Tree Physiology 22, 661–666
© 2002 Heron Publishing—Victoria, Canada
Neutral lipids and phospholipids in Scots pine (Pinus sylvestris)
sapwood and heartwood
R. PIISPANEN1,2 and P. SARANPÄÄ1
1
The Finnish Forest Research Institute, P.O. Box 18 (Jokiniemenkuja 1), FIN-01301 Vantaa, Finland
2
Author to whom correspondence should be addressed ([email protected])
Received February 26, 2001; accepted October 14, 2001; published online May 1, 2002
Summary Variations in the concentration and composition
of triacylglycerols, free fatty acids and phospholipids were analyzed in Scots pine (Pinus sylvestris L.) trees at five sites.
Disks were taken at breast height or at a height of 4 m from the
stems of 81 trees differing in diameter and growth rate. The
mean concentration of triacylglycerols in sapwood was 26 mg
g –1 dry mass; however, variation among trees was large
(16–51 mg gdm –1). The concentration of triacylglycerols was
slightly larger at 4 m height in the stem than at breast height.
Concentrations of triacylglycerols did not differ between the
sapwood of young and small-diameter stems (DBH < 12 cm)
and the sapwood of old stems (DBH > 36 cm). Concentrations
of free fatty acids were negligible in the outer sapwood, but
ranged between 5 and 18 mg gdm–1 in the heartwood. The most
abundant fatty acids of triacylglycerols were oleic (18:1),
linoleic (18:2ω6, 18:2∆5,9), linolenic (pinolenic, 18:3∆5,9,12
and 18:3ω3) and eicosatrienoic acid (20:3∆5,11,14 and
20:3ω6). The concentration of linoleic acid comprised 39–
46% of the triacylglycerol fatty acids and the concentration
was higher in the slow-growing stem from northern Finland
than in the stems from southern Finland. Major phospholipids
were detected only in sapwood, and only traces of lipid phosphorus were detected in heartwood.
Keywords: fatty acids, secondary xylem, senescence, triacylglycerols, wood aging.
Introduction
Large differences among trees in anatomy and chemical composition of wood are reflected in differences in physiology and
are the result of genetic and environmental factors, which affect tree growth and development. The proportions and characteristics of the various structural elements in wood remain
largely unchanged following cell enlargement, but several
structural and chemical changes occur as the tree passes from a
juvenile to a mature stage.
After wood has been formed in the living tree, the aging process begins. The outermost growth rings conduct xylem sap
and periodically store reserve materials in the living ray parenchyma cells. Changes related to cellular senescence of the parenchyma commonly occur over a few rows of cells. These
changes are initiated by internal factors, and though their nature is genetically determined, they can be modified by both
internal and external factors (Hillis 1977, 1987). Secondary
changes, which occur as a result of the transformation of sapwood into heartwood, can provide the tree with chemical or
physical defense mechanisms that delay degradation and can
also affect wood quality. Heartwood is defined as “the inner
layers of wood which, in the growing tree, have ceased to contain living cells and in which the reserve materials (e.g.,
starch) have been removed or converted into heartwood substances” (Anonymous 1957). It has been suggested that several factors are involved in heartwood formation: aging and
loss of vitality of the ray parenchyma cells (Frey-Wyssling and
Bosshard 1959); toxic effect of polyphenols (Stewart 1966);
production of ethylene (Hillis 1977); and growth regulating
substances (Bamber 1976).
Triacylglycerols are stored in large quantities in the ray parenchyma cells of Scots pine (Pinus sylvestris L.) wood. The
concentration and fatty acid composition of triacylglycerols in
Scots pine sapwood remain stable throughout the year (Saranpää and Nyberg 1987b, Fischer and Höll 1992). In contrast,
Höll and Priebe (1985) reported marked seasonal variation in
triacylglycerols in the wood of the deciduous tree Tilia cordata
(Miller).
