Transpiration from shoots triggers diurnal changes in root aquaporin expression

Climate Change Research Team, National Agricultural Research Center for Tohoku Region, Morioka, Japan.
Plant Cell and Environment (Impact Factor: 6.96). 03/2011; 34(7):1150-63. DOI: 10.1111/j.1365-3040.2011.02313.x
Source: PubMed


Root hydraulic conductivity (Lp(r)) and aquaporin amounts change diurnally. Previously, these changes were considered to be spontaneously driven by a circadian rhythm. Here, we evaluated the new hypothesis that diurnal changes could be triggered and enhanced by transpirational demand from shoots. When rice plants were grown under a 12h light/12h dark regime, Lp(r) was low in the dark and high in the light period. Root aquaporin mRNA levels also changed diurnally, but the amplitudes differed among aquaporin isoforms. Aquaporins, such as OsPIP2;1, showed moderate changes, whereas root-specific aquaporins, such as OsPIP2;5, showed temporal and dramatic induction around 2h after light initiation. When darkness was extended for 12h after the usual dark period, no such induction was observed. Furthermore, plants under 100% relative humidity (RH) showed no induction even in the presence of light. These results suggest that transpirational demand triggers a dramatic increase in gene expressions such as OsPIP2;5. Immunocytochemistry showed that OsPIP2;5 accumulated on the proximal end of the endodermis and of the cell surface around xylem. The strong induction by transpirational demand and the polar localization suggest that OsPIP2;5 contributes to fine adjustment of radial water transport in roots to sustain high Lp(r) during the day.

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    • "For instance, AtPIP2;5 and AtPIP2;7 showed a coupled profile with AtPIP1;4 and AtPIP1;3, as well as AtPIP2;1 and AtPIP2;2 with AtPIP1;2 and AtPIP1;1[58,69,70,104,111112113114115. In rice, transcriptional correlations were corroborated by the in situ co-localization of OsPIP2;1, OsPIP1;2 and OsPIP1;1[109,116]. Interestingly, OsPIP2;1 and OsPIP1;2 show similar transcriptional patterns in rice mutant lines under water deficit[117]. "
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    ABSTRACT: The highly conserved plant aquaporins, known as PIPs, are the main gateways for cell membrane water exchange. Years of research have described in detail the properties of the PIP2 subfamily. However, characterizing the PIP1 subfamily has been difficult due to the failure to localize to the plasma membrane. In addition, the discovery of the PIP1-PIP2 interaction suggested that PIP1 aquaporins could be regulated by a complex posttranslational mechanism that involves trafficking, heteromerization and fine-tuning of channel activity. This review not only considers the evidence and findings but also discusses the complexity of PIP aquaporins. To establish a new benchmark in PIP regulation, we propose to consider PIP1-PIP2 pairs as functional units for the purpose of future research into their physiological roles.
    Full-text · Article · Nov 2015 · FEBS letters
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    • "The abundance of many isoforms of PIPs and TIPs in the roots of rice plants grown in controlled growth chambers showed clear diurnal changes at both mRNA and protein levels: it is low at night and gradually increases toward the onset of the light period, although the amplitudes differ significantly among the aquaporin isoforms. For example, for diurnally regulated OsPIP2;5 the mRNA level was 100 times and the protein level was 4 times the respective minimum levels during dark period (Sakurai-Ishikawa et al., 2011). However, up-regulation of root aquaporins during the light period was strongly inhibited when the shoots are exposed to over-humid condition (Sakurai-Ishikawa et al., 2011). "
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    ABSTRACT: Transpiration, the evaporation from aerial parts of plants, is major driving force for the roots to uptake water from the soil. Aquaporins, the water channel proteins, are thought to play crucial roles in regulation of root hydraulic conductivity. Here we demonstrate that the evaporative demand plays a dominant role in the induction of specific aquaporins in rice (Oryza sativa) roots in seedlings grown hydroponically and then transferred to an open field. We found that the abundance of the root-specific aquaporin transcripts, OsPIP2;4, OsPIP2;5 and OsTIP2;1 at 8 a.m. is highly correlated with the evaporative demand in the morning (evaluated from potential evaporation averaged over 4 h before root sampling). Aquaporin isoforms with higher correlation to potential evaporation showed higher diurnal amplitude of their expression. Our study suggests that rice plants sense daily weather and responded to it by adjusting the expression of specific root aq-uaporin genes. © 2015, Society of Agricultural Meteorology of Japan. All rights reserved.
    Preview · Article · Jun 2015 · Journal of Agricultural Meteorology
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    • "This highlights the need for genome-wide studies on the expression of aquaporins in relation to water status in field-grown plants in order to drive a more informative and precise conclusion on how to manipulate aquaporin genes to improve plant productivity. Sakurai-Ishikawa et al. [45] have shown that most of root aquaporins in rice were upregulated during periods of high transpiration demand (beginning of the light period) probably to maintain a positive plant water status. However, the relevance of this information to plant responses in the field is limited because the authors grew the plants under non-saturating conditions of 370 ␮mole m −2 s −1 light intensity and 75% relative humidity (RH), where stomatal depression did not occur but rather the rates of transpiration increased progressively during the whole light period. "
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    ABSTRACT: This study aimed at specifying the reasons of unbalanced water relations of rice in the field at midday which results in slowing down photosynthesis and reducing water use efficiency (WUE) in japonica and indica rice under well-watered and droughted conditions. Leaf relative water content (RWC) decreased in the well-watered plants at midday in the field, but more dramatically in the droughted indica (75.6 and 71.4%) than japonica cultivars (85.5 and 80.8%). Gas exchange was measured at three points during the day (9:00, 13:00 and 17:00). Leaf internal CO2 (Ci) was not depleted when midday stomatal depression was highest indicating that Ci was not limiting to photosynthesis. Most aquaporins were predominantly expressed in leaves suggesting higher water permeability in leaves than in roots. The expression of leaf aquaporins was further induced by drought at 9:00 without comparable responses in roots. The data suggests that aquaporin expression in the root endodermis was limiting to water uptake. Upon removal of the radial barriers to water flow in roots, transpiration increased instantly and photosynthesis increased after 4 h resulting in increasing WUE after 4 h, demonstrating that WUE in rice is largely limited by the inadequate aquaporin expression profiles in roots.
    Full-text · Article · Oct 2014 · Plant Science
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