Changes in Carbohydrate Levels and Associated Enzyme Activities During Flower Development in Easter Lilies
Anil P. Ranwala and William B. Miller
Department of Horticulture, Clemson University
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Flower growth, development, and senescence are very important processed
in floricultural crops, both in cut flowers and pot plants. The pattern
and the rate of growth and senescence are usually determined by the genetics
of the plant as well as external environmental factors. Studies on fundamental
physiological processes involved in flower growth are valuable for several
reasons. Information on the enzymes and genes involved in regulating these
growth processes will facilitate breeding programs for the selection of
better flower qualities and other desirable traits. On the other hand, this
information will be helpful to manipulate environmental factors to adjust
flower growth and development according to growers needs.
Carbohydrates are necessary for the growth of any plant part as carbohydrates
provide energy and the building blocks for growth processes. Flowers usually
do not have chlorophyll, and therefore cannot carry out photosynthesis to
produce carbohydrates for their needs. In addition, flowers have very rapid
growth rates that require large amounts of carbohydrates. For these reasons,
flowers are dependent upon other parts, especially leaves, for their carbohydrate
supply. Therefore, the ability of flower buds to import carbohydrates is
vital in flower development.
Usually, sucrose (i.e. table sugar) is the form of sugar translocated
from leaves to flowers. Once sucrose enters the flower, it has to be broken
down to glucose and fructose before it can be used for growth. The ability
to break down sucrose is determined by the activity of sucrose-degrading
enzymes present in flower tissues. One enzyme, invertase has been suggested
as the major sucrose-hydrolyzing enzyme active in flower tissues.
Here we report the results of several experiments conducted to investigate
carbohydrate changes during the flower development of Easter lilies (Lilium
). Since flower buds contain various organs that have various
growth patterns, individual organs were studied. The changes in carbohydrates,
and its relationship to invertase activity were studied throughout flower
development, from young buds to flowering.
Materials and Methods
(image: Stages of Easter lily flower development selected in this study) Easter lily (Lilium longiflorum cv Nellie White) plants were grown
in greenhouses at Clemson University under standard conditions. Flower buds
were harvested at five different stages of development (3-4 cm in length,
6-7 cm, 9-10 cm. 13-14 cm (mature bud), and open flower). Flower buds were
dissected into tepal, anther, filament, stigma, style, and ovary, and fresh
weights of individual organs were recorded. Soluble carbohydrates were extracted
from freeze-dried tissue with water at 70°C, and extractable sugars
were separated and quantified by liquid chromatography. The proteins were
extracted under appropriate conditions to stabilize enzyme activities, and
invertase activity was assayed in the extracts.
Results and Discussion
The growth of individual flower organs varied depending on the organ.
Most of the total weight increase came from expansion and growth of the
tepals. Tepal fresh and dry weights increased at very high rate throughout
the development until the mature bud stage. Filament, style, stigma, and
ovary fresh and dry weight also increased gradually until the flower opened.
However, anther fresh weight was highest in 6-7 cm long flower buds and
then declined during later flower bud maturation. Glucose, and fructose
levels of tepal, style, stigma, and filaments increased dramatically during
the growth (Figure 1). However, sucrose
levels didn't show this rapid increase, and either remained constant or
decreased during development. In anther, glucose and fructose levels increased
up to 6-7 cm long buds and then decreased in mature buds, whereas sucrose
Figure 1: Soluble sugar concentrations of Easter lily flower organs during flower bud development.
Invertase activity increased throughout bud development in tepal,
style, filament, stigma, and ovary (Figure 2).
In anther, invertase activity increased from 3-4 cm to 6-7 cm long bud and
then decreased in the mature bud. These results show that glucose and fructose
are high in periods of rapid growth, and that invertase activity has a positive
correlation with the sugar levels. Invertase seems to play an important
role in supplying carbohydrates for flower growth. We have conducted further
experiments and isolated three different types of invertases contributing
to this activity. Also, the genes of these enzymes are being investigated
to gain a better understanding of this process.
Figure 2. Changes in invertase activity of Easter lily flower organs during flower bud development
This research was conducted with financial support from the Clemson University
Ornamental Enhancement program, and the Fred C. Gloeckner Foundation, and
plant materials donated from Dahlstrom and Watt Bulb Farms, Inc., Smith
Last Updated 7/16/98