Low levels of strigolactones in roots as a component of the systemic signal of drought stress in tomato.

Ivan Visentin,Yanxia Zhang,Andrea Schubert,Carolien Ruyter‐Spira,Miroslav Strnad,Claudio Lovisolo,Marco Vitali,Ondřej Novák,Francesca Cardinale,Manuela Ferrero

doi:10.1111/nph.14190

Ivan Visentin, Yanxia Zhang + Show 8 more

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https://doi.org/10.1111/nph.14190

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Abstract

Strigolactones (SL) contribute to drought acclimatization in shoots, because SL-depleted plants are hypersensitive to drought due to stomatal hyposensitivity to abscisic acid (ABA). However, under drought, SL biosynthesis is repressed in roots, suggesting organ specificity in their metabolism and role. Because SL can be transported acropetally, such a drop may also affect shoots, as a systemic indication of stress. We investigated this hypothesis by analysing molecularly and physiologically wild-type (WT) tomato (Solanum lycopersicum) scions grafted onto SL-depleted rootstocks, compared with self-grafted WT and SL-depleted genotypes, during a drought time-course. Shoots receiving few SL from the roots behaved as if under mild stress even if irrigated. Their stomata were hypersensitive to ABA (likely via a localized enhancement of SL synthesis in shoots). Exogenous SL also enhanced stomata sensitivity to ABA. As the partial shift of SL synthesis from roots to shoots mimics what happens under drought, a reduction of root-produced SL might represent a systemic signal unlinked from shootward ABA translocation, and sufficient to prime the plant for better stress avoidance.

Highlights

Drought stress counts among the most recurrent and limiting environmental conditions for plant development and full productivity; under water scarcity, phytohormones cooperatively interact to allow resource optimization (Christmann et al, 2006)
We investigated in tomato the possible systemic implications of the drop in SL
Our physiological data are in agreement with this theory: stomatal conductance values of WT shoots grafted onto SL-depleted rootstocks are significantly lower than those of WT shoots self-grafted onto WT rootstocks in irrigated conditions, and are accompanied by less negative leaf water potential values and, as expected, higher intrinsic water use efficiency

Summary

Introduction

Drought stress counts among the most recurrent and limiting environmental conditions for plant development and full productivity; under water scarcity, phytohormones cooperatively interact to allow resource optimization (Christmann et al, 2006). Root-synthesized ABA is, in some plants, a systemic stress signal, travelling shootward to prevent, among others effects, the negative consequences of soil water deficit (Comstock, 2002). It was shown in tomato that ABA travels from shoots to roots under long-term drought, inverting the original hypothesis (Manzi et al, 2015) Other signals, such as hydraulic, electrical and chemical signals, including other phytohormones and changes in xylem sap pH, are thought to contribute [reviewed by (Huber & Bauerle, 2016)]. It is argued that positive chemical signals alone cannot account for the initial stomatal responses to root drying, because of the relatively low xylem transport velocity (Huber & Bauerle, 2016)

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