The Effect of Red Irradiation on Plastid Ribosomal RNA Synthesis in Dark-grown Pea Seedlings

Abstract

Dark-grown pea seedlings (Pisum sativum L.) were irradiated for a short period each day with low intensity red light (662 nm), red light immediately followed by far red light (730 nm), or far red light alone. Other plants were transferred to a white light regime (14 hours light/10 hours dark). There was no change in the amount of RNA in the tissue on a fresh weight basis after the various treatinents. However, compared with dark-grown seedlings, those plants irradiated with red light showed an increase in the net RNA content per stem apex. In addition there was a two-to threefold increase in ribosomal RNA of the etioplasts relative to the total ribosomal RNA. These increases were comparable to those found in plants grown in the white light regime. The changes were much smaller if the dark-grown plants were irradiated either with red light followed by far red light, or with far red light alone. Thus continuous light is not essential for the production of ribosomal RNA in plastids, and the levels of ribosomal RNA found in chloroplasts can also be attained in etioplasts of pea leaves in the dark provided the leaf phytochrome is maintained in its active form.Evidence from several laboratories has shown that phytochrome mediates in photoregulating the synthesis of chloroplast proteins (3,5,(13)(14)(15)19). Thus activation of the phytochrome system in dark-grown pea seedlings by a brief irradiation with red light results in a marked increase in the synthesis of ribulose-1 ,5-diphosphate carboxylase and other chloroplast enzymes in the dark (3,19). Continuous light then is not required for the synthesis of Calvin cycle enzymes, nor is it required for svnthesis of enzymes of the C4-dicarboxylic acid pathway of photosynthesis (4).At least some of these chloroplast proteins appear to be synthesized on chloroplast ribosomes (17,19,20), but it is not known whether the phytochrome-mediated increase in plastid protein synthesis involves an increase in the number of plastid ribosomes or whether these ribosomes are already present in the etioplasts of dark-grown plants. Continuous light is known to increase the amount of plastid rRNA (1,8,22) and also plastid RNA polymerase (2) In the experiments reported here, we have measured the amount of plastid and cytoplasmic rRNA in the apices of darkgrown pea seedlings and in seedlings subjected to various light regimes. The leaves of dark-grown seedlings contained lower amounts of chloroplast-type rRNA (16 S and 23 S) compared with green leaves, but after irradiating the seedlings with light at 662 nm for short periods, the 16 S and 23 S RNA increased to the levels found in the leaves of green plants of the same chronological age. MATERIALS AND METHODSPea seeds (Pisum sativum L., cv Greenfeast, obtained from Yates Seed Co., Sydney) which had not been treated with fungicide or preservatives were used. The seeds were washed in a dilute solution of detergent (1% Teepol, Shell Chemical Co.), soaked in 3% (v/v) Chlorize (Nightingale Chemical Co., Sydney) for 15 min and then washed...

Control by Phytochrome of Cytoplasmic and Plastid rRNA Accumulation in Cotyledons of Mustard Seedlings in the Absence of Photosynthesis

“…2) and therefore may not directly be related to a differential effect of phytochrome on the formation of rRNA (and ribosomes) in the two cellular compartments. In principle, the increase of the relative level of plastid rRNA by phytochrome agrees with the findings of Scott et al (27) who reported a pro-CONCLUSION The data presented in this paper demonstrate the involvement of phytochrome in the photocontrol of the coordinate accumulation of the RNA of large and small ribosomal subunits in the cytoplasm and in the plastids of mustard cotyledons. A difference in the rate of RNA accumulation based on the biological unit (e.g.…”

“…The involvement of phytochrome in the control of RNA metabolism of higher plants is well documented (2,10,20,27,32). So far there is no information regarding the species of RNA affected or the mechanism(s) by which the observed responses on the RNA level are produced.…”

“…Continuous white fluorescent light (which saturates chlorophyll synthesis) is less effective than contintuous far red light (essentially no chlorophyll synthesis) in producing the response, indicating that the accumulation of plastid rRNA is independent of the buildup of a functional photosynthetic apparatus. We conclude that the transcription of cytoplasmic and plastid rRNA cistrons is uinder phytochrome control.The involvement of phytochrome in the control of RNA metabolism of higher plants is well documented (2,10,20,27,32). So far there is no information regarding the species of RNA affected or the mechanism(s) by which the observed responses on the RNA level are produced.…”

Factors in Chloroplast Differentiation

“…Of particular interest in this connection is the phytochrome-governed synthesis of the protein which, together with protochlorophyll(ide), forms the holochrome capable of phototransformation (Sundqvist 1970) and the effects on the esterification with phytol (Liljenberg 1966), on carotenoid synthesis (Cohen and Goodwin 1962), on lipoquinone synthesis (Mitrakos 1961) and on the content of plastid RNA (Scott et al 1971). An important fact in this connection is that continuous irradiation is not essential for the production of RNA.…”

Biochemistry of Protein Synthesis in Plants

“…The enzymes appear to be very similar, but a detailed physicochemical characterization has yet to be carried out. It is known that the synthesis of chloroplast ribosomal RNA in dark-grown plants is phytochrome-mediated (Scott, Nair & Smillie, 1971). Brief irradiation of etiolated pea seedlings with red light results in an increase in the activities of both the plastid and nuclear polymerases, but the response is too slow to be considered an early iesult of the phytochrome control of metabolism, and the increase in the plastid activity was not prevented by far-red light (Bottomley, 1970).…”