Regulatory role of auxin in adventitious root formation in two species of Rumex, differing in their sensitivity to waterlogging

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Abstract
Adventitious rooting in Rumex plants, in which the root systems were in hypoxic conditions, differed considerably between two species. R. palustris, a species from frequently flooded river forelands, developed a large number of adventitious roots during hypoxia, whereas adventitious root formation was poor in R. thyrsiflorus, a species from seldom flooded dykes and river dunes. Adventitious rooting could also be evoked in aerated plants of both species by application of auxin (1‐naphthaleneacetic acid or indoleacetic acid) to the leaves. The response to auxin was dose‐dependent, but even high auxin doses could not stimulate R. thyrsiflorus to produce as many adventitious roots as R. palustris. Consequently, the difference between the species in the amount of adventitious root formation was probably genetically determined, and not a result of a different response to auxin.A prerequisite for hypoxia‐induced adventitious root formation is the basipetal transport of auxin within the shoot, as specific inhibition of this transport by N‐1‐naphthylphthalamic acid severely decreased the number of roots in hypoxia‐treated plants. It is suggested that hypoxia of the root system causes stagnation of auxin transport in the root system. This can lead to an accumulation of auxin at the base of the shoot rosette, resulting in adventitious root formation.

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