Tuberization in potato involves a switch from apoplastic to symplastic phloem unloading

Citation
R. Viola et al., Tuberization in potato involves a switch from apoplastic to symplastic phloem unloading, PL CELL, 13(2), 2001, pp. 385-398
Citations number
53
Categorie Soggetti
Plant Sciences","Animal & Plant Sciences
Journal title
PLANT CELL
ISSN journal
10404651 → ACNP
Volume
13
Issue
2
Year of publication
2001
Pages
385 - 398
Database
ISI
SICI code
1040-4651(200102)13:2<385:TIPIAS>2.0.ZU;2-F
Abstract
Phloem unloading was studied in potato plants in real time during the early stages of tuberization using carboxyfluorescein (CF) as a phloem-mobile tr acer, and the unloading pattern was compared with autoradiography of tubers that had transported C-14 assimilates. In stolons undergoing extension gro wth, apoplastic phloem unloading predominated. However, during the first vi sible signs of tuberization, a transition occurred from apoplastic to sympl astic transport, and both CF and C-14 assimilates subsequently followed ide ntical patterns of phloem unloading. It is suggested that the switch to sym plastic sucrose unloading may be responsible for the upregulation of severa l genes involved in sucrose metabolism. A detailed analysis of sugar levels and C-14 sugar partitioning in tuberizing stolons revealed a distinct diff erence between the apical region of the tuber and the subapical region. Ana lysis of invertase activity in nontuberizing and tuberizing stolons reveale d a marked decline in soluble invertase in the subapical region of swelling stolons, consistent with the switch from apoplastic to symplastic unloadin g. However, cell wall-hound invertase activity remained high in the apical 1 to 2 mm of tuberizing stolons. Histochemical analysis of potato lines tra nsformed with the promoter of an apoplastic invertase gene (invGE) linked t o a reporter gene also revealed discrete gene expression in the apical bud region. Evidence is presented that the apical and lateral tuber buds functi on as isolated domains with respect to sucrose unloading and metabolism.