Characterization of proteases during flower senescence in gladiolus (Gladiolus grandiflora Hort.)

Gladiolus is an ethylene-insensitive flowers, where ethylene does not play much role in its senescence. The role of proteases were explored such as metalloprotease, aspartate protease, serine protease and cysteine protease during flower development in gladiolus. Gladiolus spikes were treated with various protease inhibitors viz., 1,10-phenanthroline (10 mM), pepstatin (5 mM), E-64 (0.01 mM), aprotinin (5 mM) and distilled water (control) for 24 hours at 25°C. We concluded from the study that most effective protease of all the protease inhibitors used was that of cysteine protease (E-64) in delaying the process of flower senescence (by 3 days) as compared with control. Among the compounds used, the best compound was salicylic acid (400 μM) which delayed flower senescence by 5 days in comparison to the control. Moreover, salicylic acid also regulates other senescence regulating factors such as ascorbic acid (AsA), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and ROS (O₂⁻ and H₂O₂) in addition to cysteine protease. Further, loss in fresh weight as well as turgidity was maintained by salicylic acid treatment in comparison to control flowers and other studied treatments. Thus, inhibition of cysteine proteases and enhanced activities of antioxidant enzymes viz-a-viz lower activity of oxidative stress could possibly contribute towards the increase in vase life of gladiolus flowers.