the signal is released by the plastids only during this time span.
Phytochrome (far red form) alone can mediate anthocyanin synthesis in the mustard seedling (Sinapis alba L.). Complete photoreversibility and reciprocity, for both red and far red light exposures over a period of at least 5 minutes, demonstrate this phytochrome involvement.The duration of the initial lag-phase is constant (about 3 hours at 25 C) for seedlings more than 30 hours old and is specific for the system, being independent of the dose or quality of light. Since a complete reversal by far red of a red light induction is possible only during a 5 minute period, phytochrome (far red form) obviously mediates anthocyanin synthesis during the lag-phase although the actual synthesis of pigment can proceed only after the lag-phase is overcome. We suggest that phytochrome (far red form) exerts a double function during the initial lag-phase. It mediates both the build up of a biosynthetic potential ("capacity") and anthocyanin synthesis.However, the sequence of events leading to anthocyanin is arrested at some intermediate stage until this "capacity" is built up after 3 hours. Once "capacity" is achieved it does not decay readily. Therefore, no significant "secondary lag-phase" occurs if the seedling, under appropriate conditions, is reirradiated after an intervening dark period. The rate or extent of synthesis for both anthocyanin and lipoxygenase, previously reported (32), are functions of the amount of phytochrome (far red form). No "phytochrome paradoxes," i.e., nonrational relationships between the amount of phytochrome (far red form) and rate or extent of response, were detected. This fact suggests that the mustard seedling is especially well suited for investigating the biophysical and molecular mechanisms of phytochrome action.Since the well known report by Arthur (1), the effect of light on anthocyanin synthesis has attracted the attention of many plant physiologists (5, 21, 37). However, the general mechanism of this light effect has not yet been formulated. This failure is due partly to the descriptive nature of many reports and, in the main, because light appears to exert its influence through different photochemical mechanisms which probably are mixed in the usual experimental approaches. Recently, (e.g.,2,6,7,9,10,11,35,40) anin synthesis be mediated exclusively without the interference of any other photochemical mechanism? These advantages are that (24) anthocyanin synthesis by light is predominantly controlled by phytochrome without the requirement of any prolonged "high energy pretreatment" (e.g., 2, 6, 10, 35), and the mustard seedling does not produce significant amounts of anthocyanin in complete darkness. Seedlings can easily be handled under standardized conditions, and a great amount of information, including spectrophotometric measurements of P,, is available on this system (26). While the mustard seedling forms five anthocyanins, the aglycon is always cyanidin (17). At 25 C the stored fat and protein of the cotyledons allow development in total darkness without any indications of ...
Expression of nuclear genes involved in plastidogenesis is known to be controlled by light via phytochrome. Examples are the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase and the light harvesting chlorophyll a/b binding protein of photosystem II (LHCP). In the present study we show that, beside phytochrome, the integrity of the plastid is essential for the expression of the pertinent nuclear genes as measured at the level of translatable mRNA. When the plastids are severely damaged by photooxidation in virtually carotenoid-free mustard (Sinapis alba L.) seedling cotyledons (made carotenoid-free by the application of Norflurazon, NF), almost no SSU, no SSU precursor, LHCP and LHCP precursor can be detected by immunological assays, and almost no translatable mRNA of SSU and LHCP can be found, although the levels and rates of phytochrome-mediated syntheses of representative cytoplasmic, mitochondrial and glyoxisomal enzymes are not adversely affected and morphogenesis of the mustard seedling proceeds normally (Reiß et al. 1983; Planta 159, 518-528). Norflurazon per se has no effect on the amount of translatable mRNA of SSU and LHCP as shown by irradiation of NF-treated seedlings with far-red light (FR) which strongly activates phytochrome but does not cause photooxidation in the plastids. It is concluded that a signal from the plastid is required to allow the phytochrome-mediated appearance of translatable mRNA for SSU and LHCP. Seedlings not treated with NF show a higher level of translatable mRNALHCP in red light (RL) compared to FR, whereas the mRNASSU levels are the same in RL and FR. These facts indicate that the level of translatable mRNALHCP is adversely affected if the apoprotein is not incorporated into the thylakoid membrane.
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.