Effects of an NO donor during senescence of soybean cotyledons.

GALATRO A; JASID S; VILLORDO JJ; PUNTARULO S; SIMONTACCHI M

Montevideo Uruguay

Congreso; V Meeting of SFRBM-South American Group, V International Conference on Preoxynitrite and Reactive Nitrogen Species; 2007

SFRBM-South American Group

Cotyledons were excised from soybean plants (Glycine max) at days 10 and 25 after germination. Chlorophyll content upon this period showed a decrease of 0.14 ± 0.02 microg chlorophyll mg-1 FW. Electrolyte leakage, an index of membrane damage, increased by 2.1 microS g-1 FW from day 10 to day 25. After the 25 days period 18% of the cotyledons were abscised. Lipid radical content, assessed by EPR, showed a rise of 24 ± 2 nmol mg-1 prot upon the 25 day period. A model of non-senescent cotyledons was previously described by removing epicotyls from seedlings (BBA, 2003 [1627]: 129-139). Under these conditions, the cotyledons showed a slight decrease in chlorophyll content from day 10 to day 25 (0.06 ± 0.01 microg mg-1 FW) with no changes in conductivity and lack of cotyledon abscission. Moreover, non-senescent cotyledons showed an increase in lipid radical content non-significantly different from control cotyledons between day 10 and day 25. To assess nitric oxide (NO) role in the senescence of soybean cotyledons, the seedlings were daily sprayed with 0.1 mM sodium nitroprusside and NO content was evaluated by spin trapping EPR. Both control and non-senescent cotyledons showed non-detectable NO content upon the studied period. Cotyledons exposed to the NO donor showed a NO content of 5.0 ± 0.5 micromol NO g-1 FW, with non-significant changes until day 25, a decrease of 0.11 ± 0.01 microg mg-1 FW in chlorophyll content and an increment of 0.84 microS g-1 FW on the electrolyte leakage, from day 10 to 25. Moreover, the rise in lipid radical content in cotyledons exposed to the NO donor was significantly lower that the value found in control cotyledons. These results suggested that exogenous application of NO could partially reduce the senescence phenotype in cotyledons. However, the mechanism of NO action seems to differ from that of the non-senescent cotyledons model since the antioxidant properties of NO could play a role in the membrane protection of the cotyledons.