Senescence Of Carnation Flowers Research Articles

Regulation of Ethylene Biosynthesis and Action in Cut Carnation Flower Senescence by Cytokinins

Abstract Cytokinins delay the onset of senescence in cut carnation flowers (Dianthus caryophyllus) by affecting the biosynthesis and action of ethylene in the tissue. The onset of senescence is marked by an increase in ethylene sensitivity and production by the tissue. A characteristic rise in 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, accompanies the initial stages, but the greatest increases in ACC are associated with the decline in ethylene production during the later stages of senescence. Cytokinins delay the onset of senescence and reduce ethylene sensitivity and production. Benzyladenine (BA), a cytokinin, prevents the rise in endogenous ACC levels and reduces the capacity of the tissue to convert ACC to ethylene. The effects of other anti-senescence agents, aminoethoxy vinylglycine (AVG), silver ions and cobalt ions, are compared with those of BA on ethylene sensitivity and production. The mechanism of action of BA in the delay in flower senescence is discussed.

Changes in parameters of cell senescence in carnation flowers after cold storage

The effects of cold storage on vase life, ethylene (C 2H 4) production, and parameters of cell senescence, were measured in flowers of spray carnation ( Dianthus caryophyllus L.), cultivar ‘Pink Royalette’. Storage for 6 or 12 days at 2°C led to a reduction in the subsequent vase life at 20°C. In addition, storage caused a reduction in the time between the rise in ethylene production and the end of vase life. That is, cold storage increased the sensitivity of the petal cells to endogenous C 2H 4. Normal aging of flowers for 6 days at 20°C led to decreased capacity of petals to take up [ 14C] sucrose, decreased activity of membrane ATPase, increased membrane microviscosity and decreased membrane phospholipid content, relative to the levels in fresh flowers. However, cold storage of flowers for 6 days at 2°C caused opposite changes in the levels of these senescence parameters (measured at constant temperature). It was concluded that cold storage does not simply lead to a slow rate of senescence, but has other effects on cell properties.

Correlative changes in sucrose uptake, ATPase activity and membrane fluidity in carnation petals during senescence

Apparent sucrose uptake. ATPase activity and membrane fluidity changes were studied during the development and senescence of carnation flowers (Dianthus caryophyllus L., cv. Cerise Royallette). Typical changes associated with senescence of a cut flower, such as respiration, ethylene production and fresh weight, were measured. Concomitant with a rise in respiration and ethylene production and a decline in fresh weight, a sharp decrease in apparent sucrose uptake was observed. Sucrose uptake was pH dependent (pH optimum, 5.5) and influenced by membrane integrity. Apparently, the activity of ATPase is related to sucrose uptake, because similar changes occurred during flower development. In addition, the activity of ATPase was well correlated with membrane fluidity.It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1‐aminocyclopropane‐l‐carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed.

Superoxide radical production by microsomal membranes from senescing carnation flowers: an effect on membrane fluidity

The lipid fluidity of carnation microsomal membranes decreases during in vitro aging in a manner that correlates with enzymatic production of superoxide anion (O 2 − dot ) by the membranes. Levels of (O 2 − dot ) were determined from ESR spectra of the semiquinone formed when (O 2 − dot ) reacts with Tiron (1,2-dihydroxybenzene-3,5-disulfonic acid). Heat denaturation of the microsomes or addition of n-propyl gallate, a free radical scavenger, eliminated the Tiron radical signal and prevented the change in membrane fluidity. By contrast, the addition of xanthine/xanthine oxidase, a reputed (O 2 − dot )-generating system, accentuated the decrease in membrane fluidity and greatly increased the Tiron radical signal. Superoxide dismutase, an enzyme that catalyses the dismutation of (O 2 − dot ), reduced the amplitude of the Tiron radical signal. When Tiron was used as a scavenger of (O 2 − dot ), there was no change in membrane fluidity. The data collectively suggest that (O 2 − dot ) or highly reactive derivatives of (O 2 − dot ) induce membrane rigidification. In addition, microsomes from senescent flowers produce more (O 2 − dot ) than those from freshly cut flowers, suggesting that this reactive species of oxygen also contributes to membrane rigidification during natural senescence.

Senescence of cut carnation flowers: Ovary development and CO2 fixation

In the presence of ethylene, which enhances carnation flower senescence, carbohydrates contribute to ovary growth not only from the stem and calyx but also from the petals. With silver thiosulphate and ethanol treatments which delay flower senescence, the petals remain the active sink and ovary development is suppressed. Ethylene stimulated chloroplast development in the ovary wall. However, the calyx plus stem of all treatments showed the greater photosynthetic ability and transported a major portion of the synthesised products to the ovary.

