Impaired carotenogenesis can affect organization and functionality of etioplast membranes

Abstract

The effects of impaired carotenogenesis on plastid membrane organization, functionality and stability were studied in etiolated barley plants grown at 20 and 30degreesC. The plants were treated with norflurazon or amitrole, two herbicides affecting phytoene desaturation and lycopene cyclization, respectively. At 20degreesC, the amitrole-treated etioplasts, which accumulated lycopene in their inner membranes, exhibited disorganized prolamellar bodies, containing a prevalent form of non-phototransformable protochlorophyllide (Pchlide). They also showed a certain difficulty in reducing the phototransformable pigment to chlorophyllide when exposed to light, and were unable to reform the active ternary complex [protochlorophyllide-oxidoreductase (POR)-Pchlide-NADPH] when placed back in darkness. No ultrastructural alterations were found in norflurazon-treated etioplasts, with carotenogenesis inhibited at the phytoene desaturation step. In these latter organelles, Pchlide, whose forms were comparable with those of the control etioplasts, was photoreduced quickly after illumination and the ternary complex was reformed during a subsequent dark period. Thus, the impaired carotenogenesis leading to the accumulation of lycopene showed greater interference with the etioplast membrane arrangement and functionality than did the earlier interruption of the biosynthetic pathway at the phytoene level. This might be due to the different interactions of the distinct carotenoid precursors with other membrane components. However, in etioplasts of norflurazon-treated plants, a rise in growth temperature caused a partial demolition of prolamellar bodies, showing a lowered thermostability of the carotenoid-deficient membranes. This latter effect strengthens the concept that a correct and complete carotenogenesis pathway, leading to the synthesis of polar carotenoids (i.e. xanthophylls), is required for the maintenance of stable plastid membranes

Inhibition of lycopene cyclase results in accumulation of chlorophyll precursors

“…7c) indicates that perturbation of the inner membranes is not caused by tetrapyrroles that accumulate after CPTA treatment. Al-Babili et al (1999) found a similar membrane perturbation in chromoplasts after CPTA treatment and Moro et al (2004) notiWed analogous alterations in barley etioplasts after treatment with amitrole. In both cases the authors concluded that it was due to lycopene accumulation: lycopene crystals did not withstand extraction by dehydrating and embedding after glutaraldehydeOsO 4 Wxation and left empty spaces with undulating membranes.…”

Regulation of lutein biosynthesis and prolamellar body formation in Arabidopsis

“…6C). Thus, the effect of amitrole on PLB formation (Rascio et al 1996;Moro et al 2004) is not due to all-trans-lycopene accumulation. So whether the amount of phytoene, lycopene, β-carotene and xanthophylls in amitrole-treated barley is insufficient to form a PLB or the effect is not related to carotenoids requires a quantitative analysis of all carotenoids in amitrole treatedtissue.…”

“…Whether all-trans-lycopene permits the formation of PLBs is less clear. Amitrole is a herbicide that prevents PLB formation and has been reported to cause lycopene accumulation (Rascio et al 1996;Moro et al 2004). However, a study has examined the accumulation of all carotenoids in response to amitrole treatment (Barry and Pallett 1990), not just those that absorb in the visible spectrum (Rascio et al 1996;Dalla Vecchia et al 2001).…”

Protochlorophyllide reduction - what is new in 2005?

“…ND: non-determined. In the presence of norflurazon or amitrole the accumulation of colourless Car precursors phytoene and phytofluene or the accumulation of lycopene and upstream precursors is triggered, respectively (Moro et al 2004). The structure of PLB was severely disturbed in amitrole-treated plants, but not in norflurazon-treated plants.…”

“…The possibility that Cars and Pchlide interfere with the prolamellar body (PLB) organization was investigated in the presence of metabolic inhibitors. Moro et al (2004) changed the Car composition using two different Car inhibitors and Savchenko et al (2004) studied the consequence(s) of inhibition of tetrapyrrole synthesis by levulinic acid. Table 1.…”