Ethylene Enhances Water Transport in Hypoxic Aspen

Abstract

Water transport was examined in solution culture grown seedlings of aspen (Populus tremuloides) after short-term exposures of roots to exogenous ethylene. Ethylene significantly increased stomatal conductance, root hydraulic conductivity (L p ), and root oxygen uptake in hypoxic seedlings. Aerated roots that were exposed to ethylene also showed enhanced L p . An ethylene action inhibitor, silver thiosulphate, significantly reversed the enhancement of L p by ethylene. A short-term exposure of excised roots to ethylene significantly enhanced the root water flow (Q v ), measured by pressurizing the roots at 0.3 MPa. The Q v values in ethylene-treated roots declined significantly when 50 m HgCl 2 was added to the root medium and this decline was reversed by the addition of 20 mm 2-mercaptoethanol. The results suggest that the response of Q v to ethylene involves mercury-sensitive water channels and that root-absorbed ethylene enhanced water permeation through roots, resulting in an increase in root water transport and stomatal opening in hypoxic seedlings.Hypoxia, a condition of oxygen deficiency in plant roots, is the main consequence of flooding or waterlogging. Plants respond to hypoxia with reduced root permeability, closure of stomata, hypertrophy of lenticels, epinasty, formation of aerenchyma, and adventitious roots (Vartapetian and Jackson, 1997). Ethylene accumulation is often assumed to be the factor responsible for many of the responses observed in plants exposed to hypoxia (Mattoo and Suttle, 1991; Abeles et al., 1992). Hypoxia induces the formation in roots of the immediate precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid, which is transported in the xylem to the shoots and there rapidly oxidized to ethylene (Mattoo and Suttle, 1991). The synthesis of ethylene and the response of plants to ethylene differ among tissues and different plant species (Abeles et al., 1992), and can be affected by different internal and environmental factors (Sharp et al., 2000; Grichko and Glick, 2001).The effects of ethylene on stomatal closure are not clear. Several studies on the effects of exogenous ethylene on stomatal movements demonstrated differential responses between the examined species (Taylor and Gunderson, 1986; Woodrow et al., 1988; Gunderson and Taylor, 1991; Abeles et al., 1992). Exogenous ethylene is known to increase membrane permeability in petal cells (Mayak et al., 1977; Borochov and Woodson, 1989); however, its impact on cell-to-cell water transport has not been thoroughly examined.Water transport across intact higher plant cell membranes occurs predominantly through water channels (aquaporins; Chrispeels et al., 1997). Aquaporins are located in root cell membranes (Chrispeels and Maurel, 1994) at a high density (Johansson et al., 1998). In our previous work (Wan and Zwiazek, 1999, 2001;Kamaluddin and Zwiazek, 2001), we showed that the root water channels in aspen (Populus tremuloides) and Cornus stolonifera rapidly responded to changes in root metabolism. Phosphorylation of the aquapor...

Ecophysiological adaptations of black spruce ( Picea mariana ) and tamarack ( Larix laricina ) seedlings to flooding

“…Root respiration was measured 2, 8, 16 and 27 days after flooding treatment was imposed. Root systems of black spruce and tamarack seedlings (n=5 per species treatment combination) were placed in an airtight cylinder containing half-strength Hoagland's solution (Kamaluddin and Zwiazek 2002). Oxygen uptake rates were recorded every 2 min for 20 min.…”

“…Root respiration has been shown to decline as a result of hypoxia in wheat (Huang and Johnson 1995), and aspen (Kamaluddin and Zwiazek 2002). Carbohydrate concentrations may remain the same or increase in roots and shoots under hypoxic conditions (Huang 1995).…”

Aquaporins: Highly Regulated Channels Controlling Plant Water Relations

“…Auxin inhibits the endocytosis of PIP2 in Arabidopsis (Paciorek et al, 2005), while exogenous auxin has been found to inhibit root and cell hydraulic conductivity in Arabidopsis (Péret et al, 2012). Ethylene can enhance (Kamaluddin and Zwiazek, 2002) or inhibit (Li et al, 2009) L pr . In the case of the latter, inhibition caused by phosphorus deficiency appears to be mediated by ethylene.…”

Rh-PIP2;1, a Rose Aquaporin Gene, Is Involved in Ethylene-Regulated Petal Expansion

“…A general inhibitor of AQP activities, HgCl 2 , decreased ethylene-enhanced water flow in aspen (Populus spp.) roots (Kamaluddin and Zwiazek, 2002). A protein kinase inhibitor, okadaic acid, could inhibit the ethylene-induced phosphorylation in mung bean (Vigna radiata) hypocotyls (Kim et al, 1997), orchid petals (Wang et al, 2001), and pea (Berry et al, 1996;Kwak and Lee, 1997), and the inhibitor also inhibited the phosphorylation of AQP PM28A in spinach leaves (Johansson et al, 1996).…”