Download Formation of Earlywood, Latewood, and Heartwood Regulation of

Formation of Earlywood,
Latewood, and Heartwood
David Wang’s Wood formation Class
Regulation of Formation of Earlywood
and Latewood
l
Growing ring – an annual ring in
temperate and warm-temperate
zones.
l
The light and dark colors are ascribed
to the different cells formed in the
earlier and the later parts of the
growing season.
l
Wood formed in the first half of
growing season is composed of cells
with large diameters in the radial
direction and thin cell walls. In the
latter half is composed of cells with
small diameters and thick cell walls.
Thujopsis dolabrata
Larix leptolepis
Transition from earlywood to latewood
The process of
earlywood and latewood
formation, that is the
frequency of division of
cambial cells, the
enlargement of newly
formed xylem cells, and
cell wall thicken are
controlled by plant
hormones.
Regulation of Formation of EW and LW – Formation
and Distribution of Auxins in Conifers
l
IAA is largely synthesized by buds in the tree crown,
developing needles, shoots.
l
In the dormant period in winter, IAA is synthesized by
dormant buds and old leaves.
l
The occurrence of small amounts of endogenous IAA in the
cambial zone suggests the formation of IAA by cambial cells.
l
IAA synthesized by the tree crown is basipetally transported
mainly to cambial cells and their differentiating cells.
Regulation of Formation of EW and LW –
Formation and Distribution of Auxins in Conifers
l
When radioactive IAA was fed to Pinus echinata a high radioactivity
was found in cambial and differentiating cells.
l
The transport rate of IAA was estimated to be about 5-7 mm/h in Pinus
densiflora.
l
The transport rate did not change with seasonal changes or with active
and resting periods of cambial activity.
l
The occurrence of IAA in the cambial zone (cambium, differentiating
phloem, and xylem) of conifers has been confirmed in many tree
species.
Regulation of Formation of EW and LW – Effect
of IAA on Formation of Tree Stems
l
When disbudding or defoliation was effected before initiation of cambial activity
in early spring cambial activity was inhibited, except when IAA was administered.
l
The amount of xylem formed increased in accordance with the amount of IAA
added.
l
A continuous supply of IAA to cambial cells was required to maintain fusiform
initials, and IAA was lacking these cells were differentiated into axial parenchyma
cells and not to tracheids.
Regulation of Formation of EW and LW –
Effect of IAA on Formation of Tree Stems
l
When Pinus sylvestris and Pinus resinosa were subject to a long-day
treatment, continuous shoot elongation and formation of earlywood cells
occurred, whereas on a short-day treatment shoot elongation ceased and
latewood cells are induced.
l
When IAA was supplied externally to the latewood-forming sapling in the
short-day treatments, a band of earlywood cells was formed.
l
This results indicate the changes in cell diameter are regulated by IAA.
Regulation of Formation of EW and LW –
Effect of IAA on Formation of Tree Stems
l
Concentration of endogenous IAA in the cambial zone of a tree stem
exhibits a seasonal change.
l
The concentration of IAA increased from spring to early summer, and then
decreased toward the autumn to the level found in the spring.
l
In winter, IAA was present at a low level. The stage of rapid decrease of IAA
coincides well with the change from earlywood to latewood formation.
l
IAA is a major factor in the control of elongation of xylem-differentiating
cells, the formation of earlywood and latewood, and the transition of
earlywood to latewood.
Regulation of Formation of EW and LW – Effect of
IAA on Formation of Tree Stems
l
Even if IAA is supplied, cambial activity ceased at a certain time of the
season.
l
For termination of cambial activity (dormancy), other factors may be
involved.
l
A change in the sensitivity of cambial cells to IAA has been suggested to
be one of the factors involved.
l
When IAA was supplied to tree stems cambial activity increased, but the
effect changed seasonally, and after summer the effect was very small.
