Harmannus Harkema

Effects of vase-water bacteria on the senescence of cut carnation flowers

Abstract Cut flowering carnation stems (Dianthus caryophyllus L. cvs. Scania and White Sim) were held in water for 7 days at 20°C, after which a low hydraulic conductance and a high number of bacteria were found in the basal 5-cm stem segment. This suggested that bacteria may play a role in determining flower longevity. When taking special precautions, it was possible to keep flowering stems sterile until flower senescence. Petal wilting in the sterile stems occurred at thesame time as in non-sterile controls. Inclusion of antibacterial chemicals in the water also prevented accumulation of bacteria in the solution and in flower stems, but had no effect on flower longevity. Inclusion of bacteria, originating from the vase water of carnation flowers, in vase water at a number that is normally reached after 7 days (107 cfu ml−1) did not significantly hasten flower senescence. It is concluded that the bacterial population developing in the stems of cut carnation flowers during vase life leads to vascular occlusion but this apparently has little effect on flower longevity.

Water relations and senescence of cut Iris flowers: effects of cycloheximide

Abstract When placed in water directly after harvest, flowering stems of Iris x hollandica Tub., cultivar ‘Blue Magic’, showed inrolling of the tepal edges after about five days and tepal wilting after about six days. These senescence symptoms were not due to an occlusion in the stems as both the water balance and the water potential did not decrease substantially when the stem ends were held in water. Cycloheximide at 50 μM, included in the water after flower opening, delayed inrolling by about two and wilting by about four days. Cycloheximide resulted in rapid stomatal closure and a decrease in the rates of transpiration and water uptake, but its effect on senescence was not related with improvement of the water balance of the flowers. The results show that the delay of tepal senescence by cycloheximide is located in the tepal cells, and not in the overall water relations. Irreversible water loss from the tepals is apparently controlled by de novo synthesis of proteins. The results also indicate that flower senescence in ethylene-insensitive species, such as Iris , responds similarly to cycloheximide as carnation, an ethylene-sensitive flower.

Delay of Iris flower senescence by cytokinins and jasmonates

It is not known whether tepal senescence in Iris flowers is regulated by hormones. We applied hormones and hormone inhibitors to cut flowers and isolated tepals of Iris × hollandica cv. Blue Magic. Treatments with ethylene or ethylene antagonists indicated lack of ethylene involvement. Auxins or auxin inhibitors also did not change the time to senescence. Abscisic acid (ABA) hastened senescence, but an inhibitor of ABA synthesis (norflurazon) had no effect. Gibberellic acid (GA3 ) slightly delayed senescence in some experiments, but in other experiments it was without effect, and gibberellin inhibitors [ancymidol or 4-hydroxy-5-isopropyl-2-methylphenyltrimethyl ammonium chloride-1-piperidine carboxylate (AMO-1618)] were ineffective as well. Salicylic acid (SA) also had no effect. Ethylene, auxins, GA3 and SA affected flower opening, therefore did reach the flower cells. Jasmonates delayed senescence by about 2.0 days. Similarly, cytokinins delayed senescence by about 1.5-2.0 days. Antagonists of the phosphatidylinositol signal transduction pathway (lithium), calcium channels (niguldipine and verapamil), calmodulin action [fluphenazine, trifluoroperazine, phenoxybenzamide and N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide hydrochloride (W-7)] or protein kinase activity [1-(5-isoquinolinesulfonyl)-2-methylpiperazine hydrochloride (H-7), N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) and N-(2-aminoethyl)-5-isoquinolinesulfonamide dihydrochloride (H-9)] had no effect on senescence, indicating no role of a few common signal transduction pathways relating to hormone effects on senescence. The results indicate that tepal senescence in Iris cv. Blue Magic is not regulated by endogenous ethylene, auxin, gibberellins or SA. A role of ABA can at present not be excluded. The data suggest the hypothesis that cytokinins and jasmonates are among the natural regulators.

Opening of Iris flowers is regulated by endogenous auxins

Flower opening in Iris (Iris×hollandica) requires elongation of the pedicel and ovary. This moves the floral bud upwards, thereby allowing the tepals to move laterally. Flower opening is requires with elongation of the pedicel and ovary. In cv. Blue Magic, we investigated the possible role of hormones other than ethylene in pedicel and ovary elongation and flower opening. Exogenous salicylic acid (SA) and the cytokinins benzyladenine (N6-benzyladenine, BA) and zeatin did not affect opening. Jasmonic acid (JA) and abscisic acid (ABA) were slightly inhibitory, but an inhibitor of ABA synthesis (norflurazon) was without effect. Flower opening was promoted by gibberellic acid (GA(3)), but two inhibitors of gibberellin synthesis (4-hydroxy-5-isopropyl-2-methylphenyltrimethyl ammonium chloride-1-piperidine carboxylate, AMO-1618; ancymidol) did not change opening. The auxins indoleacetic acid (IAA) and naphthaleneacetic acid (NAA) strongly promoted elongation and opening. An inhibitor of auxin transport (2,3,5-triodobenzoic acid, TIBA) and an inhibitor of auxin effects [α-(p-chlorophenoxy)-isobutyric acid; PCIB] inhibited elongation and opening. The data suggest that endogenous auxins are among the regulators of the pedicel and ovary elongation and thus of flower opening in Iris.