Root-to-Shoot Hormonal Communication in Contrasting Rootstocks Suggests an Important Role for the Ethylene Precursor Aminocyclopropane-1-carboxylic Acid in Mediating Plant Growth under Low-Potassium Nutrition in Tomato

Abstract

Selection and breeding of rootstocks that can tolerate low K supply may increase crop productivity in low fertility soils and reduce fertilizer application. However, the underlying physiological traits are still largely unknown. In this study, 16 contrasting recombinant inbred lines (RILs) derived from a cross between domestic and wild tomato species (Solanum lycopersicum × Solanum pimpinellifolium) have been used to analyse traits related to the rootstock-mediated induction of low (L, low shoot fresh weight) or high (H, high shoot fresh weight) vigor to a commercial F1 hybrid grown under control (6 mM, c) and low-K (1 mM, k). Based on hormonal and ionomic composition in the root xylem sap and the leaf nutritional status after long-term (7 weeks) exposure low-K supply, a model can be proposed to explain the rootstocks effects on shoot performance with the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) playing a pivotal negative role. The concentration of this hormone was higher in the low-vigor Lc and Lk rootstocks under both conditions, increased in the sensitive HcLk plants under low-K while it was reduced in the high-vigor Hk ones. Low ACC levels would promote the transport of K vs. Na in the vigorous Hk grafted plants. Along with K, Ca, and S, micronutrient uptake and transport were also activated in the tolerant Hk combinations under low-K. Additionally, an interconversion of trans-zeatin into trans-zeatin riboside would contribute to decrease ACC in the tolerant LcHk plants. The high vigor induced by the Hk plants can also be explained by an interaction of ACC with other hormones (cytokinins and salicylic, abscisic and jasmonic acids). Therefore, Hk rootstocks convert an elite tomato F1 cultivar into a (micro) nutrient-efficient phenotype, improving growth under reduced K fertilization.

Hormonal and Nutritional Features in Contrasting Rootstock-mediated Tomato Growth under Low-phosphorus Nutrition

“…Interestingly, the ACC levels were depressed in the tolerant LcHp rootstocks, which showed increased growth under low-P. These ACC responses in contrasting rootstocks under low-P were similar to those observed under low-K ( Martínez-Andújar et al, 2016 ), and under non-stress conditions in hydroponics ( Cantero-Navarro et al, 2016 ), suggesting that ethylene-precursor is a constitutive or stress-induced root-to-shoot negative signal regulating shoot growth.…”

“…Besides P, xylem Ca concentration was also correlated with SDW and RDW under both high and low-P conditions ( Table 1 ). Constitutive rootstock capacities to uptake Ca and to maintain high foliar Ca concentrations seem related to the general vigor ( HcHp ) and adaptability to low-P ( LcHp ), as under low-K conditions ( Martínez-Andújar et al, 2016 ). The positive role of Ca in adaptation to low-P was supported by the consistent correlation between xylem Ca and P concentrations ( r = 0.6, P ≤ 0.01), and with RDW under low-P, suggesting that root biomass significantly influences the uptake of those nutrients.…”

“…Similarly to Ca, rootstock-mediated capacities to maintain high leaf S ( r = 0.67, P ≤ 0.01) and Mn ( r = 0.81, P ≤ 0.01) concentration were related to the shoot biomass produced under low-P ( Table 1 ). Therefore, it seems that the rootstock-mediated shoot growth improvement under low-K or -P supply is related to the capacity to maintain high nutritional status for other nutrients such as Ca, S, and Mn, while the role of some micronutrients such as B and Zn seems more specific to positive rootstock effects under low-K ( Martínez-Andújar et al, 2016 ). The physiological role of those nutrients in adapting to low-P could be explained by hormonal or metabolic interactions, as discussed below.…”

Tissue‐specific hormone profiles from woody poplar roots under bending stress

“…The t ZR, apart from being in the cambium, is generally abundant in the xylem sap (Hirose et al ). Interestingly, in tomato plants subjected to K‐deficiency the amount of t ZR in root xylem sap has been found inversely correlated to the presence of ethylene precursor, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), which controls the expression of the ERF gene thereby regulating root development and root‐shoot communication (Martínez‐Andújar et al ). Based on above, the t ZR accumulation in the concave Xy dev could be associated with the complete absence of ACC oxidase and the concomitant decrease of ERF protein levels observed in the later stages of bending stress (De Zio et al ), regulating wood development and/or deposition of cell wall polymers (Vahala et al , Rossi et al ).…”

Water Availability and Potassium Doses in Cherry Tomato Quality

“…The increased contents of soluble solids in fruits with the increased potassium fertilization occurs by the transport of sucrose in the phloem, which is favored by potassium. This, in turn, potentiates the transport from leaves to fruits, meeting the source-drain relation (Coskun et al, 2016;Martínez-Andújar et al, 2016). Rebouças Neto et al (2016) worked with the hybrid Dominador F1 of the persimmon group and also observed an increase in the concentration of total soluble solids as potassium doses increased.…”