Effects of temperature and stem length on changes in
carbohydrate content in summer-grown cut chrysanthemums
during development and senescence
Megumi Adachi *, Saneyuki Kawabata, Ryozo Sakiyama
Laboratory of Horticultural Science,Graduate School of Agricultural Life Sciences,Uni6ersity of Tokyo,1-1 Yayoi,Bunkyo-ku,
Tokyo,113-8657, Japan
Received 28 June 1999; accepted 17 April 2000
Abstract
Changes in the carbohydrate content in capitula, stems, and leaves were investigated in cut chrysanthemum
Dendranthema×grandiflorum(Ramat.) Kitamura ‘Seiun’ plants with 60-cm stems held at 20, 25 and 30°C for 27 days postharvest. In addition, plants with 20-cm stems were studied at 25°C. Diameter of the capitula, the angle of the florets, fresh weight (FW) and dry weight (DW) increased more slowly at 30°C/60 cm and 25°C/20 cm than at 20°C/60 cm and 25°C/60 cm. The number of well-developed florets was notably smaller, and the number of tubular-shaped florets was larger at 30°C/60 cm than at 20°C/60 cm. Glucose and fructose concentrations in the capitula increased, although they decreased midway through treatment at 30°C/60 cm. Fructose concentrations in the stems, and in particular in the middle stems, were greater at 30°C/60 cm than at 20°C/60 cm and 25°C/60 cm. The increase in the total DW during treatments suggested that photosynthesis was occurring in the leaves and that photosynthates were a main source for the capitula and stems. Development of the capitula was suppressed, which was related to the reduction in its carbohydrate supply. Wilting of petals was not accelerated at high temperatures and with short-stem treatments. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Cut chrysanthemum; Flower opening; Carbohydrate content; Senescence; Temperature; Stem length
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1. Introduction
Chrysanthemums are the most popular cut flower in Japan and account for one-third of the
total floricultural production (Funakoshi, 1984). Although cut chrysanthemums have a long vase life in general, they deteriorate sooner and have a shorter vase life under high temperatures (Fu-nakoshi, 1984; Whealy et al., 1987; Cockshull and Kofranek, 1994; Adachi et al., 1999).
The main cultivar, ‘Shuho-no-chikara’, is usu-ally produced year-round, except in summer. This cultivar is sensitive to high temperatures, which * Corresponding author. Present address: People-Plant
Re-lationship Laboratory, Department of Agriculture, Tokyo University of Agriculture, 1737 Funako, Atsugi City, Kana-gawa, 228-0011, Japan. Tel./fax: +81-46-2706541.
E-mail address:[email protected] (M. Adachi).
seasons, the characteristics of cut ‘Seiun’ flowers under high temperatures have not been investi-gated. This study aimed (1) to confirm that senes-cence is not accelerated at high temperatures in ‘Seiun’; (2) to investigate the effects of high tem-peratures on carbohydrate content in these plants, and (3) to investigate the effects of restricting carbon sources on flower opening and senescence.
2. Materials and methods
2.1. Plant materials
Cut chrysanthemumDendranthema×grandiflo
-rum (Ramat.) Kitamura ‘Seiun’ plants were ob-tained from a commercial grower in Aichi Prefecture. The plants were cut to a length of approximately 80 cm on 3rd August and were immediately boxed and transported to our labora-tory at the University of Tokyo. When they ar-rived on 4th August, the stems were cut to a length of 60 cm and placed in a 200-ml glass jar containing 100 ml of deionised water. The cut plants were divided into three groups of 25 shoots each and placed in a growth room controlled at 20, 25, or 30°C (6070% RH). Another group of plants with 20-cm stems were also placed at 25°C (25°C/20 cm). The light intensity was constantly adjusted to 30 mmol m−2 s−1 by metalhalide
lamps (Yoko lamp, Toshiba) at the top of the shoots since changes in light conditions will affect photosynthesis and carbohydrate analysis. The shoots were placed 15×20 cm apart and samples were collected at 0, 2, 4, 8, 16 and 26 days after the start of treatment. Five shoots were randomly selected from each room based on a table of random numbers.
2.2. De6elopment
To provide indices for the three-dimensional
was based on an average of the four angles be-tween a line passing through the edge of one of the four outermost ray florets and the centre point of the involucre and a vertical line (Fig. 1). When the angle of the florets reached 90°, the capitula were regarded as fully opened. When the petals started to wilt, the edges fell downwards and the angle of the florets increased notably. When the petals wilted after the capitula fully opened, the angle increased to greater than 90°. This, the angle of the florets was considered to be one of indicators of wilting in the capitula.
The numbers of well-developed ray florets with petals greater than 1 cm in length, less-developed ray florets with petals less than 1 cm in length, and tubular-shaped florets with petals never de-veloped, were counted at 10, 18, and 27 days. The tubular-shaped florets could contain both real tubular florets and ray florets since this could not be distinguished by appearance.