A large reduction in the concentration of triacylglycerols
occurs during heartwood formation in Scots pine. Consequently, the concentration of free fatty acids is highest in
heartwood and increases toward the inner heartwood, whereas
the concentration of triacylgycerols decreases almost to zero
in the inner heartwood (Saranpää and Nyberg 1987a, Fischer
and Höll 1992). Fatty acid composition of triacylglycerols in
the inner sapwood and free fatty acids in the outer heartwood
are similar (Saranpää and Nyberg 1987a), suggesting that free
fatty acids in heartwood are formed by hydrolysis of sapwood
triacylglycerols. Fatty acids may be partly deposited in the cell
lumen and pit membranes, where they decrease the permeability of wood during heartwood formation (Saranpää 1990).
Glycerophospholipids are the major lipids of plant plasma
membranes (Harwood and Russell 1984). The concentration
of phospholipids is known to decrease with depth in the heartwood, probably indicating reduced vitality and membrane de-
662
PIISPANEN AND SARANPÄÄ
terioration of the parenchyma cells in the heartwood (Höll and
Lipp 1987, Hillinger et al. 1996a, Magel et al. 1997).
Our objective was to identify age- and diameter-related
changes in the concentrations of triacylglycerols, free fatty acids and phospholipids in the sapwood and heartwood of Scots
pine. Neutral lipids were analyzed from 70 mature stems and
10 young stems growing on five sites in southern Finland and
from an old large stem growing in northern Finland. Samples
were taken from pith to cambium of the selected trees, representing inner and outer heartwood and sapwood from trees of
different sizes, i.e., ages.
and Höll 1990, Saranpää and Piispanen 1994) or (2) fatty acids
were analyzed by gas–liquid chromatography with mass spectrometry (GLC–MS) (Saranpää and Nyberg 1987a, 1987b).
Heptadecanoic acid and triheptadecanoin were used as internal standards for GLC analysis.
Phospholipids
Stem disks were taken from five trees (DBH = 33 cm, Age
122 years) at the Sauvo forest in southern Finland (Table 1).
Samples of the wood powder (300 mg of sapwood and
4000 mg of heartwood) were extracted with acetone for 6 h
and further diluted with chloroform:methanol (2:1, v/v; Bligh
and Dyer 1959). We used a larger sample of heartwood powder
than sapwood powder, because the concentration of phospholipids was much smaller in the heartwood. Water and Polyclar
AT were added to each sample and the upper layer was discarded. Extracts were washed three times as described by
Folch et al. (1957).
Total lipids were fractionated by silicic acid column chromatography (Unisil 100–120 mesh, Clarkson Chemical, Williamsport, PA; Rouser et al. 1976). The eluant for neutral lipids
was chloroform. For glycolipids we used acetone and for
phospholipids we used chloroform:methanol (1:1, v/v) and
methanol. The neutral lipid and glycolipid fractions were discarded. Phospholipids were analyzed as the total concentration of lipid phosphorus in the dried phospholipid fractions.
The concentration of lipid phosphorus was determined spectrophotometrically after hydrolysis in 1.5 ml of 3.3 N H2SO4
for 6 h at 150 °C followed by the addition of 50 µl of H2O2 and
incubation for another 6 h at 150 °C (Fiske and Subbarow
1925).
The phospholipid fractions of sapwood and transition zones
were further separated by TLC (Merck 1.05715, 0.25 mm
silica gel 60 F254). The plates were developed in chloroform:methanol:25% ammonia:water (115:45:3.75:3.75, v/v;
Abramson and Blecher 1964) and sprayed with 0.001%
primuline (Sigma P-7522) in acetone:water (4:1; Wright
1971) and, while wet, the fractions were located in 366 nm UV
light. The lipids were scraped off the plates and hydrolyzed
and the concentration of phosphorus was determined as above.
The phospholipids were identified using authentic standard
components.
Materials and methods
Stem disks were taken from 70 large dominant pine trees
growing in Scots pine forests in southern Finland (Sauvo:
66°95′ N, 32°64′ E; Vihti: 67°07′ N, 33°56′ E; and Ruotsinkylä: 66°96′ N, 33°89′ E; Table 1). In addition, 10 young trees
without any heartwood from southern Finland (Ruotsinkylä:
66°96′ N, 33°89′ E; Table 1) and a 395-year-old large stem
(DBH = 51 cm) from northern Finland (Koierivaara: 76°04′ N,
35°12′ E) were also studied.
