Ranunculus sceleratus as a Model Species to Decrypt the Role of Ethylene in Plant Adaptation to Salinity

Abstract

The aim of the present study was to develop an experimental system for an exploration of ethylene-dependent responses using intact growing Ranunculus sceleratus plants and to approbate the system for assessing the role of ethylene in salinity tolerance and ion accumulation. Plants were cultivated in sealed plastic containers in a modified gaseous atmosphere by introducing ethylene or 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene action. High humidity inside the containers induced a fast elongation of the leaf petioles of R. sceleratus. The effect was ethylene-dependent, as 1-MCP completely blocked it, but exogenous ethylene further promoted petiole elongation. Exogenous ethylene decreased (by 48%) but 1-MCP increased (by 48%) the Na⁺ accumulation in leaf blades of NaCl-treated plants. The experimental system was further calibrated with ethylene and silica xerogel, and the optimum concentrations were found for inducing leaf petiole elongation (10 μL L^-1 ethylene) and preventing leaf petiole elongation (200 g silica xerogel per 24 L), respectively. The second experiment involved a treatment with NaCl in the presence of 1-MCP, ethylene, or 1-MCP + ethylene, both in normal and high air humidity conditions. In high humidity conditions, NaCl inhibited petiole elongation by 25% and ethylene treatment fully reversed this inhibition and stimulated elongation by 12% in comparison to the response of the control plants. Treatment with 1-MCP fully prevented this ethylene effect. In normal humidity conditions, NaCl inhibited petiole elongation by 20%, which was reversed by ethylene without additional elongation stimulation. However, 1-MCP only partially inhibited the ethylene effect on petiole elongation. In high humidity conditions, ethylene inhibited Na⁺ accumulation in NaCl-treated plants by 14%, but 1-MCP reversed this effect. In conclusion, the stimulation of endogenous ethylene production in R. sceleratus plants at a high air humidity or in flooded conditions reverses the inhibitory effect of salinity on plant growth and concomitantly inhibits the accumulation of Na⁺ in tissues. R. sceleratus is a highly promising model species for use in studies regarding ethylene-dependent salinity responses and ion accumulation potential involving the manipulation of a gaseous environment.

Keywords: 1-methylcyclopropene; NaCl; air humidity; aquatic species; ethephon; ethylene; growth stimulation; ion accumulation; silica xerogel.

Figure 1

Characteristic morphology of Ranunculus sceleratus plants before treatment ((A), day 0) and cultivated in closed 48 L containers at high humidity in presence of 1-methylcyclopropene (MCP) and C₂H₄. Plants at day 3 (B), at day 5 (C), and day 7 (D). Treatment with C₂H₄ was terminated on day 6. NH, normal humidity; HH, high humidity. Red arrows indicate presence of leaves with short petioles in control plants. Blue arrows indicate absence of leaves with short petioles in C₂H₄-treated plants (C) and appearance of new leaves after termination of the treatment (D).

Figure 2

Effect of NaCl, 1-methylcyclopropene (MCP) and C₂H₄ treatment on leaf petiole elongation of intact Ranunculus sceleratus plants cultivated in closed 48 L containers in high humidity conditions for 7 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from six replicates ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 3

Effect of NaCl, 1-methylcyclopropene (MCP) and C₂H₄ treatment on concentration of Na⁺ in leaf petioles and leaf blades of intact Ranunculus sceleratus plants cultivated in closed 48 L containers in high humidity conditions for 7 days on dry mass (A) and tissue water (B) basis. Data are means from six independent measurements ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 4

Effect of NaCl, 1-methylcyclopropene (MCP) and C₂H₄ treatment on concentration of K⁺ in leaf petioles and leaf blades of intact Ranunculus sceleratus plants cultivated in closed 48 L containers in high humidity conditions for 7 days on dry mass (A) and tissue water (B) basis. Data are means from six independent measurements ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 5

Effect of increasing amount of silica xerogel on leaf petiole elongation of intact Ranunculus sceleratus plants cultivated in closed 24 L containers for 4 days. Silica xerogel was replaced each day. Control plants were cultivated outside the containers in greenhouse. Data are means from six replicates ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 6

Effect of increasing concentration of C₂H₄ (without or with 1-methylcyclopropene, MCP) on leaf petiole elongation (A) and leaf petiole water content (B) of intact Ranunculus sceleratus plants cultivated in closed 24 L containers in normal humidity conditions (with silica xerogel) for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions that were replaced every day. Data are means from six replicates ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 7

Effect of NaCl, 1-methylcyclopropene (MCP), C₂H₄ treatment on elongation of leaf petioles (A), leaf petiole dry mass (B), and leaf blade dry mass (C) of intact Ranunculus sceleratus plants cultivated at high humidity and normal humidity. Plants were cultivated in closed 48 L (high humidity) and 24 L (normal humidity with desiccation) containers for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from six replicates ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05).

Figure 8

Effect of NaCl, 1-methylcyclopropene (MCP), C₂H₄ treatment on water content in leaf petioles (A), leaf blades (B), and stems (C) of intact Ranunculus sceleratus plants cultivated at high humidity and normal humidity. Plants were cultivated in closed 48 L (high humidity) and 24 L (normal humidity, with desiccation) containers for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from six replicates ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05). DM, dry mass.

Figure 9

Effect of NaCl, 1-methylcyclopropene (MCP), C₂H₄ treatment on Na⁺ concentration in leaf petioles (A), leaf blades (B), and stems (C) of intact Ranunculus sceleratus plants cultivated at high humidity and normal humidity. Plants were cultivated in closed 48 L (high humidity) and 24 L (normal humidity, with desiccation) containers for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from five independent samples ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05). DM, dry mass.

Figure 10

Effect of NaCl, 1-methylcyclopropene (MCP), C₂H₄ treatment on K⁺ concentration in leaf petioles (A), leaf blades (B) and stems (C) of intact Ranunculus sceleratus plants cultivated at high humidity and normal humidity. Plants were cultivated in closed 48 L (high humidity) and 24 L (normal humidity, with desiccation) containers for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from five independent samples ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05). DM, dry mass.

Figure 11

Effect of NaCl, 1-methylcyclopropene (MCP), C₂H₄ treatment on electrical conductivity (EC) in leaf petioles (A), leaf blades (B), and stems (C) of intact Ranunculus sceleratus plants cultivated at high humidity and normal humidity. Plants were cultivated in closed 48 L (high humidity) and 24 L (normal humidity, with desiccation) containers for 6 days. Containers were ventilated for 1 h and new C₂H₄ and 1-methylcyclopropene (MCP) releasing solutions were replaced every day. Data are means from five independent samples ± SE for each treatment. Different letters indicate statistically significant differences between treatments (p < 0.05). DM, dry mass.