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CELL BIOLOGY AND SIGNAL TRANSDUCTION

The Acropetal Wave of Developmental Cell Death of Tobacco Corolla Is Preceded by Activation of Transglutaminase in Different Cell Compartments^1,[C],[W]

Dipartimento di Biologia Evoluzionistica Sperimentale, Università di Bologna, 40126 Bologna, Italy

The activity of transglutaminase (TGase), an enzyme responsible for polyamine conjugation to proteins, was analyzed in relationship to developmental cell death (DCD) during the flower life span stages of the tobacco (Nicotiana tabacum) corolla. As the DCD exhibits an acropetal gradient, TGase was studied in corolla proximal, medial, and distal parts. TGase was immunorecognized by three TGase antibodies; the main 58-kD band decreased during corolla life, whereas a 38-kD band localized progressively from basal to distal parts. The former was present in the soluble, microsomal, plastidial (together with the 38-kD band), and cell wall fractions. The endogenous TGase activity increased during DCD reaching a maximum soon after the corolla opening. The activity maximum shifted from proximal to distal part, preceding the DCD acropetal pattern. A similar activity increase was observed by the exogenous TGase substrate (histidine₆-Xpr-green fluorescent protein). Subcellular activities were detected in (1) the microsomes, where TGase activity is in general higher in the proximal part, peaking at the corolla opening; (2) the soluble fraction, where it is present only in the proximal part at senescence; (3) the plastids, where it shows an increasing trend; and (4) cell walls, prevailing in the distal part and progressively increasing. These data suggest a relationship between DCD and TGase; the latter, possibly released in the cell wall through the Golgi vesicles, could cooperate to cell wall strengthening, especially at the abscission zone and possibly during corolla shape change. The plastid TGase, stabilizing the photosystems, could sustain the energy requirements for the senescence progression.

² Present address: Consorci CSIC-IRTA Laboratori de Genètica Molecular Vegetal, Jordi Girona 18–26, 08034 Barcelona, Spain.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Stefano Del Duca (stefano.delduca{at}unibo.it).

^[C] Some figures in this article are displayed in color online but in black and white in print.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.092072

^* Corresponding author; e-mail stefano.delduca{at}unibo.it; fax 39–051242576.

Received November 14, 2006; accepted April 3, 2007; published April 13, 2007.