Growth enhancement by silicon in cucumber (Cucumis sativus) plants depends on imbalance in phosphorus and zinc supply

Based on results from water culture experiments with tomato and cucumber plants where severe leaf chlorosis and depression in flower and fruit formation occurred without silicon (Si) supply, Miyake and Takahashi (1978; 1983) concluded that Si is an essential mineral element for these two plant species. Using the same nutrient solution which is high in phosphorus (P) but low in zinc (Zn) we could confirm these results. Severe chlorosis occurred in cucumber when Si was omitted, and the addition of Si prevented these visual symptoms. Simultaneously the concentrations of P drastically decreased in the leaves and the proportions of water extractable Zn increased. Normal growth and absence of chlorosis were, however, also obtained without the addition of Si when either the external concentration of P was lowered or of Zn was increased. Short-term experiments revealed that Si has no direct effect on uptake or translocation of P to the shoot. According to these results, the experimental evidences so far are insufficient for the classification of Si as an essential mineral element for cucumber. Instead, Si may act as beneficial element under conditions of nutrient imbalances, for example, in P and Zn supply and corresponding P-induced Zn deficiency. The mechanism by which Si increases the physiological availability of Zn in leaf tissue is not yet clear. © 1990 Kluwer Academic Publishers