Iron Is Involved in the Maintenance of Circadian Period Length in Arabidopsis      

Abstract

The homeostasis of iron (Fe) in plants is strictly regulated to maintain an optimal level for plant growth and development but not cause oxidative stress. About 30% of arable land is considered Fe deficient because of calcareous soil that renders Fe unavailable to plants. Under Fe-deficient conditions, Arabidopsis (Arabidopsis thaliana) shows retarded growth, disordered chloroplast development, and delayed flowering time. In this study, we explored the possible connection between Fe availability and the circadian clock in growth and development. Circadian period length in Arabidopsis was longer under Fe-deficient conditions, but the lengthened period was not regulated by the canonical Fe-deficiency signaling pathway involving nitric oxide. However, plants with impaired chloroplast function showed long circadian periods. Fe deficiency and impaired chloroplast function combined did not show additive effects on the circadian period, which suggests that plastid-to-nucleus retrograde signaling is involved in the lengthening of circadian period under Fe deficiency. Expression pattern analyses of the central oscillator genes in mutants defective in CIRCADIAN CLOCK ASSOCIATED1/LATE ELONGATED HYPOCOTYL or GIGANTEA demonstrated their requirement for Fe deficiency-induced long circadian period. In conclusion, Fe is involved in maintaining the period length of circadian rhythm, possibly by acting on specific central oscillators through a retrograde signaling pathway.

Night Light-Adaptation Strategies for Photosynthetic Apparatus in Yellow-Poplar (Liriodendron tulipifera L.) Exposed to Artificial Night Lighting

“…Several studies have shown that the chlorophyll a transient has become one of the most popular tools to estimate stress-induced changes in photosynthetic performance. For example, the shape of the OJIP transient seems to be particularly sensitive to environmental stresses, such as drought [55], salt stress [56], high temperature [57], and heat stress [58]. The chlorophyll fluorescence parameter Fv/Fm has been used as an indicator of physiological stress.…”

“…Artificial night lighting significantly damaged the donor side of PSII, which was indicated by significant increase of the K step in the OJIP transients and the relative variable fluorescence at the K step ( Figure 2). Specifically, the peak of the K-step under stress is an effective injury indicator relative to the inactivation of the oxygen-evolving complex (OEC) to the donor side of PSII [32,57,60]. The dramatic inhibition of the O 2 evolution capacity of leaves exposed to artificial night lighting suggested that the donor side of PSII was damaged during artificial night lighting.…”

The Plant Circadian Clock: From a Simple Timekeeper to a Complex Developmental Manager

“…In 2013, three independent studies showed that Fe-deficiency slows down the pace of the core clock (Chen et al 2013;Hong et al 2013;Salomé et al 2013). Functional chloroplasts, but not photosynthetic activity, were shown to be necessary for the period lengthening induced by Fe deficiency (Chen et al 2013;Salomé et al 2013).…”

Influence of plastids on light signalling and development

“…These data indicate that gun mutant screens specifically disrupted a few distinct mechanisms that downregulate the expression of PhANGs when chloroplast biogenesis is blocked, not complex metabolic situations. The findings that these mechanisms appear conserved in all plants tested [17] and contribute to stress tolerance [4,5,11,14], the circadian rhythm [7,8] and development [38][39][40][41] provide evidence that they contribute plastid-to-nucleus signalling in natural environments.…”

“…Extraplastidic signalling mechanisms, plastid-to-nucleus signalling mechanisms and the integration of these signalling mechanisms are major regulators of photosynthesis-associated nuclear genes (PhANGs) [1][2][3]. Plastidto-nucleus signalling affects numerous plastidic and extraplastidic processes, such as the biogenesis of chloroplasts and amyloplasts [3][4][5][6], the circadian rhythm [7,8], DNA replication [3], the transcription of genes that encode ribosomal RNA by RNA polymerase I [9], development [10] and the optimization of photosynthesis to various qualities of light [3]. Plastid-to-nucleus signalling also contributes to the response to wounding, biotic stress, abiotic stress and sugar [2,3,9,[11][12][13][14].…”