The timing of cambial reactivation plays an important role in determination of the amount and quality of wood and the environmental adaptavity of trees. Environmental factors, such as temperatures, influence the growth and development of trees. Temperatures from late winter to early spring affect the physiological process that are involved in the initiation of cambial cell division and xylem differentiation in trees. Cumulative elevated temperatures from late winter to early spring result in earlier initiation of cambial reactivation and xylem differentiation in tree stems and an extended growth period. However, earlier cambial reactivation increases the risk for frost damage because the cold tolerance of cambium decreases after cambial reactivation. A better understanding of the mechanisms that regulate wood formation in trees and the influence of environmental conditions on such mechanisms should help in efforts to improve and enhance the exploitation of wood for commercial applications and to prepare for climatic change. Wood is the product of vascular cambium, and the formation of wood depends on the cambial activity of trees. In temperate and cool zones, the vascular cambium of the stems of trees undergoes seasonal cycles of activity and dormancy, which are collectively known as annual periodicity. This periodicity plays an important role in the formation of wood and reflects the environmental adaptivity of trees, for example their tolerance to cold in winter in cool and temperate zones. The quantity and quality of wood depend on the division of cambial cells and the differentiation of cambial derivatives. Cambial activity in trees is regulated by both internal factors, such as plant hormones, and environmental factors, such as, temperature, rainfall and photoperiod. Temperature provides the appropriate physical conditions for the growth and development of trees in temperate and cool climates. Timing of cambial reactivation is controlled by temperature, which influences both the quantity and quality of wood. During the period from late winter to early spring, new cell plates are formed in the cambium and this springtime phenomenon is referred to as cambial reactivation.

1. SEASONAL VARIATION IN
CAMBIAL ACTIVITY
ALEN SHAJI
P1914015

2. VASCULAR CAMBIUM
 Lateral meristem forming vascular
tissues.
 Innermost layer of bark, between
the xylem and phloem tissues.
 Grows both to the inside and to
the outside,
1] Cells on inside- secondary xylem.
2] Cells to outside- secondary phloem.
 Secondary differentiates these new
tissues from the primary xylem and
phloem, which derive from the apical
meristem.

3. ORIGIN OF CAMBIUM
EPIDERMIS
PROTODERM
PRIMARY XYLEM 2 XYLEM
APICAL PROCAMBIUM VASCULAR
MERISTEM CAMBIUM
PRIMARY PHLOEM
2 PHLOEM
GROUND MERISTEM
CORTEX CORK PHELLODERM
CAMBIUM
PITH CORK

4. ANATOMY OF VASCULAR CAMBIUM
A] Technically vascular cambium is equals to cambial initials.
1] Difficult to distinguish between initials and their
derivatives.
2] Refer to a cambial zone.
B] Vascular cambium meristamatic cells- highly vacuolated.
1] Fusiform initials- vertically elongated.
2] Ray initials- horizontally elongated or squarish.

5.  Ray initials,
1] Produces the radial [lateral] transport system cells.
2] In xylem and phloem these are the parenchyma.
 Fusiform initials,
1] Produces the axial [vertical] transport system cells.
2] In xylem and phloem these are the sieve tube
member, companion cells, tracheids, vessels, and fibres.
3] Can be storied [more advanced; less common] or
nonstoried.

6. C] Two possible planes of cell division,
1] Periclinal division- new cells in front or behind the
other.
a] Yields secondary xylem and phloem.
b] New cells toward the inside- xylem; cells to the
outside- phloem.
2] Anticlinal division-
cells side by side.
a] Adds new cells to
the vascular cambium as
stem grows in girth.

7. ACTIVITY OF VASCULAR CAMBIUM
 Cambium active from spring to fall; inactive in winter.
 Patterns of yearly activity produces annual rings in the
xylem.
 Generally the xylem producing cells are more active than
the phloem producing cells.

8. DEVELOPMENT OF VASCULAR CAMBIUM
 Function is to produce secondary growth.
 Vascular cambium must be formed before secondary
growth can occur.

