Lithium distinguishes between growth and circumnutation and augments glutamate-induced excitation of Helianthus annuus seedlings

Abstract

An effect of lithium (Li ? ) on growth, circumnutation, and glutamate-induced excitation in sunflower (Helianthus annuus L.) seedlings was investigated using time-lapse photography and extracellular electrical potential measurements. The seedlings were treated with a micro and millimolar concentration of lithium chloride (LiCl) both persistently in a hydroponic medium and acutely through Li ? injection. The length of hypocotyls, fresh weight of seedlings, intensity and period of circumnutation, and the number of action potentials (APs) after glutamate (Glu) injection were determined. It was found that the circumnutation intensity and period did not depend on hypocotyl length and fresh weight of seedlings. Under persistent Li ? treatment, the circumnutation intensity was constant at a concentration between 0.2 and 20 mM although the hypocotyls were significantly shorter in relation to the control, whereas at a concentration of 40 mM circumnutation intensity decreased without any changes in the hypocotyl length. Under persistent treatment with 0.5 and 20 mM Li ? , the period of circumnutation was significantly prolonged. The number of APs in a Glu-induced series significantly increased in the seedlings exhibiting an Li ? -induced decrease in circumnutation intensity (in 40 and 60 mM Li ? ). Additionally Li ? injection before Glu injection also augmented the series of APs in seedlings growing without Li ? in hydroponic medium. These Li ? -sensitive responses demonstrated that circumnutation and growth are partly independent processes and reveal a relationship between circumnutation intensity and excitability in Helianthus annuus seedlings.

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

“…This confirms a strong resistance of the CN period to osmotic and salt stress (Erdei et al, 1998 ). The independence of the CN period of the growth of hypocotyls confirmed some degree of independence between growth and CN behavior, as in the case of lithium treatment (Stolarz et al, 2015 ).…”

“…Glutamate is a major amino acid involved both in nitrogen metabolism and in nitrogen signaling (Forde and Lea, 2007 ; Mousavi et al, 2013 ). Previously, we showed that lithium modulated Glu-induced excitability and CN in sunflower seedlings (Stolarz et al, 2015 ). Thus, we expected that also the external concentration of K, Na, and Cl could modulate the Glu-induced series of APs.…”

“…The problem of CN dependence on growth has been considered many times (Spurny, 1975 ; Johnsson, 1979 , 1997 ; Millet and Badot, 1996 ; Stolarz et al, 2008 ). In general, CNs are dependent on growth, but in some environmental conditions, for example under lithium, red light, or ethylene treatment, growth and CN uncoupling was observed (Spurny, 1968 ; Zachariassen and Johnsson, 1988 ; Millet and Badot, 1996 ; Yoshihara and Iino, 2005 ; Binder et al, 2006 ; Stolarz et al, 2008 , 2015 ). This study has shown that the osmotic and salt stress treatments distinguish between growth and CN behavior (Figures 1A,B ).…”

“…Growth inhibition in plants is a most frequently defined effect of environmental stress, including salt stress (Zhu, 2003 ; Foster and Miklavcic, 2015 ; Wu et al, 2015a ). CNs are closely related to growth, and CN changes after many environmental stimuli have been described (Buda et al, 2003 ; Stolarz et al, 2008 , 2015 ; Stolarz, 2009 ; Kurenda et al, 2015 ). An endogenous motor activity and electrical long-distance signaling in the form of CNs and APs have been well-characterized in H. annuus .…”