The evaluation of paclobutrazol effects on increase cold hardiness in tomato seedlings (lycopersicum esculentum L.)

Paclobutrazol in one the most important substance from triazol grope. These substance are plant growth retardants which mitigate stress in plants. The aim of the present study was to determine whether the plant growth regulator, such as paclobutrazol can protect tomato seedling from injuries caused by low temperature stress (LTS). In this study two different concentrations (30, 60 mg/l) of PBZ were sprayed on 5-week-old plants. After 3 days, seedlings were exposed to LTS by placing them in cold incubator at 1±0.2 ºC for 6 h for consecutive day and returned to their original place, treatment were applied daily for 5 day. After treatment of seedlings, morphological parameters (such as shoot and root fresh weight, shoot and root dry matter and shoot and root length) and biochemical parameters (such as, proline, leaf chlorophyll, carotenoids, cell membrane lipids peroxidation) were measured. Data of all parameters were analysed with spss software version 9.0. Results showed that LTS inhibited plant growth and induced membrane lipid peroxidation, and increased proline content. On the other hand, LTS decreased the chlorophyll and carotenoids content. PBZ treatment caused shoot dry weight. Internode and shoot length were reduced by this treatment. Instead PBZ, increased root dry weight and root were more extended. Moreover PBZ treated plants when exposed to the cold stress condition, showed reduction in lipid peroxidation and proline content. Treatment of seedlings with PBZ led to an increase in chlorophyll and carotenoid contents either in stress or non stress conditions. Our results showed that PBZ treatment improve chilling injury and responses to the cold stress.