Stem Flashcards
general stem functions
support and conduction (principle functions)
- also place leaves and flowers in favourable positions
- nutrient/water storage
- metabolism, including hormones and auxin
stems consists of
nodes and internodes
phytomere production
the apical meristem produces a succession of repeating units
phytomere consists of
- node with an attached leaf
- internode below
- axillary bud at the base of the internode
shoot
stem + leaves
shoot tip
- More complex organization than root
- Leaf primordia arise at the tip and develop into leaves
ie. exogenous origin - Bud primordia develop into axillary buds, ultimately become branches or lateral shoots
- No structure analogous to the root cap
- Leaf primordia overarch and enclose SAM for protection
SAM
-tunica corpus arrangement
tunica
the outermost layer(s) of cells (1-4 layers) at the tip
-layers are L1, L2, L3, L4
-divides anticlinally
-causes and increase in surface area at the tip without an increase in number of layers
(pushes derivatives to the side
anticlinally
in a plane perpendicular to the plant surface
-the newly formed walls are oriented at 90 degrees to surface or organ
corpus
- body of cells below the tunica
- divide anitclinally and periclinally
- outermost layer of the corpus tends to divide mostly periclinally
- often counted as the 3rd layer of the tunica
periclinally
in a plane parallel to the surface
-the newly formed walls are oriented parallel to the surface of the organ
tunica and corpus have their own initials
- tend to be found in the central zone -central mother cells
- cell division are infrequent in the central zone, anallogous to - quiescent zone
exogenous origin
leaf primordia arise at the tip and develop into leaves
derivates
adjacent to the central zone in the peripheral meristem
zone beneath the corpus is
the pith meristem
seedless vascular plants have a single …
apical initial eg. horsetails and ferns
most gymnosperms have a SAM with..
multiple initials but without a tunica-corpus arrangement
outer tunica produces the
protoderm
procambium and part of ground meristem comes from
peripheral meristem
rest of ground meristem comes from
pith meristem
peripheral meristem also produces
leaf and bud primordia
bud development
a) terminal and axillary buds. each bud has its own SAM, leaf, bud primordia
b) bud emergence. scales dropped; growing tips start to elongate
c) Nodes separated after internodal elongation. leaves fully developed
zonation
no zonation of shoot tip as in root tip
cell elongation
New leaf primordia and buds are produced close
together
Later, internodal regions behind SAM elongate
Internodal elongation produces an increase in length of the shoot ie. primary growth
Can be occurring simultaneously in several internodal regions
Part of the increase due to cell elongation
Growth also due to presence of intercalary meristems
stem elongation
- starts in primary meristems
- slows further back form the tip
- intercalary meristems are regions of parenchyma found between differentiated cells - elongation can continue to occur in mature regions
- parenchyma dedifferentiate and begin dividing
- division amy be anticlinal or periclinal
- mature primary tissues arise from same primary meristems as in roots
leaf trace
represents mature vascular tissue
leaf trace gap
is in a stem above the location where a bundle has entered a leaf
procambium in stems
typically leads to vascular tissue, but can also produce some ground tissue
Three main patterns of organization in stems
- vascular bundles throughout the ground tissue
- primary bundles are discrete and in a ring around the stem’s circumference
- vascular tissues in a continuous cylinder
Vascular bundles throughout the ground tissue
ie. a complex arrangement
Pattern found in most monocots eg. Zea (corn)
Called an atactostele
-no distinction of ground tissue between cortex and pith
Primary bundles are discrete and in a ring around the stem’s circumference
ie. delineates pith and cortex regions
Pattern found in most eudicots eg. Helianthus
(sunflower) and Ranunculus (buttercup)
Called a eustele
-vascular tissue in discrete bundles or fascicles
-interfascicular regions vary from wide to narrow
Vascular tissues in a continuous cylinder
ie. central pith with cortex outside
Pattern found in some eudicots eg. Tilia (basswood), magnoliids, conifers
-called siphonostele
-sometimes a very narrow region of ground tissue between each bundle is present early on
steles in roots
-monocot roots are a siphonostele- has a pith regions
-eudicot roots are protostele -solid core of vascular tissue
(also in stems of seedless, vascular plants)
stomata
more stomata on leaves than on stem
stem to leaf vascular connections
pattern reflects pattern of leaf arrangement
- at nodes, one or more vascular bundles diverge and enter a leaf attached at that node
- extensions called leaf traces
- leave a gap in the ring of stem bundles just above called a leaf trace gap
stem bundle and its associated leaf traces
sympodium
steles
sympodia may be interconnected or independent
- may also be branch traces entering an axillary bud
- must also be continuity b/w root and shoot
stem and leaf modifications
- some stems are modified and have specialized functions
- tendrils are modified for climbing
- may be of stem (grape) or leaf (pea) origin
- cladophylls (asparagus) and phyloodes (orchids) are fleshy, photosynthetic stems and leaves
- fleshy leaves may also stor water (agave)
- thorns are modified branches, originate in axils of leaves (hawthorn)
reproductive structures
- stolons
- rhizomes
- tubers
- bulbs
- corms
- spines
- prickles
- colorful leaves
- carnivorous leaves
- fleshy petioles
stolons
aboveground, horizontal stems (strawberry)
rhizomes
below ground horizontal stems (ginger)
tubers
stem tissue modified for storage (potato)
- arise at the tips of stolons or rhizomes
- eyes are buds
bulbs
large buds with a small conical stem and many fleshy leaves (onion)
-food stored in leaves
corms
are thickened, fleshy stems with a few small scaly leaves (water chestnut)
-food stored in stem tissue
enlarged above ground stem or leaf
area can also store nutrients
cactus
stems may also store water and be photosynthetic
spines
- usually hard, dry and non-photosynthetic
- sometimes softer and very numerous
- spines deter herbivory
- reduce water loss
prickles
on rose stems are epidermal or cortex outgrowths
-technically trichomes
fleshy petioles
-store nutrients and photosynthesize (celery)
colorful leaves
to attract pollinators
