Chapter 25 Flashcards
The shoot
Stem and it’s leaves above ground, initiated during the development of embryo plumule
Plumule: epicotyl, young leaves, apical meristem
Provide support and conduction
Shoot apex vs root apex
Includes apical meristem together with the subapical region bearing young leaf primordia. Produces leaves, axillary buds (Lateral shoots)
Root apex produces no lateral organs
Apical meristem
The only part of the shoot lying distal or above the youngest leaf primordium.
Adds cells to the primary plant body, continuously produces leaf primordia and bud primordia this process is called phytomeres
Leaf primordia vs bud primordia
Leaf primordia develops into leaves
Bud primordia develops into Lateral shoots
Tunica-Corpus
Tunics- the outermost layer of cells that divide anticlinically (perpenducular to apical surface), surface growth without increasing cell layers on meristem
Corpus- body of cells that lie beneath tunica layers, add bulk to developing shoot, add cells by dividing periclinally (parallel to apical surface)
Eudicot apices layers (3)
Two tunica layers and one initial layer of the corpus
L1 outermost, divides anticlinically or periclinally SOMETIMES
L2 Mid
L3 innermost
Central Zone
The corpus and the portions of the tunica layers overlying the corpus, corresponds to the promeristem of the shoot apical meristem
Beneath is the pith meristem
Mitotically inactive
Peripheral zone
Surrounds central zone, originates partly from Tunica layers L1, L2, and corpus
Mitotically active (cell division)
Zones and Primary meristems
The protoderm always originates from the outer most layer (L1)
The procambium and part of the ground meristem derived from the peripheral meristem
The rest of the ground meristem is formed by the pith meristem
Intercalary meristem
A localized meristematic region in the elongating internode
Tissue maturation
Protoderm becomes epidermis, procambium becomes primary vascular tissues, and ground meristem becomes ground tissue
Interfascicular regions
Parenchyma regions that interconnect the cortex and the pith
Herbaceous
The stems of many eudicots undergo little or no secondary growth, nonwoody
Closed/open vascular bundles
Closed vascular bundles are usually entirely surrounded by a sheath composed of Sclerenchyma cells
Vascular bundles that do give rise to a cambium are said to be open
Leaf traces
The extension from the vascular system in the stem toward the leaves
A single leaf may have one or more leaf traces connecting its vascular system in the stem
Leaf trace gaps
The gaps of ground tissue in vascular cylinder above the level where leaf traces diverge toward leaves
Sympodium
A stem bundle and it’s associated leaf traces
Some or all of the sympodia are interconnected
OR
All the sympodia are independent units of the vascular system
Phyllotaxis or phallotaxy
The arrangement of leaves on a stem
The most common type of phyllotaxis is spiral, or helical
Types of phyllotaxis
Distichous: plants with a single leaf at each node
Opposite: plants with pairs of leaves at each node
Decussate: each successive pair of leaves at a right
Whorled: three or more leaves at each node
Initiation of leaves hypothesis’s
First available space: when sufficient width and distance front the apex is attained
Inhibitory field: preexisting leaf primordia inhibit the formation of new ones in their immediate vicinity
Biophysical forces: a leaf primordium is initiated when a portion of the tunica surface bulges or buckles
Auxin: the plant hormone that initiates primordium, generates by L1 layer
Sessile
Leaves without petiole, ex. Corn/Grass
Plant water requirements
Mesophytes: plants that require am environment that is neither too wet nor too dry
Hydrophytes: plants that require a large supply of water or grow wholly or partly submerged in water
Xerophytes: plants that are adapted to arid habitats
Stomata arrangement
Submerged hydrophytes lack stomata
Xerophytes contain a greater number of stomata than other
Most angiosperms the stomata scatter
Most monocots, the stomata are arranged in rows parallel with the long axis of the leaf
Mesophyll
The ground tissue of the leaf, large number of intercellular spaces and chloroplasts, stomata
Mesophyll parenchyma
Palisade parenchyma: columnar tissue, long and right angle to the epidermis, 2-4 times greater than spongy surface, upper side
Spongy parenchyma: irregular in shape, lower side
Venation
Netted venation: reticulate venation, Veins arranged in a branching pattern, with success of the smaller veins branching from somewhat larger veins
Parallel venation: striate venation, almost equal in size or may vary in size with larger veins alternating with smaller ones
Xylem: upper side
Phloem: lower side
Minor veins: embedded in mesophyll tissue, collect photosynthases
Major veins: large veins within leaf rib, export photosynthases
Bundle sheath extensions
They connect bundle sheaths to the upper or lower epidermis, by offering mechanical support to the leaf, some conduct water from the xylem to epidermis
C3 vs C4 grasses
C4: The mesophyll cells and bundle sheath cells typically form to concentric layers around the vascular bundles (Kranz anatomy), there are very large parenchyma cells that contain large chloroplasts, export photosynthases rapidly, 2-4 mesophyll cells intervene between laterally adjacent bundle sheaths
C3: The mesophyll cells and bundle sheath cells are not concentrically arranged. They consist of small chloroplast and cells appear to be empty and clear, unless thick walled sheath called the mestome sheath, more than 4 mesophyll cells intervene
Founder cells
The group of cells that span the 3 layers of meristem—L1, L2, L3
Found her cells divide forming a ball just called the leaf buttress, each buttress develops into a leaf primordium, next a band of cells form the blade called marginal meristems or marginal blastozones, Lastly the central region of the primordium differentiate into the midrib or rachis
Light and leaf development
Sun leaves are smaller and thicker than shade leaves that develop under low light intensity’s
The thickness of sun leaves is due to greater development of Palisade parenchyma, There also more extensive vascularly and the walls of epidermal cells are thicker
Sun and shade leaves also occurred and shrubs and in herbaceous plants
Abscission zone
Separation layer: relatively short cells with poorly developed for thickening that make it structurally weak, enzymes break down cell walls in the separation layer
Protective layer: heavily suberized cells is formed, further isolating the leaves from the main body of the plant before the leaf drops.
Leaf scar: After the leaf falls, the protective layer is left with is
Transition Region
Where changes take place on the type of structure found in the route to that found in the shoot
Initiated during the appearance of the procambium system in the embryo and differentiates procambium tissues in the seedling
Homeotic mutations
Wrong organ in the wrong place
Homeotic genes
Genes affecting floral organ identity
MADS box genes: control species of development
ABCDE model
B: loss of function results in the formation of Sepas instead of petals in the second world and of carpools instead of stamens in the third whorl
C: encoded by AG, loss results in the formation of petals instead of stamens in the third whorl and loss of carpels with additional sepals and petals
D: Arabidopsis, discovered and petunia this (STK) gene is involved in all of your development and is required for the disposal of seed in the true flowers
E: SEP genes mediate interactions between the organ identity proteins