9.  Two regions of primary stem contribute to the vascular
cambium,
1] Fascicular cambium- meristem cells within vascular
bundles.
2] Interfascicular cambium- meristem cells between
vascular bundles.

10. FUNCTIONAL VASCULAR CAMBIUM
 Becomes vascular cambium when the fascicular
and interfascicular cambium join to form a
complete cylinder around the stem.
 As soon as the cylinder is formed, vascular
cambium becomes active.
1] Divides on both the inner and outer surface of
the vascular cambium surfaces.
 Activity of the vascular cambium,
1] New xylem cells are formed inwardly and
attached to the previously produced xylem.
2] New phloem cells are formed outwardly and
are attached to the previously produced phloem.

11. DURATION OF CAMBIUM
 Duration of the functional life of the cambium
varies greatly in different species and also in
different parts of the same plant.
 In a perennial woody plant, the cambium of the
stem lives from the time of the formation untill the
death of the plant.
 In leaves, inflorescences and other deciduos parts,
the functional life of the cambium is short.

12. STRUCTURE OF CAMBIUM
 There are two concepts;
1] It consists of a uniserate layer of permanent initials with
derivatives which may divide a few times had seen
becomes converted into permanent tissues.
2] There are several rows of initiating cells which forms a
cambial zone, a few individual rows of which persists a cell
forming layers for sometimes.

13.  During growing periods the cells mature continuosly on
both sides of the cambium it becomes quite obvious that
only a single layer of cells have permanent existence as
cambium.

14. SINGLE CAMBIAL CELL

15.  Other layers if present, function only temporarily and
become completely transformed into permanent cells.
 In a strict sense, only the initials constitue the cambium,
but frequently the term is used with reference to the
cambial zone, because it is difficult to distinguish the
initials from their recent derivatives.

17. CAMBIUM GROWTH ABOUT WOUNDS
 When wounds occurs on plants, a large amount of
soft parenchymatous tissue is formed on or below
the injures surface, this tissue is known as callus.
 Callus develops from the cambium and by the
division of parenchyma cells in the phloem and the
cortex.

18. CAMBIUM IN BUDDING AND GRAFTING
 Cambium of both stock and scion gives rise to
callus which unites and develops continous
cambium layer that gives rise to normal conducting
tissues.

19. CAMBIUM IN MONOCOTYLEDONS
 In dracaena, aloe, yucca, veratrum,
Cambium layers
develops from the meristamatic
parenchyma of the pericycle or the
innermost cells of the cortex.
 In the case of roots, the cambium of
this develops in the endodermis, the
initials of cambium strands tiers to
forms a storied cambium as found in
the normal cambium of some
dicotyledons.

20. SEASONAL VARIATION IN CAMBIAL ACTIVITY
INTRODUCTION
 The timing of cambial reactivation plays an important role
in determination of the amount and quality of wood and
the environmental adaptavity of trees.
 Environmental factors, such as temperatures, influence the
growth and development of trees.
 Temperatures from late winter to early spring affect the
physiological process that are involved in the initiation of
cambial cell division and xylem differentiation in trees.
 Cumulative elevated temperatures from late winter to
early spring result in earlier initiation of cambial
reactivation and xylem differentiation in tree stems and
an extended growth period.

21.  However, earlier cambial reactivation increases the
risk for frost damage because the cold tolerance of
cambium decreases after cambial reactivation.
 A better understanding of the mechanisms that
regulate wood formation in trees and the influence
of environmental conditions on such mechanisms
should help in efforts to improve and enhance the
exploitation of wood for commercial applications
and to prepare for climatic change.
 Wood is the product of vascular cambium, and the
formation of wood depends on the cambial
activity of trees.

22.  In temperate and cool zones, the vascular cambium
of the stems of trees undergoes seasonal cycles of
activity and dormancy, which are collectively
known as annual periodicity.

23.  This periodicity plays an important role in the
formation of wood and reflects the environmental
adaptivity of trees, for example their tolerance to
cold in winter in cool and temperate zones.
 The quantity and quality of wood depend on the
division of cambial cells and the differentiation of
cambial derivatives.

