Abstract

In the developing seedling light quality, quantity, and duration strongly influence establishment. A rich history of reports clearly show that red, blue and far-red light have specific effects that control the processes in this developmental transition. During acclimation to the light environment, light drives many morphological and molecular-genetic processes, such as inhibition of hypocotyl elongation and increase in plastid transcripts encoding proteins required for photosynthesis. Our laboratory has demonstrated specific effects of narrow-bandwidth green light that oppose these processes, independently of known sensory systems. Additionally, we have expanded on recent evidence that indicates a role for green light in directly reversing cryptochrome-mediated responses. Our findings support a hypothesis that green light signals integrate and balance the developmental effects induced by red and/or blue light acting through the phytochrome and cryptochrome systems. Co-irradiation with red, blue and green light using our specialized LED chambers indicates that green light can conditionally reverse stem elongation and anthocyanin driven by blue and/or red light. This effect is cryptochrome dependent. Supplemental green light induces changes in plant architecture reminiscent of shaded growth habits. When dark-grown seedlings were treated with a short, single pulse of red light, a pulse of dim green light (1/500th the fluence, approximately “safelight” fluence rates), or a combination of both treatments, the minor green treatment can negate red-induced transcript accumulation. The effects of green are apparent only during specific windows in seedling development. Together, these data support a hypothesis that a green light sensing system works carefully in concert with known sensory systems to optimize seedling morphology and physiology during establishment, and are most relevant in low light environments. http://www.arabidopsisthaliana.com/