Root stem

transition
KARUN. A
1st MSC BOTANY
SNC KOLLAM
ORIGIN OF STEM

 Embryo has an axis called Hypocotyl .

 It has an :
Upper – Shoot primodium & one or more Cotyledons
Lower – Root primodium & Root cap
 Embryonic root – Radicle
 Embryonic shoot – Plumule
 Shoot arises from a region above the cotyledon called Epicotyl .
ROOT-STEM TRANSITION
 Root and stem makes a continuous structure called axis of the plant.
Vascular bundles are continues from root to stem.
 Stem possess collateral bundles with endarch xylem,
Root possess radial bundles with exarch xylem.
 The change of vascular structures from one type to another by
twisting and inversion of vascular strands is called vascular transition.
The region where such changes occur is called transition region .
 The epidermis, cortex, endodermis, pericycle, secondary vascular
tissues are also continuous.
 Only primary vascular tissues undergoes change in position and
orientation.
 Usually transition zone occurs at the basal, middle or top portion of
hypocotyl.
 Varies form few millimeters to several centimeters.
TYPES
Transitions are of four types :

1. Type A ( Fumaria type)

2. Type B (Cucurbita type)
3. Type C (Lathyrus type)
4. Type D (Anemarrhena type)
TYPE A (Fumaria Type Root-Stem Transition)
 Occurs in Mirabilis, Fumaria, Dipsacus
 Xylem strand of root divides by radial division into two branches.
 As these branches pass upwards, they swing in lateral direction.
 One band swings towards left and other towards right.
 These branches joins the phloem strand.
 The phloem strands do not change their position and
orientation.Remains continuous from root to stem.
 Number of primary bundles formed in stem Is equal to number of
phloem strands in root.
TYPE B (Cucurbita Type Root-Stem Transition)
 Seen in Cucurbita, Phaseolus, Acer
 The strands of both xylem and phloem divides.
 Xylem and phloem strands fork into two branches.
 The xylem swings and joins with phloem strand.
 Xylem becomes inverted and phloem does not change its orientation.
 Number of vascular bundles in stem becomes double the number of
phloem strands in root.
 Most common type of transition.
TYPE C (Lathyrus Type Root-Stem Transition)
 Seen in Medicago, Lathyrus
 Xylem strands do not fork, they continue their direct course into the
stem.
 Xylem strands twists 180°
 The phloem strands divides and the resulting halves swing in lateral
direction to the xylem postion and they fuses together.
 Phloem strands joins with xylem
 Number of vascular bundles in stem equals the number of phloem
strands in root.
TYPE D (Anemarrhena Type Root-Stem
Transition)
 Seen in few monocots such as Anemarrhena.
 In this type, half of the xylem strands fork .
 The branches swings in lateral direction to join other undivided strand
of xylem.
 The xylem strand becomes inverted.
 The phloem strands do not divide, but becomes united in pair.
 These united phloem strands unites with the triple strands of xylem.
 A single bundle of 2 phloem and 3 xylem strands are formed.
 Number of vascular bundles in stem will be half the number of
vascular strands in root.
TRANSFER
CELLS
 TRANSFER CELLS
 Transfer cells are specialized parenchyma cells containing cell
wall ingrowths, which often greatly increase the surface area of
the plasma membrane.
 Develops during late stages of cell maturation.
 It plays an important role in transfer of solutes over short
distances (Gunning 1977) .
 They are deposited on primary walls, hence considered as
specialized form of secondary wall (Pate & Gunning 1972) .
 Their presence is correlated with existence of intensive solute
fluxes (either uptake or secretion across plasma membrane).
 Actively involved in solute transport.
 Transfer cells are sites of membrane transport of sucrose to and
from the seed apoplast.
 The transport of sucrose across the membrane involves a proton-
sucrose cotransport mechanism (McDonald et al., 1996a, b).
 Transfer cells can also be induced to form by external stimuli,
such as by nematode infection (Sharma and Tiagi, 1989; Dorhout
et al., 1993), in a plant that does not normally develop such cells.
TYPES OF WALL INGROWTHS
Reticulate type
Reticulate-type wall ingrowths originate as small, randomly
distributed papillae from the underlying wall. The papillae then branch
and fuse laterally to form a complex labyrinth of variable morphology.
Flange type
Flange-type ingrowths arise as curvilinear, rib-shaped
projections that are in contact with the underlying wall along their
length.

Some transfer cells exhibit both reticulate and flage like wall ingrowths.
Some others have wall ingrowths that fit neither category.
Reticulate wall ingrowths

Flange wall ingrowths

OCCURRENCE
Occurs in wide range of locations in the plant body including :
• Xylem and phloem
• Veins of cotyledons
• Foliage leaves of many herbaceous eudicots
• At nodes of both eudicots and monocots
• Various reproductive tissues ( placentae, embryosac, aleurone
cells,
endosperm etc..)
• In root nodules
• In glandular structures
 THANK
YOU