V.
DETERMINING FACTORS IN
CELL GROWTH
231
for continued and proliferative growth seem to be the price paid for
morphological specialization and this 'debit' in the balance sheet of the
cells may only be restored chemically by growth substances, in their
pre-climacteric state.
The biochemical equivalent of the crisis which is recognized as the
climacteric of fruits may be seen also in the factors that determine
longevity when we consider the plant as a whole. Monocarpic perennials
like Agave may have organs and tissues that persist for many years.
But with the single act of flowering and fruiting the entire plant dies.
Prior to flowering, the cells have a prolonged ability to grow, and even
mature leaf parenchyma can be grown into a continuously proliferating
tissue by the application of the synergistic combination of coconut milk
and 2,4-D (first used by Caplin and Steward, 1949) as demonstrated by
Weinstein et al. (1959).
The type of death following fruiting in monocarpic plants was termed
'Exhaustion-death' (Erschopfungstod) by Molisch (1938), who thought
that the depletion of reserve food materials was the cause. Doflein (1919,
quoted by Molisch), however, considered that it was 'metabolic-death'
(Stoffwechseltod) that ensued from flowering and fruiting. Indeed very
little is known about this so-called 'metabolic-death'.
In perennials like the banana, the individual aerial shoot dies down
after bearing a bunch, while the underground rhizome renews growth
periodically. Biennials like Brassica may be maintained indefinitely in a
vegetative state by the control of minimum night temperature (Miller,
as cited by Thompson, 1953), but subsequent to flowering the entire
plant perishes.
All this suggests that the vegetative plant body or the perennating
organ retains a balance of growth regulators which permit longevity and
renewed growth in its cells. With the onset of flowering and fruiting,
however, this balance may often be irreversibly impaired, perhaps due
to production of inhibitory substances. (The familiar fact that cuttings
bearing flowers are harder to root than those which are purely vegetative
is a case in point and is suggestive of such an inhibitory effect.) In the
formation of a tumour, the balance is tipped in the opposite direction
toward autonomous proliferative growth.
Thus the emerging knowledge of the chemical factors that are conducive to the prolonged growth of cells in culture, as discussed above,
may shed light on the operative factors that control these events
in the plant body. In other words, although problems of senescence,
death and continued proliferative (cancerous) growth have been much
emphasized in animals, the resources of the plant kingdom to contribute
to an understanding of the biochemistry of these problems seem hardly
to have been tapped.
DETERMINING FACTORS IN
CELL GROWTH
231
for continued and proliferative growth seem to be the price paid for
morphological specialization and this 'debit' in the balance sheet of the
cells may only be restored chemically by growth substances, in their
pre-climacteric state.
The biochemical equivalent of the crisis which is recognized as the
climacteric of fruits may be seen also in the factors that determine
longevity when we consider the plant as a whole. Monocarpic perennials
like Agave may have organs and tissues that persist for many years.
But with the single act of flowering and fruiting the entire plant dies.
Prior to flowering, the cells have a prolonged ability to grow, and even
mature leaf parenchyma can be grown into a continuously proliferating
tissue by the application of the synergistic combination of coconut milk
and 2,4-D (first used by Caplin and Steward, 1949) as demonstrated by
Weinstein et al. (1959).
The type of death following fruiting in monocarpic plants was termed
'Exhaustion-death' (Erschopfungstod) by Molisch (1938), who thought
that the depletion of reserve food materials was the cause. Doflein (1919,
quoted by Molisch), however, considered that it was 'metabolic-death'
(Stoffwechseltod) that ensued from flowering and fruiting. Indeed very
little is known about this so-called 'metabolic-death'.
In perennials like the banana, the individual aerial shoot dies down
after bearing a bunch, while the underground rhizome renews growth
periodically. Biennials like Brassica may be maintained indefinitely in a
vegetative state by the control of minimum night temperature (Miller,
as cited by Thompson, 1953), but subsequent to flowering the entire
plant perishes.
All this suggests that the vegetative plant body or the perennating
organ retains a balance of growth regulators which permit longevity and
renewed growth in its cells. With the onset of flowering and fruiting,
however, this balance may often be irreversibly impaired, perhaps due
to production of inhibitory substances. (The familiar fact that cuttings
bearing flowers are harder to root than those which are purely vegetative
is a case in point and is suggestive of such an inhibitory effect.) In the
formation of a tumour, the balance is tipped in the opposite direction
toward autonomous proliferative growth.
Thus the emerging knowledge of the chemical factors that are conducive to the prolonged growth of cells in culture, as discussed above,
may shed light on the operative factors that control these events
in the plant body. In other words, although problems of senescence,
death and continued proliferative (cancerous) growth have been much
emphasized in animals, the resources of the plant kingdom to contribute
to an understanding of the biochemistry of these problems seem hardly
to have been tapped.