Using Aphids to Sample Phloem Sap

Phloem transport is crucial for plant growth and development because it mediates the transport of metabolites, mineral nutrients, proteins, and secondary compounds between plant tissues. The type of phloem loading with such compounds depends on their concentration in the phloem and the surrounding cells. To investigate these processes, it is very important to collect phloem sap from intact plants and determine the concentrations of the various compounds. This chapter describes aphid stylectomy, in which severed aphid stylets are used to collect phloem sap. Compared to other methods for collecting phloem exudate (e.g., direct stem incisions, EDTA-facilitated exudation), aphid stylectomy is probably the method to collect the most authentic phloem sap. With some modifications, this method can be used for various plant species, including monocots, herbaceous dicots, and tree seedlings. The probability that sufficient phloem sap will exude from the severed aphid stylet is often unpredictable and should therefore be tested for the respective plant species and the respective experimental conditions. It should also be noted that aphid stylectomy is time-consuming and requires specialized equipment and extensive experience.