engleski

Influence of stress-hormone treatments (ABA, SA, JA) on the Brassica rapa seedlings

Abscisic acid (ABA), Salicylic acid (SA) and Jasmonic acid (JA) are well known endogenous plant signaling molecules involved in many aspects of plant growth, and in response to abiotic and biotic stress. They can contribute to stress tolerance by stimulating highly- branched metabolic responses. Oxidative-stress related parameters may be affected by exposure to these plant hormones. In our study we determined the influence of three hormone treatments on the Chinese cabbage (Brassica rapa L.) seedlings using the root growth bioassay. Some phenolic compounds have important roles in plant stress protection against lipid peroxidation, so total phenol content and lipid peroxidation of treated seedlings were determined. Seeds of Chinese cabbage (Brassica rapa L. ssp. pekinensis (Lour.) Hanelt cv. Cantonner Witkrop) were purchased from ISP International Seed Processing GmbH, Quedlinburg, Germany. Seeds were washed, sterilized in 3% NaClO, rinsed in sterile distilled water, and incubated on 1% agar plates at 4 oC for 24 hours. The plates were then placed under continuous light, at 22 oC, for the next 24 hours, for seed germination. One day old seedlings, with the root of about 10 mm in length, were placed on 1% agar plates supplemented with the ABA, SA, and JA at concentrations of 0.1 µM, 1 µM, 10 µM, 100 µM. Control experiments were performed on 1% agar plates without any treatment. Following incubation of the seedlings under continuous light for a further 24 hours, at 22 oC, the increase of root lengths was monitored. Seedlings treated with the highest concentration of ABA, SA, and JA were extracted in 80% methanol and methanol extracts were used for determination of total phenol (TO) content (Folin Ciocalteu method) and lipid peroxidation (thiobarbituric acid assay). The inhibition of root growth has been observed upon treatment with all three types of signaling molecules (ABA, SA, and JA) in a dose dependent manner. ABA showed the most inhibitory effect, then JA and finally SA. The highest concentration used in these bioassays (100 µM) of SA, JA and ABA caused inhibition of root growth: 31%, 56%, and 69%, respectively, in comparison to untreated control seedlings. JA and SA induced slightly increase in MDA (both 7%) and total phenol content (14% and 18%, respectively). ABA in concentration of 100 µM did not shown effect on MDA and TP content. Our results suggest that root growth is negatively affected by ABA, JA and SA. Higher MDA and TP content levels in seedlings treated with 100 µM JA and SA indicated effect on lipid peroxidation and phenolic metabolism. Further HPLC studies on phenolic compounds, such as chlorogenic acid and proto- catechuic acid which have important roles in plant stress protection, need to be done.

B. rapa ; Abscisic acid ; Jasmonic acid ; Salicylic acid

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