title: Role of root hydrophobic barriers in salt exclusion of a mangrove plant Avicennia officinalis.
abstract: Salt exclusion at the roots and salt secretion in the leaves were examined in a mangrove, Avicennia officinalis. The non-secretor mangrove Bruguiera cylindrica was used for comparative study of hydrophobic barrier formation in the roots. Bypass flow was reduced when seedlings were previously treated with high salt concentration. A biseriate exodermis was detected in the salt-treated roots, along with an enhanced deposition of hydrophobic barriers in the endodermis. These barriers reduced Na(+) loading into the xylem, accounting for a 90-95% salt exclusion in A. officinalis. Prominent barriers were found in the roots of B. cylindrica even in the absence of salt treatment. A cytochrome P450 gene that may regulate suberin biosynthesis was up-regulated within hours of salt treatment in A. officinalis roots and leaves, corresponding with increased suberin deposition. X-ray microanalysis showed preferential deposition of Na(+) and Cl(-) in the root cortex compared with the stele, suggesting that the endodermis is the primary site of salt exclusion. Enhanced salt secretion and increased suberin deposition surrounding the salt glands were seen in the leaves with salt treatment. Overall, these data show that the deposition of apoplastic barriers increases resistance to bypass flow leading to efficient salt exclusion at the roots in mangroves.
authors.affiliation: Department of Biological Sciences, National University of Singapore, 117543, Singapore; NUS Environmental Research Institute (NERI), National University of Singapore, 117411, Singapore.
authors.forename: Pannaga
authors.initials: P
authors.lastname: Krishnamurthy
authors.forename: Pavithra A
authors.initials: PA
authors.lastname: Jyothi-Prakash
authors.forename: Lin
authors.initials: L
authors.lastname: Qin
authors.forename: Jie
authors.initials: J
authors.lastname: He
authors.forename: Qingsong
authors.initials: Q
authors.lastname: Lin
authors.forename: Chiang-Shiong
authors.initials: CS
authors.lastname: Loh
authors.forename: Prakash P
authors.initials: PP
authors.lastname: Kumar
mesh_terms: D032407:Avicennia / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D057927:Hydrophobic and Hydrophilic Interactions; D007477:Ions; D008055:Lipids; D010788:Photosynthesis / Q000187:drug effects; D053147:Plant Exudates / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000033:anatomy & histology* / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*; D052584:Xylem / Q000187:drug effects / Q000378:metabolism
chemical_list: D007477:Ions; D008055:Lipids; D053147:Plant Exudates; D002734:Chlorophyll; D012965:Sodium Chloride; C065875:suberin; D003577:Cytochrome P-450 Enzyme System; D012964:Sodium
keywords: Casparian bands; bypass flow; mangroves; salt glands; salt secretion; suberin; xylem sap