RAPID QUANTITATIVE EVALUATION OF PLANT MEMBRANE RESISTANCE TO DAMAGING EFFECTS OF SALINE SOLUTIONS
The specific site or sites of action of supraoptimal concentrations of salt solution on plants are not yet clearly defined. Early hypotheses which blamed inhibition of plant growth by saline irrigation water on purely osmotic considerations have had to be modified by the finding that plants can adjust their internal osmotic concentration in response to the environment. Excess sodium or chloride ions have been shown to have adverse or toxic effects on numerous aspects of cell metabolism such as protein synthesis, photosynthesis and respiration but the initial site or mode of action is not known.
Comparisons between mesophyte and halophyte plants have, helped in elucidating possible plant defence mechanisms against salinity eg. proline or betaine accumulation, salt excretion.
Because of our interest in foliar application of solutions of fertilizer salts we set out to develop an assay which would indicate the degree of membrane damage induced by brief (4 minute) exposures to various salt solutions. Using this assay we have been able to compare and correctly predict the concentrations of various fertilizer salts which cause rapid leaf burn when sprayed onto plants growing in the field.
Clearly the method is also applicable to the evaluation of plant membrane resistance to damage induced by NaCl. Preliminary experiments have been carried out to determine the response of the cell membranes of salt tolerant and salt susceptible varieties of barley to exogenous salt solutions.
The time course for leakage of U.V. absorbing materials from leaf segments following a 4 minute infiltration with test solution, rinsing and incubation in distilled water, is of influence on the degree of damage. The per cent damage is a function of the OD at 12 minutes as compared with the OD obtained by treatment with surfactant (100%) and SnMCaSO4 (0%). We have defined per cent damage values greater than 20 as representing irreversible damage to the cell membrane of infiltrated leaves within 4 minutes.
The plots of % damage are studied in relation with concentration for NaCl, glycool and mannitol and urea. From this one can