Early detection of plant stress using the internal electrical conductivity of Capsicum annuum in response to temperature and salinity stress

The internal electrical conductivity in plant stem (ECps) reflects its physiological activity including ion and water transport. Thus, monitoring the ECps can be used to predict physiological changes in plants due to environmental stresses that affect water and ion transport in them. The purpose of this study was to determine if ECps monitoring data could be used to indicate environmental stress induced by low temperature and salt by comparing ECps with chlorophyll and proline contents. Capsicum annuum was progressively exposed to day/night temperature of 21/16 degrees C and 14/9 degrees C as low-temperature stress. Salt stress was incrementally applied at 20 and 40 mmol/kg NaCl. The ECps of C. annuum was monitored over the experimental period. The ECps was lower under low-temperature stress, although visible changes were not observed. Both chlorophyll a and b contents were lower, and the proline content was higher in leaves under low-temperature stress compared to the control. The initial salt treatment increased the ECps and the subsequent salt treatment at 40 mmol/kg NaCl resulted in a sudden increase of the ECps. The decreased chlorophyll a and b, and the increased proline content of the leaves under salt stress were stress-induced responses. Sodium and chloride accumulation increased, and the potassium/sodium ratio decreased in salt-treated plants. The ECps reflected reduced ion and water transport under low-temperature stress and increased salt transport in stems under salt stress. Therefore, ECps monitoring can be used to diagnose physiological changes in plants caused by environmental stress conditions before symptoms appear.