PLASTID GENOME STRUCTURE AND PLASTID-RELATED TRANSCRIPT LEVELS IN ALBINO BARLEY PLANTS DERIVED FROM ANTHER CULTURE

Southern analysis of DNA from four albino barley plants regenerated from microspores by direct embryogenesis revealed the presence of plastid genomes which had undergone deletion or alteration of specific restriction fragments (DELTA-ptDNAs). In contrast, a fifth plant appeared to contain an intact plastid genome. All the albino plants studied contained reduced amounts of ptDNA, the most abundant restriction fragments being present at levels between 6% and 20% of those found in the leaves of green seedlings. Steady-state levels of transcripts from plastid and nuclear genes encoding plastid components were estimated by Northern analysis of RNA from albino plants. Transcripts from the plastid genes rbcL, psbD-psbC and the 16S and 23S rRNAs were undetectable or were present at greatly reduced levels in albino plants compared to those found in green leaves. Transcripts from the nuclear genes rbcS and cab, which encode chloroplast localised proteins, were also present at reduced levels in albino pollen plants. Levels of the nuclear encoded 25S rRNA, which is not a plastid component, were found to be identical in albino plants and green leaves suggesting that only the expression of plastid-related genes may be affected in albino plants. The general reduction of plastid-related transcripts was independent of the different patterns of ptDNA alteration seen in albino pollen plants.