Red Light-grown Seedlings Research Articles

Retrograde Induction of phyB Orchestrates Ethylene-Auxin Hierarchy to Regulate Growth.

Exquisitely regulated plastid-to-nucleus communication by retrograde signaling pathways is essential for fine-tuning of responses to the prevailing environmental conditions. The plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) has emerged as a stress signal transduced into a diverse ensemble of response outputs. Here, we demonstrate enhanced phytochrome B protein abundance in red light-grown MEcPP-accumulating ceh1 mutant Arabidopsis (Arabidopsis thaliana) plants relative to wild-type seedlings. We further establish MEcPP-mediated coordination of phytochrome B with auxin and ethylene signaling pathways and uncover differential hypocotyl growth of red light-grown seedlings in response to these phytohormones. Genetic and pharmacological interference with ethylene and auxin pathways outlines the hierarchy of responses, placing ethylene epistatic to the auxin signaling pathway. Collectively, our findings establish a key role of a plastidial retrograde metabolite in orchestrating the transduction of a repertoire of signaling cascades. This work positions plastids at the zenith of relaying information coordinating external signals and internal regulatory circuitry to secure organismal integrity.

Nitric Oxide, Ethylene, and Auxin Cross Talk Mediates Greening and Plastid Development in Deetiolating Tomato Seedlings.

The transition from etiolated to green seedlings involves the conversion of etioplasts into mature chloroplasts via a multifaceted, light-driven process comprising multiple, tightly coordinated signaling networks. Here, we demonstrate that light-induced greening and chloroplast differentiation in tomato (Solanum lycopersicum) seedlings are mediated by an intricate cross talk among phytochromes, nitric oxide (NO), ethylene, and auxins. Genetic and pharmacological evidence indicated that either endogenously produced or exogenously applied NO promotes seedling greening by repressing ethylene biosynthesis and inducing auxin accumulation in tomato cotyledons. Analysis performed in hormonal tomato mutants also demonstrated that NO production itself is negatively and positively regulated by ethylene and auxins, respectively. Representing a major biosynthetic source of NO in tomato cotyledons, nitrate reductase was shown to be under strict control of both phytochrome and hormonal signals. A close NO-phytochrome interaction was revealed by the almost complete recovery of the etiolated phenotype of red light-grown seedlings of the tomato phytochrome-deficient aurea mutant upon NO fumigation. In this mutant, NO supplementation induced cotyledon greening, chloroplast differentiation, and hormonal and gene expression alterations similar to those detected in light-exposed wild-type seedlings. NO negatively impacted the transcript accumulation of genes encoding phytochromes, photomorphogenesis-repressor factors, and plastid division proteins, revealing that this free radical can mimic transcriptional changes typically triggered by phytochrome-dependent light perception. Therefore, our data indicate that negative and positive regulatory feedback loops orchestrate ethylene-NO and auxin-NO interactions, respectively, during the conversion of colorless etiolated seedlings into green, photosynthetically competent young plants.

Responses of intact and excised young bean plants to fusicoccin

The effect of fusicoccin (FC) on the growth of epicotyls and leaves of Phaseolus vulgaris L. intact and excised seedlings has been examined, and several unexpected responses were observed. FC was added either to small wounds on one side of the epicotyl of 10 day old red-light grown seedlings or to the base of shoots excised at the base of the hypocotyl. Plants were kept in either dim red light (4 μmol m-2sec-1) or bright white light (175 μmol m-2sec-1) during the FC treatment. FC added to the base of the shoots was found to inhibit leaf expansion in either light condition. At the same time stem elongation was enhanced. The active concentration range was 10-7–10-5M. The basal fed FC caused a rapid and severe bending of the epicotyl starting at the base of the elongation zone. The direction of curvature was random, not related to the plane of the cotyledons or the direction of the gravity vector. Application of FC to one side of the epicotyl caused a similar but smaller bending away from the treated side. The bending occurred at either end of the elongation zone in accordance with site of FC application above or anywhere below it along the epicotyl and hypocotyl. It is concluded that the curvature of the epicotyl induced by FC fed in the transpiration stream may either be due to a differential loss of the capacity of cells at the base of the elongation zone to grow in response to FC or as a result of elongation of the first responsive cells encountered by the FC.

Ethylene Is Not Involved in the Blue Light-Induced Growth Inhibition of Red Light-Grown Peas

Although the growth of intact plants is inhibited by irradiation with blue light, the growth rate of isolated stem segments is largely unaffected by blue light. We hypothesized that this loss of responsiveness was a result of ethylene production as part of the wounding response. However, we found no interaction between ethylene- and blue light-induced growth inhibition in dark- or red light-grown seedlings of pea (Pisum sativum L.). Inhibition of growth begins in dark-grown seedlings exposed to blue light within 3 min of the onset of blue light, as was known for red light-grown seedlings. By contrast, ethylene-induced inhibition of growth occurs only after a lag of 20 to 30 min or more (dark-grown seedlings) or 60 min (red light-grown seedlings). Also, the inhibition response of red light-grown seedlings is the same whether ethylene is present from the onset of continuous blue-light treatment or not. Finally the spatial distribution of inhibition following blue light was different from that following ethylene treatment.