The disks were immediately frozen. The samples were separated into zones corresponding to: outer sapwood (10–
20 mm from the cambium, OS), transition zone (next to the
sapwood and heartwood border, TZ), outer heartwood (10 mm
from the heartwood border, OH), inner heartwood (center part
of the heartwood, IH) and innermost heartwood (heartwood
around the pith, IMH). Samples were homogenized to a fine
wood powder with a Cyclotech mill (Tecator, Hoganas, Sweden).
Neutral lipids
Immediately after samples were homogenized to a fine powder they were extracted with acetone (6 h, mini-soxhlet). Triacylglycerols and free fatty acids in the acetone extract were
separated by thin-layer chromatography (TLC) (0.20-mm silica gel; Ekman 1979, Kates 1986, Saranpää and Nyberg
1987a). Corresponding zones on the plates were scraped off
and extracted in ethyl acetate.
Two methods were used to quantify triacylglycerols: (1) the
glycerol concentration was determined enzymatically (Fischer
Table 1. Scots pine material for lipid analysis. Abbreviations: DBH = diameter at breast height; TG = triacylglycerols; and FA = fatty acids.
Location
No. of trees
Age (year)
DBH (cm)
Sapwood thickness (mm)
Analyzed components
Vihti
Vihti
Ruotsinkylä
Sauvo (A)
Sauvo (B)
Koierivaara
Sauvo (B)
10
20
10
20
20
1
5
79
69
16
117
119
395
122
33
24
10
42
42
51
33
62
46
–1
54
55
22
60
TG/FA2
TG/FA2
TG/FA2
TG/FA
TG/FA
TG/FA
Phospholipids
1
2
Only sapwood was detected.
Data from Saranpää and Piispanen 1994.
TREE PHYSIOLOGY VOLUME 22, 2002
NEUTRAL LIPIDS AND PHOSPHOLIPIDS IN SCOTS PINE WOOD
Results
Neutral lipids
The mean concentration of triacylglycerols in the outer sapwood was about 26 mg gdm –1 (Figure 1a); however, variation
among trees was large (15.9–50.6 mg gdm –1). There was no
correlation between triacylglycerol concentration and stem diameter (Figure 1a). Although the highest concentrations of triacylglycerols were found in stems with the largest diameters
(Figure 1a), the lowest concentration of triacylglycerols was
found in a stem with a diameter of 36 cm. An old stem with
395 growth rings and a diameter of 51 cm from northern Finland had a high concentration of triacylglycerols in the sapwood.
The triacylglycerol concentration was slightly higher at 4 m
height in the stem than at breast height (50 versus 43 mg gdm –1;
Figure 1b). The concentration of free fatty acids was low in the
sapwood, about 0.7 mg gdm –1, whereas the concentration of
free fatty acids in the heartwood was high and varied from
18 mg gdm –1 in the outer heartwood to 12 mg gdm –1 in the inner-
Figure 1. (a) Relationship between the concentration of triacylglycerols and stem diameter of 80 stems of Pinus sylvestris L. Samples were
taken from the outer sapwood (2 cm from cambium) at breast height
(1.3 m, small (Ú) and medium (ⵧ; Saranpää and Piispanen 1994) size
stems, mean DBH = 8–12 and 12–42 cm, respectively) or at 4 m
above ground (large (䉫) stems, mean DBH = 36–50 cm). Values are
expressed as mg gdm –1. (b) Concentrations of triacylglycerols and free
fatty acids in the sapwood and heartwood of a slow-grown
395-year-old stem from northern Finland. Samples were taken from
stem disks at breast height and at 4 m above ground. Values are expressed as % of dry mass. Abbreviations: OS = outer sapwood, OH =
outer heartwood, IH = inner heartwood and IMH = innermost heartwood.
663
most heartwood (Figure 1b). Thus, the concentration of the
free fatty acids in the heartwood was almost 40% of the concentration of triacylglycerols in the outer sapwood.
