ISHS Acta Horticulturae 361: International Symposium on New Cultivation Systems in Greenhouse
EFFECT OF PH IN THE ROOT ENVIRONMENT ON LEAKAGE FROM PLANT ROOTS |
| Author: | N. Zieslin |
| Abstract:
Plant growth and development are greatly influenced by alterations of pH in the root environment (Arnon and Johnson, 1942; Islam et al., 1980). These may be due to chemical composition of the soil or may develop as a result of root function (Findenegg et al, 1986). Leaf chlorosis, reduced root growth and decay, stunted shoot growth, poor flower development and other symptoms associated with uptake, transport and function of mineral ions are frequently appearing at inappropriate pH conditions in the rhizophere (Arnon et al., 1942; Hoagland, 1917; Findenegg et al., 1986; Moore, 1974; Wallace, 1953), especially in the inert soilless media without the soil buffering capacity. Appearance of those symptoms may stem from the influence of pH on the solubility of ions such as iron. Due to reaction with hydroxyl ions at highl pH conditions ferrous from (Fe2+) of iron is transformed in ferric form (Fe3+) which is inactive in plant tissues (Marschner, 1986). On the other hand, certain ions such as manganese, aluminum and iron may become overavailiable and even toxic to plants at high concentration of hydrogen ions or low pH conditions (Foy et al., 1978). High concentration of hydrogen ions (low pH) may also have a direct effect on root function by affecting negatively the permeability of root cell membranes and impose leakage of various ions from the roots (Moore, 1974; Yan et al., 1992). A rapidly developed decay of the root system has been observed (Fig. 1) when rose plants were transferred for 48h from low (6.0) to high (7.5) ph conditions (Zieslin and Snir, 1989) (Fig. 1). This and numerous similar observations indicate the possibility that in addition to the known effects of high pH on uptake of ions, high concentrations of hydroxyl ions may also have a direct effect on the root function in analogy to the direct effects of hydrogen ions. This hypothesis was investigated by mesurements of leakage from intact roots or root segments of rose (Rosa indica major) plants or from root segments of beans (Phaseoulus vulgaris) or african lilies (Agapanthus africanus) incubated in solutions of potassium phosphate buffer of different concentrations with pH 6.2 or 7.6. A high correlation has been found previously (Chalker-Scott et al., 1989) between leakage of electrolytes and leakage of phenolic compounds. Due to the minute amounts of root tissue required for spectrophotometric measurements of uv-absorbing substances without possible interference of mineral buffer residues, mesurement of leakage of uv-absorbing substances (phenols for simplicity) was adopted for evaluation of injury to root cell membranes (Redmann et al., 1986). | |
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