دانلود رایگان مقاله متابولیت ثانویه تغییر مورفوفیزیولوژیکی نعناع

Abstract

Germination and growth of plants are influenced by allelochemicals that mostly cause crops, yield reduction. In the present study, the effect of stress arising from allelopathic compounds in the water extract (WE) of peppermint (Mentha×piperita L. CV. Mitcham) on the morphophysiological and biochemical characteristics of tomato (Lycopersicon esculentum Mill. CV. Rio Grande) was investigated. Different concentrations (0, 2, 4, 6, 8, and 10% (v/v)) of the WE were examined. Some phenolic compounds of the WE determined by the HPLC instrument were trans-ferulic acid (10.8 mg/g), hesperidin (9.3 mg/g), ellagic acid (6.8 mg/g), and sinapic acid (4.2 mg/g). The results showed that the maximum inhibitory effect on germination and growth (dry weight, and leaf area) was obtained at the concentration of 10% (v/v) extract, and its compounds had significant effect on the amount of proline (PRO), soluble sugar and starch, as well as on the activities of tomato,s antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) at the 5% level. None of the treatments had a significant effect on the SPAD chlorophyll meter reading of tomato plants. It could be stated that the compounds present in the extract of peppermint must lead to high levels of reactive oxygen species (ROS), and subsequent oxidative stress inhibits the growth of the seedlings; however, more research is still required in this regard.

5. Conclusions

In conclusion, the present study demonstrated that different concentrations of peppermint WE caused decrease in seed germination and the growth of tomato seedlings; especially the 10% (v/v) concentration showed potent allelopathic and phytotoxic effects. These inhibitory effects are, generally, due to allelochemical components of peppermint WE. The action of allelochemicals in the target plant is diverse, and affects a large number of biochemical reactions resulting in modification of various processes (Bogatek and Gniazdowska, 2007). Increase in RMP and accumulation of PRO show that phenolic compounds induce oxidative stress in tomato. It was accompanied by upregulation in the activity of scavenging enzymes including APX, CAT, POD and SOD in the aerial parts of tomato in response to exposure to the WE. Both soluble sugar and starch were decreased by increasing the WE concentration. Eventually, oxidation stress inhibited the growth of the seedlings. It can be concluded that the increased activity of antioxidant enzymes under allelochemical stress could play an important role in allelopathy phenomenon. More research is still required in this regard. It is necessary to find out the effective allelochemicals of WE from peppermint for assessing their effects on tomato under field conditions, as field experiments in natural soils can show more natural allelopathic effects of other plants including peppermint.