The possible correlation between blue light-dependent phosphorylation of a 11 6-kD protein and phototropic responses of etiolated oat (Avena sativa 1.) seedlings was tested by a micromethod for protein phosphorylation. Quantitation of the basipetal distribution of this protein showed that the in vitro 32P phosphorylation values declined exponentially from tip to node, with more than 50% of the total label being found in the uppermost 5 mm. Nonsaturating preirradiation of the coleoptiles in vivo resulted in partia1 phosphorylation with endogenous ATP. Subsequent in vitro phosphorylation under saturating irradiation allowed the determination of the degree of in vivo phosphorylation. Unilateral preirradiation resulted in higher in vivo phosphorylation on the irradiated than on the shaded side of the coleoptile. The fluence-response curve for the difference in phosphorylation between both sides of the coleoptile resembles the fluence-response curve for first-positive phototropic curvature, although it is shifted by two orders of magnitude to higher fluences. Possible reasons for this shift are discussed. In the coleoptile base the phosphorylation gradient across the coleoptile becomes larger with increasing time of irradiation at a constant fluence. Thus, phosphorylation of the 116-kD protein, in accordance with second-positive phototropic curvature, does not obey the Bunsen-Roscoe reciprocity law.
Blue light induces the phosphorylation of a 116 kDa oat protein found in plasma membrane preparations from coleoptile tips. We developed a very sensitive in vitro method that allowed us to determine the tissue distribution of protein phosphorylation after applying unilateral and bilateral blue light pulses in vivo. We found that following unilateral in vivo irradiation the degree in phosphorylation of the 116 kDa protein is significantly higher at the irradiated than at the shaded side of the coleoptile tip. This asymmetry can be considered as previously missing criterion that protein phosphorylation represents an early event within the transduction chain for phototropism.
Dark recovery of blue light-induced i n vitro phosphorylation in oat (Avena safiva L.) seedlings after in vivo preirradiation with blue light revealed different recovery kinetics for the coleoptile base and tip. Although, in both cases, maximum in vitro phosphorylation was observed 90 min after i n vivo blue light treatment, the phosphorylation levels for the entire base were about 3-fold higher than those found in nonpreirradiated plants. l h e tip response only slightly exceeded that of the dark controls. l h e fluence applied during preirradiation determined the extent of the increase in phosphorylation. Consequently, unilateral irradiation and subsequent dark incubation resulted in a more pronounced increase in phosphorylation in the irradiated than in the shaded side of the coleoptile base. Furthermore, blue light-irradiation conditions, known to induce neither first-nor second-positive curvature in nonpreirradiated plants, stimulated both asymmetric distribution of protein phosphorylation and second-positive phototropic curvature in the coleoptile base when administered to blue light-pretreated plants. Based on these data, we conclude that photosensitivity of the coleoptile base increases upon exposure to blue light i n a time-and fluence-dependent manner, providing an excellent explanation of the invalidity of the Bunsen-Roscoe reciprocity law for secondpositive phototropism.Phototropism has been studied in a variety of dicotyledoneous and monocotyledoneous plants over the last century (for reviews, see Firn and Digby, 1980;Briggs and Baskin, 1988;Iino, 1990; Firn, 1994). The most extensive studies on phototropic-curvature reactions were done on the coleoptile of etiolated oat (Avena sativa L.) seedlings, a classic object of phototropism research. From the fluenceresponse curves obtained by unilateral irradiation of oat coleoptiles with blue or white light at least three different types of bending reactions have been distinguished with respect to the light-stimulus intensity and duration (Briggs,
Blue light induced the phosphorylation of a 116-kDa plasma-membrane-associated protein in dark-grown seedlings from Avena sativa L. The response was restricted to the phototropically sensitive tissue of the coleoptile tip. Surprisingly, this protein showed different properties in membrane preparations from plants that were grown for 3 d than in those from 5-d-old seedlings. In contrast to the younger coleoptiles, in 5-d-old seedlings phosphorylation of the 116-kDa protein depended strictly on the addition of Triton X-100 or other non-ionic detergents and was not abolished when the membranes were pretreated with trypsin. These latter membranes were also characterized by the appearance of two additional blue-light-regulated phosphoproteins of slightly lower molecular masses, exhibiting properties similar to the 116-kDa protein from 3-d-old plants. The data, together with solubilization studies, indicate that the 116-kDa protein is strongly membrane-bound only at the very beginning of seedling development and becomes more loosely associated in the course of coleoptile growth. In addition, we demonstrate that the capacity of the light-activated photoreceptor to recover photosensitivity in the dark also can occur under in-vitro conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.