Increase in Maize Plastid Photogene RNAs under Con...
The time courses of increases in the levels of RNAs complementary to photoregulated plastid genes in response to continuous or brief intermittent illumination were determined in the following experiment conducted to establish conditions for illumination with monochromatic light.Eight dold dark-grown maize plants were exposed to continuous white light；a single 1-min white light pulse（‘1’）；or two 1-min white light pulses separated by a 3-h interval of darkness（‘2’）.Plants were harvested 3，6，or 9 h after initiation of illumination（see Figure 1，bottom right）.The changes in the level of transcripts of rcL，ps2B，ps1Al，pslA2，and maize plastid Bam fragment 3 containing cflA and cfOlll were measured by dot hybridization and are shown as time-course curves as show in Figure 1.The results indicate that not only continuous white light but also a single white light pulse（1 min）is sufficient to bring about an increase in the level of RNAs complementary to variousphotoregulated genes that is detectable after 3 h of dark incubation following the light pulse.However，the levels of complementary RNAs under continuous light increased more than under light pulses，and two light pulses separated by 3 h induced higher levels of complementary RNAs than a single light pulse.Brief illumination with R resulted in similar kinetics for the appearance of RNAs（data not shown）.A program of briefillumination，3 h of darkness，brief illumination，and harvest after 3 h of additional darkness was used in subsequent experiments to study the involvement of phytochrome.This experimental sequence resulted in changes in RNA pool sizes that were adequate to measure while it reduced the probability of secondary effects that might occur when using continuous illumination or repeated brief illumination over periods of days rather than hours.
Table 1 Plasmids Used for Probing Transcripts of Plastid and Nuclear Genes of Maize
ⓐ Two parallel nomenclatures given are presented in references［18］and［19］.ⓑ Plastid probes were cloned maize plastid DNA sequences as designated by Larrinua et al.［19］and listed in the“Inserts”column.© Krebbers E T，Muskavitch K M T，Bogorad L，unpublished data.ⓓ Schantz R，Orr E A，Bogorad L，unpublished data.(https://www.daowen.com)
Figure 1 Levels of maize photogene transcripts after illumination of etiolated seedlings with pulses of white light.Eight d-old dark-grown plants were treated with（line CL）continuous white light；one（line 1）or two（line 2）1-min pulses of white light（WL）at 0 and 3 h as marked by arrows.The treatment program is shown in the diagram at the lower right-hand corner.Total RNA was isolated at 0，3，6，9，h and hybridized with plasmid probes for rcL（a），ps2B（b），cf1A，and cfOⅢ included in plastid chromosome fragments Bam 3（c），plAl（d），and ps1A2（e）.The transcript levels were measured by dot hybridization and expressed as scanning units.The numbers are the averages of three measurements for a given RNA.The variations in values were from 4 to 15%ofthe average