Regulation of Formation of EW and LW – Effect
of IAA on Formation of Tree Stems
l
The extract natural of any cambial sensitivity to IAA is scarcely known,
but it seems that the change is induced by a change of temperature and
day length, and is related to structural and histochemical changes in
the cambial cells.
l
It was found that a reconstructure of cell membrane occurred before
dormancy. If IAA receptor or carrier proteins are present on the plasma
membranes these proteins may tentatively be transported of decreased,
thus inducing a low sensitivity for IAA.
Regulation of Formation of EW and LW – Effect
of IAA on Formation of Tree Stems
l
When IAA was supplied to Picea abies, both the thickening period
and the cell was thickness increased.
l
IAA is involved in enlargement of cells and promotion of cell
division.
l
It is suggested that in differentiation of cambial cells, a tracheiddifferentiation factor (TDF) is essential, and that earlywood
formation requires high concentrations of IAA and TDF, while
latewood formation is induced by low concentration of IAA and
high concentration of TDF.
Regulation of Formation of EW and LW – Abscisic
Acid (ABA)
• The formation of latewood of Larix occidentalis is induced by growth
inhibiting substances.
• The amount of these substances increases at the stage of latewood
formation.
• It has been suggested that ABA, which is a dormancy-inducing
substance, may be involved in the formation of latewood.
• ABA has been found in the cambial zone of conifers. When exogenous
ABA was administered to stems, it inhibited division and enlargement
of the cambial cells.
Regulation of Formation of EW and LW – Abscisic
Acid (ABA)
• A high concentration ABA was found in dormant shoots of
Pseudotsuga menziesii. These results suggest that ABA acts as a
growth inhibiting substances and regulates cambial activity.
• However, recently investigations on the concentrations of ABA in the
cambial zones of several tree species have shown that the
concentration of ABA did not change seasonally and that it did not
change when earlywood was transformed into latewood or the
termination of cambial activity.
Regulation of Formation of EW and LW – Cytokinins
• Cytokinins are substances promoting cell division, and many
physiological effects of cytokinins are known.
• When cytokinins are added externally to tree stems, cambial activity is
stimulated, and the stimulation is promoted by IAA.
• Cytokinins are essential for tissue and cell cultures.
• Native cytokinins are all adenine derivatives, and classified into free
base, riboside, ribotide, and glucoside types.
Regulation of Formation of EW and LW –
Cytokinins
• The biosynthetic pathway of cytokinins is not fully elucidated, but it has been
suggested that they are synthesized by the root apical meristem, and transported
to the stem through vascular bundles.
• Several kinds of cytokinins were found in the roots of Pseudotsuga
menziesii, while in the cambial zones of Abies balsamea trans-zeatin,
and trans-ribosylzeatin were identified.
• In Cryptomeria joponica and Larix leptolepis zeatin, transribosylzeatin, cis-ribosylzeatin, isopentenyladenine, and isopentenyladenosine
are present.
Regulation of Formation of EW and
LW – Cytokinins
• Analysis of endogenous cytokinins in trees have not been
successful so far.
• The reason for this is that there are many cytokinin
derivatives with different polarities, they are present in very
low quantities, and extraction and purification from plant
materials is difficult.
Regulation of Formation of EW and LW
– Gibberellins
n Gibberellins
are synthesized via ent-kaurene, a
diterpene, derived from mevalonic acid.
n Gibberellins
contain an ent-gibberellan skeleton (C20
gibberellins) or ent-nor gibberellan skelton (C19
gibberellins) and are numbered in the order of their
identification from plants.
n More
than 70 gibberellins have been isolated, and
their glucosides have been identified.
Regulation of Formation of EW and LW
– Gibberellins
n
Gibberellins promote elongation growth, floral bud formation
and fructification, and are involved in dwarf expression.
n
When a small amount of gibberellins was added to a stem of
Pinus radiata, trunk xylem formation and tracheid diameter
increased.
n
The effect of gibberellins is expressed in coordination with
IAA.
