PHYTOCHROME REGULATION OF STEM GROWTH AND INDOLE‐3‐ACETIC ACID LEVELS IN THE lv AND Lv GENOTYPES OF Pisum
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Abstract— Phytochrome influences stem elongation and the mechanism for this is not understood. The levels of indole‐3‐acetic acid (IAA) were analyzed in an leLv genotype of Pisum sativum L. which responded to end‐of‐day far‐red light by doubling growth rate. The IAA levels in epidermal peels increased 40% after far‐red light whereas IAA levels of the entire stem tissue changed insignificantly. This increase was reversible by red light. Under light‐grown conditions, the lv mutation increases stem elongation rates by 2–3‐fold and is thought to block the transduction of a phytochrome signal. Analysis of the short‐term stem elongation kinetics of dark‐ and light‐grown Lv and lv seedlings suggests that lv blocks the action of the light‐stable form of phytochrome. The higher growth rate of lv plants was found to be associated with abnormally high epidermal IAA levels typical of far‐red treated Lv plants. End‐of‐day far‐red treatments did not substantially increase epidermal IAA levels in lv plants. These observations support the view that phytochrome regulation of stem elongation may occur in part through modulation of epidermal IAA levels. The lv mutation may result in increased internode growth in part by blocking the ability of phytochrome to decrease epidermal IAA levels.Keywords:
Phytochrome
Elongation
Far-red
Shade avoidance
Thermo-dormant lettuce seeds can be induced to germinate by small doses of far-red light. The dose-effect curve appears to be an optimum curve. After having been irradiated with a supra-optimal inhibiting dose of far-red the seeds can be reinduced by red light, the threshold red dose for induction being now 104 times as large as it is without the far-red preirradiation. It is concluded that the inductive effect of far-red light is mediated by an uncommon form of phytochrome which is considered to be also present in etiolated Avena seedlings and Sinapis seedlings, and in cells of Mougeotia.
Phytochrome
Far-red
Sinapis
Etiolation
Avena
Phytochrome A
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Abstract The wavelength dependence for a radiation induced increase of phytochrome in mung bean hooks ( Vigna radiata L.), preirradiated with red light, was determined between 640 to 800 nm. Radiation between 640 to 700 nm and 780 to 800 nm had little effect on phytochrome concentration in hooks pretreated with red. Two bands of far‐red light, one at 710 nm and the other at 750 to 760 nm, were found to increase phytochrome content about four times. Besides the requirement for a photochemical process, one or more dark processes appear to be necessary for the induction of phytochrome increase.
Phytochrome
Radiata
Mung bean
Far-red
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Abstract Germination of Kalanchoé blossfeldiana seeds is absolutely light‐requiring and needs repeated daily light periods. With increasing length of the photoperiod there was a gradual escape from the far‐red inhibition. This escape depended also upon the duration of the far‐red exposure: 10‐second far‐red caused a strong inhibition after a 10‐ to 30‐minute photoperiod and did not inhibit after a 4‐hour day, although the effect of the latter was completely suppressed by 5 minutes far‐red. The action of a 12‐hour photoperiod was not reversed by 10 minutes far‐red but it was by 12 hours far‐red. Light intensity and temperature during the photoperiod were two other important factors influencing the escape from far‐red inhibition. The common features of this escape displayed in very different photomorphological responses are stressed. In order to explain our results in terms of phytochrome action, we distinguish two effects of white light: 1) on the initial photoconversion of the inactive to the active P FR form 2) on the much slower transformation of P FR to a reacted form P* FR ; the latter reaction can also proceed in darkness, but is enhanced by light and is dependent upon light intensity and temperature; this reacted phytochrome is not reversible by a brief far‐red illumination.
Phytochrome
Far-red
Darkness
Kalanchoe
Light intensity
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Phytochrome
Phytochrome A
Photomorphogenesis
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Phytochrome
Far-red
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Seeds of lettuce (Lactuca sativa L. cv. Grand Rapids) were imbibed and given either short irradiation with red or far red light prior to drying or dried under continuous red or far red light. Seeds treated with either short or continuous red germinate in darkness, whereas seeds treated with either short or continuous far red require a short exposure to red light, after a period of imbibition, to stimulate germination. Irradiation of dry red seeds with far red light immediately before sowing results in a marked inhibition of germination. This result was predicted since far red-absorbing form phytochrome can be photoconverted to the intermediate P650 (absorbance maximum 650 nm) in freeze-dried tissue. A similar far red treatment to continuous red seeds is less effective and it is concluded that in these seeds a proportion of total phytochrome is blocked as intermediates between red-absorbing and far red-absorbing form phytochrome, which only form the far red-absorbing form of phytochrome on imbibition. The inhibition of dry short red seeds by far red light can be reversed by an irradiation with short red light given immediately before sowing, confirming that P650 can be photoconverted back to the far red-absorbing form of phytochrome. The results are discussed in relation to seed maturation (dehydration) on the parent plant.
Phytochrome
Imbibition
Far-red
Darkness
Absorbance
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Phytochrome
Far-red
Etiolation
Squash
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ABSTRACT The effects of overexpression of oat phytochrome A on neighbour detection and on stem‐growth responses to changes in red light (R), far‐red light (FR) and blue light (B) simulating neighbours were investigated in transgenic tobacco seedlings grown under natural radiation. In wild‐type (WT) seedlings, stem extension growth was promoted: (1) by lowering the R:FR by means of daytime supplementary FR, end‐of‐day FR, neighbours reflecting FR, or selective light filters placed around the base of the shoot to reduce R without affecting FR; and (2) by lowering phytochrome‐absorbable radiation (R+FR) reaching the stem. Transgenic seedlings only responded to reductions in R:FR involving no significant changes in FR irra‐diance, i.e. end‐of‐day FR and filters placed around the stem to reduce R. Neither daytime supplementary R nor selective filters placed around the stem to reduce B affected stem growth in any genotype. In growing canopies, WT seedlings responded to the reduction of R:FR caused by FR reflected in neighbour plants. Transgenic seedlings responded to plant density about a week later, when mutual plant shading reduced R and (to a lesser extent) FR below sunlight levels. Overexpression of phytochrome A impaired early neighbour detection.
Phytochrome
Far-red
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Seed germination percentage of multiflora rose (Rosa multiflora Thunh.) was much higher under continuous white light than in complete darkness. Red light was the most effective in inducing germination, and far-red light was ineffective. Exposure to red light for 1 min increased germination; this effect was saturated at an exposure of2 min. The red-light effect was reversed by subsequent exposure to far-red light. The results indicate that rose seeds are positively photoblastic, and that the photoreceptor involved is most likely phytochrome.
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Darkness
Far-red
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In photoresponses regulated by phytochrome the effect of a red irradiation is not always reversed by far‐red. This applies for instance to the influence of red light on the geotropic reactions of Avena coleoptiles. We could induce red/far‐red reversibility by a short de‐etiolating exposure to red light about 20 h prior to the experimental irradiations. This, was due to a decrease of the sensitivity to the low level of the far‐red absorbing form of phytochrome that is established by far‐red. Since etiolated plants react also to a wavelength of 520 nm (green light), it is advisable to expose the coleoptiles to a de‐etiolating irradiation prior to manipulations in green safelight in order to prevent the plants from reacting to the green light.
Coleoptile
Phytochrome
Avena
Etiolation
Far-red
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