The transglutaminase activation precedes the developmental cell death wave (DCD) of Nicotiana tabacum flower. Oral presentation.

The activity of transglutaminase (TGase), an enzyme responsible for polyamine conjugation to proteins, was analysed in relationship to developmental cell death (DCD) during the flower life span stages of the Nicotiana tabacum corolla. As the DCD exhibits an acropetal gradient, TGase was studied in corolla proximal, medial and distal parts. TGase was immunorecognised by three TGase antibodies; the main 58 kDa band decreased during corolla life, whereas a 38 kDa band localised progressively from basal to distal parts. The former was present in the soluble, microsomal, plastidial (together with the 38 kDa 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 (His6-Xpr-GFP). 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; 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, stabilising the photosystems, could sustain the energy requirements for the senescence progression.