Evidence for the involvement of ethene in aerenchyma formation in adventitious roots of rice (Oryza sativa L.)

Abstract

SUMM.\RYTwo varieties of rice (cv, Norin 36 and RB3) were either grown in stagnant or aerated |-strength Hoagland's solution with or without exogenous ethene and a range of silver concentrations (an ethene antagonist), or were grown in flooded and drained soils.With cultivar Norin 36, AgNO^ was very effective in reducing porosity by inhibiting aerenchyma developnnem. This effect was antagonized by gassing with increasing concentrations (1 or 2 jtX 1"') of ethene. The results are consistent, therefore, with reports that cavity formation in roots is controlled by endogenous levels of ethene. Also, porosity varied with root length, and if a correction was made for this, the inhibitory effect of the silver ion on aerenchyma development appeared to be even greater.For the cultivar RB3, root porosities in solution culture appeared initially to be unaffected by ethene or AgNO^j, but root lengths were reduced and root numbers increased by increasing ethene concentration. When these effects on root length were taken Into account, it was concluded that ethene had increased root porosity, and AgNO^ had decreased it. Consistent with earlier studies, and with the ethene hypothesis, aerenchyma development in both \arieties was also enhanced by soil waterlogging, with percentage porosities 12 units higher in flooded than in drained soil. The porosities of c\', RB3 were higher than those for cv. Norin 36, however, and the regression line of porosity against root length was steeper, indicating a greater predisposition to form aerenchyma in cv. RB3. This was confirmed in solution-grown roots, where AgNO^ had no signiflcant effect on porosity in stagnant or in aerated roots of cv. RB3, and hoth 1 and 2 /d 1"' ethene increased the porosity in cv. RB3 roots to a similar level. Silver nitrate, however, did antagonize the effects of 1 and 2 fi\ 1"' ethene. In contrast, porosity in cv. Norin 36 was progressively reduced by AgNOg, It is concluded that, although there are intervarietal differences in sensitivity', an ethene promotion of gas-space formation can occur in rice, and ethene should not be ruled out as the endogenous promoter.

Acclimation to soil flooding — sensing and signal-transduction

“…In the latter cultivar aerenchyma formation was not affected by ethylene inhibition, which led the authors to conclude that ethylene does not play a role in constitutive aerenchyma development. In response to this paper, Justin and Armstrong (1991b) partly repeated the experiments, but corrected the data for the negative effect of the treatments on the elongation rate of the aerenchymatous roots. With this correction, they concluded that ethylene did play a role.…”

Waterlogging tolerance and capacity for oxygen transport in Brachypodium distachyon (Bd21)

“…In Oryza sativa (rice) and Hordeum marinum, suberin and/or lignin in the outer part of roots are thought to contribute to the barrier (Garthwaite et al 2008, Kotula et al 2009a, Kotula et al 2009b, Ranathunge et al 2011 can be detected ). These strategies for acclimating to waterlogged conditions are found in several wetland plants, including rice (Justin and Armstrong 1991, Colmer et al 1998, Colmer et al 2006, Rumex palustris (Visser et al 1995, Visser et al 2000 and H. marinum (Garthwaite et al 2003, Garthwaite et al 2008). However, other crops, such as wheat (McDonald et al 2001b), barley (Garthwaite et al 2003) and maize (Zea mays) (Drew et al 1979, Abiko et al 2012b, can form aerenchyma and newly formed roots, but cannot form an ROL barrier.…”

Epidermal Cell Death in Rice Is Regulated by Ethylene, Gibberellin, and Abscisic Acid

“…In Rumex palustris, ethylene promotes petiole elongation (Voesenek et al, 1993;Cox et al, 2004). In deepwater rice (Oryza sativa), elevated ethylene levels regulate such diverse responses as accelerated growth of mesocotyls, coleoptiles (Ohwaki and Nagao, 1967), internodes (Métraux and Kende, 1983;Kende, 1984a, 1984b;Suge, 1985), and adventitious roots (Bleecker et al, 1986;Lorbiecke and Sauter, 1999) and cell death processes such as those underlying enhanced formation of aerenchyma (Justin and Armstrong, 1991;Inada et al, 2002) and epidermal cell death at the sites where adventitious roots emerge (Mergemann and Sauter, 2000). Since some of these processes need to be tightly coordinated in time and space, the question arises how the ethylene signal is perceived and interpreted by different organs and tissues to allow for these diverse responses in a timely fashion.…”