2.3. Weight measurements
The plants were divided into capitula, upper leaves (about five to six leaves), middle leaves (about four leaves), upper stems, middle stems and lower stems parts, and the fresh weight (FW) of each part was measured. Involucres were not used for the measurements since they were too small in volume and weight. The parts were then freeze-dried, and the dry weight (DW) was measured.
2.4. Carbohydrate analysis
Fig. 1. Changes in diameter (a) and angle of florets (b) in capitula of cut chrysanthemum ‘Seiun’ plants placed at 20°C/60 cm stem length ( ), 25°C/60 cm (), 30°C/60 cm () and 25°C/20 cm (). The bars represent SEs,n=5. Average of the longest diameter (D1) and the diameter vertical to the longest one (D2) were measured. Four angles between a line passing through the edge of the outermost floret (f1, f2, f3, or f4) and the centre point of the involucre and a vertical line (u1) were measured and averaged.
and Duncan’s multiple range test (PB0.05). A
t-test was used for comparison between two treat-ments or between 2 days.
3. Results and discussion
3.1. Effects of high temperature on changes in the capitula
High temperatures suppressed development but did not accelerate senescence in the capitula. The diameter (Fig. 1a), the angle of the florets (Fig. 1b), FW (Fig. 2a), DW (Fig. 2b) and fructose (Fig. 2c) and glucose (Fig. 2d) concentrations increased more slowly at 30°C/60 cm than at 20°C/60 cm and 25°C/60 cm, until the capitula slightly wilted at 26 days. The number of well-de-veloped florets was significantly smaller, but the number of tubular-shaped florets was significantly Mannheim). The residue was used for the
mea-surement of starch with the F-kit. Fructans in the supernatant were completely hydrolysed to fruc-tose and glucose by 0.1 M sulphuric acid for 20 min at 100°C (Kennedy and White, 1983; Trusty and Miller, 1991), followed by neutralisation with 0.1 M sodium carbonate. Concentrations of the hydrolysed fructose and glucose were measured by the same enzymic method as mentioned above. The concentration of fructans was calculated by subtracting the concentrations of fructose and glucose before the hydrolysis from those after hydrolysis.
2.5. Statistical analysis
Fig. 2. Changes in fresh weight (a), dry weight (b), fructose (c) and glucose (d) concentrations in capitula of cut chrysanthemum ‘Seiun’ plants placed at 20°C/60 cm ( ), 25°C/60 cm (), 30°C/60 cm () and 25°C/20 cm (). The bars represent SEs,n=5.
larger at 30°C than at 20°C (Table 1). It can be assumed that high temperatures would restrict development in the petals of the ray florets, since Fukai et al. (1997) have reported that there are 5 – 10 tubular florets that develop during corolla formation and that this number does not change in chrysanthemums. A carbohydrate supply is nec-essary for expansion in cut flowers (Rogers, 1973). The shortage of carbohydrates can possibly be attributed to a suppression of the development of the capitula.
High temperature accelerates respiratory activ-ity and the consumption of water and carbohy-drates in cut flowers (Siegelman et al., 1958; Coorts, 1973). The slight decrease in sugars from 4 to 8 days observed only at 30°C/60 cm (Fig. 2c,d) may be due to a slight respiratory accelera-tion at high temperatures during this period. Mayak and Halevy (1980) have reported that the start of the senescent phase in cut flowers is characterised by a decrease in FW, DW and sugars following increases that occur during the
pre-senescent stage. In ‘Shuho-no-chikara’ cut flowers, high temperatures trigger rapid increases and then subsequent decreases in FW, DW and sugar content and promote rapid senescence in the capitula (Adachi et al., 1999). High temperatures can induce climacteric respiration in ‘Shuho-no-chikara’ flowers. On the other hand, high temper-atures help to maintain water content and carbohydrates in the capitula in ‘Seiun’ flowers, suggesting that a rapid respiratory rise and con-sumption of carbohydrates does not occur. ‘Seiun’ flowers might show non-climacteric respiration at both high and moderate temperatures. Wu et al. (1989) have reported that ‘White Sim’ cut carna-tions show a climacteric rise and a short-vase life, while ‘Sandra’ flowers show a non-climacteric rise and a long vase life.
Table 1
Effects of temperature on numbers of well-developed ray florets, less-developed ray florets, tubular florets and total florets in cut chrysanthemum ‘Seiun’ plants at 20 and 30°C
Treatment Days after start of
treatment
20°C 30°C
16895.4
10 Ray florets (well-developed) 67.398.6***
36913.6
Ray florets (less-developed) 152.592.5** 135.3913.5
Tubular florets 93.3910.7*
330.394.2 31497.6 Total
222918.8
18 Ray florets (well-developed) 60.392.8***
Ray florets (less-developed) 85917.9 15694.3* 090
Tubular florets 126.396.1
Total 307931.8 34390.6
Ray florets (well-developed)
27 157.5940.2 94.3932.7a
131.5910.5
Ray florets (less-developed) 11293.5a
Tubular florets 090 111.593.6
Total 289939.9 318.394.4
* Significant differences between treatments atP=0.1. ** Significant differences between treatments atP=0.01. *** Significant differences between treatments atP=0.001.
aNon significance, n.s.