The fatty acid composition of triacylglycerols in the transition zone corresponded to the free fatty acids in the outer and
inner heartwood (Figure 2a); however, the proportion of saturated fatty acids increased slightly (Figure 2a). The most abundant fatty acids were oleic (18:1), linoleic (18:26, the
dominant fatty acid), linolenic (pinolenic 18:35,9,12) and
eicosatrienoic acid (20:35,11,14 and 20:36). Minor concentrations of 16:0, 16:1, 17:0ai, 18:0, 18:25,9, 18:33,
18:4, 20:1 and 20:2 were also found. The concentration of
linoleic acid comprised 39–46% of the total fatty acids in
triacylglycerols and together oleic and linoleic acid formed
about 70% of the total triacylglycerol fatty acids (Figure 2b).
Stem samples taken at breast height and 4 m above ground
from trees in southern Finland had similar fatty acid compositions (Figure 2b) as did stem samples taken from trees at different sites (cf. Sauvo A and Sauvo B, Table 1, Figure 2b). In
contrast, stem samples from a slow-growing tree in northern
Finland had a larger proportion of linoleic acid and a smaller
Figure 2. (a) The proportion of major fatty acids of triacylglycerols in
the transition zone (TAG) and free fatty acids (FA) in the outer and inner heartwood (OH FA and IH FA, respectively; redrawn from
Saranpää and Nyberg (1987a)). (b) Major fatty acid composition of
triacylglycerols in the stems of Pinus sylvestris from southern Finland
and in a slow-grown 395-year-old stem from northern Finland. Samples were taken from stem disks at breast height (three stems from
southern Finland, Saranpää and Nyberg (1987a)) and at 4 m above
ground (20 stems from two sites (Sauvo A and B, see Table 1) in
southern Finland). Values are expressed as % of total triacylglycerol
fatty acids.
TREE PHYSIOLOGY ONLINE at http://heronpublishing.com
664
PIISPANEN AND SARANPÄÄ
proportion of oleic acid than stem samples from trees in southern Finland (Figure 2b).
In contrast, the relative proportion of PC increased from the
outer sapwood toward the transition zone (Figure 3b).
Phospholipids
The maximum concentration of lipid phosphorus was detected
in outer sapwood (Figure 3a). The total concentration of lipid
phosphorus decreased gradually toward the inner heartwood,
where only trace concentrations were detected (Figure 3a).
Variation in the concentration of lipid phosphorus between
stems was small (cf. error bars in Figure 3a). In the outer sapwood and in the transition zone, phosphatidyl choline (PC),
phosphatidyl ethanolamine (PE), phosphatidyl glycerol (PG),
phosphatidyl inositol (PI) and traces of phosphatidic acid
(PA), phosphatidyl serine (PS) and lysophosphatidyl ethanolamine (LPE) were found. The dominant phospholipid in the
outer sapwood and in the transition zone was PC (about 4.5 µg
gdm –1). The relative proportions of PE, PG and PI decreased
from the outer sapwood toward the transition zone (Figure 3b).
Figure 3. (a) Concentrations of total lipid phosphorus in stems of
Pinus sylvestris grown at Ruotsinkylä, southern Finland. Each column represents the mean concentration of lipid phosphorus (µg gdm –1)
at various distances from the pith at a stem height of 4 m. Error bars
show the standard deviation (s, n = 5). Abbreviations: OS = outer sapwood, TZ = transition zone, OH = outer heartwood and IH = inner
heartwood. (b) The relative proportion of phospholipids in the outer
sapwood (OS) and in the transition zone (TZ) of Pinus sylvestris expressed as a percentage of the total concentration of measured lipid
phosphorus at a stem height of 4 m. Five stems were analyzed. Abbreviations: PI = phosphatidyl inositol, PC = phosphatidyl choline, PE =
phosphatidyl ethanolamine and PG = phosphatidyl glycerol.
Discussion
The concentration of triacylglycerols in the outer sapwood of
Scots pine varied between 16 and 51 mg gdm –1. Fischer and
Höll (1992) reported a value of about 18 mg gdm –1 (20 µmol
g dm –1) in Scots pine stems in southern Germany. The concentration of triacylglycerols has been found to increase slightly
from outermost sapwood toward inner sapwood, and decrease
again in the transition zone between sapwood and heartwood
(Saranpää and Nyberg 1987a). Concentrations of fats are 10
times higher in Scots pine than in Norway spruce (Picea abies
(L.) Karsten; Ekman 1979) or Siberian larch (Larix sibirica
Ledeb.; P. Saranpää, unpublished data) grown in Finland.
