and “mixed chemotype” (with both jacobine- and erucifoline-like PAs as dominating
PAs) were described [11]. The distribution of the chemotypes showed a geographic
pattern: jacobine chemotypes mostly occur in the coastal areas and erucifoline
chemotypes mainly in the inland of Europe [11, 38, 39]. Plants from same population
often belong to the same chemotype but have variation in relation to PAs. For
instance, the plants from Meijendel (Wassenaar, the Netherlands) contain mainly
jacobine, but the percentage of jacobine ranged from 41% to 100% of total PA, and
the percentage of erucifoline ranged from 0% to 19% of total PA [11].
3.3
Intraplant Variation
The PAs do not distribute equally over the organs of individual plants. PAs are stored
in vacuoles and typically accumulate in the inflorescences and the peripheral
stem tissues, i.e., epidermal and subepidermal cell layers in the plants of Senecio
vulgaris [31]. The total concentration of PAs in vegetative J. vulgaris plants was
found to decrease with leaf age [40], and inflorescences often have a higher
concentration of PAs than leaves in reproductive vegetative J. vulgaris [38].
PA composition differs in the root and shoot of the vegetative plants of
J. vulgaris, J. aquatica, and the F2 hybrids: generally, shoots have more variation
in the composition and more jacobine-like PAs compared to the roots [10, 25].
Within a reproductive J. vulgaris plants, leaves have less senecionine-like PAs but
more jacobine-like PAs or erucifoline-like PAs. In erucifoline chemotype the proportion of acetylerucifoline was much higher in leaves than in inflorescences [38].
PA amount on the leave surface of J. vulgaris plants is much lower (less than 1%
of that of whole leaf) compared to that inside leaves, the concentration on leaf
surface was marginally correlated with PA concentration of the total leaf tissues,
and PA spectrum on the leaf differed from the PA spectrum of the total leaf [41].
3.4
Genetic Control and Environmental Influence on PA Variation
It is estimated that 50–100% of the variation in total PA concentration is due
to genetic variation under climate chamber conditions [13]. PA measurement results
of replicated genotypes illustrated that the PA concentration and composition were
genotype-dependent [11, 25]. PA accumulation in plants is also affected by abiotic
environmental factor such as nutrients and water. It was found that in drought or
nutrient stress environment, the J. vulgaris plants tend to have higher concentration
of PA than those in normal condition [42]. Increasing nutrients lead to a significant
reduction in total PA concentration in shoots of J. vulgaris plants [43]. Hol et al. [43]
postulated that the decreasing level of total PA in shoots under rich nutrient treatment
may be resulted from a dilution effect: increasing nutrient supplies favor a relative
increase of shoot biomass over root biomass, and as PA production increases with
root growth, plants in nutrient-rich conditions relatively produce less PAs. Some
genotypes of J. vulgaris, J. aquatica, and the hybrids between them produce
11 Variation in Leaf-Surface and Leaf-Tissue Secondary Metabolites:. . .
255
PAs) were described [11]. The distribution of the chemotypes showed a geographic
pattern: jacobine chemotypes mostly occur in the coastal areas and erucifoline
chemotypes mainly in the inland of Europe [11, 38, 39]. Plants from same population
often belong to the same chemotype but have variation in relation to PAs. For
instance, the plants from Meijendel (Wassenaar, the Netherlands) contain mainly
jacobine, but the percentage of jacobine ranged from 41% to 100% of total PA, and
the percentage of erucifoline ranged from 0% to 19% of total PA [11].
3.3
Intraplant Variation
The PAs do not distribute equally over the organs of individual plants. PAs are stored
in vacuoles and typically accumulate in the inflorescences and the peripheral
stem tissues, i.e., epidermal and subepidermal cell layers in the plants of Senecio
vulgaris [31]. The total concentration of PAs in vegetative J. vulgaris plants was
found to decrease with leaf age [40], and inflorescences often have a higher
concentration of PAs than leaves in reproductive vegetative J. vulgaris [38].
PA composition differs in the root and shoot of the vegetative plants of
J. vulgaris, J. aquatica, and the F2 hybrids: generally, shoots have more variation
in the composition and more jacobine-like PAs compared to the roots [10, 25].
Within a reproductive J. vulgaris plants, leaves have less senecionine-like PAs but
more jacobine-like PAs or erucifoline-like PAs. In erucifoline chemotype the proportion of acetylerucifoline was much higher in leaves than in inflorescences [38].
PA amount on the leave surface of J. vulgaris plants is much lower (less than 1%
of that of whole leaf) compared to that inside leaves, the concentration on leaf
surface was marginally correlated with PA concentration of the total leaf tissues,
and PA spectrum on the leaf differed from the PA spectrum of the total leaf [41].
3.4
Genetic Control and Environmental Influence on PA Variation
It is estimated that 50–100% of the variation in total PA concentration is due
to genetic variation under climate chamber conditions [13]. PA measurement results
of replicated genotypes illustrated that the PA concentration and composition were
genotype-dependent [11, 25]. PA accumulation in plants is also affected by abiotic
environmental factor such as nutrients and water. It was found that in drought or
nutrient stress environment, the J. vulgaris plants tend to have higher concentration
of PA than those in normal condition [42]. Increasing nutrients lead to a significant
reduction in total PA concentration in shoots of J. vulgaris plants [43]. Hol et al. [43]
postulated that the decreasing level of total PA in shoots under rich nutrient treatment
may be resulted from a dilution effect: increasing nutrient supplies favor a relative
increase of shoot biomass over root biomass, and as PA production increases with
root growth, plants in nutrient-rich conditions relatively produce less PAs. Some
genotypes of J. vulgaris, J. aquatica, and the hybrids between them produce
11 Variation in Leaf-Surface and Leaf-Tissue Secondary Metabolites:. . .
255