3.2. Effects of short-stem treatment on changes in the capitula
The short-stem treatment also suppressed devel-opment in the capitula but did not accelerate senescence. The diameter (Fig. 1a), the angle of the florets (Fig. 1b), FW (Fig. 2a), DW (Fig. 2b) and fructose (Fig. 2c) and glucose concentrations (Fig. 2d) increased more slowly at 25°C/20 cm than at 25°C/60 cm. Because the short-stem treat-ment reduced the number of leaves and stems, the restriction of a carbohydrate source could be linked to the suppression in the capitula but might not be related to the senescence. In the short-stem treatment, fructose (Fig. 3a) and glucose (Fig. 3b) concentrations in the upper leaves, and the con-centrations of fructose (Fig. 4a), glucose (Fig. 4b) and fructans (Fig. 5a) in the upper stems, notably decreased and then increased. These results indi-cate that sugars in the leaves and stems were mostly serving as a carbohydrate source for the capitula, but that this supply was insufficient for full development to occur.
The total DW in the cut plants increased during all treatments, suggesting that carbohydrates could be produced during the treatments. Mor and Halevy (1979), Emmett (1987) and Mc-Conchie et al. (1991) suggested that photosyn-thates were produced in leaves and supplied flower parts in cut flowers. In the present study, yellowing in the leaves was not observed in any treatments. The increase in the concentrations of sugars in the capitula, leaves and stems during the latter stages of the short-stem treatments might have resulted from increased supply of photo-synthates.
3.3. Effects of high temperature on changes in the lea6es
Fig. 3. Changes in fructose (a,c), glucose (b,d) concentrations in upper (a,b) and middle (c,d) leaves of cut chrysanthemums ‘Seiun’ plants placed at 20°C/60 cm ( ), 25°C/60 cm (), 30°C/60 cm () and 25°C/20 cm (). The bars represent SEs,n=5.
high temperatures promote water loss in the leaves during the earlier stages of treatment.
Patterns in the concentration changes for fruc-tose (Fig. 3c), glucose (Fig. 3d) and sucrose in the upper leaves at 30°C were different from those at 20°C/60 cm and 25°C/60 cm. Considering that fructose and glucose concentrations were similar in the leaves, these concentrations in the upper leaves could be converted from those of sucrose by invertase during the treatment. High tempera-tures can change the levels of hydrolytic enzy-matic activity and change the proportion of sugars (Markus, et al., 1981; Yamane et al., 1991; Bancal and Triboi, 1993), resulting in changes in the carbohydrate content. Our results also suggest that fructose and glucose could be the main translocating sugars, since very little sucrose was in the capitula and stems in ‘Seiun’.
High temperatures can affect photosynthesis due to changes in the enzymic activity (Markus, et al., 1981; Wolf, et al., 1990), and in the present study, water loss could reduce the carbohydrate supply of the capitula if there was photosynthesis
occurring in ‘Seiun’ leaves during the treatments. The slower increase in sugar concentrations at 30°C/60 cm than at 20°C/60 cm and 25°C/60 cm in the middle leaves (Fig. 3b,d) may have been due to suppression of photosynthetic activity by high temperatures.
3.4. Effects of high temperature on changes in the stems
Fig. 4. Changes in fructose (a,c) and glucose concentrations (b,d) in upper (a,b) and middle (c,d) stems of cut chrysanthemum ‘Seiun’ plants placed at 20°C/60 cm ( ), 25°C/60 cm (), 30°C/60 cm () and 25°C/20 cm (). The bars represent SEs,n=5.
High temperatures appeared to reduce the sup-ply from leaves or accelerate the consumption of carbohydrates as respiratory substances in the stems as well as the capitula. In addition, high temperatures appeared to accelerate the hydroly-sis of fructans and increase fructose (Fig. 4a,c) and glucose (Fig. 4b,d) concentrations in the stems. In ‘Shuho-no-chikara’ cut flowers, sugars in the stems notably decrease under these condi-tions, particularly, in the middle stems, suggesting that these could be a source for the capitula (Adachi et al., 1999). Middle stems might also be a source for the capitula at moderate tempera-tures in ‘Seiun’ cut flowers.
In summary, high temperatures and short-stem treatments suppress development but do not ac-celerate senescence in the capitula. A carbohy-drate supply might be necessary for the development of the capitula. High temperatures and the short-stem treatment could not rapidly reduce the water and carbohydrate content in the
capitula. In addition, respiration and the con-sumption of carbohydrates do not appear to change significantly during the treatments, result-ing in the maintenance of the carbohydrate and the retarding of senescence. Because cut chrysan-themums are sold before the capitula are fully opened, high temperatures after harvest may re-sult in poor development of the capitula, and subsequent loss of quality.
Acknowledgements
Fig. 5. Changes in concentration of fructans in upper (a), middle (b) and lower (c) stems of cut chrysanthemum ‘Seiun’ plants placed at 20°C/60 cm ( ), 25°C/60 cm (), 30°C/60 cm () and 25°C/20 cm (). The bars represent SEs,n=5.
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