ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
3-Amino- 1,2,4-triazole (amitrole) provided to germinating barley at 20°C in the light led to bleached seedling leaves and photodynamic destruction of chloroplast structure, whereas normal greening and chloroplast ultrastructure was obtained when the seedlings developed in the presence of amitrole in the light at 30°C. Mass spectrometric analysis of the extractable herbicide demonstrated the same content of amitrole in leaves developed at 20 and 30°C. A very similar temperature-sensitive syndrome is characteristic for the nuclear gene mutant ligrina-o34 in barley. Amitrole and the mutation were shown to inhibit the cyclization of lycopene, leading to severe deficiencies in β-carotene and its xanthophyll derivative lutein. Besides accumulation of lycopene, also its precursors phytoene, phytofluene and ξ-carotene accumulated. Inhibition of carotenoid biosynthesis by amitrole and the mutation at 20°C in the light led to a strong reduction of both transcript and protein levels for chloroplastic glutamine synthetase (GS2) while transcript amount and protein of the cytosolic isoenzyme (GS1) were unaffected. At 30°C increased levels of mRNA for the chloroplastic isoform GS2 were observed in wild type, mutant and amitrole-treated seedlings, but protein levels remained unchanged. Turnover rates of the GS2 protein were the same at 20 and 30°C. This extensive translational control of chloroplastic GS2 synthesis was also observed in a heat shock experiment, which revealed transiently increased mRNA levels for chloroplastic GS2 but unchanged protein levels.Permissive synthesis of β-carotene and chloroplastic glutamine synthetase (GS2) at 30°C in the presence of amitrole or the tigrina-o34 mutation might be due to two alternative pathways of ionone ring formation using either lycopene or neurosporene as substrates for cyclization.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1995.tb00965.x
