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.
Highlights
Potassium (K) is the most abundant cation in plant tissues and is required for plant development and crop yield (Wang and Wu, 2013)
16 grafted recombinant inbred lines (RILs) were phenotypically selected for the vigor induced to the scion and classified into four groups (12 plants per group) on the basis of their growth response to each treatment: the first group comprised four rootstocks (RILs 27, 60, 267, and 240) having low vigor irrespective of K treatment (LcLk); the second group was four rootstocks (1, 62, 204, and 148) showing high vigor under c and low vigor under k conditions (HcLk); the third group consisted of four rootstocks (47, 132, 167, and 209) with low vigor under c and high vigor under k conditions (LcHk); and a fourth group comprising four rootstocks with high vigor regardless of treatment (HcHk; Figure S1)
Root biomass was not affected by the rootstock genotype, while only the low-K decreased (HcLk) or increased (LcHk) plants registered a significant decrease in root biomass under lowK compared with control conditions (Figure 1C)
Summary
Potassium (K) is the most abundant cation in plant tissues and is required for plant development and crop yield (Wang and Wu, 2013). K starvation triggers an upregulation of K transporters, and involves changes in different signaling molecules including reactive oxygen species (ROS), Ca and several phytohormones such us ethylene, jasmonic acid (JA), and auxins (Armengaud et al, 2004; Shin and Schachtman, 2004; Cao et al, 2006; Hafsi et al, 2014). Ethylene signaling is a key component of the plant response to low K that stimulates the production of ROS and induces changes in root morphology, and gene expression of high affinity transporters (Jung et al, 2009). Little is known about the roles of abscisic acid (ABA), salicylic acid (SA), gibberellins (GAs), and cytokinins (CKs) under K deficiency
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