Exogenous Easily Extractable Glomalin-Related Soil Protein Stimulates Plant Growth by Regulating Tonoplast Intrinsic Protein Expression in Lemon

Abstract

Arbuscular mycorrhizal fungi (AMF) have the function of promoting water absorption for the host plant, whereas the role of easily extractable glomalin-related soil protein (GRSP), an N-linked glycoprotein secreted by AMF hyphae and spores, is unexplored for citrus plants. In this study, the effects on plant growth performance, root system characteristics, and leaf water status, along with the changes of mineral element content and relative expressions of tonoplast intrinsic protein (TIP) genes in lemon (Citrus limon L.) seedlings, were investigated under varying strengths of exogenous EE-GRSP application under potted conditions. The results showed that 1/2, 3/4, and full-strength exogenous EE-GRSP significantly promoted plant growth performance, as well as increased the biomass and root system architecture traits including root surface area, volume, taproot length, and lateral root numbers of lemon seedlings. The four different strengths of exogenous GRSP displayed differential effects on mineral element content: notably increased the content of phosphorus (P) and iron (Fe) in both leaves and roots, as well as magnesium (Mg) and zinc (Zn) content in the roots, but dramatically decreased the content of calcium (Ca) and manganese (Mn) in the roots, as well as Zn and Mn in the leaves. Exogenous EE-GRSP improved leaf water status, manifesting as decreases in leaf water potential, which was associated with the upregulated expressions of tonoplast intrinsic proteins (TIPs), including ClTIP1;1, ClTIP1;2, ClTIP1;3, ClTIP2;1, ClTIP2;2, ClTIP4;1, and ClTIP5;1 both in leaves and roots, and TIPs expressions exhibited diverse responses to EE-GRSP application. It was concluded that exogenous EE-GRSP exhibited differential responses on plant growth performance, which was related to its strength, and the effects were associated with nutrient concentration and root morphology, especially in the improvement in water status related to TIPs expressions. Therefore, EE-GRSP can be used as a biological promoter in plant cultivation, especially in citrus.

Exogenous Easily Extractable Glomalin-Related Soil Protein Induces Differential Response in Plant Growth of Tea Plants via Regulating Water Channel Protein Expression

“…Soluble protein is an important osmoregulatory substance, which can improve the water retention capacity of cells as it accumulates [31]. Furthermore, the present study also revealed that the LWP in the tea leaves was dramatically reduced under all exogenous EE-GRSP treatments, and these findings were consistent with those of Guo et al [18] on lemon seedlings, but contrary to those of Chi et al [9] on trifoliate orange seedlings, which may be attributed to an increase in the solute concentration in tea leaves. Ultimately, exogenous EE-GRSP application accelerated nutrient accumulation in plant leaves, thereby increasing the cytoplasmic concentration and osmotic pressure [32], which may be the main reason for the decrease in the water potential.…”

“…In this study, the application of exogenous EE-GRSP promoted the growth and increased the biomass of tea seedlings at different ranges; plant growth was optimal under the 1/2 EE-GRSP treatment, while the biomass was greatest under the 3/4 EE-GRSP treatment, which was consistent with the results from previous studies on trifoliate orange seedlings [11,18]. These results further confirmed that GRSP exerts a positive effect on plant growth.…”

“…In the present study, four different strengths of exogenous EE-GRSP all markedly regulated the root system architecture of tea seedlings to different degrees and increased the root system architecture parameters; these indexes were correlated with the strength of exogenous EE-GRSP in a positive curvilinear manner, which was in agreement with the results of Liu et al [11] on trifoliate orange seedlings. However, the relative parameters of the root system architecture performed best under the 3/4 EE-GRSP treatment, which contradicts the previous research on citrus fruits in terms of lateral root development [18]. This is most likely because different plants have different genotypes, resulting in varying responses to exogenous EE-GRSP application, thus leading to different growth performance results.…”

“…For this experiment, a completely randomized design was used and five treatments were included: (1) citrate buffer solution (20 mmol/L, pH 7.0), which was used as the control; (2) quarter-strength EE-GRSP solution (1/4 EE-GRSP); (3) half-strength EE-GRSP solution (1/2 EE-GRSP); (4) three-quarter-strength EE-GRSP solution (3/4 EE-GRSP); and (5) full-strength EE-GRSP solution (full EE-GRSP). According to our previous study on citrus plants [11,18], the solutions of EE-GRSP at 1/4, 1/2, and 3/4 strength were prepared by diluting the full-strength EE-GRSP solution with a certain proportion of the 20 mmol/L, pH 7.0, of citric acid buffer solution. Six replications of each treatment were performed.…”

“…The leaf relative water content (LRWC) and leaf water potential (LWP) were determined according to Guo et al [18].…”