Influx and efflux of K(+) in sunflower roots after transfer between solutions with different K(+) concentrations

It was investigated whether K(+) efflux, like K(+) influx, is affected when roots are transferred between solutions with different K(+) concentrations. Sunflower plants (Hehanthus annuus L. cv. Uniflorus) were grown on complete nutrient solutions with 0.1, 1.0, 10 or 25 mM K(+) . This produced plants with K(+) concentrations in the roots varying between 9 and 110 μmol (g fresh weight)(-1) . At the beginning of the experiments the plants were transferred to an (86) Rb-labelled experimental solution initially containing 0.1 mM K(+) . At intervals during 6.5 h samples were removed from the solution and analyzed for K(+) and radioactivity. Based on the analyses K(+) ((86) Rb) influx, K(+) net uptake and K(+) efflux could be computed. In'low K(+) 'roots, K(+) ((86) Rb) influx and K(+) net uptake agreed, suggesting a very low K(+) efflux. This was contrary to'high K(+) 'roots, where K(+) efflux was initially higher than K(+) ((86) Rb) influx. After about 4 h, K(+) efflux declined to a low value also in these roots. When 2-4-dinitrophenol was included in the experimental solution, K(+) ((86) Rb) influx was generally depressed, whereas K(+) efflux was high throughout the experiment and directly proportional to the K(+) status of the roots. Our hypothesis is that after transfer of'high K(+) 'roots to a solution with low K(+) concentration, the K(+) efflux from the vacuoles of root cells transiently increases, until a new electrochemical equilibrium is attained.     

The Use of High-resolution Infrared Thermography (HRIT) for the Study of Ice Nucleation and Ice Propagation in Plants

Freezing events that occur when plants are actively growing can be a lethal event, particularly if the plant has no freezing tolerance. Such frost events often have devastating effects on agricultural production and can also play an important role in shaping community structure in natural populations of plants, especially in alpine, sub-arctic, and arctic ecosystems. Therefore, a better understanding of the freezing process in plants can play an important role in the development of methods of frost protection and understanding mechanisms of freeze avoidance. Here, we describe a protocol to visualize the freezing process in plants using high-resolution infrared thermography (HRIT). The use of this technology allows one to determine the primary sites of ice formation in plants, how ice propagates, and the presence of ice barriers. Furthermore, it allows one to examine the role of extrinsic and intrinsic nucleators in determining the temperature at which plants freeze and evaluate the ability of various compounds to either affect the freezing process or increase freezing tolerance. The use of HRIT allows one to visualize the many adaptations that have evolved in plants, which directly or indirectly impact the freezing process and ultimately enables plants to survive frost events.