Chromoplast facts for kids
Chromoplasts are tiny parts inside plant cells called plastids. They are like small factories that make and store pigments. These pigments give plants their bright colors. Scientists believe chromoplasts, like other plastids such as chloroplasts, came from tiny living things called prokaryotes that lived inside early plant cells a long time ago.
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What Chromoplasts Do
Chromoplasts are found in many parts of plants. You can see them in fruits, flowers, roots, and even in old or stressed leaves. They are the reason these parts have their special colors. This color often comes from a lot of carotenoid pigments being made. For example, when a fruit ripens, its green chloroplasts often turn into colorful chromoplasts.
Chromoplasts usually appear in mature plant parts. Fruits and flowers are common places where they make carotenoids. But chromoplasts also help make other important things. These include sugars, starches, fats, scents, vitamins, and hormones. The genetic material (DNA) in chloroplasts and chromoplasts is almost the same.
Chromoplasts create and store pigments like orange carotene, yellow xanthophylls, and various red colors. So, their color depends on the pigments they hold. The main reason plants have chromoplasts is probably to attract pollinators. These are animals like bees that help plants reproduce. They also attract animals that eat colorful fruits. These animals then help disperse seeds to new places. Chromoplasts are also found in roots, like those of carrots and sweet potatoes. They help plants store large amounts of colorful compounds that don't dissolve in water.
When leaves change color in autumn, it's because the green chlorophyll disappears. This reveals the yellow and orange carotenoids that were already there. In this case, not much new carotenoid is made. This is a bit different from how fruits and flowers actively make new chromoplasts.
Some flowering plants have very few carotenoids. Their petals might still have plastids that look like chromoplasts. Other colors in plants, like purple, red, or blue, often come from pigments called Anthocyanins and flavonoids. These are found in the cell's water-filled sacs, called vacuoles.
Sometimes, the word "chromoplast" is used for any plastid that has color. This helps tell them apart from leucoplasts, which are plastids with no color. In this broader sense, chloroplasts (which are green) would be a type of chromoplast. But usually, "chromoplast" means plastids that have colors other than green.
How Chromoplasts Look and Are Grouped
Scientists can see chromoplasts using a light microscope. They group them into four main types based on what they see.
- The first type has a jelly-like inside (called stroma) with small colored bits.
- The second type has protein crystals and shapeless pigment bits.
- The third type has both protein and pigment crystals.
- The fourth type only contains crystals.
Using a more powerful electron microscope, scientists can see even more detail. They can spot tiny parts like globules, crystals, membranes, fibrils (small fibers), and tubules (small tubes). These tiny parts are not found in the mature plastids that chromoplasts came from.
Based on these tiny parts, chromoplasts are further divided into five main groups:
- Globular chromoplasts: These have round, ball-like structures. Mangoes have this type.
- Crystalline chromoplasts: These have crystal shapes. Carrots have these.
- Fibrillar chromoplasts: These have tiny fibers.
- Tubular chromoplasts: These have tiny tubes.
- Membranous chromoplasts: These have many layers of membranes.
Sometimes, it's hard to put a chromoplast into just one group. For example, Tomatoes have a lot of lycopene crystals inside membrane-like structures. This means they could fit into either the crystalline or membranous group.
How Chromoplasts Evolved
The colors made by Plastids can affect which pollinators visit a flower. Different colors attract different animals. For example:
- White flowers often attract beetles.
- Bees are usually drawn to violet and blue flowers.
- Butterflies often like warmer colors like yellow and orange. This shows how chromoplasts play a role in the plant's survival and reproduction.
Research on Chromoplasts
Chromoplasts are not studied as much as some other plant parts. But they are often looked at in research on the tomato plant (Solanum lycopersicum). The red color of a ripe tomato comes from a pigment called Lycopene. The yellow color of tomato flowers comes from xanthophylls like violaxanthin and neoxanthin.
Carotenoids are made in both chromoplasts and chloroplasts. In tomato flowers, genes like Psyl, Pds, Lcy-b, and Cyc-b control how carotenoids are made in chromoplasts. These genes, along with others, are responsible for making carotenoids in different plant parts. For instance, the Lcy-e gene is very active in leaves, leading to the production of a carotenoid called lutein.
Some tomato plants have white flowers because of a specific gene. These white flowers are not as good for farming. This is because they don't get pollinated as much. One study found that even white flowers still have chromoplasts. They just lack yellow pigment because a gene called CrtR-b2 is changed. This change stops the plant from making carotenoids properly.
Scientists don't fully understand how chromoplasts form at a tiny, molecular level. But using electron microscopes, they have seen parts of the change from a chloroplast to a chromoplast. This change starts with the inner membrane system of the chloroplast being rebuilt. The green parts (thylakoids and grana) break down. New membrane systems form in organized groups called thylakoid plexus. These new membranes are where carotenoid crystals are made. These new membranes don't come from the old thylakoids. Instead, they come from small sacs (vesicles) that form from the inner membrane of the plastid. The most obvious change is that the plant stops making things for photosynthetic activity, and it loses its green chlorophyll.
In oranges, the fruit changes color from green to yellow because carotenoids are made and chlorophyll disappears. The bright orange color you often see is sometimes added artificially. The natural color from chromoplasts is usually a light yellow-orange.
Valencia oranges (Citris sinensis L) are a type of orange grown a lot in Florida. In winter, they turn their best orange color. But in spring and summer, they can turn green again. For a long time, people thought chromoplasts were the final stage of a plastid. But in 1966, it was proven that chromoplasts can actually change back into chloroplasts. This is why Valencia oranges can turn green again.
Compare Plastids
- Plastids are a group of tiny parts in plant cells.
- Chloroplasts are green plastids that do photosynthesis.
- Chromoplasts are colorful plastids that store pigments.
- Lycopene: Makes tomatoes red.
- Capsanthin: Makes peppers red.
- β-Carotene: Makes carrots red.
- Xanthophyll: Makes things yellow.
- Anthocyanin: Makes things purple, red, blue, or black.
- Leucoplasts are colorless plastids.
- Amyloplast: Stores starch.
- Elaioplast: Stores fats.
- Proteinoplast: Stores proteins.
See also
In Spanish: Cromoplasto para niños
