Refine
Year of publication
- 2021 (143)
- 2020 (110)
- 2022 (76)
- 2014 (75)
- 2016 (70)
- 2019 (69)
- 2017 (63)
- 2018 (59)
- 2013 (55)
- 2012 (50)
- 2015 (45)
- 2010 (34)
- 2011 (27)
- 2009 (23)
- 2008 (21)
- 2007 (15)
- 2006 (13)
- 2023 (13)
- 2004 (6)
- 2005 (6)
- 2024 (6)
- 1981 (5)
- 1990 (4)
- 2000 (4)
- 2003 (4)
- 1975 (3)
- 1996 (3)
- 2001 (3)
- 1971 (2)
- 1974 (2)
- 1982 (2)
- 1984 (2)
- 1985 (2)
- 1986 (2)
- 1993 (2)
- 1994 (2)
- 1998 (2)
- 2002 (2)
- 1969 (1)
- 1970 (1)
- 1976 (1)
- 1977 (1)
- 1983 (1)
- 1989 (1)
- 1992 (1)
- 1997 (1)
- 1999 (1)
Document Type
- Article (1034) (remove)
Language
- English (1034) (remove)
Has Fulltext
- yes (1034)
Is part of the Bibliography
- no (1034)
Keywords
- aging (17)
- Podospora anserina (16)
- mitochondria (10)
- Haloferax volcanii (8)
- autophagy (8)
- Archaea (7)
- Phylogeny (7)
- SARS-CoV-2 (7)
- heat stress (7)
- phylogeny (7)
Institute
- Biowissenschaften (1034) (remove)
One of the earliest consequences of slicing plant storage organs such as potato tubers into thin disks is the formation of polysomes, which in potato slices is complete after 9 hours and is dependent on transcription. Fresh disks do not incorporate 32P, 3H-uridine or 14C-leucine into their ribosomes, whereas ribosomes and polysomes of aged disks use these precursors effectively. This development can be completely blocked by actinomycin D. Among the different RNAs synthesized during aging is 28S- and 16S—rRNA, 5S—RNA, tRNA, and a component sedimenting around 15—18S with a base-composition different from 16S—rRNA, 5S- and 4S—RNA and which supports peptide formation in an in vitro incorporation system.
It is suggested that this compound represents mRNA, which is not available immediately after slicing the tissue. These findings are consistent with the view of a derepression phenomenon in sliced storage tissue.
Whereas ribosome preparations of freshly sliced potato disks do not show appreciable activity in an in-vitro amino acid incorporation system, aging of the tissue leads to a greatly enhanced incorporation activity which reaches its maximum 24 hours after slicing. If ribosomes from freshly excised disks are provided with polyuridylic acid, their activity in the incorporation of phenylalanine is increased about 8 fold.
Moreover, an RNA-fraction can be dissociated by EDTA from ribosomes of aged potato tuber slices, which sediments at 15 —18S, has a base composition different from that of 16S — rRNA, 5S-and 4S —RNA, and is not present on ribosomes of fresh slices. Its appearance is inhibited by actinomycin D and therefore most probably dependent on transcription. This compound, purified from sucrose gradients, enhances in vitro leucine incorporation into peptide material by ribosomes of fresh potato slices.
The possibility is discussed that this fraction-among other factors-is responsible for the enhanced protein synthesis after slicing plant storage organs, and is indicative of a general derepression phenomenon in these tissues.
At pH 5.3 and 4.5 the half life of valyl-, threonyl-, leucyl- and seryl-tRNA from E. coli K 12 is significantly higher than at pH 6.8. While no changes were observed in the MAK elution patterns of valyl- and threonyl-tRNA, leucyl-tRNA was eluted in two peaks at pH 6.8 and 5.3 and in one broad peak at pH 4.5. Seryl-TRNA - two peaks at pH 6.8 - was separated in three peaks at pH 5.3 and 4.5. Rechromatography of these peaks at the other pH suggests the existence of at least four species of seryl-tRNA in E. coli K 12.
Differential derepression of the genome of potato tuber cells can be initiated by slicing the tissue into disks. The consequence of this procedure on the cells of the wound surface is dedifferentiation and cell division followed by redifferentiation to a suberized phellem cell. The drift of glucose-, glucose-1-phosphate-, glucose-6-phosphate-, fructose-6-phosphate- and 6-phospho-gluconatelevels has been determined in the derepressed tissue. With the exception of 6-phospho-gluconate all intermediates so far investigated showed a rise in concentration after derepression.
This is interpreted as a consequence of altered enzymic activities which were estimated for phosphoglucomutase, hexokinase, phosphoglucoisomerase, gluco-6-phosphate- and 6-phosphogluconatedehydrogenase. The two dehydrogenases were activated after derepression, the activation represented a de-novo-synthesis, as was demonstrated with the inhibitors Actidione (translation) and p-Fluorophenyl-alanine (protein synthesis in general). Hexokinase and phosphoglucoisomerase were not severely affected by cutting the tissue. Phosphoglucomutase was degrated rapidly, the degradation being dependent on protein synthesis. The importance of an enhanced activity of the pentose phosphate shunt for the stressed cell is emphasized and the possibility of an alteration in the osmotic pressure within the cell and especially in the nucleus — a primary consequence of wounding — as a cause of derepression in potato tuber cells is discussed.