Regulation of K⁺ Influx in Barley

Abstract

Influx and accumulation of K' in barley (Hordeum vulgare L. cv Fergus) roots were measured at two temperatures (10°C and 20C) in plants which had been grown with roots and shoots at 20°C (HT plants), with roots and shoots at 10°C (LT plants), and with roots at 10°C and shoots at 20°C (DT plants example, compared to control plants grown at 200C continuously, plants whose roots had been maintained at 8°C demonstrated increased rates of nutrient absorption, accumulation, translocation, and xylem exudation when these processes were measured at 20C.Clarkson and his co-workers (4, 5, 7) have emphasized that the observed responses represent a strategy which compensates for the lower root activity and higher shoot activity associated with the temperature differential. However, similar increases in ion fluxes in response to pretreatment at low temperatures have been demonstrated in a giant alga where differential temperatures were not involved (12,13). It is therefore important to resolve, in higher plants, whether the stimulation of ion fluxes is due to differential (root/shoot) temperature or due to exposure of roots to low temperature per se irrespective ofshoot temperature. This may have important implications as to the source(s) of the signal(s) responsible for the observed adjustments of ion fluxes.Moreover, the extent of the accommodation of ion fluxes may have been considerably underestimated in previous studies. At face value it would appear that roots, maintained at 10°C below shoot temperatures, achieve higher levels of ion accumulation and ion fluxes which are equal to or even slightly higher (on a per unit weight basis) than those of roots where roots and shoots are maintained at the higher temperature. However, it is well documented that ion uptake is negatively correlated with tissue ion concentration (8,10,14

Kinetics of nutrient uptake by roots: responses to global change

“…Indeed, a number of studies have demonstrated that changes in soil temperature can directly effect plant nutrient acquisition by changing root transport properties for NH % + (Chapin et al, 1986), NO $ − (Cumbus & Nye, 1982 ;BassiriRad et al, 1991BassiriRad et al, , 1993, PO % $− (Chapin, 1974(Chapin, , 1977Cumbus & Nye, 1985), and K + (Siddiqi et al, 1984). The exact mechanism for temperature-induced changes in nutrient uptake capacity is not clearly understood.…”

A Model for the Regulation of K+ Influx, and Tissue Potassium Concentrations by Negative Feedback Effects upon Plasmalemma Influx

“…Although largely speculative, there is some experimental data supporting the idea of increased b values from our previously published study of low temperature effects on K+ uptake (29 concerning the effects of K+ and Pi supply on cytoplasmic and vacuoler concentrations of these ions emphasize that the use of the term homeostasis in reference to tissue [ion] is probably better limited to the cytoplasmic phase.…”

“…16 for review). Likewise, while temperature sensitivity is a characteristic feature of short-term temperature perturbations (1,9), long-term studies have shown that acclimation to the ambient temperature tends to make ion absorption temperature-independent (4,29).…”

“…This transience should not be interpreted as applying uniquely to 'low-salt' (CaSO4-grown) plants. High-salt tissues are equally sensitive to short-term concentration and temperature perturbations (13,15,29). In the long-term, fluxes appear to be determined by intrinsic characteristics associated with the maintenance of tissue [ion] at some prescribed level rather than by extrinsic factors (such as concentration or temperature).…”

Study of Nutrient Solution Management in Soilless Rose Cultivation Through the Analysis of Physiological Parameters and Nutrient Absorption

“…A decrease in N uptake has been measured at low temperatures (Dong et al, 2001). In contrast, after long-term exposure to low temperature, roots of rye, barley and maize increased their capacity for ion uptake (Siddiqi et al, 1984;Clarkson, 1986;White et al, 1987;Engels et al, 1992). This has been attributed to an increased number of ion transporters in the root plasma membrane (Siddiqi et al, 1984) maybe the consequence of higher shoot demand per unit root fresh weight (Clarkson et al, 1986;White et al, 1987;Engels et al, 1992).…”