Changes in Amounts of Chloroplast and Cytoplasmic Ribosomal‐RNAs and Photomorphogenesis in Dryopteris Gametophytes

Abstract

The basis for the difference in total-RNA base composition between the filamentous and the prothallial gametophytes of the fern Dryopteris has been examined. Analyses of the relative amounts of chloroplast rRNA {i.e.^M°^°P^^" -'^-^^^ ) indicate a shift to a higher chloroplast + cytoplasmic rRNA level of chloroplast rRNA in the transition from filamentous to prothallial growth. This increased level of chloroplast rRNA is of sufficient magnitude to be entirely responsible for the observed change in total-RNA base composition. Time-lapse analysis of the photomorphogenetic transition to prothallial growth shows that a 2-3 h lag preceeds the first response (tip swelling). Pulse-labelling experiments reveal an increased synthesis of chloroplast rRNA during the transition to prothallial growth; but this increase occurs after the onset of the photomorphogenetic change and therefore cannot be considered causally involved. These results provide a biochemical correlate for the cytological observations on size changes in the nucleoli and chloroplasts of these gametophytes.

The Control of the Orientation of Cell Divisions in Fern Gametophytes

“…For instance, after a transfer from red to blue light, fern filaments undergo a rapid transition to two-dimensional growth. But Howland (1972) demonstrated that an increase in the relative level of plastid rRNA accounts for this observed shift in RNA base composition. Hotta ( 1960) observed that the RN As of two-dimensional gametophytes have higher proportions of the nucleic acid bases guanine and cytosine than do the RNAs of filamentous gametophytes.…”

Photocontrol of the Orientation of Cell Division in Adiantum. Iii. Effects of Metabolic Inhibitors

“…However, little attention was paid to this point in previous works (SCHRAUDOLI MILLER, 1968;BURNS andINGLE, 1968, 1970;DAVIS, 1968DAVIS, , 1970SCHRAUDOLF and LEGLER, 1969;HOWLAND, 1972). On the contrary, the influences of the inhibitors o n the orientation of the cell plate were successfully examined for the first time under a microscope using an appropriate experimental system.…”

“…BEKCFELD (1964) also pointed out that much of the blue-light-induced protein synthesis resulted from chloroplast development. Lately, evidence has accumulated against the hypothesis (SOBOTA andPARTANW, 1966, 1967;SCHRAUDOLF, 1967;MILLER, 1968;DAVIS, 1968DAVIS, , 1970BURNS andINGLE, 1968,1970;SCHRAUDOLF and LEGLER, 1969;HOWLAND, 1972).…”

The Transition From Filamentous to Two‐dimensional Growth in Fern Gametophytes. Iv. Initial Events

“…These changes have been studied in detail in only a few instances. In a timelapse study of Dryopteris [ilix-mas, Howland ( 1972) concluded that the newly synthesized wall on the flanks as well as at the extreme tip of the apical swelling had been formed after the plants had been transferred from red to blue light; cell wall produced prior to blue light exposure was not involved in the cell expansion. This apical swelling was associated with a reduction in the rate of elongation (Davis, 1969).…”

“…Certain biochemical changes occur later (Drumm and Mohr, 1967;Howland, 1972); therefore, these events cannot be part of the mechanism leading to the morphological change. Certain biochemical changes occur later (Drumm and Mohr, 1967;Howland, 1972); therefore, these events cannot be part of the mechanism leading to the morphological change.…”