Go with the Phloem: A Review of the Methods to Collect Plant Phloem Tissue

The study of plant phloem tissue is important for understanding plant physiology, yet the anatomy and small size of the phloem tissue make direct sampling challenging. Due to the absence of a single method that allows for phloem extraction in every species, researchers have developed several strategies to address this drawback. These strategies can be categorized into three groups: classical, advanced, and mechanical extraction methods. Classical methods, including cucurbit drip, EDTA-facilitated exudation, stylectomy, and heterografting, have a long history in phloem research but are generally less precise. Advanced methods, such as TRAP-seq, FACS, scRNA-seq, and LCM, leverage recent technological advancements to provide precise measurements, with the drawback of requiring specialized expertise and costly reagents. Mechanical methods focus on species from which phloem can be directly sampled, Plantago and celery. This review discusses these methods, detailing their advantages and disadvantages, and how they can be applied to current phloem studies.