Na + Efflux from Apple Dwarfing Rootstocks is Associated with High-Salt Resistance of Their Scions

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Na+ Efflux from Apple Dwarfing Rootstocks is Associated with High‑Salt Resistance of Their Scions Xingliang Li1,2   · Minji Li1,2 · Beibei Zhou1,2 · Yuzhang Yang1,2 · Jia Zhou1,2 · Qinping Wei1,2 · Junke Zhang1,2 Received: 15 October 2019 / Accepted: 4 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract In apple (Malus) cultivation, the adaptability of rootstocks has a fundamental influence on multiple abiotic-stress resistance properties of their scions. Here, we investigated the high-salt resistance of apple rootstocks, by treating 2-year-old apple trees consisting of the ‘Fuji’ cultivar grafted onto three different dwarfing rootstocks (SH6, M9-T337 and G935) with a high-salt solution for 30 days. We found that the high-salt stress caused leaf yellowing and growth inhibition to all apple plants, and that the most serious reduction in relative chlorophyll content, plant height and biomass accumulation was associated with the SH6 rootstock. In addition, based on the salt injury index, the high-salt resistance of the ‘Fuji’ scion on the three dwarfing rootstocks was ranked as G935 > M9-T337 > SH6. In addition, analysis of mineral elemental composition showed that the ­Na+ content in ‘Fuji’ leaves on the G935 rootstock increased less than twofold compared to the control, whereas those on the SH6 rootstock increased nearly 20-fold, accompanied with reduced K and Fe element absorption under high-salt treatments. Expression analysis of nine ­Na+ transport-related genes indicated that in the salt overly sensitive (SOS) pathway, the SOS1, SOS2 and SOS3 genes showed considerably greater induction by high-salt stress in G935 roots than in SH6 roots. Given the N ­ a+ content detected in roots of different rootstocks, we propose that more efficient N ­ a+ extracellular efflux in G935 roots, rather than intracellular N ­ a+ compartmentalization, contributed to the improved characteristics of the G935 rootstock under high-salt conditions. Keywords  Apple · Dwarfing rootstock · Salt stress · Salt injury index

Introduction

Communicated by Fabrizio Costa. Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s0034​4-020-10264​-4) contains supplementary material, which is available to authorized users. * Junke Zhang [email protected] Xingliang Li [email protected] 1



Beijing Engineering Research Center for Deciduous Fruit Trees, Beijing Academy of Forestry and Pomology Sciences, Beijing 100093, China



Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Ministry of Agriculture and Rural Affairs, Beijing 100093, China

2

Apple (Malus) is one of the most widely cultivated and economically important temperate fruit tree crops. Together with the development of dwarf phenotypes and high-density cultivation, the importance of appropriate apple rootstocks for modern production systems is widely recognized (Ibanez and Dandekar 2007; Pereira-Lorenzo et al. 2009). Accordingly, in recent decades, several dwarfin