Decline in ascorbate peroxidase activity--a prerequisite factor for tepal senescence in gladiolus.
Flower senescence was studied in Gladiolus cv. "Snow Princess" over five arbitrarily divided developmental stages (stage 1, half bloom; stage 2, full bloom; stage 3, beginning of wilting; stage 4, 50% wilting; stage 5, complete wilting) in terms of changes in fresh weight, antioxidant enzymes (superoxide dismutase, SOD; ascorbate peroxidase, APX; glutathione reductase, GR) activities and membrane integrity. A significant decrease in tepal fresh weight was observed over the senescence period (after stage 2). Membrane integrity was studied by measuring lipid peroxidation [in terms of thiobarbituric acid reactive substances (TBARS) content] and membrane stability index (MSI) percentage. Maximum TBARS content was recorded in stage 4 (50% wilting). This increase in lipid peroxidation over the senescence period was in close association with high degree of membrane deterioration expressed as decrease in membrane stability index percentage. A significant decrease (two and half-fold) in MSI% in stage 5 (as compared to stage 1) indicates complete membrane deterioration. Progressive increase in endogenous H2O2 level was recorded over senescence period. Maximum H2O2 content (19.7+/-1.4 micromol g(-1) DW) was recorded at stage 5 (complete wilting). Three different patterns were observed in antioxidant enzymes behavior over the senescence period. APX activity was declined significantly as, the flower entered stage 3 (beginning of wilting) from full bloom condition (stage 2). Progressive and significant increase in SOD activity was measured as a function of time. Maximum SOD activity (24.2+/-0.8 U mg(-1) DW) was recorded in stage 5 (three-fold increase over stage 1). GR activity initially increased up to stage 4 (50% wilting) and declined significantly thereafter (approximately seven-fold). An increase in endogenous H2O2 level during senescence may be the result of a programmed down-regulation of APX enzyme activity, which seems to be the prerequisite factor for initiating senescence process in gladiolus tepal.
Hossain
Zahed
Z
Botanic Garden & Floriculture, National Botanical Research Institute, Lucknow-226001, Uttar Pradesh, India.
Mandal
Abul Kalam Azad
AK
Kumar Datta
Subodh
S
Krishna Biswas
Amal
A
D000975:Antioxidants / Q000378:metabolism; D060387:Ascorbate Peroxidases; D002462:Cell Membrane / Q000502:physiology; D035264:Flowers / Q000201:enzymology / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D027621:Iridaceae / Q000201:enzymology / Q000502:physiology*; D015227:Lipid Peroxidation; D010544:Peroxidases / Q000378:metabolism*
D000975:Antioxidants; D006861:Hydrogen Peroxide; D010544:Peroxidases; D060387:Ascorbate Peroxidases