24.  Cambial activity in trees is regulated by both
internal factors, such as plant hormones, and
environmental factors, such as, temperature,
rainfall and photoperiod.
 Temperature provides the appropriate physical
conditions for the growth and development of
trees in temperate and cool climates.
 Timing of cambial reactivation is controlled by
temperature, which influences both the quantity
and quality of wood.

25. INDUCTION OF CAMBIAL REACTIVATION BY
LOCALIZED HEATING
 During the period from late winter to early spring,
new cell plates are formed in the cambium and this
springtime phenomenon is referred to as cambial
reactivation.

26.  Studies failed to identify the factors that regulate the
timing of cambial reactivation in trees.
 Winter cambial dormancy in trees consists of two
stages, namely, the resting and the quiescent stages.
 During the first 2–4 weeks of dormancy, the cambium
is unable to produce new cells even when IAA is
supplied under favorable environmental conditions.
 This stage of dormancy, which is regulated by internal
factors, is referred to as the resting stage.
 After exposure to natural or artificial chilling, the
cambium gradually regains the ability to produce new
xylem cells in response to IAA under appropriate
environmental conditions.

27.  When fully responsive to IAA in this way, the
cambium is deemed to be in the quiescent stage of
dormancy, which is imposed by adverse external
factors.
 The transition from rest to quiescence involves
structural, histochemical and functional changes in
cambial cells.
 An increase in temperature might be a limiting
factor in the onset of cambial reactivation during
the quiescent dormancy of trees.
 Localized heating for 4 weeks induced cambial
reactivation that occurred earlier than natural
cambial reactivation.

28.  Two weeks of localized
heating of stems of the
deciduous conifer Larix
leptolepis failed to activate
the division of cambial cells,
while localized heating of
stems of C. japonica induced
cambial reactivation 6 days
after the start of heating, with
xylem differentiation starting
after heating for 14 or 21 days.

29.  Longer localized heating of the stems of
deciduous trees, as compared to those of
evergreen conifers, might be required for
conversion of cambium from a quiescent to an
active state.
 Increase in temperature of the stem might be a
direct trigger for cambial reactivation in trees.

30.  It has been reported that bud burst and the development
of new leaves are related to cambial reactivation and
xylem differentiation.
 Xylem differentiation in heated portions of stems started
only after bud flushing, suggesting that some factors from
expanding new leaves might be required for the
differentiation of xylem.

31.  In 55-year-old cambium, cambial reactivation and xylem
differentiation occurred earlier than in 80-year-old
cambium both under heated and under natural
conditions.
 In Larix , Pinus, Picea and Juniperus, the duration of
cambial activity and xylem differentiation differed between
adult and old trees even when the trees had been grown
under the same climatic conditions.

32.  Duration of cambial activity appears to differ between
adult and old trees.
 Cambial sensitivity to temperature might be related to
cambial age and the state of cambial dormancy in C.
japonica stems.
CHANGES IN LEVELS AND LOCALIZATION OF
STORAGE MATERIALS DURING CAMBIAL
ACTIVITY
 In temperate and cool zones, the low rates of
photosynthesis in late winter and early spring might
be expected to limit the supply of sucrose to stems.
 Under natural conditions, cambial reactivation in trees
occurs from late winter to early spring, when
photosynthesis is minimal or almost non-existent.

33.  Stored materials are crucial
for radial growth.
 Utilization of reserve
materials at various stages of
growth might provide clues to
a full understanding of the
growth and development of
trees.
 Not only starch but also
lipid droplets in the cambium
might be used as sources of
energy for cambial activity
and the initiation of xylem
differentiation in locally
heated stems of C. japonica.

34. CAMBIAL REACTIVATION UNDER NATURAL
CONDITIONS
 In Pinus leucodermis, the calculated threshold
minimum, mean and maximum daily temperatures
for wood formation were approximately 5.5, 8.2
and 11.5◦C, respectively.
 In Larix decidua, Pinus cembra and P. abies,
cambial activity and xylem differentiation occurred
above a certain threshold value of mean daily
temperature, which ranged from 5.6 to 8.5◦C.
 In Abies balsamea, L. decidua, P. cembra, P.
sylvestris, P. leucodermis, Pinus uncinata and P.
abies, the critical average temperature for onset of
cambial activity ranged between 8 and 9◦C.

