Effects of HgCl2 on CO2 Dependence of Leaf Photosynthesis: Evidence Indicating Involvement of Aquaporins in CO2 Diffusion across the Plasma Membrane

Abstract

Experiments were conducted to examine whether mercury-sensitive aquaporins facilitate photosynthetic CO(2) diffusion across the plasma membrane of leaf mesophyll cells. Discs without abaxial epidermes from Vicia faba leaflets were treated with HgCl(2), an inhibitor of aquaporins. Hydraulic conductivity of the plasma membrane of these discs, measured as the weight loss of the discs in the 1 M sorbitol solution, was inhibited by sub-mM concentrations of HgCl(2) by 70 to 80%. Photosynthetic CO(2) fixation was also inhibited by the HgCl(2) treatment in a similar concentration range. When 0.3 mM HgCl(2) solution was fed to the V. faba leaflets with intact epidermes via the transpiration stream, the rate of photosynthesis on leaf area basis (A) measured at photosynthetically active photon flux density of 700 micromol m(-2) s(-1) and at leaf temperature of 25 degrees C, decreased by about 20 to 30% at any CO(2) concentration in the intercellular spaces (C(i)). However, when CO(2) concentration in the chloroplast stroma (C(c)) was calculated from fluorescence and gas exchange data and A was plotted against C(c), A at low C(c) concentrations did not differ before and after the treatment. The conductance for CO(2) diffusion from the intercellular spaces to the chloroplast stroma (g(i)) decreased to 40 and 30% of the control value, when the leaflets were fed with 0.3 mM and 1.2 mM HgCl(2), respectively. Similar results were obtained with leaves of Phaseolus vulgaris. Although effects of HgCl(2) were not specific, the present results showed that HgCl(2) consistently lowered g(i). It is, thus, probable that the photosynthetic CO(2) uptake across the plasma membrane of the mesophyll cells is facilitated by mercury-sensitive aquaporins.

Rootstock control of scion response to water stress in grapevine

“…In order to compare the four cultivars for their transmembrane water movement on foliar tissues, the methodology proposed by Terashima and Ono (2002) was followed and adapted. Each detached leaf was divided in two parts along the median vein.…”

“…Their activity was measured with the application of an inhibitor of cell metabolism, HgCl 2 , to root and leaf tissues. Mercurial reagents cannot affect all plant aquaporins (Daniels et al, 1994), and could produce side effects (Gaspar et al, 2001;Hachez et al, 2006), however they remain general but nonspecific aquaporin inhibitors (Wudick et al, 2009) useful for obtaining preliminary information on transmembrane water transport (Javot and Maurel, 2002;Moshelion et al, 2002;Terashima and Ono, 2002;Lovisolo et al, 2008;Miyazawa et al, 2008;Knipfer et al, 2011). While the water symplastic path in the root is mainly driven by osmotic forces, the apoplastic path, radial and axial, is maintained by hydrostatic forces, limited by the resistance produced by cavitation events (Aroca et al, 2012).…”

Expression Analysis of Aquaporins from Desert Truffle Mycorrhizal Symbiosis Reveals a Fine-Tuned Regulation Under Drought

“…The concept of CO 2 diffusion through the plasma membrane has been changed by cooporins (Terashima et al 2006). Several studies, such as inhibition with mercury (Terashima and Ono 2002) and transgenic plants with altered AQP expression systems (Flexas et al 2006;Hanba et al 2004;Uehlein et al 2003Uehlein et al , 2008, have demon- strated that PIP1 proteins can alter leaf mesophyll conductance to CO 2 (g m ) and assimilation capacity. One of the most studied cooporins is NtAQP1 from tobacco, which also increases CO 2 conductivity when expressed in yeast (Otto et al 2010).…”

Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2‐ and O3‐ enriched atmospheres

“…In both clones the increased mesophyll diffusion resistance r md contrib-uted to the reduction of photosynthesis under +O 3 , although less significantly in clone 4. This may indicate that aquaporins, involved in the CO 2 diffusion across the plasma membrane (Terashima & Ono 2002) were also affected by ozone.…”