ROLE OF STEM CUT-SURFACE IN CUT-ROSE PERFORMANCE

The following observations show that the very cut-surface of the stem plays an important role in the diminishing water-uptake capacity:

• During vase-life, resistance to water flow through stem segments increases, predominantly in the lowermost 1 cm of stem.
• Cooling the lower end of the stem to 0°C, with leaves and flower exposed to high light intensity and normal temperature (20°C), markedly improves performance, fresh-weight evolution and water turnover.
• Cooling the lowermost 2 ½ cm portion of stem, including the cut-surface, has more effect than cooling a 5 cm portion a little higher up the stem but leaving the cut-surface at 20°C.
• Daily repeated, one-minute exposure of the stem base to 0.1 % silver nitrate likewise improves performance.
• Elimination of cut-end uptake, and substituting lateral uptake for it, via bark-stripped lengths of stem, results in a low but nearly constant level of water turnover, and good performance.

Time-series of scanning electron micrographs show that the cut-surface very quickly becomes the site of prolific bacterial and fungal growth, in spite of the vase water staying clear and having a low level of microbial contamination.

Although the abundant presence of bacteria and fungal growth on the cut-surface is very suggestive of a primarily microbial explanation for diminishing water uptake, there is no decisive evidence yet in favour of either a micro-organismal or physiological interpretation. Cooling lowers both kinds of activities. Silver effects can result from disinfection, but also from anti-(wound)-ethylene action. SEM-evidence of caked (and desiccated) bacterial deposits and fungal mats is no conclusive proof of water-impenetrability in the live situation (cf. deposits of Al(OH)₃ precipitate, other paper of ours in this volume).

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