Abstract: This work was aimed to investigate relationship between induction of endoprotease (EP)activity and classes and acceleration of flower senescence process by water deficit stress (WDS) in cut rose ( Rosa hybrida L. cv. Samantha). Cut flowers at opening stage 2 were treated by repeated WDS, namely 24 h WDS (the first WDS), 12 water recovery, and 24 h WDS (the second WDS), or by 24 h WDS followed 12 h 50 M ABA pretreatment, or held in distilled water directly as untreated control. The results showed that, A) Between the first WDS and the second WDS, no difference was observed in bend neck phenomena during the treatment, but obvious difference was in vase quality of cut flowers after the treatment, and severe phenomena of bull bud was obtained during vase after the second WDS. However, Bend neck degree of flowers could be alleviated obviously by ABA pretreatment. B) When the first WDS was finished, water potential of flower recovered to a level of before the treatment after 6 h water recovery, while fresh weight loss of branch and EP activity of petals recovered to the low level of before the treatment after 12 h water recovery. As the second WDS was given, the changes of EP activity in petals was much dramatic compared to the first WDS finished, although almost no difference was in water potential and fresh weight loss between the first WDS and the second WDS. The WDS-inducible falling of water potential, loss of fresh weight and raise of EP activity were effectively suppressed by ABA pretreatment. C) For control flowers, during the processes of flower opening and senescence, the hydrolytic activity of metalloprotease and cysteine protease in petals was undetectable, while serine protease hydrolytic activity was dominant, and further increased during senescence. The changes of EP activity and types in petals induced by WDS were consistent with that induced by flower opening and senescence. Serine protease activity in petals was induced strongly by the first WDS, and recovered to the primary level after water recovery; and the activity was elevated dramatically by the second WDS. The increment of serine protease activity induced by WDS was significantly depressed by ABA pretreatment. These results above suggested that increment of serine protease activity induced by WDS might be related to acceleration of flower senescence process after WDS.

Key words: cut rose, water deficit stress, serine protease, flower senescence process