Anti-oxidant metabolism during rose (Rosa hybrida L.) petal senescence

Abstract

SummaryThe role of the ascorbic acid-reduced glutathione (ASA-GSH) cycle was explored in relation to petal senescence in ‘First Red’ rose (Rosa hybrida L.). The contents of reduced ASA [5.43 µmol g–1 FW at Stage-2 (bud still closed and heavily pigmented) to 12.22 µmol g–1 FW at Stage-4, (flowers 3 d after harvest, sepals completely opened, petal beginning to unfold)] and GSH (2.43 µmol g–1 FW at Stage-2 to 3.77 µmol g–1 FW at Stage 4), were higher during the earlier stages of petal development. Maximum activities of dehydroascorbate reductase (DHAR; 6.28 µmol ascorbate min–1 mg–1 protein), monodehydroascorbate reductase (MDHAR; 4.24 µmol NADH min–1 mg–1 protein), ascorbate peroxidase (APOD; 6.28 µmol ascorbate min–1 mg–1 protein), and glutathione reductase (GR; 2.46 A412 min–1 mg–1 protein) were observed at Stage 4. Consequently, this reduced redox status may protect cells from deleterious oxidative stress. The APOD/DHAR system was more active than the APOD/MDHAR system in the regeneration of ASA in petals of ‘First Red’ rose. However, the APOD/MDHAR system may play a significant role during the later stages of senescence, when the supply of reduced glutathione [GSH; 0.42 µmol g–1 FW at Stage-5 (flowers 6 d after harvest, petals completely unfolded) declined to 0.20 µmol g–1 FW at Stage-6 (flowers 9 d after harvest, flowers completely senesced with petal blueing]. The terminal stages of senescence were characterised by significant declines in the activities of DHAR (Stage-6, 1.94 µmol ascorbate min–1 mg–1 protein), MDHAR (Stage-6, 0.98 µmol NADH min–1 mg–1 protein), and APOD (Stage-6, 2.91 µmol ascorbate min–1 mg–1 protein), with higher levels of DHA (3.24 µmol g–1 FW at Stage-4 to 6.25 µmol g–1 FW at Stage-5) and oxidised glutathione (GSSG; 0.22 µmol g–1 FW at Stage 4 to 0.62 µmol g–1 FW at Stage 5). This highly oxidative redox state appeared to be the cause of petal senescence in ‘First Red’ rose.