PIP1 Plasma Membrane Aquaporins in Tobacco

Abstract

The molecular functions of several aquaporins are well characterized (e.g., by analysis of aquaporin-expressing Xenopus oocytes). However, their significance in the physiology of water transport in multicellular organisms remains uncertain. The tobacco plasma membrane aquaporin NtAQP1 was used to elucidate this issue. By comparing antisense plants that were inhibited in NtAQP1 expression with control plants, we found evidence for NtAQP1 function in cellular and whole-plant water relations. The consequences of a decrease in cellular water permeability were determined by measurement of transpiration rate and stem and leaf water potential as well as growth experiments under extreme soil water depletion. Plants impaired in NtAQP1 expression showed reduced root hydraulic conductivity and lower water stress resistance. In conclusion, our results emphasize the importance of symplastic aquaporin-mediated water transport in whole-plant water relations.

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.…”

“…In the plant kingdom, a single plant expresses a considerably large number of MIP homologues. These homologues can be subdivided into four groups with highly conserved amino acid sequences and intron positions in each group: the tonoplast intrinsic proteins (TIPs) [19][20][21], the plasma membrane intrinsic proteins (PIPs) [22,23], the nodulin like plasma membrane intrinsic proteins (NIP) [24], and the small intrinsic proteins (SIP) [25]. There are various isoforms of plant TIP: alpha (seed), gamma, root (Rt), and water-stress induced (Wsi).…”

“…There are various isoforms of plant TIP: alpha (seed), gamma, root (Rt), and water-stress induced (Wsi). These proteins may allow the diffusion of water, amino acids and/or peptides from the tonoplast interior to the cytoplasm [21][22][23][24][25][26]. The plasma membrane aquaporins (PIPs) can be divided into two subfamilies: PIP1 with inactive or low waterchannel activity and PIP2 with high water-channel activity [27].…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…Diurnal changes in root hydraulic conductance have been ascribed to changes in plasmalemna or tonoplast aquaporins that act as water channels controlling water fluxes between cells [96,129]. At leaf level, irradiance dependence of K L was found to be also driven by aquaporins or hydrogel effect on extravascular (and/or vascular) tissues [145].…”

Members of the aquaporin family in the developing pea seed coat include representatives of the PIP, TIP, and NIP subfamilies

“…First, it may be noted that the amino acid residues predicted to border the selectivity filter are the same in PIP1 and PIP2 members (exemplified in Table 1 for PsPIP1-1 and PsPIP2-1). Secondly, recent studies in which the expression of PIP1 members was either impaired or enhanced have provided strong evidence that PIP1 members function in cellular and whole-plant water relations (Siefritz et al, 2002;Martre et al, 2002;Aharon et al, 2003).…”