Osmotic and Salt Stresses Modulate Spontaneous and Glutamate-Induced Action Potentials and Distinguish between Growth and Circumnutation in Helianthus annuus Seedlings

Abstract

Action potentials (APs), i.e., long-distance electrical signals, and circumnutations (CN), i.e., endogenous plant organ movements, are shaped by ion fluxes and content in excitable and motor tissues. The appearance of APs and CN as well as growth parameters in seedlings and 3-week old plants of Helianthus annuus treated with osmotic and salt stress (0–500 mOsm) were studied. Time-lapse photography and extracellular measurements of electrical potential changes were performed. The hypocotyl length was strongly reduced by the osmotic and salt stress. CN intensity declined due to the osmotic but not salt stress. The period of CN in mild salt stress was similar to the control (~164 min) and increased to more than 200 min in osmotic stress. In sunflower seedlings growing in a hydroponic medium, spontaneous APs (SAPs) propagating basipetally and acropetally with a velocity of 12–20 cm min−1 were observed. The number of SAPs increased 2–3 times (7–10 SAPs 24 h−1plant−1) in the mild salt stress (160 mOsm NaCl and KCl), compared to the control and strong salt stress (3–4 SAPs 24 h−1 plant−1 in the control and 300 mOsm KCl and NaCl). Glutamate-induced series of APs were inhibited in the strong salt stress-treated seedlings but not at the mild salt stress and osmotic stress. Additionally, in 3-week old plants, the injection of the hypo- or hyperosmotic solution at the base of the sunflower stem evoked series of APs (3–24 APs) transmitted along the stem. It has been shown that osmotic and salt stresses modulate differently hypocotyl growth and CN and have an effect on spontaneous and evoked APs in sunflower seedlings. We suggested that potassium, sodium, and chloride ions at stress concentrations in the nutrient medium modulate sunflower excitability and CN.

Fertigation of Ajwain (Trachyspermum ammi L.) with Fe-Glutamate Confers Better Plant Performance and Drought Tolerance in Comparison with FeSO4

“…The endogenous excessive accumulation of the glutamate under normal or stressed conditions or through its exogenous application, confirms its role as a signaling molecule in ameliorating the deleterious effects of multiple abiotic stresses [31]. For example, the exogenous application of glutamate on Brassica compestris reduced the negative impacts of salt and osmotic stress [33]. Ramos et al [34] reported an endogenous increase in glutamate of Glycine max L. grown under water deficiency, resulting in the increased accumulation of many other amino acids along with its own accumulation.…”

“…It might be the fact that glutamate might also have played an additional role in improving the water stress tolerance of ajwain plants [35]. It has been found earlier that foliar-supplied glutamate was found helpful in enhancing plant performance and alleviating the harmful effects of stress in faba bean and Brassica napus plants [33,35], respectively. In rice, Jie et al [67] reported that amino acidchelated Zn and Fe better improved the yield as compared with respective chemical fertilizers.…”

Chloride as a Beneficial Macronutrient in Higher Plants: New Roles and Regulation

“…Consistent with the role of Cl − in the regulation of water transport and cell volume in plants, Cl − fluxes are specifically required for the proper functioning of specialized motor cells like the pulvini of leguminous plants during seismonastic and nystinastic leaf movements [39,40,41], and guard cells during stomatal opening and closure [42,43]. Osmotically-driven water fluxes are also essential for endogenous plant organ movement or circumnutation [44]. While transmembrane ionic fluxes necessarily involve electroneutral transport with K + , the activation of PM anion channels is often the triggering element that connects environmental cues with the response of the corresponding motor cell, as observed in the stomatal closure or the circadian-regulated leaf opening [45,46].…”

Effects of Ca(NO3)2 Stress on Mitochondria and Nitrogen Metabolism in Roots of Cucumber Seedlings

“…In response to Ca(NO 3 ) 2 , the mitochondrial numbers and structure of the two cultivars of cucumber showed great changes. This result could be explained through the osmotic stress effects of plant root growth [24]. Previous work showed that salt stress conditions had a suppression role in the growth of plants [25].…”