Ameliorating effect of zinc on water transport in rice plants under saline-sodic stress

Abstract

Saline-sodic stress not only impacts the absorption of nutrient ions, such as Zn²⁺, in rice but also induces physiological water shortages and ion toxicity in rice plants, significantly hindering their growth. To investigate this phenomenon, the present study utilized two rice varieties, 'Changbai 9' and 'Tonghe 899', as test subjects to simulate conditions of saline-sodic soil stress. Four-week-old rice seeds under four treatments: control (CT), 2 μmol L^-1 zinc treatment alone (Z), 50 mmol L^-1 saline-sodic treatment (S), and 50 mmol L^-1 saline-sodic treatment with 2 μmol L^-1 zinc (Z+S). The study aimed to examine the effect of zinc on water transport in rice plants under conditions of saline-sodic stress. Research indicates that the application of zinc positively influences the growth of rice under saline-sodic stress.The application of zinc not only reduces the Na⁺/K⁺ ratio and malondialdehyde (MDA) content, but also increases the levels of Zn²⁺, Cu²⁺, and other ions. Additionally, it enhances the expression of aquaporins in the plasma membrane of rice roots, which in turn increases the hydraulic conductance of the roots and ultimately improves the water absorption capacity of the root system under stress conditions. Additionally, zinc application promotes auxin (IAA) synthesis, facilitating root growth and expanding the root absorption area, which in turn enhances the water absorption rate and helps maintain higher leaf water content. Moreover, zinc application regulates stomatal conductance through an increase in potassium ion concentration and abscisic acid (ABA) content, thereby elevating the transpiration rate of rice leaves and promoting water absorption and transportation within the rice plants. Therefore, the addition of zinc under saline-sodic stress not only alleviates the effects of such stress but also enhances water absorption and transportation in rice plants. This results in a higher water content within the plants, positively influencing their growth and development under saline-sodic conditions.

Keywords: aquaporin; rice; saline-sodic stress; water transport; zinc.

Figure 1

The effects of zinc on the growth state (A: Growth of ‘Changbai 9’, B: The growth of ‘Tonghe 899’), dynamic water content (C:Total water content, D: Free water content, E: Bound water content), and gas exchange parameters (F: Net photosynthetic rate, G: Transpiration rate, H: Stomatal conductance) of rice subjected to saline-sodic stress. The mean values of three repetitions ± SE (n=3) were used. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. C, ‘Changbai 9’ rice; T, ‘Tonghe 899’ rice.

Figure 2

This study investigates the effects of zinc on the concentrations of Na⁺ (A, D), K⁺ (B, E), malondialdehyde (MDA) (G), Na⁺/K⁺ (C, F), and relative electrolyte leakage (REL) (H) in the leaves (A-C) and roots (D-F) of two rice varieties subjected to saline-sodic stress. The mean values of three repetitions ± SE (n=3) were used. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. CB-L, ‘Changbai 9’ rice leaves; TH-L, ‘Tonghe 899’ rice leaves; CB-R, ‘Changbai 9’ rice root; TH-R, ‘Tonghe 899’ rice root.

Figure 3

The effects of zinc on the nutrient ion content in the leaves and roots of two rice varieties under saline-sodic stress. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. CB-L, ‘Changbai 9’ rice leaves; TH-L, ‘Tonghe 899’ rice leaves; CB-R, ‘Changbai 9’ rice root; TH-R, ‘Tonghe 899’ rice root.

Figure 4

The effects of zinc on various root characteristics, including total root length (A), root diameter (B), root surface area (C), root hydraulic conductivity (D), root water absorption area (E), root water absorption rate (F), xylem penetration type (G) and total soluble sugar content (H) in the roots of two rice varieties subjected under saline-sodic stress. (I) illustrates the correlation analysis between root xylem penetration potential and total soluble sugar content. The mean values of three repetitions ± SE (n=3) were used, and different letters were used to indicate statistical significance at the p < 0.05 level. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment.

Figure 5

The effects of zinc on the aquaporin genes OsPIP1;1, OsPIP1;2, OsPIP2;1, OsPIP2;2, OsPIP2;4, and OsPIP2;6 in the leaves and roots of rice under under saline-sodic stress. The mean values of three repetitions were used, and different letters were used to indicate statistical significance at the p < 0.05 level. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. CB-L, ‘Changbai 9’ rice leaves; TH-L, Tonghe 899 rice leaves; CB-R, ‘Changbai 9’ rice root; TH-R, ‘Tonghe 899’ rice root.

Figure 6

The effects of zinc on the concentrations of auxin (A), abscisic acid (B), and salicylic acid (C) in the leaves and roots of rice under saline-sodic stress. The mean values of three repetitions were used, and different letters were used to indicate statistical significance at the p < 0.05 level. CT, no saline-sodic and no zinc treatment; Z, zinc treatment; S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. CB-L, ‘Changbai 9’ rice leaves; TH-L, ‘Tonghe 899’ rice leaves; CB-R, ‘Changbai 9’ rice root; TH-R, ‘Tonghe 899’ rice root.

Figure 7

The correlation analysis of leaf ion content, gas exchange parameters, leaf water content, and leaf hormones (A), as well as root morphology, ion content, root water absorption, and root hormones (B). Asterisks (*) indicate significant correlations at P < 0.05. Abbreviations used include: REL for relative electricity leakage, MDA, malondialdehyde; IAA, auxin; ABA, abscisic acid; SA, salicylic acid; TW, total water content; BW, bound water; FW, free water; Tr, Transpiration rate; Pn, net photosynthetic rate; g_s, stomatal conductance; RL, total root length; RD, root diameter; RS, root surface area; RHC, root hydraulic conductivity; RAA, root water absorption area; and RUR, root water absorption rate.

Figure 8

Presents a structural equation model (SEM) that illustrates the relationships among various factors in rice leaves (A) and roots (B). The significance levels are indicated as *P < 0.05, **P < 0.01, and ***P < 0.001. REL, relative electricity leakage; MDA, malondialdehyde; IAA, auxin; ABA, abscisic acid; TW, total water content; Tr, Transpiration rate; Pn, net photosynthetic rate; gs, stomatal conductance; RL, total root length; RHC, root hydraulic conductivity; TSS, Total soluble sugar; RXOP, Root xylem penetration potential; AG, Aquaporin gene.

Figure 9

the effects of mercuric chloride (HgCl₂) and dithiothreitol (DTT) on the transpiration rate of rice leaves subjected to saline-sodic stress and zinc treatment. The mean values of three repetitions were used, and different letters were used to indicate statistical significance at the p < 0.05 level. S, saline-sodic treatment; Z+S, saline-sodic and zinc treatment. CB, ‘Changbai 9’ rice; TH, ‘Tonghe 899’ rice.