Effects of Light Illumination on the Population of Translatable mRNA in Radish Cotyledons during Dark-Induced Senescence

Abstract

The population of translatable mRNA in radish cotyledons has been shown to change strikingly during dark-induced senescence by analyzing cell-free translation products from polyadenylated RNA using two-dimensional electrophoresis (Kawakami and Watanabe 1988, Plant Cell Physiol. 29: 33–42). In the present study, the translatable mRNAs in the cotyledons were studied after re-illumination of seedlings which had been induced to senesce by dark treatment. All of the mRNA species which showed relative increase or decrease during a 24-h dark treatment returned to their initial levels after a subsequent 24-h illumination with white light. When seedlings were kept in the dark for 48 h, 21 mRNA species increased, but the increase in some of them was no longer reversible; 9 out of the 21 mRNA species remained at the same level even after 48 h of re-illumination. All of the 18 mRNA species which decreased during 48 h in the dark returned to their initial levels upon re-illumination. The mRNA species that showed irreversible increase were also found to accumulate in cotyledons senesced after a lengthy growth period under light. There were also some mRNA species whose content was not affected by dark treatment, but increased transiently after re-illumination of the seedlings. These observations are discussed in relation to the progress of senescence in the cotyledons.