Cellular and whole-plant chloride dynamics in barley: insights into chloride?nitrogen interactions and salinity responses

Abstract

The first analysis of chloride fluxes and compartmentation in a non-excised plant system is presented, examining ten ecologically pertinent conditions. The short-lived radiotracer couple (38)Cl/(39)Cl was used as a Cl(-) tracer in intact barley ( Hordeum vulgare L. cv. Klondike) seedlings, which were cultured and investigated under four external [Cl(-)], from abundant (0.1 mM) to potentially toxic (100 mM). Chloride-nitrogen interactions were investigated by varying N source (NO(3)(-) or NH(4)(+)) and strength (0.1 or 10 mM), in order to examine, at the subcellular compartmentation level, the antagonism, previously documented at the influx level, between Cl(-) and NO(3)(-), and the potential role of Cl(-) as a counterion for NH(4)(+) under conditions in which cytosolic [NH(4)(+)] is excessive. Cytosolic [Cl(-)] increased with external [Cl(-)] from 6 mM to 360 mM. Cl(-) influx, fluxes to vacuole and shoot, and, in particular, efflux to the external medium, also increased along this gradient. Efflux reached 90% of influx at the highest external [Cl(-)]. Half-times of cytosolic Cl(-) exchange decreased between high-affinity and low-affinity influx conditions. The relationship between cytosolic [Cl(-)] and shoot flux indicated the presence of a saturable low-affinity transport system ("SLATS") responsible for xylem loading of Cl(-). N source strongly influenced Cl(-) flux to the vacuole, and moderately influenced Cl(-) influx and shoot flux, whereas efflux and half-time were insensitive to N source. Cytosolic pool sizes were not strongly or consistently influenced by N source, indicating the low potential for Cl(-) to act as a counterion to hyperaccumulating NH(4)(+). We discuss our results in relation to salinity responses in cereals.

The cytosolic Na+ : K+ ratio does not explain salinity‐induced growth impairment in barley: a dual‐tracer study using 42K+ and 24Na+

“…These differential Na + effects upon K + turnover underscore the fundamental differences between HATS and LATS transport modes that we have previously demonstrated (Kronzucker et al 2003;Britto et al 2006), and have important consequences for cytosolic K + concentration estimates (see subsequent discussion). (Britto et al 2004), and has also been seen with relatively non-toxic ions including K + and NO 3 − (Scheurwater et al 1999;Kronzucker, Glass & Siddiqi 1999). For all ions, it is now recognized that this condition is energetically burdensome to the plant (Schubert & Läuchli 1990;Poorter et al 1991;Yeo 1998;Scheurwater et al 1999;Kronzucker et al 2001;, and the high cost of futile cycling has been calculated for some ions .…”

Photosynthesis sensitivity to NH₄⁺-N change with nitrogen fertilizer type

“…These plants would suffer ammonium toxicity when supplied with high ammonium in the root medium as the sole N source. Having a higher ammonium assimilation capacity than other plant species, those plants could avoid ammonium toxicity and exhibited a preference for ammonium nutrition (Britto et al 2004, Guo et al 2007. Although the toxicity of ammonium regardless its origin, has been observed for more than one hundred years (Britto et al 275 2001), most reports concentrated on the study of animal (Alonso andCamargo 2003, Arauzo 2003), bacterium (Muller et al 2006), and higher plants (Gerendás 1997, Britto andKronzucker 2002).…”

Chloride (Cl−) Uptake

“…Influx of Cl − into the symplasm appears to be active, whereas efflux is passive since there is a gradient for passive efflux of anions from cytoplasm to the external medium (Teakle and Tyerman 2009 (Britto et al 2004). According to White and Broadly (2001), chloride uptake by roots is through a symplastic pathway, and the nature of chloride fluxes depends on the chloride concentration in the roots.…”