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Abstract:
Phytoplasmas colonize specifically the phloem sieve elements (SEs) of plants and influence effectively the
plant physiology. To study and understand the interaction of phytoplasmas and host plants an access to the
cellular, microscale volume of SEs is demanded. Different methods are suitable to collect phloem sap of
phytoplasma-infected plants. The two most common methods are the EDTA-facilitated exudation and the
stylectomy. For the EDTA-facilitated method, the cut end of a leaf is placed into an EDTA solution. The
EDTA prevents and avoids the Ca2+ dependent (re-) occlusion of SEs by binding Ca2+ ions and the mass
flow of SEs is restarted which results in an outflow of the SE content into the EDTA bathing solution. The
advantage is on the one hand a simple application and secondly, feasible for all plant species.
The stylectomy method requires piercing-sucking insects like any aphids. During phloem-sap ingestion,
the stylet is severed by a microcautery device or a laser from the insect body. Due to the high turgor pressure
of the SEs the phloem sap is forced out through the remaining stylet and can be collected with a glass
capillary, for example. The stylectomy delivers pure phloem sap, however, the collected volumes are in the
range of nano liters and the temporal and staff costs are tremendous. A third method is the spontaneous
exudation in phytoplasma-infected apple trees providing only in springtime large volumes of vascular sap
after cutting along the bark. For the spontaneous exudation the proportion of phloem sap is unclear. Thus,
this third method still needs a closer examination in prospective surveys.
