Hormone-mediated plant responses to light quality and quantity

Light is the energy source for photosynthesis and the key environmental factor for a plant's life processes from seedling development to vegetative growth and flowering, including chlorophyll production, phototropism, photoperiodism, photomorphogenesis, and circadian rhythms. During daylight hours, plants must adjust to changes of several orders of magnitude in light quantity and quality. Excessive variations in light quality and quantity, however, can harm plants causing photodamage and photoinhibition of the photosynthetic apparatus. Fluctuations in hormone levels and signaling are commonly used to respond to light conditions by generating appropriate alterations in growth and development. Because of their significance as growth and developmental regulators, as well as their crucial role in controlling photosynthesis, phytohormones play a critical role in developmental processes ranging from organogenesis to senescence. Phytohormones are also instrumental in protecting the photosynthetic system during stress. In this comprehensive review of the current literature, we aim to provide a detailed picture of the various light-regulated processes, the harmful effects triggered by excess light, and the mechanisms developed by plants to cope with such stress. By reexamining well-established linkages between light perception and hormone changes, we also provide fresh insights into the processes that allow plants to flourish under fluctuating light conditions.