SCIENTIA HORTICULTURJE

ELSEV I ER Scientia Horticulturae 58 (1994) 351-355

S h o r t c o m m u n i c a t i o n

Sites of ethylene production in flowers of sweet pea ( Lathyrus odoratus L. )

Kushal Singh*, K.G. Moore School of Biological Sciences, University of Bath, Claverton Down, Bath BA2 7A Y,, UK

Accepted 16 March 1994

Abstract

Flowers of sweet pea showed climacteric rise in ethylene production. The style and stigma, collectively, showed an initial rise in ethylene production which later extended to the other flower parts. A very high amount of ethylene was produced by the staminal sheath which is suggested to play an important role in flower senescence.

Keywords: Ethylene production; Sweet pea; Staminal sheath

1. Introduction

Role of ethylene in flower senescence has been well documented in the litera- ture (Halevy and Mayak, 1981; Reid, 1989). Senescence of many flowers is ac- companied by a climacteric increase in ethylene production (Nichols, 1977; Stead and Moore, 1979; Reid, 1989). Pollination stimulates the production of ethylene which ultimately results in wilting (Whitehead et al., 1984) or abscission (Stead and Moore, 1979) of petals. There is some evidence that the style is a potential source of ethylene in some flowers (Lipe and Morgan, 1973; Nichols, 1977; Stead and Moore, 1983).

The sweet pea flower has a typical structure. The corolla is papillionaceous and nine out of ten stamens are united below to form a sheath around the ovary (re- ferred to as 'staminal sheath' in the text). The flowers are an attractive floristry item and their senescence is associated with a climacteric rise in ethylene produc-

*Corresponding author. Present address: Department of Vegetable Crops, Landscaping and Floricul- ture, Punjab Agricultural University, Ludhiana- 141 004, India.

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352 K. Singh, K,G. Moore / Scientia Horticulturae 58 (1994) 351-355

tion (Mor et al., 1984). The studies reported here were conducted to determine the sites of ethylene production in sweet pea flowers.

2. Material and methods

2.1. Plant material

Plants of sweet pea (Lathyrus odoratus L.) cultivar 'Spencer Festival' were raised from seeds under glasshouse conditions. To maintain uniformity, two to three floral buds were retained on each inflorescence. Freshly opened flowers were tagged and sampled daily until they showed complete wilting of the petals.

2.2. Ethylene measurements

Groups of ten excised flowers were placed in glass jars of 250 ml volume. The jars were ventilated with water-saturated air at the rate of 1.01 min- l for 30 s and immediately sealed with subaseal caps. Air samples were taken from the head- space after 30 min for gas chromatographic measurement of ethylene. The gas chromatograph was equipped with an alumina column and photoionization de- tector. The carrier gas was N2 at 40 ml rain-~, the injection temperature 150°C and the column temperature 80°C. Peak heights and retention times for ethylene were compared with those for ethylene reference standards.

Since flower ethylene production started to increase on the second day after opening, different flower parts were sampled during this stage for measurement of ethylene production. After estimating the ethylene produced by the flower, the petals were excised and their ethylene production was measured after enclosing them in glass jars of 150 ml capacity for 30 min. The ethylene produced by the rest of the flower (after excising petals and staminal sheath) and by the different flower parts, i.e. style and stigma, ovary and receptacle, was measured after en- closing them in vials of 25 ml volume for 10 min, according to the method de- scribed earlier. The average weights of the flowers and their components used for the ethylene measurements on the second day after opening were: whole flowers, 3.86 g; petals, 2.81 g; staminal sheath, 0.37 g; style and stigma, 0.07 g; ovary, 0.22 g; receptacle, 0.11 g.

The data presented are a mean of three replications with ten flowers in each.

3. Results

Ethylene produced by the flowers was initially low but increased on the second day of opening and reached a peak on the fourth day (Fig. 1 ). This was followed by a decline in ethylene production and subsequent wilting of the petals.

After excision of the petals and then the staminal sheath, the flower showed a continuous decline in ethylene production (Fig. 1 ). The reduction in ethylene

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K. Singh, K.G. Moore/Scientia Horticulturae 58 (1994) 351-355 353

Fig. 1. Ethylene production by the whole flower ((3), by the flower after excision of the petals ( • ) and after excision of the petals and staminal sheath ( A ). Ethylene production was measured on the second to sixth days of flower opening. The arrow indicates the time at which the flowers wilted. Vertical bars show the standard error for each mean.

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Fig. 2. Ethylene production by the style and stigma (O) , ovary ( • ), receptacle ( • ) and petals ( A ) on the second to sixth days of flower opening. The arrow indicates the time at which the flowers wilted. Vertical bars show the standard error for each mean.

production after the removal of the staminal sheath was 42, 74, 69, 50 and 47% on the second to sixth days of flower opening, respectively. Since the staminal sheath could not be separated intact, direct measurement of its ethylene produc- tion was not possible.

354 K. Singh, K.G. Moore / Scientia Horticulturae 58 (1994) 351-355

On the second day of flower opening, the style and stigma each produced a relatively high amount of ethylene until the fourth day (Fig. 2). Ethylene produc- tion by the ovary, receptacle and petals was low initially, then later increased and reached its maximum on the fourth day of flower opening (Fig. 2). This was followed by a reduction in ethylene production and subsequent wilting of the petals.

4. Discussion

The climacteric increase in ethylene production by sweet pea flowers is in line with that reported earlier (Mor et al., 1984). In the sweet pea, flowers become pollinated before they are fully open. Hence, on the second day of opening, when various flower parts were sampled, pollination had already taken place. At this stage, the style and stigma collectively produced more ethylene than the petals, ovary and receptacle collectively. This indicates that ethylene production first increases in the stigma and style and then extends to various other flower parts. It has been reported that, in carnation flowers, pollination stimulates a sequential increase in ethylene production by stigmas, ovaries, receptacles and petals (Ni- chols et al., 1983).

The separated petals on the second and third days of flower opening showed a higher ethylene production than that estimated by comparing flowers with or without petals (Fig. 2). This appears to be the result of a wounding effect caused by the excision of the petals. Wounding of tissues is already known to induce ethylene production (Yang, 1980). On the fourth and fifth days of flower open- ing, however, separated petals showed less ethylene production than that esti- mated from Fig. 2. This indicates that the tendency to produce wound-induced ethylene decreases with physiological maturity of the petals. It had earlier been reported that immature green apple fruits which do not produce ethylene respond to wounding by producing ethylene in increasing amounts. Mature fruits which produced high levels of ethylene, however, did not respond to wounding (Lieber- man, 1979).

A most interesting point which emerges from this investigation is that the staminal sheath produces such a high amount of ethylene. On the third and fourth days of flower opening, when the flower ethylene production was increasing (Fig. 1 ), the staminal sheath alone produced as much ethylene as was produced collec- tively by the other flower parts. The staminal sheath is in fact designed to hold stamens near the stigma so as to ensure pollination. Since it is also a major con- tributor towards the total ethylene produced by the flower, it also appears to play an important role in inducing petal senescence.

References

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K. Singh, K.G. Moore/Scientia Horticulturae 58 (1994) 351-355 355

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