[Show abstract][Hide abstract] ABSTRACT: Plants grown in shade exhibit changes in architecture and gene expression to best accommodate growth in photosynthetically challenging conditions. Adaptive changes in morphology include stem and petiole elongation and leaf hyponasty. These changes can be induced by low red to far-red ratio (R/Fr ratio) or by enrichment of green light relative to red and blue. In this report we demonstrate the relationship between far-red and green light in combination. Wild-type Arabidopsis thaliana plants were treated with a high and low R/Fr ratio background with or without supplemental green light. The addition of green light augmented the far-red response. Genetic analysis showed that the green effect operates independently of cry1, cry2, phot1, and phot2 receptors. Additive effects are not observed in phyA and phyB double mutants, but are observed in the phy signal transduction mutants pif4, pif5, pif7. The transcript levels of shade-associated genes (PIL1, ATHB2, and HFR1), are induced by low R/Fr ratio conditions and are reduced in the presence of green light, but not in phyAphyB mutants. The reduction in shade-related gene expression caused by supplementation of green light is inconsistent with the elongated petiole phenotype observed. These results suggest that phyA or phyB is required for the green light shade response, but they are not the main receptors because green light would increase the R/Fr ratio, leading to a non-shade phenotype.
[Show abstract][Hide abstract] ABSTRACT: To a plant, the sun's light is not exclusively energy for photosynthesis, it also provides information about time and prevailing conditions. The plant's surroundings may dampen or filter solar energies, presenting plants with different spectral profiles of their light environment. Plants use this information to adjust form and physiology, tailoring gene expression to best match ambient conditions. Extensive literature exists on how blue, red and far-red light contribute to plant adaptive responses. A growing body of work identifies effects of green light (500-565 nm) that also shape plant biology. Green light responses are known to be either mediated through, or independent of, the cryptochrome blue light receptors. Responses to green light share a general tendency to oppose blue- or red-light-induced responses, including stem growth rate inhibition, anthocyanin accumulation and chloroplast gene expression. Recent evidence demonstrates a role for green light in sensing a shaded environment, independent from far-red shade responses.
[Show abstract][Hide abstract] ABSTRACT: Light quality and quantity affect plant adaptation to changing light conditions. Certain wavelengths in the visible and near-visible spectrum are known to have discrete effects on plant growth and development, and the effects of red, far-red, blue, and ultraviolet light have been well described. In this report, an effect of green light on Arabidopsis (Arabidopsis thaliana) rosette architecture is demonstrated using a narrow-bandwidth light-emitting diode-based lighting system. When green light was added to a background of constant red and blue light, plants exhibited elongation of petioles and upward leaf reorientation, symptoms consistent with those observed in a shaded light environment. The same green light-induced phenotypes were also observed in phytochrome (phy) and cryptochrome (cry) mutant backgrounds. To explore the molecular mechanism underlying the green light-induced response, the accumulation of shade-induced transcripts was measured in response to enriched green light environments. Transcripts that have been demonstrated to increase in abundance under far-red-induced shade avoidance conditions either decrease or exhibit no change when green light is added. However, normal far-red light-associated transcript accumulation patterns are observed in cryptochrome mutants grown with supplemental green light, indicating that the green-absorbing form of cryptochrome is the photoreceptor active in limiting the green light induction of shade-associated transcripts. These results indicate that shade symptoms can be induced by the addition of green light and that cryptochrome receptors and an unknown light sensor participate in acclimation to the enriched green environment.