Co-Authors:
Carmi, A., Institute of Soils and Water, ARO, Volcani Center P.O. Box 6, Bet Dagan 50250, Israel
Abstract:
The possibility that the suppression of shoot growth in restricted root zone plants (RRZP) is caused by a deficiency in N-amino compounds (NAC) in the shoot, possibly due to an insufficient supply from the roots, was studied in bean (Phaseolus vulgaris L.). Root zone restriction to 10 cm3 in an aerated nutrient solution resulted in suppressed plant growth, as compared with control plants grown in a non-limiting root zone volume. Root xylem exudation of solution and N-amino compunds (NAC) following decapitation was much greater in the control, as compared with RRZP, both per plant and per unit root fresh weight (FWT). In both treatments, asparagine comprised more than 52% of the NAC fraction in the root xylem exudate (RE). Its reduced exudation in the RRZP was of a proportion similar to the combined fraction of NAC left over in both treatments. Asparagine accumulation in leaves of the control plants was very high, comprising 73% of the total NAC pool, while in RRZP, it was much smaller and did not exceed 25%. The total NAC amount per unit of leaf FWT was 3·3 times smaller for the RRZP, as compared with the control, resulting mainly from the dramatic drop in asparagine accumulation. In the roots, RRZP accumulated more NAC per unit root FWT than the control. Raising both treatments in distilled water reduced considerably the accumulation of NAC, including asparagine, in their leaves. RRZP was relatively more suppressed by the absence of nutrients than control plants. This phenomenon did occur, despite the fact that NAC and asparagine concentrations in the root and shoot of RRZP were greater than in the control when grown in distilled water; Therefore, it was concluded that root zone restriction might affect the accumulation of NAC and asparagine in the leaves, but that deficiency in these compounds is not the primary or the major cause of growth suppression in RRZP. © 1993 Oxford University Press.
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