Flashcards in Processes of Plant Development L1 Deck (49)
What do plant embryos consist of?
Cotyledons (The seed leaves)
Shoot Apical Meristem which is separated from a:
Root Apical Meristem by a short stem.
Hypocotyl (Figure 1).
Explain the two types of Arresting cells
The arresting cells also fall into two types: (1) those that promptly expand and differentiate.
(2) those for which arrest is a temporary phase. These occupy fixed positions, and resume cell division again later to build additional structures: branch roots, branch shoots, and extra girth.
Where is the size of a Apical Meristem?
Small: approx 100 - 250um
What is a Apical Meristem?
Dome of dividing cells at the very tip of every shoot or root
What does the root and shoot of a Apical meristem consist of?
Root and shoot consist of a central group of cells
-function: Organisational and outer layers of cells dividing rapidly to generate new
Where is the distinction of Apical meristem marked?
The distinction is more marked in roots, where the central cells are called a quiescent center.
What do the Meristematic cells form?
The meristematic cells form 2 bowl shaped layers:
-The root initials
What are Angiosperm shoots?
The central zone grades off less distinctly into the meristematic regions.
Why are zonations much easy to see in gymnosperms?
The zonation is much easier to see in gymnosperm shoot apical meristems. This is because the central mother cells will divide more slowly than their angiosperm counter parts
Isolated SAMs and RAMs can be cultured, plants and roots on nutrient media. What does this show?
This shows their independence to the rest of the plant, meaning they are able to self-contain as a developmental unit.
When moving back from the apex, what emerges?
the patterns of mitotic arrest emerge.
When the patterns of mitotic arrest emerge, what is this different from?
This is different from qc and cz = cycling slowly: further back, cells are rapidly or not cycling.
In relation to a root apical meristem and a shoot apical meristem.
Why do cells which continue to divide show up?
Cells which continue to divide show up because they are smaller than other cells
What do roots show?
Roots show a clear and simple sequence of overlapping zones:
-Apical zone of cell elongation
-Tissue more basal, a separate zone of differentiation of root hairs
-Casparian strip as well as xylem and phloem
What makes development more complicated up in shoot?
When it comes to leaf shape and size, this is generated by a sequence of meristems, which are each independently controlled
During morphogeneis, a not yet fully formed lead is called a?
Explain phase 1 in leaf morphogenesis?
Accelerated cell division and expansion, some few cell layers under the surface of the flanks of the apical dome heaves up a bump or buttress, the position of which is determined only by the 2 nearest primordia (Inhibitory), so that the leaves arise in a constant arrangement
Older leaves, a pattern of leaf position/ arrangement known as phyllotaxis
What does phase 1 of leaf morphogenesis determine?
Explain phase 2: The apical meristem of the leaf
The positive and negative random divisions shown on phase one stop and is taken over by growth by a cell, or a small number of cells, this is just under the outermost layer.
The proximal (Back) cells stop dividing however the distal (Front) cells keep dividing and the bump or buttress will grow to form a peg, this will expand to become the mid-rib.
Cells of the apical meristem of the leaf then crease to divide and vacuolate before the leaf is 1mm long in dicots, 0.3mm in gymnosperms and monocots
What does phase two determine?
Phase two determines LF length
Explain phase 3: The marginal meristem
A stripe of cells down the sides of the peg as well as the extending 4 cells into it re-commence active cell division.
The accumulated cells form 2 wings laterally
Cell division concentrated along the margin of the growing curved plate which will later expand to become the leaf blade or lamina.
Explain phase 4: Plate enlargment
The plate is enlarged by a phase of anticlinal (add area) divisions scattered throughout.
Anticlinal: Divisions add to the area
Periclinal: divisions add to the thickness
What does phases 3 and 4 determine?
Phases 3 and 4 determine LF width
Explain phase 5: The plate meristem
A sudden wave of periclinal divisions from the tip to the base will generate the final 7 to 10 cell thickness
What does phase 5 determine?
This phase determines LF thickness
How are different leaf shapes determined?
This is achieved by restricting the duration and/or distribution of individual phases
Conifer needles are generated by a similar sequence except the activity of the marginal meristem is very limited.
The differences between species are genetically determined, however phases 4 and 5 can be under environmental control for production of specific features.
What can counter predation include?
Counter predation can include fenestrations in leaf, for example nettles.
What follows cell division phase?
Cell division phase is followed by a phase of cell expansion as well as differentiation. The spongy mesophyll cells stop expanding earlier than other cells and therefore get ripped apart, this gives rise to larger intercellular spaces.
What happens when the LF tip cell expansion stops first?
In the LF tip cell expansion stops first, this is then passing as a wave back down the petiole. If there is one, the plants entire development is very much later than the rest of the leaf.