Wednesday, September 4, 2013


Plastids are organelles that are unique to plants.  There are several different types with different functions.  Here is a quick visual overview of the types:

I won't go over the developmental stages of them (proplastid, etioplast), but we'll cover the other types.
These are what give a plant its green color because they are full of thylakoids busy doing photosynthesis.  They absorb all kinds of light except green and turn it into ATP.  Since green is the light reflected back, that's what color they look to us.
These pictures came out a little bit blurry, but they are taken from a water weed leaf slide we prepared ourselves in lab.  All the green dots everywhere are chloroplasts.

Inside a chloroplast:
  • thylakoids- where photosynthesis (light reaction) happens (the thylakoid is full of electron transport chains and ATP Synthase, same as in animals.  Click here for a post about the electron transport chain and ATP Synthase.)  Thylakoids are organized into:
    • grana - stacks of thylakoids
    • frets - intergranal thylakoids (in other words, thylakoids that are hanging out between the stacks)
  • stroma - spaces outside the thylakoids.  This is like the "cytosol" of the chloroplast.  The Calvin cycle (dark reactions) take place here.

These are like chloroplasts but aren't green.  They make and store pigments.  Here you can see the orange specks are chromoplasts from a carrot:

And some red ones from a tomato:

Leucoplast is a category of plastids which aren't pigmented.  Leuco means "white". They are storage for various types of organic molecules.  The types are amyloplasts, Elaioplasts, and Proteinoplasts, discussed below.

Amyloplasts store starch (food storage form of carbohydrates/ sugars in plants).  The tiny purple speckles in the middle of the picture are the amyloplasts which have starch crammed inside.  They are purple because they've been stained, otherwise we couldn't see them.

Elaioplasts/ oleoplasts
Elaioplasts store lipids. Here are some from an avocado:

Lastly, proteinoplasts store - you guessed it - protein.  I couldn't find a picture that I had confidence actually represented a proteinoplast rather than any of the other types of leucoplasts.  According to wikipedia, not much research has been done on proteinoplasts specifically, in the last 25 years.  Which would explain why I can't find pictures.  You can use your imagination. :)

Stay curious.

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