Discussion:
We demonstrate here that fruit development (and thus by extension, seed
production) in an annual plant species is prioritised at the expense of
vegetative tissues under water stress through relatively greater xylem
resistance to cavitation in those tissues supplying water to fruit. We
found that the xylem of vegetative tissues cavitated early during
drought, while the loss of xylem function in the main stem and the
peduncle occurred much later. These cavitation resistant tissues
provided a xylem pathway that prioritized water supply to fruit from
other plant parts even when the plant is fully disconnected from a soil
water source. The prioritisation of water supply to reproduction in
tomato means that unlike observations in perennial plants, the fruit of
tomato behaves as a hydraulic parasite upon the vegetative body.