Effects of calcium deficiency on nutrient concentration of xylem sap of excised tomato plants

The effects of calcium (Ca) deficiency on cation uptake and concentration o f xylem sap from tomato roots after excision of the aerial parts, were stud ied. The measurements were made on tomato plants grown on nutrient solution s with + Ca or without -Ca, over a period of 48 hours. Calcium deficiency e ntailed a significant increase of the flux of xylem sap between the 6th and 14th hour on the first day after excision. In spite of the lack of Ca in t he nutrient solution, the Ca concentration in xylem sap was unaffected in r egard to that of excised roots with +Ca. The maintenance of the Ca concentr ation in xylem sap of plants grown on a Ca deficient solution was related t o a reuse of the Ca from the apoplastic root stores, So, this regulation in dicates a possible translocation of the Ca available in the root supply and a mobility of this element out of the roots only during the early stages o f exposure to a Ca deficiency. The presence of NH,I in xylem sap with both +Ca and -Ca treatments confirms the nitrogenous reduction activity of tomat o roots. The accumulation of free ammonium 24 h after excision in both xyle m saps (+Ca and -Ca) is likely to be evidence of an alteration process of p rotein synthesis which is related to the depletion of the root water solubl e carbohydrate supply.