We found a high concentration of free fatty acids (12–18 mg
gdm –1) in the heartwood of Scots pine. Fischer and Höll (1992)
found a nearly three times higher molar concentration of free
fatty acids (about 50 µM; 14 mg gdm –1) in the heartwood than
of triacylglycerols (about 20 µM; 18 mg gdm –1) in the sapwood
of Scots pine grown in southern Germany. They concluded
that if the free fatty acids originated from triacylglycerols, almost none of the energy stored in fat was used for heartwood
formation. Thus, secondary substances synthesized during
heartwood formation must originate mainly from stored carbohydrates (Fischer and Höll 1992). The concentration of triacylglycerols in Scots pine sapwood has been reported to remain constant throughout the year (Saranpää and Nyberg
1987b, Fischer and Höll 1992), indicating that the energy
stored in the fat is not used for either growth or needle formation in the spring.
We found no difference in the concentrations of triacylglycerols between young and old sapwood samples, indicating
that triacylglycerols are always present at the same concentration at the time of heartwood formation. Hemingway and
Hillis (1971) suggested that biological degradation of fatty
acid esters does not occur in the heartwood and that heartwood
contains various concentrations of fatty acid esters that have
not been metabolized. However, the concentration of triacylglycerols in the inner heartwood of Scots pine was low and
some lipases may still be active in the outer heartwood, because all parenchyma cells do not die simultaneously at the
time of heartwood formation.
Fatty acid composition of triacylglycerols showed little
variation among trees from southern Finland (Figure 2b).
Oleic and linoleic acid together comprised about 70% of the
total triacylglycerol fatty acids, with linoleic acid making the
major contribution (39–46%). According to Fischer and Höll
(1992), oleic acid is the principal fatty acid of triacylglycerols
in stems of Scots pine trees grown in southern Germany. They
also reported a much lower concentration of linolenic acid
than we detected. It seems reasonable to assume that a lower
growth temperature and low winter temperatures lead to an increase in the unsaturated fatty acid composition of triacylglycerols, because linoleic acid reached its highest concentration in the stem from northern Finland. The concentration of
TREE PHYSIOLOGY VOLUME 22, 2002
NEUTRAL LIPIDS AND PHOSPHOLIPIDS IN SCOTS PINE WOOD
polyunsaturated fatty acids in Scots pine wood has been reported to increase threefold with an increase in latitude from
59 to 68° (Fuksman and Komshilov 1981). The degree of saturation in membrane lipids decreases during the dormant period
at low temperatures in many plants (Harwood and Russell
1984). In response to cold stress and during winter, the concentration of polyunsaturated fatty acids in triacylglycerols increases in Scots pine wood (Fuksman and Komshilov 1979,
1980).
The fatty acid composition changes in the transition zone
between sapwood and heartwood. The concentrations of both
oleic and linoleic acid of triacylglycerols decreased towards
the heartwood, whereas the concentrations of linolenic and
eicosatrienoic acid increased (Saranpää and Nyberg 1987a). It
has been suggested that the free fatty acids of the heartwood
are hydrolyzed from the triacylglycerols of the sapwood, because the free fatty acid composition of the heartwood resembles that of the triacylglycerol fraction of the transition zone
(Saranpää and Nyberg 1987a).
The concentration of lipid phosphorus decreased toward the
inner heartwood zone in the five Scots pine stems studied (Figure 3a). The largest concentration of phospholipids was detected in the outer sapwood, indicating the presence of a large
quantity of membrane components in the sapwood. A similar
lipid phosphorus profile has been detected in the trunkwood of
heartwood-forming Robinia pseudoacacia L. (Hillinger et al.
1996a), with almost no phospholipids in the heartwood. In
poplar cortex, the concentration of phospholipids reached a
maximum in winter and a minimum in summer (Yoshida
1973). Our five Scots pine stems were felled in May at a time
when rapid turnover of phospholipids might occur. The agerelated decrease in growth potential has been associated with
membrane degradation (Hillinger et al. 1996a). Lipoxygenase, which influences membrane integrity, is activated during
heartwood formation (Hillinger et al. 1996b). Membrane disintegration in the inner heartwood of Scots pine stems was reflected in the radial distribution of lipid phosphorus.
