Oxidative stress and antioxidant activity as the basis of senescence in Hemerocallis (day lily) flowers

Abstract

Senescence can be viewed as a developmental change that leads to the death of plant tissues. Naturally senescence is generally accepted as being genetically programmed. Petals are the floral organs which primarily determine the commercial longevity of flowers and as a consequence, it is necessary to study the physiological, biochemical and genetic processes that occur during floret senescence. Most of the early work on flower senescence focused on ethylene sensitive flowering plants. It has also been reported that lipid peroxidation and membrane damage are involved in deterioration of petals of several ethylene sensitive or insensitive plants. However, little information is available on the actual role of oxidative stress and the protective enzymatic systems with their corresponding isoenzymes in relation to progression of flower senescence in plants. One important bulbous ornamentals (Hemerocallis) was used as experimental materials in order to establish a proposed model of petal senescence based on the changes in antioxidant enzymes behavior over the senescence period. Hemerocallis flower blooms and fades at the end of same day. The vase life parameters were evaluated at 21°C and 16 h illumination (36 mol m-2 s-1) under laboratory condition. The stage of flower bud development was arbitrarily divided into 4 different developmental stages. Different parameters selected for the studies were changes in fresh weight, antioxidant enzymes like ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and Guaiacol peroxidase (G-POD), membrane integrity, H2O2 etc. Significant decrease in petal fresh weight, increase in lipid peroxidation, decrease in membrane stability index, decline in APX activity, progressive increase in SOD activity, changes in GR activity and increase in endogenous H2O2 were observed over the senescence period. All the parameters have been critically analysed and compared over the senescence period to understand the petal senescence in day lily.