Adventitious root initiation in hypocotyl and epicotyl cuttings of eastern white pine (Pinus strobus) seedlings

Abstract

The present paper reports results of experiments to develop a system for studying adventitious root initiation in cuttings derived from seedlings. Hypocotyl cuttings of 2‐week‐old eastern white pine (Pinus strobus L.) seedlings were treated for 5 min with 0, 100, 200, 300, 400, 500 or 600 mg l−1 (0, 0.54, 1.07, 1.61, 2.15, 2.69 or 3.22 mM) 1‐naphthaleneacetic acid (NAA) to determine the effect on root initiation. The number of root primordia per cutting was correlated with NAA concentration and the square of NAA concentration. Thus, the number increased from less than one per cutting in the 0 NAA treatment to approximately 40 per cutting at 300 mg l‐1 NAA, above which no substantial further increase was observed. The larger number of root primordia formed in response to increasing concentrations of NAA was due to the formation of primordia over a larger proportion of the hypocotyls. Histological analysis of the timing of root primordium formation in hypocotyl cuttings revealed three discernible stages. Progression through these stages was relatively synchronous among NAA‐treated hypocotyl cuttings and within a given cutting, but variation was observed in the portion of different cuttings undergoing root formation. Control‐treated hypocotyl cuttings formed root primordia at lower frequencies and more slowly than NAA‐treated cuttings, with fewer primordia per cutting. Epicotyl cuttings from 11‐week‐old seedlings also formed adventitious roots, but more slowly than hypocotyl cuttings. NAA treatment of epicotyl cuttings caused more rapid root initiation and also affected the origin of adventitious roots in comparison with nontreated cuttings. NAA‐treated epicotyl cuttings formed roots in a manner analogous to that of the hypocotyl cuttings, directly from preformed vascular tissue, while control‐treated epicotyl cuttings first formed a wound or callus tissue and subsequently differentiated root primordia within that tissue. This system of inducing adventitious roots in pine stem cuttings lends itself to studying the molecular and biochemical steps that occur during root initiation and development.

Auxin Control in the Formation of Adventitious Roots

“…High endogenous auxin concentration is normally associated with a high rooting rate at the beginning of the rooting process (Blažková et al, 1997;Caboni et al, 1997). Auxins have been shown to be effective inducers of adventitious roots in many woody species (de Klerk et al, 1999;Diaz-Sala et al, 1996;Goldfarb et al, 1998;Selby et al, 1992) and are usually synthesized in the stem tip and tender leaves of aerial parts of plants and then transportted to the action site (Ljung et al, 2001). When applying exogenous auxin on cuttings, the endogenous auxin concentration reaches a peak after wounding (Gaspar et al, 1996;Gatineau et al, 1997) coinciding with the initiation of the rooting process.…”

Strigolactones Suppress Adventitious Rooting in Arabidopsis and Pea

“…Indirect root formation involves the production of callus tissue prior to adventitious root development and is different from lateral root formation because the earliest events include divisions from cambium and cambium-associated cells, while lateral root formation occurs specifically from the pericycle. This type of adventitious rooting is most commonly found where roots form from stem cuttings (Goldfarb et al, 1998).…”

“…Direct root formation involves roots forming from stem tissues such as the pericycle in the hypocotyl of Arabidopsis (Arabidopsis thaliana; Goldfarb et al, 1998) and is similar to lateral root development. Indirect root formation involves the production of callus tissue prior to adventitious root development and is different from lateral root formation because the earliest events include divisions from cambium and cambium-associated cells, while lateral root formation occurs specifically from the pericycle.…”

Proteomic Analysis of Different Mutant Genotypes of Arabidopsis Led to the Identification of 11 Proteins Correlating with Adventitious Root Development

“…One of the major endogenous factors known to play a role in adventitious rooting is the hormone auxin. Auxins have been shown to be effective inducers of adventitious roots in many woody species (Selby et al, 1992;Díaz-Sala et al, 1996;Goldfarb et al, 1998;De Klerk et al, 1999). Light is one of the major environmental factors known to influence adventitious root development, and light and auxin act antagonistically in adventitious root development in Eucalyptus saligna and Eucalyptus globulus (Fett-Neto et al, 2001).…”