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  • Title: Suborganellar localisation and effect of light on Helianthus tuberosus chloroplast transglutaminases and their substrates.
    Author: Dondini L, Del Duca S, Dall'Agata L, Bassi R, Gastaldelli M, Della Mea M, Di Sandro A, Claparols I, Serafini-Fracassini D.
    Journal: Planta; 2003 May; 217(1):84-95. PubMed ID: 12721852.
    Abstract:
    The light stimulation of transglutaminase (TGase EC 2.3.2.13) activity was verified by incubating isolated chloroplasts of Helianthus tuberosus L. continuously or for alternate periods of light or dark (light/dark and dark/light). The first 10 min of incubation always represented the critical period. Light-harvesting complexes of photosystem II (LHCII) were more intensely labelled by (14)C-polyamines under light and light/dark than under dark and dark/light conditions. Chloroplasts were fractionated into thylakoid- and stroma-enriched fractions in which multiple TGase forms and substrates were found. Antibodies against TGase recognised 58- and 24-kDa bands in thylakoids and a 150-kDa band in the stroma. The latter, and its 150-kDa fraction, catalysed the conjugation of 14C-polyamines to Rubisco. In both fractions (thylakoid-pre and stroma-pre) the analysis of polyamine glutamyl derivatives showed a significant light-affected conjugation of polyamines to endogenous proteins. Alternatively, entire chloroplasts were incubated and afterwards their sub-fractions were isolated (thylakoid-post and stroma-post). The PSII and LHCII complexes were more intensely immunodetected in thylakoid-post than in thylakoid-pre, especially under dark conditions. Conversely, the conjugation of polyamines to thylakoid proteins was clearly light-stimulated in thylakoid-post, and much less in thylakoid-pre. Stroma-pre proteins were poorly polyamine-conjugated and not light-affected; on the contrary, stroma-post proteins were much more polyamine-modified and strongly light-stimulated. Thus, the light-activated conjugation depends mainly on the presence of the thylakoid fraction during the assay. The protective effect on chloroplasts under photo-damage, stress or senescence conditions attributed in the literature to free polyamines is discussed with regard to the occurrence of polyamine conjugates catalysed by TGases.
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