Calcium nutrition nanoagent rescues tomatoes from mosaic virus disease by accelerating calcium transport and activating antiviral immunity

Abstract

As an essential structural, metabolic and signaling element, calcium shows low remobilization from old to young tissues in plants, restricting the nutrient-use efficiency and control efficacy against mosaic virus disease. Nanotechnology has been applied to prevent/minimize nutrient losses and improve the accessibility of poorly-available nutrients. Herein, the current study applied a star polycation (SPc) to prepare a calcium nutrition nanoagent. The SPc could assemble with calcium glycinate through hydrogen bond and Van der Waals force, forming stable spherical particles with nanoscale size (17.72 nm). Transcriptomic results revealed that the calcium glycinate/SPc complex could activate the expression of many transport-related genes and disease resistance genes in tomatoes, suggesting the enhanced transport and antiviral immunity of SPc-loaded calcium glycinate. Reasonably, the calcium transport was accelerated by 3.17 times into tomato leaves with the help of SPc, and the protective effect of calcium glycinate was remarkably improved to 77.40% and 67.31% toward tomato mosaic virus with the help of SPc after the third and fifth applications. Furthermore, SPc-loaded calcium glycinate could be applied to increase the leaf photosynthetic rate and control the unusual fast growth of tomatoes. The current study is the first success to apply nano-delivery system for enhanced calcium transport and antiviral immunity, which is beneficial for increasing nutrient-use efficiency and shows good prospects for field application.

Keywords: calcium nutrition; calcium transport; nano-fertilizer; nutrient-use efficiency; polymer.

Figure 1

Schematic illustration of calcium glycinate/SPc complex (A) and ITC titration of SPc (250 μmol/L) into calcium glycinate solution (200 μmol/L) (B).

Figure 2

Transmission electron microscope image and particle size distribution of calcium glycinate/SPc complex at the mass ratio of 1:8.8.

Figure 3

RNA-seq analysis of tomatoes treated with calcium glycinate and calcium glycinate/SPc complex. (A) Analysis of differentially expressed genes (DEGs) in tomatoes with a volcano plot. Up-regulated and down-regulated DEGs are represented by red and green dots, respectively. (B) GO enrichment analysis of DEGs in biological process, cellular component and molecular function. (C) Heatmaps of differentially expressed genes. Highly and lowly expressed genes are labeled as red and blue, respectively. Gene names are listed in the middle.

Figure 4

Enhanced transport of SPc-loaded calcium glycinate. (A) Schematic diagram. Tomato seedlings were cultured in the solutions of calcium glycinate and calcium glycinate/SPc complex for 24 h. All leaves were collected, dried and homogenized for calcium content measurement. (B) Standard calibration curve of calcium. (C) Calcium content in leaves. Each treatment included 3 independent samples. Different letters indicate significant differences according to Tukey HSD test (P < 0.05).

Figure 5

Enhanced bioactivity of SPc-loaded calcium glycinate toward tomato mosaic virus. (A) Photos of healthy and infected seedlings. (B) Disease indexes of seedlings were evaluated at 10 d post the third, fourth and fifth applications, respectively. All seedlings from each plot were observed to record the disease grades. (C) Protective effect was assessed by disease index. The “*” and “**” indicate significant differences (Independent t test, P < 0.05 and P < 0.01), and “n.s.” indicates no significant difference.

Figure 6

Effects of SPc-loaded calcium glycinate on the photosynthetic rate (A) and internodes length (B) of tomato leaves/seedlings. The seedlings were sprayed with various formulations at 80% and 40% recommended field concentration. The photosynthetic rate and internodes length were measured at 9:00-10:00 a.m. at 10 d post the first and second applications. Five leaves/seedlings were tested in each plot. The “*” and “**” indicate significant differences (Independent t test, P < 0.05 and P < 0.01), and “n.s.” indicates no significant difference.