Acceleration of Membrane Senescence in Cut Carnation Flowers by Treatment with Ethylene

The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporally with petal-inrolling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or aminoethoxyvinylglycine-treated flowers were exposed to exogenous ethylene (1 microliter per liter), the microviscosity of microsomal membranes rose sharply within 24 hours, and inrolling of petals was clearly evident. Thus, treatment with ethylene accelerates membrane rigidification. Silver thiosulphate, a potent anti-ethylene agent, delayed the rise in microsomal membrane microviscosity even when the flowers were exposed to exogenous ethylene. Membrane rigidification in both naturally senescing and ethylene-treated flowers was accompanied by an increased sterol:phospholipid ratio reflecting the selective loss of membrane phospholipid that accompanies senescence. The results collectively indicate that the climacteric-like surge in ethylene production during senescence of carnation flowers facilitates physical changes in membrane lipids that presumably lead to loss of membrane function.

Ethylene formation from 1-aminocyclopropane-1-carboxylic acid by microsomal membranes from senescing carnation flowers

Isolated membranes from the petals of senescing carnation flowers (Dianthus caryophyllus L. cv. White-Sim) catalyze the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. A microsomal membrane fraction obtained by centrifugation at 131,000 g for 1 h proved to be more active than the membrane pellet isolated by centrifugation at 10,000 g for 20 min. The ethylene-producing activity of the microsomal membranes is oxygen-dependent, heat-denaturable, sensitive to n-propyl gallate, and saturable with ACC. Corresponding cytosol fractions from the petals are incapable of converting ACC to ethylene. Moreover, the addition of soluble fraction back to the membrane fraction strongly inhibits the ACC to ethylene conversion activity of the membranes. The efficiency with which isolated membranes convert ACC to ethylene is lower than that exhibited by intact flowers based on the relative yield of membranes per flower. This may be due to the presence of the endogenous soluble inhibitor of the reaction, for residual soluble fraction inevitably remains trapped in membrane vesicles isolated from a homogenate.

Aminooxyacetic acid as an inhibitor of ethylenesynthesis and senescence in carnation flowers

α-Aminooxyacetic acid delayed ethylene (C 2H 4) production by cut carnation flowers at a concentration of 3 × 10 −4 M. It also prevented the development of petal in-rolling (“sleepiness”) symptoms. The efficacy of inhibition is similar to that reported in apple tissue, but 10 times less efficient than in mung bean hypocotyls. The inhibitor had a slight delaying effect on the response of the flowers to exposure to C 2H 4. This apparent effect of the inhibitor on the action of C 2H 4 is discussed. The data are in agreement with the proposal that aminooxyacetic acid inhibits C 2H 4 biosynthesis.

Influence of ethanol on ethylene biosynthesis and flower senescence of cut carnation

Ethanol in the holding-solution inhibited climacteric ethylene (C 2H 4) biosynthesis and decreased the respiration rate 60% during a 7-day period in cut carnation flowers. Conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to C 2H 4 was inhibited by adding ethanol to the holding-solution. Simultaneously, ACC-induced senescence in carnation flowers was inhibited by ethanol. Ethanol was the most effective alcohol in delaying carnation flower senescence of the tested series methanol, ethanol, propanol, tert-butanol and n-butanol. Ovary development was also inhibited in carnation flowers by ethanol. The senescence of Easter lily flowers ( Lilium longiflorum) and tulip flowers ( Tulipa gesneriana) was not delayed by ethanol.

Role of Cytokinins in Carnation Flower Senescence

Stem and leaf tissues of carnation (Dianthus caryophyllus) plants appear to contain a natural antisenescence factor since removal of most of these tissues from cut carnation flowers hastened their senescence. However, kinetin (5-10 mug/ml) significantly delayed senescence of flowers with stem and leaf tissues removed. In addition, the life span of cut flowers with intact (30-cm) stems was increased with kinetin treatment. Peak ethylene production by presenescent flowers was reduced 55% or more with kinetin treatment and was delayed by 1 day. Kinetin-treated flowers were less responsive to applied ethylene (100 mul/l for 3 hours) than untreated flowers. Possible natural roles of cytokinins in carnation flower senescence are discussed.

Regulation of Senescence in Carnation (Dianthus caryophyllus)

Abscisic acid hastened senescence of carnation flowers and this was preceded by stimulation of accelerated ethylene production. Carbon dioxide delayed the onset of autocatalytic ethylene production in flowers regardless of treatment with abscisic acid. Flowers exhibited a low and transient climacteric of ethylene production without wilting while in 4% carbon dioxide and underwent accelerated ethylene production culminating in wilting when removed from carbon dioxide. Hypobaric ventilation, which lowers ethylene to hyponormal levels within tissues, extended flower longevity and largely negated enhancement of senescence by abscisic acid. Supplementing hypobarically ventilated flowers with ethylene hastened senescence irrespective of abscisic acid treatment. Collectively, the data indicate that abscisic acid hastens senescence of carnations largely as a result of advancing the onset of autocatalytic ethylene production.