formation of earlywood, latewood, and...

David Wang’s Wood formation Class

Formation of Earlywood, Latewood, and Heartwood

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.

Transition from earlywood to latewood

Thujopsis dolabrata Larix leptolepis

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.


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.

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.



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.

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 tracheid-

differentiation 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 – Effect

of IAA on Formation of Tree Stems

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.


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, trans-ribosylzeatin, 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

nGibberellins are synthesized via ent-kaurene, a diterpene, derived from mevalonic acid.

nGibberellins 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.

nMore 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 woodn 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.


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.


n The following list are decreased when the differentiation of cambium to sapwood.n The volume of nuclein The amount of RNAn The numbers of mitochondrian Golgi apparatus n Endoplasmic reticulumn Plastidsn Ribosome

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.


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.


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 Extractivesn 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.


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.


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 dark-colored substances (higher than 10k Da) composed of phenolic components, arabinogalactan, and arabinoglucuronoxylan.

Yateresinol 1,4-bis-(p-Hydroxyphenyl)-butadiene

Sequirin-C Agatharesinol

Hydroxysugiresinol Dehydro-hydroxy sugiresinol

Phenol oxidation

Heartwood color material

Formation of Color Constituents in Sugi Heartwood

HPLC Chromatogram of Extracts from Taiwania Pith

0

0.3

0.6

0.9

1.3

0 2500.00005000.00007500.000010000.0000

y = 7.657E-5x + 0.2414R² = 0.9994

Taiwanin A

0

1.0

2.0

3.0

4.0

5.0

0 300 600 900 1200 1500

y = 0.0031x - 0.0537R² = 0.999

Hinokiol

0

0.3

0.6

0.9

1.3

0 250.0 500.0 750.0 1000.0

y = 0.0011x - 0.0056R² = 0.9993

Ferruginol

0

1.0

2.0

3.0

4.0

5.0

0 300 600 900 1200 1500

y = 0.0031x - 0.0537R² = 0.999

Helioxanthin

Si-60 columnUV-254 nm

0

0.3

0.5

0.8

1.0

1 2 3 4 5

Pith Inner Heartwood

OuterHeartwood

TransitionZone

%

Sapwood

The Main Constituents of Taiwania Distributed in Different Parts of Wood


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.

二羥甲基戊酸

丙二醯基輔脢A

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 shikimate-

cinnamate 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.


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.


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.


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.

formation of earlywood, latewood, and...

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