northanger (northanger) wrote,
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northanger

flora (part one)

DLNNIOBPOALEOZAA is the letter string created by the mid-characters of the 16 small crosses on the original enochian great table. "DLNNI" appears in phytochrome sequences: {1}{2}{3}{4}{5}{PHY_ADICA}{PHY_ADICA_SAPS}

Phytochromes represent a family of regulatory photoreceptors in plants that control a wide variety of growth and developmental processes. They exist in two photoreversible forms, a red light-absorbing form (Pr) with an absorption maximum at 666 nm and a far-red light-absorbing form (Pfr) with an absorption maximum at 730 nm. Based on the interconversion between the Pr and Pfr form they function as a light-regulated switch which is activated by red light and attenuated by far-red light. {Computer analysis of phytochrome sequences and reevaluation of the phytochrome secondary structure by Fourier transform infrared spectroscopy, Jürgen Sühnel, Gudrun Hermann, Utz Dornberger and Hartmut Fritzsche}

Abstract: A repertoire of various methods of computer sequence analysis was applied to phytochromes in order to gain new insights into their structure and function. A statistical analysis of 23 complete phytochrome sequences revealed regions of non-random amino acid composition, which are supposed to be of particular structural or functional importance. All phytochromes other than phyD and phyE from Arabidopsis have at least one such region at the N-terminus between residues 2 and 35. A sequence similarity search of current databases indicated striking homologies between all phytochromes and a hypothetical 84.2 kDa protein from the cyanobacteriumSynechocystis. Furthermore, scanning the phytochrome sequences for the occurrence of patterns defined in the PROSITE database detected the signature of the WD repeats of the beta transducin family within the functionally important 623-779 region (sequence numbering of phyA from Avena) in a number of phytochromes. A multiple sequence alignment performed with 23 complete phytochrome sequences is made available via the IMB Jena World-Wide Web server (http://www.imb-jena.de/PHYTO.html). It can be used as a working tool for future theoretical and experimental studies. Based on the multiple alignment striking sequence differences between phytochromes A and B were detected directly at the N-terminal end, where all phytochromes B have an additional stretch of 15 to 42 amino acids. There is also a variety of positions with totally conserved but different amino acids in phytochromes A and B. Most of these changes are found in the sequence segment 150-200. It is, therefore, suggested that this region might be of importance in determining the photosensory specificity of the two phytochromes. The secondary structure prediction based on the multiple alignment resulted in a small but significant b-sheet content. This finding is confirmed by a reevaluation of the secondary structure using FTIR spectroscopy.

Keywords: Phytochromes, Photomorphogenesis, Multiple sequence alignment, Sequence comparison, Secondary structure, FTIR spectroscopy.

Definitions

a list of definitions from 14-March-2002

phytochrome clocks — The coloring processes of plants that change the hues of ripening fruits and cause leaves to change colors with the shortened days of autumn.

phytochrome — A reversible pigment system of a protein nature, found in the cytoplasm of green plants. Phytochrome is associated with the absorption of light that affects growth, development and differentiation of a plant, independent of photosynthesis, e.g., in the photoperiodic response.

photosynthesis — A chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.

Photoperiodism — Describes the alternating periods of light and darkness which African Violets and other plants need for peak flowering. In addition to receiving plenty of indirect light, particularly in the red range of the spectrum, African Violets need at least six hours of darkness each day. Red light is absorbed by the phytochrome pigment in the leaves which activates the production of florigen, the hormone which regulates flowering. While the production of this hormone is stimulated by light, exposure to light actually destroys florigen. Thus, an African Violet must have sufficient light to produce florigen, while having enough darkness to use it in the production of flowers. Also see Florescence.

Red Light — The red portion of the light spectrum. To be effective, artificial grow lights must emit light in both the red and blue parts of the spectrum. Red light is essential for African Violets to bloom.

Florigen — Plant hormone which regulates flowering. The production of florigen is activated by phytochrome.

Phytochrome — A pigment in the leaves of African Violets and other plants which, when exposed to light, activates the production of florigen.

Phytochrome — A reversible pigment occurring in green plants that changes form in response to exposure to light and dark, permitting plants to measure the length of the dark period.

Phytochrome — A pigment protein from plants that absorbs red light. It regulates a number of light-sensitive processes, such as germination, growth and flowering.

canopy.evergreen.edu ## The state of the phytochrome, the main pigment for the developmental control of light, has been calculated at different depths in the canopy. The calculated phytochrome profile is distorted when simple radiation transfer models are used. This profile is also strongly affected by the degree of stochastic heterogeneity.

Seeds and Germination — Germination is the process whereby seeds become active and begin the production of new cells. All seeds must have a supply of water and oxygen for germination. Additionally, they germinate within a specific temperature range. For most seeds the lower temperature limit is freezing point, but some seeds, such as those from cucumbers, will not germinate unless the temperature is at least 18 degrees Celsius. The upper limit of temperature for most seeds is about 40 degrees Celsius. Most seeds will germinate with or without light, but there are some seeds that are "light-sensitive." Some seeds need the merest flash of light exposure to cause germination, while others need a few hours of light exposure.

florigen — a hypothetical hormone which induces plant flowering

Florigen — Hypothetical chemical substance causing floral initiation.

florigen — the hypothetical flowering hormone. This compound (or compounds) has never been identified chemically.

Florigen — Plant hormone which regulates flowering. The production of florigen is activated by phytochrome.

How are the activies of a plant integrated? — "What is florigen? or "If it's not florigen, then what the hell is it?" "The plant hormones seem to do everthing. They inhibit growth; they promote growth. They inhibit differentiation; they promote differentiation. The phenomena seem to well described, but how they actually work is not. Yes, there are some hormone-inducible genes, but how are they induced; how is the signal transduced?" "How are the activites of chloroplast and nuclear genomes integrated?"

Florigen — Hypothetical plant growth substance (hormone) postulated to induce flowering. Existence not proven: recently suggested that it might be an oligosaccharin

Tags: flora, juno, mars
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