Understanding the Role of Light in Seed Germination: A Comprehensive Review

Seed germination is an important stage in the plant's life cycle, and light is a key factor in regulating this stage. The regulation of seed germination by light is an intricate process that is governed by a range of photoreceptors and signaling pathways. Photoreceptors, which include phytochromes, cryptochromes, and phototropins, are the major sensors in seeds that detect and transduce light signals. These photoreceptors regulate the expression of various sets of genes, resulting in the activation or repression of germination related activities. The phytochrome system, which consists of various phytochrome species such as phyA, phyB and phyC acts critically in controlling the seed germination in response to varying light conditions. Phytochromes break seed dormancy, promote endosperm weakening, and mobilize store reserves during germination. Cryptochromes, another form of photoreceptor, are largely involved in blue light perception and have been found to influence seed germination through numerous processes, including the modulation of hormonal pathways, such as those involving gibberellic acid (GA) and abscisic acid (ABA). In addition to the photoreceptors, there are various upstream and downstream signaling components, such as transcription factors, protein kinases, and hormonal regulators, that contribute to the complex network that regulates light induced seed germination. Photoregulation of seed germination is the process by which light, as perceived by specialized photoreceptors known as phytochromes, regulates the transition of a quiescent dry seed to a metabolically active state, thereby commencing the germination process. Different wavelengths of light, red (R) and far-red (FR) light, used to regulate seed germination through the phytochrome, and used in environment signals for promoting the germination. This review examines the current state of knowledge regarding the molecular mechanisms that govern the photoregulation of seed germination. It delves into the intricate among between photoreceptors, signaling pathways, and environmental cues that play a crucial role in this process. Moreover, it explores the possible implications of this research in enhancing agricultural practices and devising strategies for maximizing crop yields.