Differences in Aquaporin Levels among Cell Types of Radish and Measurement of Osmotic Water Permeability of Individual Protoplasts

Abstract

;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 mm 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.

Water relations and an expression analysis of plasma membrane intrinsic proteins in sensitive and tolerant rice during chilling and recovery

“…Results supporting this include the fact that the relative expression of some PIP genes was not always parallel to the changes in root Lp; that Western blots showed little difference between PIP protein abundance in Wasetoitsu and Somewake during the recovery ( Figure 5), even though Lp were clearly different ( Figure 2C); and that, the changes in total PIP protein abundance were not always consistent with the transcript expression level of individual PIP isoforms as described previously [36]. This idea is also supported by the results in Figure 5 that suggest posttranscriptional actions regulate PIP protein.…”

Overexpression of PIP2;5 Aquaporin Alleviates Effects of Low Root Temperature on Cell Hydraulic Conductivity and Growth in Arabidopsis

“…The differences in low-roottemperature responses between the PIP1;4-and PIP2;5-overexpressing plants may reflect functional differences between the two aquaporins (Jang et al, 2004(Jang et al, , 2007Alexandersson et al, 2005;Wudick et al, 2009;Almeida-Rodriguez et al, 2010) or the differences in tissue distribution Suga et al, 2003;Da Ines, 2008;Alexandersson et al, 2010). However, they may also reflect possible differences in regulation mechanisms between PIP1;4 and PIP2;5 or in their water-transporting effectiveness, assuming no major differences in PIP1;4 and PIP2;5 membrane density in plants overexpressing the respective aquaporins.…”

Hypoxia-Responsive Root Hydraulic Conductivity Influences Soybean Cultivar-Specific Waterlogging Tolerance

“…However, root hydraulic conductivity must be regulated not only by root quantity, but also by root water permeability. In radish, water absorption depends mostly on the water channels of the root tissue cells [39]. Furthermore, in soybean roots, the production of an aquaporin, which is a plasma membrane intrinsic protein, varies under hypoxic conditions [40].…”