Positive root pressure and xylem repair

tomaat fruit

The main aim of this project is to further our understanding of the conditions under which positive root pressures develop in the tomato plant, and to test the hypothesis that the ability to generate positive root pressure enhances drought-resistance.

Supervisor and contact

Dr. Frederic Lens (group leader Functional Traits, Naturalis Biodiversity Center, frederic.lens@naturalis.nl)

Period and duration

Ca. 6 months, project can start now

Study and level

MSc project

Background
& context

Climate change is predicted to strongly influence rainfall patterns across the globe, with potentially disastrous consequences for crops and human food production. Recent work has greatly improved our understanding of plant function during drought, but has focused mostly on woody plants. There is therefore an urgent need to study herbaceous plants that comprise most of the world’s crops. In particular, it has been hypothesized that positive root pressure could play a crucial role in the survival of herbaceous species during drought, by removing gas bubbles (‘embolisms’) formed in the water conducting vessels due to severe drought stress, a process called ‘xylem repair’. While generation of positive root pressure has been verified in some species (including in the tomato plant, Solanum lycopersicum), its potential role xylem repair and in providing drought-tolerance is controversial in many cases and untested in herbs.

Objectives
and goals

The main aim of this project is to further our understanding of the conditions under which positive root pressures develop in the tomato plant, and to test the hypothesis that the ability to generate positive root pressure enhances drought-resistance by “refilling” embolized xylem vessels. The project also involves interacting with the tomato industry (Rijk Zwaan) to obtain different genotypes of tomato and provide feedback regarding the development of positive root pressure and any benefits during drought or fruit development (root pressure has been associated to damage fruits by bursting them open).

Material tasks
and approach

Different varieties of tomato plants will be grown under well-watered conditions. A subset of plants will be subjected to increasing levels of drought, and drought stress will be monitored daily by measuring soil water-content, leaf water-potential and gas-exchange parameters. After rewatering the droughted plants, we will monitor stem diameter variation and sap-flow, to estimate root pressure (following De Swaef et al. 2013). To visualize xylem refilling, these plants will be brought to the X ray scanning facility in Ghent University (Belgium), where they will be repeatedly scanned after rewatering to observe a direct link between positive root pressure and refilling. Vulnerability curves will assess differences in embolism resistance, by scanning plants at different levels of drought stress and measuring the area of embolized vessels relative to the area of total initially functional xylem.

Student
requirements

We are looking for a student with an interest in plant hydraulics and modelling.