Effects of low temperature on K⁺ nutrition of some barley (Hordeum vulgare. L) varieties

The main objective of the present study was to investigate the capacity to compensate for reduced root activity caused by low temperature. Potassium influx, net flux and tissue K⁺ content in 23 spring and 2 winter barley varieties grown at low (5°C) and high (15°C) root temperatures were studied. It was apparent that the rates of uptake (at low temperature) of low temperature grown winter and some spring varieties were adjusted in response to continuous low temperature so that absorption rates approached those of plants maintained at higher (15°C) temperature. The temperature sensitivity for influx varied among varieties depending on the growth temperature and internal K⁺ concentration. Halcyon, a winter variety, showed a low temperature sensitivity when grown at low temperature (5°C) and low external [KT] (0.005 mM). The acclimation potentials (the ratio of K⁺ influxes measured at the same temperature for the plants acclimated to different temperatures) were higher for winter varieties and some spring (e.g. Fergus) varieties, while most of the spring varieties exhibited a lower potential to acclimate. It was also apparent that acclimation of K⁺ uptake to low temperature could be achieved only if the external K⁺ supply was not limited. Growth rates of the whole plant, shoots and roots monitored over a short period (14 days) revealed differences in the partitioning of K⁺ under different temperatures (8° and 18°C) and at different nutrient (K4) regimes (0.1 mM and 0.005 mM) . Despite the reduction in growth rates, roots appeared to maintain a high K⁺ level when grown at low temperature. Nevertheless, such maintenance was possible only if the supply of K⁺ was adequate. A low external K⁺ content and low temperature reduced the acclimation capacity even in the winter variety, Halcyon. Therefore, the importance of K⁺ fertilization for plants to withstand cold temperatures is obvious. Net fluxes of Halcyon and Kombar (a variety bred for warm soils in California) were investigated over a period of 24 hours. Incomplete acclimation of net fluxes was observed for both varieties over that period. This revealed the importance of considering effluxes as well as influxes in determining acclimation. The amount of radioactivity (⁸⁶Rb) delivered to the shoot over a period of one hour was used to estimate the translocation rate. This was greater for the winter variety than in the spring variety. Growth temperature, and to a lesser extent the duration of exposure to low temperature, required for acclimation appeared to be the factors that determined acclimation. Halcyon seemed to acclimate much faster than Bonanza, a spring variety which showed only a very limited capacity of acclimation.Science, Faculty ofBotany, Department ofGraduat