Department of Plant Sciences

Calcium (Ca) in plants has essential roles related to tissue mechanical strength and plant tolerance to stress, and understanding what affects its translocation and partition is of high value. Ca was shown to accumulate in transpiring organs and is considered to be coupled to water transport. However, being translocated mostly in the xylem, a conduit under tension, en-route sampling cause cessation of flow yielding fragmented understanding. To enable in-vivo, real time exploration of the coupling hypothesis, we developed and used a noninvasive sensing system to track translocation of gamma emitting Sr, an accepted Ca tracer, together with transpiration measurements. Tomato seedlings were grown in a continuously aerated hydroponic solution under controlled climatic conditions. Having three fruit bearing trusses, plants were moved to a growth room and arranged in pairs were one plant was continuously weighted and the other installed with high sensitivity gamma radiation detectors at various locations. A mixture of 85Sr and 88Sr was added to the solution of the 2nd plant around noon and has been followed for several days. Root applied Sr showed a fast sequential arrival to the main stem detectors along the expected water flow path. During the first few days, early morning transpiration and Sr translocation seemed to be coupled while later in the day a complex pattern emerged probably due to absorption-desorption dynamics as well as loading-unloading activity. As days passed, upstream radiation levels declined while downstream terminal organs levels increased, showing long-term accumulation pattern there. Fruit radiation pattern showed day inflow, which contradicts with the accepted fruit night-fill of xylem-borne ions. Fruit maturity is suggested as a possible explanation. Our custom made system, having both spatial and temporal capabilities, enabled following translocation patterns of radio-Sr within the plant. Together with indicative transpiration measurements, interesting insights were gained in reference to Ca-water coupling.