When placed in the vase, cut rose flowers often exhibit symptoms of water stress such as leaf wilting, lack of flower development and bending of the stem (Mayak et al 1974). Especially the pedicel, the stem segment between the leaves and the flower head, was found to show bending.
The pedicel is less lignified than the rest of the stem and due to the presence of the flower head it may therefore bend at low turgor values (Parups and Voisy 1976).
The cause of the development of water stress in cut rose flowers has been well established.
It was found that a resistance to water flow developed in the stem (Mayak et al 1974). Because of this occlusion, the rate of water uptake becomes lower than the rate of transpiration and a net loss of water ensues (Mayak et al 1974).
The nature of the blockage in the stems of cut flowers, however, is still a matter of debate.
This paper attempts to give a (brief) review of the literature pertaining to the cause of vascular blockage in stems of cut rose flowers.
This review also includes data obtained in our lab.
Most of the latter data are unpublished, and details of the experiments will be included in papers that have either been submitted or are currently in preparation.
The literature mentions three possible causes of vascular blockage:
- Occlusion may be due to the plant itself
In intact plants, old xylem elements often become occluded with tyloses or gums (Zimmerman 1983). Some fungi known to cause wilting diseases were also found to elicit production of gum-like vascular plugs and in Ricinus communis even the culture filtrate from a pathogenic fungus resulted in vascular blockage (VanderMolen et al 1983). This filtrate contained enzymes as polygalacturonase, polygalacturonate lyase and -1,4-xylanase.
Fungus infection in tomato, cotton (Duniway 1973) and chrysanthemum (Hall and Busch 1971) was similarly found to induce vascular occlusion.
Gel-like vascular blockage in Ricinus communis was also induced by exogenous ethylene (VanderMolen et al 1983) and ethephon in aqueous solution resulted in vascular blockage in Prunus cerasus (Olien and Bukovac 1982). Since ethylene is released after cutting of plant tissues (Yang and Pratt 1978), the mere cutting of stems may possibly lead to vascular blockage.