Proteolytic activity, identification and expression profile of a KDEL-CysEP gene in common lilac flowers depending on the flowering conditions

In a temperate zone, common lilac blooms in May, and the whole flowering process lasts ca. 3 weeks. The flowering process starts in July of the previous year, during winter flower buds are in the state of deep dormancy, and their activity starts again in the spring of the next year. Forcing is a method, that may induce flowering in plants, independently of the natural blooming period. The temperatures required to start blooming in lilac during standard forcing method in November are ca. 37°C. This method is rapid, but gives panicles of poor quality. The alternative is forcing at 15°C, but in November plants forced by this method require 49 days to bloom as compared to 23 days for the standard 37°C. Anyway, the main advantage of this method is a very good quality of flowers and long vase life. In this study we investigated the cysteine protease activity and its expression profile at different stages of flowering (flower bud whitening and swelling, open flowers, wilted flowers) for lilac flowers (Syringa vulgaris L.) blooming under three different conditions: natural conditions in May and forcing in a greenhouse in November at 37°C (standard forcing) or at 15°C (alternative forcing). The gene expression did not correlate with the cysteine endoprotease activity. Alternative forcing method at 15°C affected the flowering process delaying senescence, presumably due to the low cysteine protease activity.