INVESTIGATION ON THE RELATIONSHIP BETWEEN SENESCENCE AND NITRIC OXIDE IN SUNFLOWER (HELIANTHUS ANNUUS L.) SEEDLINGS

In this study, the effects of NO (nitric oxide) on senescence occurring in the cotyledons of Helianthus annuus L. (sunflower) seedlings, were examined. Following germination of the sunflower the seedlings were grown in perlit for 10 days and then transferred into hydroponic culture containing 1/4 Hoagland solution. At day 23 approximately when senescence started occurring, 0.1, 1, 10, 100 and 400 mu M concentrations of Sodium nitroprusside prepared in 1/4 Hoagland solution used as NO donor were applied to the seedlings. The cotyledons of both control and experimental groups were harvested when the avarage green area in the control group reached 50%. Effects of NO in senescence process were determinated by measuring parameters such as Peroxidase activity, amount of chlorophyll and total soluble protein. When compared with the control cotyledons, senescence was observed to be delayed at lower SNP concentrations, especially at 0.1 mu M. As SNP concentrations were elevated chlorophyll amount gradually decreased, being under the control value at 400 mu M SNP, while total soluble protein reached a maximum at 10 mu M SNP and Peroxidase activity showed an increase parallel to increment concentrations. It would suggest that exogenously applied SNP may play a role in regulating senescence process in Helianthus annuus seedlings, depending on concentration.