Altogether seven phospholipid classes (PI, PC, PE, PG, PA,
PS and LPE) were detected in the outer sapwood and transition
zone of Scots pine (Figure 3b). In R. pseudoacacia, the proportion of phosphatidic acid increased from sapwood towards
the transition zone, whereas the innermost growth rings consisted mainly of phosphatidic acid (Hillinger et al. 1996a). In
our Scots pine trees, the lipid phosphorus concentration in
heartwood was low (about 0.61 µg gdm –1). In contrast, Höll and
Lipp (1987) reported a lipid phosphorus concentration of 6 µg
gdm –1 in Scots pine heartwood. The main phospholipid in the
outermost sapwood of Scots pine was phosphatidyl choline,
which was also prominent in the outermost growth rings of
R. pseudoacacia. In R. pseudoacacia, the proportion of total
phospholipids occurring as phosphatidic acid in the outermost
growth rings was large (about 30%) in November, whereas in
Scots pine sapwood samples collected in May, only traces of
phosphatidic acid were detected. The samples were collected
at different seasons, which may account for some of the differences in phospholipid proportions between these two heartwood-forming species.
665
We found large variations in the concentrations of triacylglycerols in the sapwood of the Scots pine trees studied (Figure 1a), although the triacylglycerol concentration did not differ significantly between juvenile and mature wood. However,
a slow-grown tree with narrow sapwood stored large concentrations of triacylglycerols in the sapwood and also released
large concentrations of free fatty acids in the heartwood. The
concentration of lipid phosphorus decreased dramatically towards the inner heartwood, indicating membrane deterioration
during heartwood formation. Although the fatty acid composition of triacylglycerols showed little variation, unsaturated
fatty acids comprised a larger proportion of triacylglycerols in
trees in northern Finland than in trees in southern Finland or
central Europe. We conclude that only a small fraction of the
large amount of energy stored in lipids is used for heartwood
formation, because free fatty acids in the heartwood seem to
originate from triacylglycerols in the sapwood.
Acknowledgments
Financial support from the Academy of Finland (Grants No. 1011255
and 661992) is gratefully acknowledged. The authors thank Mr. Tapio
Laakso, M.Sc., Mr. Tapio Järvinen and Dr. Veikko Kitunen for their
excellent technical assistance.
References
Abramson, D. and M. Blecher. 1964. Quantitative two-dimensional
thin-layer chromatography of naturally occurring phospholipids. J.
Lipid Res. 5:628–631.
Anonymous. 1957. International glossary of terms used in wood anatomy: Prepared by the Int. Assoc. Wood Anatomists. Trop. Woods
107:1–36.
Bamber, R.K. 1976. Heartwood, its function and formation. Wood
Sci. Technol. 10:1–8.
Bligh, E.G. and W.J. Dyer. 1959. A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37:911–917.
Ekman, R. 1979. Analysis of the nonvolatile extractives in Norway
spruce sapwood and heartwood. Acta Acad. Abo. Ser. B 39:1–20.
Fischer, C. and W. Höll. 1990. Lipoprotein lipase as a new tool in
steryl ester analysis. Lipids 25:292–295.
Fischer, C. and W. Höll. 1992. Food reserves of Scots pine (Pinus
sylvestris L.). II. Seasonal changes and radial distribution of carbohydrate and fat reserves in pine wood. Trees 6:147–155.
Fiske, C.H. and Y. Subbarow. 1925. The colorimetric determination
of phosphorus. J. Biol. Chem. 66:375–400.
Folch, J., M. Lees and G.H. Sloane-Stanley. 1957. A simple method
for the isolation and purification of total lipids from animal tissues.
J. Biol. Chem. 226:497–509.
Frey-Wyssling, A. and H.H. Bosshard. 1959. Cytology of the ray cells
in sapwood and heartwood. Holzforschung 13:129–137.
Fuksman, I.L. and N.F. Komshilov. 1979. Changes in the acid content
of resins and lipids in Scots pine wood at different temperatures.
