Alpha monofluoro substitution at C5 in homotyphasterol enhances shoot production and multiplication rate of in vitro-grown marubakaido apple rootstock shoots

Abstract

Key message: 5 fluoro-typhasterol is more effective than the most potent natural brassinosteroid, brassinolide, towards stimulation of shoot production in the marubakaido apple rootstock. Abstract: Brassinosteroids (BRs) comprise a class of low-abundance plant steroids required for normal plant growth. Here we demonstrate that treatment of in vitro-grown shoots of the marubakaido apple rootstock with 2.5 µg per shoot of 5α-monofluoro homotyphasterol (5F-HTY), a synthetic derivative of the natural BR homotyphasterol (HTY), resulted in significant enhancement in the formation of primary lateral shoots. This treatment also resulted in increased length of primary lateral shoots and main shoots. This growth-stimulatory effect led to a significant increase in the multiplication rate for the rootstock. In contrast to what was found for 5F-HTY, neither HTY nor the synthetic derivative 3α-monofluoro homotyphasterol (3F-HTY) were able to significantly stimulate shoot formation. HTY and 3F-HTY were not able to stimulate primary lateral shoot elongation as well. However, both HTY and 3F-HTY were able to significantly stimulate main shoot elongation. The 5F-HTY-driven enhancement of the multiplication rate described here demonstrates the potential of this compound to improve micropropagation techniques, not only for the marubakaido apple rootstock.