The direct role of chlorophyll as a chelator of
solar energy and a catalyst in carbohydrate
synthesis has been established. The Aurea mutant
used in this study was discovered and des-
Maksoud, M. A., A. A. M. Omar, and M. Marwan
Effect of the aurea gene on some chemical
activities in leaves.
cribed by A. Persson (1959), who selected it after X-ray treatment of soaked seeds with 10,000 R.
A variegated XI plant appeared which had Aurea as a ground color with green and lighter patches
occurring in it. The progeny of this plant segregated in the ratio of 1 green (++) : 2 Aurea (A+) : 1
Yellow (AA)*. The yellow seedlings appeared to develop no chlorophyll and later died. The
heterozygote was as vigorous as the normal, but could be recognized immediately by its pale green
color.
The objective of the presented experiments was to study, mainly, the indirect roles of
chlorophyll. Thus, normal green plants, Aurea mutants, graft hybrid combinations between them
and Aurea mutants sprayed with different growth regulators (biweekly throughout their life) were
used in a pot experiment. The leaves were used for the chemical analyses.
Seedlings: In the Aurea and yellow mutants, gene A reduced the concentration of chlorophylls (a)
and (b) in the same 3:1 ratio of their presence in the normal green. The change from the normal
genotype (++) to the other mutant types (A+) and (AA), showed that the two A genes were unequal
in their subtractive effect for each chlorophyll type.
Mature Plants: Chlorophyll content was higher at this stage than in the seedlings. However,
relative to the normal green, the concentration of both chlorophylls was reduced in the Aurea
mutant by the A gene in the same 3:1 ratio.
After fruit setting
Ungrafted: Chlorophyll content was the lowest of all developmental stages. Meanwhile, the
reduction in the concentration of chlorophylls in the Aurea, relative to the normal green, was still
in the 3:1 ratio. Average number of chloroplasts per guard cell, catalase activity, and C/N ratio
were lower in the Aurea than in the normal green, however, protein content was lower in the
latter than in the former. The persistence of the 3:1 ratio between chlorophyll types during all
the developmental stages, in both the normal green and the Aurea, implied that the mutation from
gene + to A probably slowed down the conversion rate of the precursor to chlorophyll (b), rather than
of chlorophyll (b) to (a).
Graft hybrids: Chlorophyll content, chloroplast number, catalase activity, and C/N ratios were
intermediate between the respective values for the ungrafted normal green and Aurea. Such a
result was attributed to the interaction between genotypically different vegetative tissues when
grafted. Relative to the respective ungrafted types, graft or stock, the normal green accumulated
more nitrogen, while the Aurea accumulated less nitrogen. The fluctuations in the nitrogen content
were significant, while those in sugar were non-significant. Consequently, the two genotypes
unequally reciprocated influence, with nitrogen as the limiting factor for the differences in the C/N
ratios amongst the graft hybrids. That the ungrafted Aurea had more protein but less sugar than
the ungrafted normal green indicated that sugar concentration seemed to be the limiting factor
for catalase activity. However, despite the apparent linear proportionality between the activity of
that enzyme and the concentration of sugar, the probability that this proportionality might have
been subject to nitrogen toxicity in the graft hybrids, as in the ungrafted Aurea, should not be
excluded.
Sprayed Aurea: Chlorophyll concentrations, and chlorophyll numbers were intermediate
between the corresponding values in the normal green and the Aurea. However, the ratio between
chlorophylls (a) and (b) fitted 3:1. Noteworthy, was that although sterol, vitamin C, methionine,
and sucrose effectively increased the number of chloroplasts, they were not as effective in
increasing chlorophyll concentration, a result indicating the non-association between chloroplast
number of multiplication and chlorophyll concentration or synthesis.
* Symbols do not refer to any standard mutant. In all respects, Persson's mutant mimics Xantha (Xa).
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