ABSTRACT
The genes for the two large ribosomal RNAs (16S and 23S) and for the 4.5S rRNA in Spirodela oligorhiza chloroplast DNA are transcribed as one large, 7,000 nucleotides long precursor rRNA.Using S1-nuclease mapping, we have determined that the transcript ends 135 nucleotides 3' distal of the 4.5S rRNA gene. 5S rRNA therefore, is most likely transcribed separately.Northern blotting of chloroplast RNA with distinct probes derived from the rDNA region reveals RNAs, which can be described as intermediates in the processing of the large precursor. With these findings a pathway for the maturation of this precursor is proposed.
ABSTRACT
The uninhibited respiration of mitochondria, isolated from potato tuber discs (Solanum tuberosum L. cv. Bintje) incubated on a callus-inducing medium at 28 degrees C, is higher than that of mitochondria from tissue incubated at 8 degrees C. This respiration is composed of a CN-sensitive and a CN-resistant part. The capacity of the CN-resistant alternative oxidase pathway is larger in mitochondria from 28 degrees C tissue than in mitochondria from 8 degrees C tissue (35% and 8% of uninhibited respiration, respectively). The alternative pathway is operative both in mitochondria from 28 degrees C tissue and 8 degrees C tissue.The observed difference in uninhibited respiration, is not only caused by lower values of respiration via the alternative pathway in mitochondria from 8 degrees C tissue, but also by lower values of respiration via the cytochrome pathway.A positive correlation has been demonstrated between the incubation temperature (ranging from 4-37 degrees C) and the relative capacity of respiration via alternative pathway in the mitochondria. Induction of alternative pathway is not directly correlated with growth (in terms of increase in fresh weight) of the potato tuber discs.
