Physiological and molecular aspects of flower senescence in Lilium longiflorum ; Aspetti fisiologici e moleculari della senescenza florale in Lilium longiflorum

Dottorato di ricerca in Ortoflorofrutticoltura ; The flower is the organ involved in plant reproduction and is removed once pollinated or after a given period of time depending from the species. Flower senescence allows resource allocation to developing ovary or to other plant organs. Understanding the underling mechanisms of flower senescence would be extremely useful for improving post-harvest flower quality and longevity. Senescence is certainly an irreversible and programmed event which culminates with cell death and several indications point to this process as a form of programmed cell death (PCD). Physiological and biochemical changes occurring during lily senescence were described. The process of senescence starts three days after flowering, before visible signs of wilting. Mesophyll cell degradation accompanies the appearance of visible signs of senescence and is associated with vacuole permeabilization and rupture. Changes in protein content are accompanied by the increase in total protease activity, caspase-like protease activation, DNA degradation and alteration of the endogenous hormone levels. cDNAs encoding cysteine proteases were isolated from lily tepals and sequenced. The genes codify for KDEL-proteases of 356 aa (LlCyp9 and LlCyp20) belonging to the papain-like family and VPEs of 480 aa (LlVPE4 and LlVPE5) belonging to the legumain family. The expression of LlCyp9 increased during tepal senescence and decreased in completely wilted tissues. Western blotting with an antibody raised against a tomato KDEL-cysteine protease identified homologous proteins in lily tepals. Transient expression of LlCyp9 fused with YFP reporter localized the protease within the ER. LlVPE4 expression was high in tepals form flower bud and opening flower, while decreased during flower senescence. Moreover, VPE activity was detected in crude extracts from lily tepals using a fluorogenic substrate. ; Il fiore è l’organo deputato alla riproduzione e viene rimosso dopo l’impollinazione o dopo un certo periodo di tempo in ...