The function of phytochrome A

Knowledge of the photoperceptive function of phytochrome A has improved substantially thanks to the availability of mutants lacking phytochrome A and transgenic plants transformed with the PHYA gene in sense or antisense orientation. In imbibed seeds, phytochrome A mediates very-low-fluence responses, In etiolated seedlings, phytochrome A mediates very-low-fluence responses, high-irradiance responses under continuous far-red light, responsivity amplification to phytochrome B and red-light enhancement of the phototropic response to blue light, In light-grown seedings, phytochrome A modulates the extent of response to reductions in red/far-red ratio perceived by phytochrome B, perceives daylength extensions and night interruptions affecting flowering, and perceives light treatments resetting endogenous rhythms, Under natural radiation these abilities are manifested during seed germination and seedling de-etiolation under dense canopies or extremely low light fluences, and during early neighbour detection, but other processes await experimental evaluation, Phytochrome A affects growth and development throughout the whole life cycle of angiosperms.