Dichotomization of mycorrhizal and NPA-treated short roots inPinus sylvestris

Abstract

Conifers like Scots pine (Pinus sylvestris) have a complicated root system consisting of morphologically and anatomically different root types, of which the short roots have a very limited ability to elongate. Short roots have an important role in nature since they are able to establish ectomycorrhizal symbiosis, in which the growth of fungal mycelium between the epidermal cells and in the intercellular space between cortical cells leads to formation of dichotomous short roots, which may, through further splitting of the meristem, form coralloid root structures. Dichotomous short roots have been suggested to result from changes in either auxin or ethylene concentrations due to the fungal growth inside the root. NPA, the inhibitor of polar auxin transport, enhances the dichotomization of P. sylvestris short root tips similarly to the fungal growth in the root, thus confirming that auxin plays a role in short root morphogenesis. Ethylene is also known to have an important role in the regulation of root morphogenesis. In future the research dealing with the root system and ectomycorrhiza development in P. sylvestris must take into account that both auxin and ethylene are involved and that there is no contradiction in obtaining the same phenotype with both hormones. The expression analysis of PIN proteins, auxin efflux carriers, could give valuable information about the role of auxin transport in regulating the root growth and morphogenesis of coniferous root system and mycorrhiza.

Dichotomous branching: the plant form and integrity upon the apical meristem bifurcation

“…The fungal symbionts are probably the source of plant growth regulators, which stimulate morphogenetic changes, including root swelling and dichotomous branching ( Barker and Tagu, 2000 ; Brundrett, 2002 ). Similar changes in the root architecture can be induced in the absence of fungi by exogenously supplied phytohormones or their inhibitors ( Wilson and Field, 1984 ; Rupp et al, 1989 ; Kaska et al, 1999 ; Laajanen et al, 2007 ; Raudaskoski and Salo, 2008 ). Application of auxin transport inhibitors [ N -(1-naphtyl)phthalamic acid (NPA); 2,3,5-triiodobenzoic acid (TIBA)], ethylene precursor [(1-aminocyclopropane-1-carboxylic acid (ACC)], or ethylene releasing compounds [2-chloroethylphosphonic acid (CEPA)] stimulates extensive dichotomous branching of Pinus roots, increasing the percentage of coralloid structures up to 25–30% ( Kaska et al, 1999 ).…”

“…The distinctiveness of superficial layers is maintained during dichotomy progression, as well as the continuity of procambium and vascular tissues in the parental and dichotomous axes. Differentiation of the meristematic cells located between dichotomizing apices ceases the growth of the central part of the original meristem starting the separation of both branches (Härtel, 1937; Nolan, 1969; Tomlinson, 1970, 1971; Boke, 1976; Tomlinson and Posluszny, 1977; Faye et al, 1981; Piche et al, 1982; Laajanen et al, 2007; Raudaskoski and Salo, 2008; Gola and Jernstedt, 2011). …”

“…Application of auxin transport inhibitors [ N -(1-naphtyl)phthalamic acid (NPA); 2,3,5-triiodobenzoic acid (TIBA)], ethylene precursor [(1-aminocyclopropane-1-carboxylic acid (ACC)], or ethylene releasing compounds [2-chloroethylphosphonic acid (CEPA)] stimulates extensive dichotomous branching of Pinus roots, increasing the percentage of coralloid structures up to 25–30% ( Kaska et al, 1999 ). It is suggested that the balance between auxin [indole-3-acetic acid (IAA)] and cytokinin, possibly mediated by the ethylene level, has a regulatory role in this process ( Rupp et al, 1989 ; Kaska et al, 1999 ; Barker and Tagu, 2000 ; Laajanen et al, 2007 ; Raudaskoski and Salo, 2008 ). Possibly, the NPA-treatment increases the auxin concentration at the root tip, whereas the moderate level of the hormone at the meristem flanks induces dichotomous root formation.…”

“…Possibly, the NPA-treatment increases the auxin concentration at the root tip, whereas the moderate level of the hormone at the meristem flanks induces dichotomous root formation. At the same time, high IAA concentration at the root tip stimulates the biosynthesis of ethylene, leading to cell differentiation in the central part of the original meristem and consequently, separation of dichotomous roots ( Laajanen et al, 2007 ; Raudaskoski and Salo, 2008 ).…”

Біоелектрика Екосистем Лісів, Заболочених Лук Та Агроекосистем Західної України

“…Так, наприклад, корені Q. robur можуть проникати на глибину понад 15 м, однак горизонтальне тонке коріння, важливе для живлення електрогенерувальних мікроорганізмів, зосереджене на глибині 15-40 см (Kalinin, Huz, & Debryniuk, 1998;Mauer, Houskova, & Mikita, 2017). Глибина проникнення коріння P. silvestris може сягати понад 10 м, однак на бідних сухих ґрунтах сосна формує потужну поверхневу кореневу систему з короткими дрібними корінцями, зазвичай з мікоризою (Munzenberge, Golldack, Ullrich, Schmincke, & Huttl, 2004;Auсina et al, 2007;Raudaskoski & Salo, 2008). Значна частина коріння сосни зосереджена на глибині до 20 см (Ganatsas & Spanos, 2005;Maliuha & Khryk, 2010).…”