An. Dubell et Je. Mullet, CONTINUOUS FAR-RED LIGHT ACTIVATES PLASTID DNA-SYNTHESIS IN PEA LEAVES BUT NOT FULL CELL ENLARGEMENT OR AN INCREASE IN PLASTID NUMBER PER CELL, Plant physiology, 109(1), 1995, pp. 95-103
The development of the primary pea (Pisum sativum L.) leaf was charact
erized in plants grown in darkness, white light, or continuous far-red
light. Leaf growth in continuous far-red light was a high-irradiance
response most likely mediated by the phytochrome PHYA. Leaf growth in
darkness and far-red and white light was similar up to 4 d postimbibit
ion (dpi). From 4 to 8 dpi, leaf length and leaf cell number increased
more rapidly in plants exposed to white and far-red light compared to
dark-grown seedlings. Furthermore, illumination of plants with contin
uous far-red light from 2 to 4.5 dpi potentiated leaf growth in white
light. White light, but not far-red light, was able to increase leaf c
ell size and plastid number per cell during seedling development from
8 to 12 dpi. Growth of plants in continuous far-red light for 8 d foll
owed by transfer to white light did not allow full leaf development. T
herefore, although continuous far-red light can stimulate increases in
leaf cell number from 4 to 8 dpi, other photoreceptors must be activa
ted during this same period to allow full leaf growth. Plastids of dar
k-grown plants contained 120 copies of the plastid DNA from 5 to 9 dpi
. In white-light-grown plants, plastid DNA synthesis activity and DNA
copy number increased between 5 and 6 dpi and DNA copy number reached
450 at 6 dpi. Far-red light illumination induced even higher rates of
DNA synthesis, and plastids in this condition accumulated 830 copies o
f the plastid DNA by 6 dpi. Plastid DNA copy number decreased with fur
ther leaf and chloroplast development primarily through dilution of DN
A into new plastids. This study demonstrates that different photorecep
tors control specific subprograms of leaf development.