Light and turgor affect the water permeability (aquaporins) of parenchyma cells in the midrib of leaves of Zea mays

Abstract

In response to light, water relation parameters (turgor, half-time of water exchange, T 1/2 , and hydraulic conductivity, Lp; T 1=2 }1=Lp) of individual cells of parenchyma sitting in the midrib of leaves of intact corn (Zea mays L.) plants were investigated using a cell pressure probe. Parenchyma cells were used as model cells for the leaf mesophyll, because they are close to photosynthetically active cells at the abaxial surface, and there are stomata at both the adaxial and abaxial sides. Turgor ranged from 0.2 to 1.0 MPa under laboratory light condition (40 lmol m 22 s 21 at the tissue level), and individual cells could be measured for up to 6 h avoiding the variability between cells. In accordance with earlier findings, there was a big variability in T 1/2 s measured ranging from 0.5 s to 100 s, but the action of light on T 1/2 s could nevertheless be worked out for cells having T 1/2 s greater than 2 s. Increasing light intensity ranging from 100 lmol m 22 s 21 to 650 lmol m 22 s 21 decreased T 1/2 by a factor up to five within 10 min and increased Lp (and aquaporin activity) by the same factor. In the presence of light, turgor decreased due to an increase in transpiration, and this tended to compensate or even overcompensated for the effect of light on T 1/2. For example, during prolonged illumination, cell turgor dropped from 0.2 to 1.0 MPa to-0.03 to 0.4 MPa, and this drop caused an increase of T 1/2 and a reduction of cell Lp, i.e. there was an effect of turgor on cell Lp besides that of light. To separate the two effects, cell turgor (water potential) was kept constant while changing light intensity by applying gas pressure to the roots using a pressure chamber. At a light intensity of 160 lmol m 22 s 21 , there was a reduction of T 1/2 by a factor of 2.5 after 10-30 min, when turgor was constant within 60.05 MPa. Overall, the effects of light on T 1/2 (Lp) were overriding those of turgor only when decreases in turgor were less than about 0.2 MPa. Otherwise, turgor became the dominant factor. The results indicate that the hydraulic conductivity increased with increasing light intensity tending to improve the water status of the shoot. However, when transpiration induced by light tends to cause a low turgidity of the tissue, cell Lp was reduced. It is concluded that, when measuring the overall hydraulic conductivity of leaves, both the effects of light and turgor should be considered. Although the mechanism(s) of how light and turgor influence the cell Lp is still missing, it most likely involves the gating of aquaporins by both parameters.

Leaf Shrinkage with Dehydration: Coordination with Hydraulic Vulnerability and Drought Tolerance

“…Previous studies showed that K leaf decline in dehydrating leaves was correlated not only with xylem embolism but also with biochemical processes outside the xylem, such as aquaporin deactivation (Johansson et al, 1998;Kim and Steudle, 2007;Scoffoni et al, 2012). To our knowledge, our study is the first to implicate a physical influence of leaf shrinkage in the decline of K leaf with dehydration, using the same correlational approach.…”

Abscisic Acid Down-Regulates Hydraulic Conductance of Grapevine Leaves in Isohydric Genotypes Only

“…Pou et al (2013) reported lower expression of aquaporin genes VvTIP2;1 and VvPIP2;1 and reduced activity of aquaporins in leaves under water deficit coinciding with a decrease of K leaf . Decline of K leaf in dehydrating leaves could also be correlated with low aquaporin activity in the mesophyll (Kim and Steudle, 2007). Importantly, ABA treatment could decrease C-terminal phosphorylation and thus activity of aquaporin AtPIP2;1 within 30 min of application in Arabidopsis seedlings (Kline et al, 2010).…”

Partitioning hydraulic resistance in Sorghum bicolor leaves reveals unique correlations with stomatal conductance during drought

“…The hydraulic resistance of the whole leaf (r * Leaf ) is tightly correlated with maximum rates of gas exchange across a broad range of species (Brodribb et al 2007), but also changes temporally in response to leaf hydration status (Brodribb and Holbrook 2003;Kim and Steudle 2007;Heinen et al 2009) and incident light Scoffoni et al 2008). These temporal responses of r * Leaf can be mediated through cavitation events within the leaf xylem Trifilò et al 2003;Johnson et al 2012), cell collapse of the xylem elements (Cochard et al 2004a;Brodribb and Holbrook 2005;Blackman et al 2010) or changes in aquaporin regulation after water leaves the vasculature (Cochard et al 2007).…”