Regulation of Heartwood
Formation
David Wang’s Wood Formation Class
Histological Characteristic of Heartwood
n
Intermediate wood and transition
wood
n
Crib (1923) found a narrow band of
pale wood around the heartwood of
Taxus sp. and the water content of
this area was lower than that of
sapwood and heartwood.
n
Crib suggested that the pale wood
was represented an initiation stage of
heartwood formation.
Histological Characteristic of Heartwood
n
It is known that when cambium is differentiated to sapwood,
prosenchyma cells are dead, but ray and axial parenchyma
cells survive in the sapwood.
n
Living parenchyma cells of sapwood of several European
conifers and hardwoods contain oval nuclei at initial stage,
but the shape of the nuclei changes to round in aged
sapwood. The nuclei later lose chromatin and disappear.
Histological Characteristic of Heartwood
n
The following list are decreased when the differentiation of
cambium to sapwood.
The volume of nuclei
n The amount of RNA
n The numbers of mitochondria
n Golgi apparatus
n
Endoplasmic reticulum
n Plastids
n Ribosome
n
n
In contrast, the volume of vacuoles which store heartwood
phenolics increase in accordance with the gradual
decrease in physiological activity of the ray parenchyma
cells.
Histological Characteristic of Heartwood
n
Chattaway (1952) showed that the physiological activity of
intermediate wood increases considerably when tyloses are
formed.
n
Hugentobler (1965) found that the volume of nuclei and
nucleoli in ray parenchyma cells of intermediate woods is
largest in particular trees that form a very dark heartwood.
He suggested that the increase in the volume of the nucleoli
is related to an increase in RNA production.
Heartwood and Extractives
n
Various wood extractives such as terpenes, flavonoids,
lignans, stilbenes, troplones, among others, are found in
heartwood.
n
The content of polyphenols is generally higher in the
heartwood of old trees than in that of young trees, and
decreases with increasing stem height and from the
periphery toward the central portion of the stem.
Heartwood and Extractives
n
The content of extractives was different in different
specimens of the same species and in different parts of
stem.
n
The heartwood of slow-growing large trees was generally
darker and contained larger amounts of extractives than did
young fast-growing trees.
n
The heartwood of birches and roots of Picea abies
contained more lignans than the stem heartwood.
Heartwood and Extractives
n
The content of arabinogalactan
was only 0.3% in the sapwood
but 24.5% in the heartwood.
n
The arabinogalactan occurs
largely in the lumen of the
heartwood tracheids.
Variation in arabinogalactan content with
distance from the center of a Larix
occidentalis.
Heartwood and Extractives
n
In Pinus sylvestris and P. radiata, triglycerides decreased
rapidly and free fatty acids increased in the narrow
intermediate wood.
n
Saturated fatty acids were more common in the heartwood
than unsaturated acids, while in the sapwood the content of
unsaturated fatty acids was higher than that of saturated
acids.
Heartwood and Extractives
n
Various lignans and tropolones were present mostly at the inner
50-100 annual rings from the dark heartwood boundary of Thuja
plicata, and there tropolones were not synthesized by very young
trees.
n
Red heartwood of Cryptomeria japonica contains significant amounts
of several norlignans such as sequirin C, agatharesinol, sugiresinol,
hydroxysugiresinol, yateresinol and hinokiresinol, whereas black
heartwood has fewer norlignans together with hot-water soluble darkcolored substances (higher than 10k Da) composed of phenolic
components, arabinogalactan, and arabinoglucuronoxylan.
