Donatella Serafini Fracassini

Polyamines and nucleic acids during the first cell cycle of Helianthus tuberosus tissue after the dormancy break

Polyamines (spermine, spermidine, and putrescine) and nucleic acids were studied during the first cell cycle after the break of dormancy of tuber slices of Helianthus tuberosus L., cv. OB1. Immediately after the break of dormancy, a marked decrease in stored arginine and glutamine and a corresponding increase of polyamines were observed. This first synthesis of polyamines were observed. This firs synthesis of polyamines occurred very early during the G1 phase, concomitant to the synthesis of RNAs. A RNA, probably messenger-like RNA, was synthesized very actively only during the first hours of activation in the culture medium plus 2,4-dichlorophenoxyacetic acid, or in water. At the onset of the S phase, after 12h of activation, an incorporation of [3H] thymidine was also detected. A second putrescine synthesis and polyamine accumulation began during the progression of the S phase. During the progression of mitosis, there was a decrease of polyamine synthesis and accumulation.

The Acropetal Wave of Developmental Cell Death of Tobacco Corolla Is Preceded by Activation of Transglutaminase in Different Cell Compartments

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.

Polyamine effects on the stability of DNA-actinomycin D complex

Abstract Simultaneous interactions of spermidine and actinomycin D on the DNA molecule were measured in vitro by means of the variations in the absorption spectrum of the actinomycin D- DNA complex after addition of polyamines. Putrescine did not show detectable effects, spermidine produced a small hyperchromism and spermine a marked hyperchromism. The separation of the actinomycin D-DNA complex labelled with [3H] actinomycin by filtration trough Sephadex columns, shows a great decrease of relative radioactivity bound to DNA when spermine is added to the medium.

Auxin-like activity of 1,2-benzisothiazole derivatives

Abstract The 1,2-benz iso thiazol-3-yl-acetic and -3-yl-butyric acids and their ethyl esters, amides and nitriles are generally active in the split pea stem test, induce an increase in both length and fresh weight of pea internodes, inhibit the development of pea roots, and, with some exceptions (1,2-benz iso thiazol-3-yl-butyric amide and nitrile), induce the production of ethylene by pea segments. Moreover they stimulate cell multiplication and raise the degree of hydration of Helianthus tuberosus explants grown in vitro . These activities are often similar or sometimes higher than those of IAA. By contrast, the 1,2-benz iso thiazole derivatives having a side chain with an odd number of carbon atoms (-3-yl-carboxylic and propionic acids, amides, ethyl esters and nitriles) are inactive or show a far lower activity.

Transglutaminase, an enzyme involved in flower senescence and developmental cell death

Abstract To acquire further knowledge on flower senescence and developmental cell death (DCD), we examined protein-protein and protein-polyamine covalent interactions mediated by transglutaminase (TGase) in the tobacco corolla model. In tobacco, corolla senescence proceeds acropetally and is characterised by the formation of a basal abscission zone (AZ) and by changes in the orientation of corolla teeth. TGase, present in various cell compartments, was analysed by using the Arabidopsis thaliana TGase antibody. A 58-kDa form was immunorecognised in micro-somal, plastidial (together with a 38-kDa band) and cell wall fraction; a 52-kDa protein was found only in the soluble fraction. The activity reached the maximum at the “no-return point” of senescence corresponding to AZ formation. TGase enzyme activity was also detected in microsome, soluble, plastid, and cell wall fractions. Our results suggest that TGase may be released in the cell wall through the Golgi vesicles. In particular, the cell wall TGase activity could be involved in cell wall strengthening, being especially active where the corolla teeth curl, and during the formation of the AZ.