LOV2 domain is essential for blue light–induced kinase activation and autophosphorylation of the phototropin photoreceptor.