Lecture 19 – Plant Cell General Features and Plant Cytoskeleton

Q: What aspects of plant cell structure and function are conserved with animal cells?

Organelles, structures, metabolic processes, and genes.

Q: Why is there no cell migration in plants?

Plant cells are "glued together" by the cell wall.

Q: Approximately how many types of plant cells exist, and how does this compare to animal cells?

~50 types, which is fewer than animal cells (e.g., xylem, phloem, epidermal cells, mesophyll cells).

Q: Which five structures are unique to plant cells (not found in animal cells)?

Tonoplast, central vacuole, cell wall, chloroplast, and plasmodesmata.

Q: What does it mean for a cell to be totipotent?

It can become any other type of cell (e.g., stem cells in humans).

Q: How do differentiated plant cells demonstrate totipotency?

Some can de-differentiate into a callus (undifferentiated) cell, divide, and form a complete new plant.

Q: What is a protoplast?

A plant cell with the cell wall removed.

Q: How does totipotency make GMO plant creation possible?

A gene of interest is introduced into a single cell, and because of totipotency, an entire transgenic plant can be grown from it — with every cell expressing that gene.

Q: What is the canola GMO example from lecture?

~95% of canola is GMO for herbicide resistance, allowing farmers to spray fields to kill weeds while the crop survives.

Q: What was the early approach to making GMO plants?

A DNA particle gun (originally modified from a .22 caliber gun) shot DNA-coated pellets into plant cells. The modern method uses a puff of air instead.

Q: What is cytoplasmic streaming?

Movement that causes mixing in the cytoplasm; driven by active organelle movement (e.g., in root hairs).

Q: How do Golgi differ in plant cells vs. animal cells?

In plants, Golgi are called stacks (not networks), there can be hundreds per cell, they move dynamically, and they are always in contact with the ER.

Q: What happens at the TGN in plant Golgi stacks?

Active sorting of vesicles occurs at the trans-Golgi network (bottom of the stack).

Q: What is special about plant myosin XI?

It is the fastest myosin and takes 35 nm steps, matching the 35 nm turn of the actin filament helix — so it stays on top of the actin without rotating.

Q: How do chloroplasts respond to light intensity in leaf mesophyll cells?

In normal light, they orient perpendicular to the light direction (maximize absorption). In too much light, they orient parallel (to avoid damage).

Q: What wavelength of light triggers chloroplast movement?

Blue light. Chloroplasts are pulled away from the exposure area by actin filaments.

Q: What cytoskeletal elements do plant cells have and lack?

They have microtubules (MTs) and actin filaments (AFs/microfilaments), but no intermediate filaments.

Q: Why are there no dyneins in plant cells, and what compensates?

There are no dyneins; kinesins perform both (+) and (−) directed movement on microtubules.

Q: Why do plant cells lack centrioles and centrosomes?

Because higher plants have no flagellated or ciliated stage in their life cycle (pollen carries sperm instead).

Q: What are the four microtubule arrays found in plant cells?

Interphase cortical array (IC), pre-prophase band (P), mitotic spindle (MS), and phragmoplast (CP).