Abstract:

This research investigated the physiological response mechanisms and growth characteristics of Viola tricolor in response to NaCl stress and explored the maximum NaCl concentration tolerated by V. tricolor. In a pot experiment， 45-day old seedlings of V. tricolor were subjected to different NaCl concentrations （0， 25， 50， 100， 150 and 200 mmol·L^-1）. It was found that NaCl treatment at higher concentrations had obvious effects on the osmotic regulation system， antioxidant enzyme system， photosynthetic pigment， malondialdehyde content and plant height of V. tricolor. With increase in NaCl concentration， soluble sugar， soluble protein， free proline and chlorophyll contents， together with catalase， peroxidase and superoxide dismutase activities， initially increased and then decreased. MDA concentration exhibited a pattern of continuous increased， and height growth decreased on the 14th day of NaCl stress with increasing NaCl concentration. A membership function analysis showed no obvious inhibitory effect of NaCl on the growth of V. tricolor when the concentration of NaCl in soil was ≤150 mmol·L^-1 but in contrast， NaCl had an obvious inhibitory effect on V. tricolor growth when the concentration was >150 mmol·L^-1. Therefore， the maximum NaCl concentration tolerance of V. tricolor was 150 mmol·L^-1， above which， the metabolic regulation system and antioxidant enzyme system were seriously affected， chlorophyll degradation was intensified， the photosynthetic system was seriously damaged， and the growth of V. tricolor was seriously reduced.

Key words: Viola tricolor, NaCl stress, stress response mechanism, tolerance limits