- In view of the stimulant effects of gibberellic acid on plant
growth, and its interesting modifications of various metabolic products,
it was decided to determine whether this growth regulator
would induce a favorable effect on total alkaloid production, especially
on the antineoplastic alkaloids, of Catharanthus roseus (L.) G. Don
(Vinca rosea L.).
Two groups, of 120 plants each, consisted of a control group,
and a gibberellic acid-treated group. Each of these groups was further
divided into four sub-groups of 30 plants each, so that four
separate harvests, each at two week intervals, could be made. The
plants were distributed at random throughout the greenhouse.
Gibberellic acid treatment was initiated nine weeks from the average
germination date. One-tenth milliliter of a solution containing
100 micrograms of gibberellic acid was applied weekly on the upper leaves of each plant. Height measurements were made weekly commencing
at the time of the first treatment.
The first harvest was made five days following the initial gibber-ellic acid treatment. Three additional harvests were made at two
week intervals. The leaves-tops, stems, and roots were separated
and fresh weight determined. These were then placed in a circulating
hot-air dryer at approximately 38° C until dry. Dry weights were
then determined. The plant parts were pooled according to their respective
groups, and reduced to a #40 powder.
In order to determine the effect of GA-treatment on the production
of the antineoplastic alkaloids, it was necessary to devise a procedure
for the quantitative determination of these alkaloids. After
several approaches to quantitate vincaleukoblastine (VLB), leurocristine,
leurosine and leurosidine, it was possible to establish a
procedure for the determination of VLB. Total alkaloid content was
determined by a modification of the procedure of Szász and coworkers.
Other metabolic products were also determined.
The pertinent differences on growth which were noted in the
gibberellin-treated group are listed below. The growth rate, based
on height measurements, was significantly increased with a maximum
of 61 percent at the second week of treatment. The dry weight of the
stems was significantly increased with a maximum of 86 percent in
the second harvest. The root dry weights were higher than controls
with a maximum of 36 percent at the second harvest; however, this
was not statistically significant. There were no other marked effects
on fresh or dry weights.
The effects of GA-treatment which were noted on the alkaloid
production are presented below. The concentration of the total alkaloids
was decreased in all plant parts of the three harvests that were
assayed, with the exception of the leaves of the second harvest. In
the leaves and roots, the concentration of the total alkaloids increased
with age then leveled off after the third harvest. A reverse trend
was found in the stems where the concentration decreased with age.
The total alkaloid content was decreased in both leaves and roots,
while it was increased in the stems. This increase was due to the
significant increase in stem dry weight. With the exception of the
third harvest plants, there was an overall increase in the vincaleukoblastine
(VLB) concentration of the leaves with a maximum of 26 percent
at the final harvest. There was no VLB detected in the other
plant parts of both control and treated plants. The concentration of
VLB was found to decrease with age.