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- Title
Symplasmic phloem unloading and radial post-phloem transport via vascular rays in tuberous roots of Manihot esculenta.
- Authors
Mehdi, Rabih; Lamm, Christian E; Anjanappa, Ravi Bodampalli; Müdsam, Christina; Saeed, Muhammad; Klima, Janine; Kraner, Max E; Ludewig, Frank; Knoblauch, Michael; Gruissem, Wilhelm; Sonnewald, Uwe; Zierer, Wolfgang
- Abstract
Cassava (Manihot esculenta) is one of the most important staple food crops worldwide. Its starchy tuberous roots supply over 800 million people with carbohydrates. Yet, surprisingly little is known about the processes involved in filling of those vital storage organs. A better understanding of cassava carbohydrate allocation and starch storage is key to improving storage root yield. Here, we studied cassava morphology and phloem sap flow from source to sink using transgenic p AtSUC2::GFP plants, the phloem tracers esculin and 5(6)-carboxyfluorescein diacetate, as well as several staining techniques. We show that cassava performs apoplasmic phloem loading in source leaves and symplasmic unloading into phloem parenchyma cells of tuberous roots. We demonstrate that vascular rays play an important role in radial transport from the phloem to xylem parenchyma cells in tuberous roots. Furthermore, enzymatic and proteomic measurements of storage root tissues confirmed high abundance and activity of enzymes involved in the sucrose synthase-mediated pathway and indicated that starch is stored most efficiently in the outer xylem layers of tuberous roots. Our findings form the basis for biotechnological approaches aimed at improved phloem loading and enhanced carbohydrate allocation and storage in order to increase tuberous root yield of cassava.
- Subjects
CASSAVA; PHLOEM; CASSAVA starch; CARBOHYDRATES; PLANT proteomics; FOOD crops
- Publication
Journal of Experimental Botany, 2019, Vol 70, Issue 20, p5559
- ISSN
0022-0957
- Publication type
Article
- DOI
10.1093/jxb/erz297