Regulation of gynophore elongation and fructification in the peanut arachis hypogaea L.
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Date
2001
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Uniiversity of California
Abstract
The regulation of peanut gynophore elongation and the fructification
process
were
studied
using Spanish bunch variety grown under constant
temperature (26.5°C), photoperiod (12 hr) and relative humidity (ca 90%) in a
growth chamber.
The experimental material consisted of tagged flowers or
gynophores continuously made available by replanting.
A technique utilizing the floral morphology was devised to study effects of
exogenous growth substances applied independently or in combinations on the
induction of IM activity (gynophore initiation) in the absence of fertilization and
syngamy. Growth substances are able to evoke IM activity thus substituting for
the syngamic stimulus. The effect of GA was dose-dependent suggesting that it
may be a critical factor in gynophore initiation, however, a mixture of GA, IAA
and BA was more effective than individual or combined effects of BA and IAA.
Morphactin showed stimulatory effect on IM activity. When applied to fertilized
flowers, CEPA and Ag+ ions inhibited IM activity, the latter by postponing
hypantha abscission.
In the absence of exogenous auxin, gynophores initiated
without fertilization failed to show geotropic curvatures denoting the role of
auxin in mediating normal geotropism.
Growth substance initiated gynophores
were incapable of fructification and their limited elongation was suggestive of
the necessity of proembryonic secondary stimuli for these processes.
Gibberellic acid promoted while other tested growth substances i.e. IAA,
BA, CEPA, TIBA, CCC and morphactin inhibited intact gynophore elongation.
Ovule removal stagnated elongation partially overcome by GA confirming the
role of the proembryos for sustained IM activity.
Auxin or BA inhibited GA-
promoted intact gynophore elongation depending on gynophore age auxin being
more inhibitory on the younger gynophores being least responsive irrespective of
concentration.
When applied to flowers at anthesis, morphactin transiently
inhibited geotropic curvature development but copiously altered gynophore
trajectory.94.
The size and activity of the IM zone decreases towards the ovule base with
progressive gynophore
lengthening.
Gibberellic acid affects elongation by
increasing length of IM cells whose elongation is basipetally polarized.
inverse
The
relationship between fructification depth and gynophore length is
attributed
the
to
decreasing
size
and
activity
together with
internal
differentiation of the IM zone with age.
A definition of peanut 'fruit-set' is suggested as being at time of IM
induction (i.e. gynophore initiation phase of fruit development) and the gynophore
as a physiologically unique young fruit.
The observation that ovule removal delayed but did not prevent curvature
development ot excised gynophores suggested the perceptive and responsive
nature of the IM to geotropic stimulus.
Morphactin enhanced elongation of
excised gynophores for all concentrations with optima at 0.1 and 10 ppm and
effectively altered geotropic curvature even at 0.1 to I ppm. Higher morphactin
concentrations
relationship
rendered
between
gynophores
the
ageotropic.
anti-geotropic
effect
There
and
was an
inverse
growth stimulation.
Morphactin, however, failed to stimulate growth in the presence of auxin which
partially reversed its effects on geotropism. Auxin inhibited excised gynophore
elongation for all concentrations but progressively reduced the degree of
curvature.
The effect of morphactin and auxin on elongation are further
evidence on gynophore physiological similarity to roots and the regulation of
geotropic curvature by auxin.
Tri-iodobenzoic acid (TIBA) and BA inhibited
elongation and curvature with increasing concentration, TIBA more drastically
than BA. While GA stimulated growth without appreciable effects on curvature,
it partially reversed concentration dependent ancymidol-induced inhibition of
these parameters.
The fructification process, characterized as simultaneous cessation of
gynophore elongation and ovule enlargement is enhanced by growth inhibitors,95.
morphactin, IAA and CEPA while GA postponed it by perpetuating IM activity
with resultant greater fructification depths. The inhibitory effects of Ag+ions,
an anti-ethylene agent on fructification suggest the involvement of ethylene in
regulating this process.
Depth perception by gynophores is attributed to
endogenous hormones acting on the IM.
Pericarp growth which is mainly by water retention by the tissue precedes
that of the seed but the latter accumulates most of the dry weight in the course
of growth.
Benzyladenine (BA) enhances fruit growth by increasing water
content and kernel dry matter. Distal seed growth was greatly improved by BA
treatment by increasing its sink strength which resulted in the reduction of pops
and single seededness.
Description
Keywords
Gynophore, Elongation, Peanut Arachis, Hypogaea L.