Yateresinol
Sequirin-C
1,4-bis-(p-Hydroxyphenyl)-butadiene
Agatharesinol
Formation of Color Constituents in Sugi
Heartwood
Phenol oxidation
Dehydro-hydroxy sugiresinol
Hydroxysugiresinol
Heartwood color material
HPLC Chromatogram of Extracts from Taiwania Pith
Taiwanin A
Hinokiol
5.0
1.3
y = 0.0031x - 0.0537
y = 7.657E-5x + 0.2414
R² = 0.999
R² = 0.9994
4.0
0.9
3.0
0.6
Si-60 column
UV-254 nm
2.0
0.3
1.0
0
0 2500.0000
5000.0000
7500.0000
10000.0000
0
0
Helioxanthin
300
600
900
1200
1500
Ferruginol
1.3
5.0
y = 0.0011x - 0.0056
y = 0.0031x - 0.0537
R² = 0.9993
R² = 0.999
4.0
0.9
3.0
0.6
2.0
0.3
1.0
0
0
300
600
900
1200
1500
0
0
250.0
500.0
750.0
1000.0
The Main Constituents of Taiwania Distributed
in Different Parts of Wood
1.0
0.8
%
0.5
0.3
01
2
Pith
Inner
Heartwood
3
Outer
Heartwood
4
Transition
Zone
5
Sapwood
Heartwood and Extractives
n
Chromatography, IR, and NMR analyses suggested that the
phenolic components of the dark-colored substances
consisted of oxidatively polymerized norlignans.
n
Extractives of C. joponica attained a maximum concentration
on the inner inside of three annual rings from the boundary of
the heartwood.
Metabolism of Ray Parenchyma Cells
n
Starch and fat are present in parenchyma cells of the
sapwood. These are used with sugars (sucrose)
transported via vascular bundles from the leaves, for
wood and phloem growth and synthesis of heartwood
extractives.
n
Sugars transported from leaves to ray parenchyma cells
of intermediate wood could be converted to acetyl-CoA via
glycolysis-TCA cycle, and then used for the synthesis of A
rings of flavonoids and stibene via the malonyl-CoA
pathway, terpenes via the mevalonic acid pathway.丙二醯基輔脢A
二羥甲基戊酸
Metabolism of Ray Parenchyma Cells
n
Sugars could be converted to pentosephosphates via the
pentosephosphate cycle, leading to the B rings of flavonoids
and stilbenes, and hydrolyzable tannins via shikimatecinnamate pathway.
n
By cooperation of the biosynthetic reactions in these
pathways, heartwood extractives could be synthesized in
parenchyma cells of the intermediate wood.
Gene Expression in Heartwood
Formation
n
It has been shown that PAL, a key enzyme leading to
phenylpropanoid metabolism is encoded by a small family
of genes in bean, parsley, rice, tobacco, and poplar.
n
In confier, PAL is encoded by a single gene, which is
exceptional.
n
The isoforms of PAL genes are expressed differently in
different organs and in response to different
environmental stimuli, which include wounding, infection,
light, and other factors.
Gene Expression in Heartwood
Formation
n
Chalcone synthesis (CHS), which regulates the first step of
flavonoid synthesis, is also encoded by a gene family
comprising several members.
n
CHS gene family is founds in such plants as soybean and
chick pea, petunia, and a French bean.
n
The various isoforms are differently regulated by various
factors and environmental stimuli.
Gene Expression in Heartwood
Formation
n
Enzymes involved in the general phenylpropanoid
metabolism are mostly encoded by several genes or gene
families.
n
The expression of genes in the syntheses of heartwood
extractives (flavonoids and anthocyamins etc.) should
therefore be regulated by various biotic and abiotic
factors.
n
The characterization of genes with promoters in flavonoid
synthesis in intermediate wood should lead to better
information regarding the mechanism of heartwood
formation.
Gene Expression in Heartwood
Formation
n
Concept of “physiological activation” in intermediate wood
proposed by Chattaway –
n
Alternation of the metabolism of sapwood ray parenchyma cells by
ethylene, such as induction and activation of PAL, 4-CL, CHS, CHI,
the pentose phosphate cycle, malonyl-CoA pathways, synthesis of
lipids and terpenes.
n
Activation of hydrolases and oxidases by destruction of vacuoles
parenchyma cells in the intermediate wood to give heartwood.