Khim. Drevesiny 4:86–92. In Russian.
Fuksman, I.L. and N.F. Komshilov. 1980. Seasonal changes in the
lipids and resins of Pinus sylvestris wood. Khim. Drevesiny 6:
94–101. In Russian.
Fuksman, I.L. and N.F. Komshilov. 1981. The effect of latitude of
growth on the content and composition of resins and lipids in Scots
pine wood. Khim. Drevesiny 2:96–102. In Russian.
Harwood, J.L. and N.J. Russel. 1984. Lipids in plants and microbes.
George Allen and Unwin, London, 161 p.
TREE PHYSIOLOGY ONLINE at http://heronpublishing.com
666
PIISPANEN AND SARANPÄÄ
Hemingway, R.W. and W.E. Hillis. 1971. Changes in fats and resins of
Pinus radiata associated with heartwood formation. Appita J. 24:
439–443.
Hillinger, C., W. Höll and H. Ziegler. 1996a. Lipids and lipolytic enzymes in the trunkwood of Robinia pseudoacacia L. during heartwood formation. I. Radial distribution of lipid classes. Trees 10:
366–375.
Hillinger, C., W. Höll and H. Ziegler. 1996b. Lipids and lipolytic
enzymes in the trunkwood of Robinia pseudoacacia L. during
heartwood formation. II. Radial distribution of lipases and phospholipases. Trees 10:376–381.
Hillis, W.E. 1977. Secondary changes in wood. In Recent Advances
in Phytochemistry. Vol. 6. Eds. F.A. Loewus and V.C. Runeckles.
Plenum, New York, pp 247–309.
Hillis, W.E. 1987. Heartwood and tree exudates. Springer-Verlag,
Berlin, 268 p.
Höll, W. and J. Lipp. 1987. Concentration gradients of free sterols,
steryl esters and lipid phosphorus in the trunkwood of Scots pine
(Pinus sylvestris L.). Trees 1:79–81.
Höll, W. and S. Priebe. 1985. Storage lipids in the trunk- and
rootwood of Tilia cordata Mill. from the dormant to the growing
period. Holzforschung 39:7–10.
Kates, M. 1986. Techniques of lipidology: isolation, analysis and
identification of lipids. Elsevier, Amsterdam, 464 p.
Magel, E., C. Hillinger, W. Höll and H. Ziegler. 1997. Biochemistry
and physiology of heartwood formation: role of reserve substances.
In Trees—Contributions to Modern Tree Physiology. Eds. H. Rennenberg, W. Eschrich and H. Ziegler. Backhuys, Leiden, pp
477–506.
Rouser, G., G. Kritchevsky and A. Yamamoto. 1976. Column chromatographic and associated procedures for separation and determination of phosphatides and glycolipids. In Lipid Chromatographic
Analysis. Vol. 3. Ed. G.V. Marinetti. Marcel Dekker, New York,
713 p.
Saranpää, P. 1990. Heartwood formation in stems of Pinus sylvestris
L. Lipids and carbohydrates of sapwood and heartwood and
ultrastructure of ray parenchyma cells. Publ. Dept. Bot., Univ. Helsinki 14:1–22.
Saranpää, P. and H. Nyberg. 1987a. Lipids and sterols of Pinus
sylvestris L. sapwood and heartwood. Trees 1:82–87.
Saranpää, P. and H. Nyberg. 1987b. Seasonal variation of neutral
lipids in Pinus sylvestris L. sapwood and heartwood. Trees
1:139–144.
Saranpää, P. and R. Piispanen. 1994. Variation in the amount of
triacylglycerols and steryl esters in the outer sapwood of Scots pine
(Pinus sylvestris L.). Trees 6:228–231.
Stewart, C.M. 1966. Excretion and heartwood formation in living
trees. Science 153:1068–1074.
Wright, R.S. 1971. A reagent for the non-destructive location of steroids and some other lipophilic materials on silica gel thin layer
chromatography. J. Chromatogr. 59:220–221.
Yoshida, S. 1973. Seasonal changes in lipids and freezing resistance
in poplar trees. Low Temp. Sci. Ser. B 31:9–20. In Japanese.
TREE PHYSIOLOGY VOLUME 22, 2002