Differences in aquaporin levels among cell types of radish and measurement of osmotic water permeability of individual protoplasts

• Published in: Plant and cell physiology Vol. 44; no. 3; pp. 277 - 286
• Main Authors: Suga, S. (Nagoya Univ. (Japan)), Murai, M, Kuwagata, T, Maeshima, M
• Format: Journal Article
• Language: English
• Published: Japan Oxford University Press 01.03.2003; Oxford Publishing Limited (England)
• Subjects: Algorithms; Aquaporins - metabolism; Cell Membrane Permeability - physiology; CELL MEMBRANES; dithiothreitol; DTT; Equipment Design; Hypocotyl - cytology; Hypocotyl - metabolism; Keywords: Aquaporin — Cell specificity — Osmotic water permeability — Plasma membrane — Protoplast assay — Radish; Microscopy; Models, Biological; OSMOTIC PRESSURE; osmotic water permeability; PBS; PERMEABILITY; phosphate-buffered saline; PIP; Plant Roots - cytology; Plant Roots - metabolism; plasma membrane; plasma membrane intrinsic protein; Pos; PROTEINS; PROTOPLASTS; Protoplasts - physiology; radish plasma membrane aquaporin; radish vacuolar membrane aquaporin; Raphanus - cytology; Raphanus - physiology; RAPHANUS SATIVUS; RsPIP; RsTIP; TIP; tonoplast intrinsic protein; VACUOLES; Water - metabolism
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcg032

We investigated tissue- and cell-specific accumulation of radish aquaporin isoforms by immunocytochemical analysis. In taproots, the plasma membrane aquaporins (RsPIP1 and RsPIP2) were accumulated at high levels in the cambium, while the tonoplast aquaporin (RsTIP) was distributed in all tissues. The three isoforms were highly accumulated in the central cylinder of seedling roots and hypocotyls, and rich in the vascular tissue of the petiole of mature plants. The results suggest that RsPIP1 and RsPIP2 are abundant in the cells surrounding the sieve tube of the radish plant. The swelling rate of protoplasts in a hypotonic solution was determined individually by a newly established method to compare the osmotic water permeability of different cell types. All cells of the cortex and endodermis in seedlings showed a high water permeability of more than 300 µm s–1. There was no marked difference in the values between the root endodermis and cortex protoplasts, although the RsPIP level was lower in the cortex than in the endodermis. This inconsistency suggests two possibilities: (1) a low level of aquaporin is enough for high water permeability and (2) the water channel activity of aquaporin in the tissues is regulated individually. The uneven distribution of aquaporins in tissues is discussed along with their physiological roles.