35. COLD STABILITY OF MICROTUBULES AND ITS
RELATIONSHIP TO CAMBIAL ACTIVITY
 Structure and organelles of cambial cells exhibited
seasonal changes that might be related to adaptation
to changes in climatic conditions.
 Microtubules, a major component of the cytoskeleton,
play important roles in the division and differentiation
of cells.
 They are sensitive to temperature, and low
temperature tends to depolymerize or disassemble
microtubules in plant cells.
 Therefore, plant-science manuals generally suggest that
low temperatures are inappropriate for the
visualization of microtubules after chemical fixation.

36.  Immunofluorescence
microscopy reveals the
presence of
microtubules in
cambium, xylem cells
and phloem cells that
have been fixed at
room temperature.

37.  By contrast, low-temperature fixation (2–3◦C)
depolymerizes microtubules in fusiform and ray
cambial cells and in differentiating cells when the
cambium is active in Abies firma, A. sachalinensis
and L. leptolepis.
 Thus, low ambient temperatures above 0◦C,
namely, chilling temperatures, might be expected
to influence and induce the disassembly of
microtubules in cambium and cambial derivatives.

38.  In A. firma, it was noted that the depolymerization
of microtubules did not occur during low-
temperature fixation (2–3◦C).
 It is possible that, during cambial dormancy,
microtubules might be resistant to the normally
depolymerizing effect of low temperatures.
 Clearly, the stability during low-temperature
fixation of microtubules in cambial cells, xylem
cells and phloem cells differs between seasons of
dormant and active cambium.
 This phenomenon might be closely related to the
seasonal changes in the cold tolerance of trees
because microtubules play such important roles in
cell division and differentiation.

39. A SCHEMATIC DIAGRAM SHOWING THE ANNUAL PERIODS OF CAMBIAL
DORMANCY AND ACTIVITY AND THE EFFECTS OF AN INCREASE IN TEMPERATURE
FROM LATE WINTER TO EARLY SPRING ON WOOD FORMATION IN TREES.

40. CONCLUSION
 Localized or environmentally induced increase in
the temperature of the stem can directly induce the
breaking of cambial dormancy in trees but the
responses to such increases in temperature differ
among species and depend on stage of dormancy.
 Prominent decreases in the levels of starch and
lipid droplets in the cambium, from cambial
reactivation to the start of xylem differentiation,
indicate that starch and lipid droplets might be
utilized as sources of energy for cell division and the
biosynthesis of new cell walls in the cambium.

41.  Differences in the behavior of microtubules during low-
temperature fixation of active and dormant cambium
suggest that microtubules might act as sensors of a
change in growth conditions.
 Future climate change, with increases in temperature
from late winter to early spring, might induce earlier
cambial reactivation and xylem differentiation,
resulting in longer periods of cambial growth and
increased production of wood biomass.
 In addition, such increases in temperature might
promote the enzymatic conversion of starch to sugar
to supply the energy required for the biosynthesis of
new cell walls and for continuous cambial activity.

42.  By contrast, a sudden decrease in temperature after
the onset of cambial reactivation, such as a late
spring frost, when the cold tolerance of the
cambium is low might induce the depolymerization
of microtubules, with a consequent negative
impact on tree growth and development.
 Therefore, the effects of future climate change
from late winter to early spring might have some
positive impact on the production of wood
biomass, but we cannot exclude the possibility that
earlier onset of cambial activity might be
associated with increased risk of frost damage to
the cambium.

43. REFERENCES
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 Shahanara Begum, Satoshi Nakaba, Yusuke Yamagishi ; Regulation
of cambial activity in relation to environmental
conditions:Understanding the role of temperature in wood
formation of trees- Article in Physiologia Plantarum · June 2012-
 Barnett JR, Miller H (1994) The effect of applied heat on graft union
formation in dormant Picea sitchensis (Bong.) Carr. J Exp Bot 45:
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44. THANK YOU GOD