Functional Analysis of Water Channels in Barley Roots

Abstract

We identified three genes homologous to water channels in the plasma membrane type subfamily from roots of barley seedlings. These genes were designated HvPIP2;1, HvPIP1;3, and HvPIP1;5 after comparison to Arabidopsis aquaporins. Competitive reverse transcription (RT)-PCR was applied in order to distinguish and to quantify their transcripts. The HvPIP2;1 transcript was the most abundant among the three in roots. Salt stress (200 mM NaCl) down-regulated HvPIP2;1 (transcript and protein), but had almost no effect on the expressions of HvPIP1;3, or HvPIP1;5. Approximately equal amounts of the transcripts of the three were detected in shoots, and salt stress enhanced the expression of HvPIP2;1 but not of HvPIP1;3, or HvPIP1;5. HvPIP2;1 protein was confirmed to be localized in the plasma membrane. Functional expression of HvPIP2;1 in Xenopus oocytes confirmed that HvPIP2;1 encoded an aquaporin that transports water. This water permeability was reduced by HgCl(2), which is a typical water channel inhibitor. This activity was not modified by some inhibitors against protein kinase and protein phosphatase.

Aquaporin structure–function relationships: Water flow through plant living cells

“…On the other hand, salt and water stresses induced the accumulation of ZmTIP2-3 transcripts [118]. Similar findings on the dominance of symplastic water transport were obtained using transgenic tobacco plants expressing an antisense construct of the tobacco NtAQP1 gene that encodes another PIP1b isoform [25], while Barley HvPIP2;1 is a plasma membrane aquaporin and its expression was downregulated after salt stress in barley [38]. Two aquaporin-encoding transcripts were found to be down-regulated during the first 15 and 60 min of a salt treatment, respectively.…”

“…The high level of expression of ZmTIP1 in maize tissues (root epidermis, root endodermis, small parenchyma cells surrounding mature xylem vessels in the root, and so on) facilitates rapid flow of water through the tonoplast to permit osmotic equilibration between the cytosol and the vacuolar content, and to permit rapid transcellular water flow through living cells when required. Specific plasma membrane aquaporins of the PIP1 subfamily are expressed in sieve elements and guard cells [37] Barley HvPIP2:1 is a plasma membrane aquaporin and its expression was down-regulated after salt stress in barley [38].…”

Identification of Differentially Expressed Genes by cDNA-AFLP Technique in Response to Drought Stress in Triticum durum

“…Its expression was generally down-regulated upon drought stress. The aquaporin PIP has been found to function in water transport through the plasma membrane in many plant species (46)(47)(48)(49). The down-regulation of the aquaporin TDF 83 in wheat leaves under drought stress may be due to an a empt to avoid the possible loss of water.…”

Barley plasma membrane intrinsic proteins (PIP Aquaporins) as water and CO2 transporters

“…Three PIPs: HvPIP2;1, HvPIP1;3, and HvPIP1;5, were first identified and barley PIPs were analyzed by the authors and collaborators [12]. Absolute amounts of these 3 transcripts were determined in the roots of barley seedlings.…”

“…During several hours to days of salt or osmotic stress, the down-regulation of several aquaporins including HvPIP2;1 was observed in many plant species [10,12,29,32]. A decrease in the level of aquaporins and reduction of Lp can prevent cell death due to continuous dehydration and gain time for intracellular osmotic adjustment.…”