The development of a novel technique for sampling xylem sap from intact, transpiring plants using Philaenus spumarius, a xylem-feeding insect.
Many approaches have been employed to extract xylem sap from plants but
uncertainty remains about exactly what is sampled by these methods and the extent to
which extracted fluid reflects the content of the transpiration stream. The aim of this
thesis was to develop a new technique for sampling xylem sap from intact, transpiring
plants, using the common spittlebug Philaenus spumarius, a xylem-feeding insect.
Continuous monitoring of the insect's excretion rate was achieved through a
balance system connected to a computer. Using this procedure, it was demonstrated that
P. spumarius feeds from the main transpiration stream and it was shown that P. spumarius
can feed against xylem tensions more negative than previously realised.
The relationship of the fluid extracted by P. spumarius to xylem sap was tested
through a xylem perfusion system. The concentration of the inorganic ions tested was not
altered by the insect's metabolism. In addition, ABA was detected in the excreta and an
increase in excreta ABA content was shown in water-stressed plants.
The P. spumarius technique was used to demonstrate the xylem dynamics of Ca2+,
ABA, and diurnal cycles of ion composition in intact, transpiring plants.
In conclusion, P. spumarius represents a powerful vehicle for the quasi-continuous
and quasi-non-invasive extraction of xylem sap from intact, transpiring plants.