Idioblasts

Idioblasts are specialized plants cells that are very different from the cells around them.

Most plant cells are grouped together with other, similar cells: leaf cells with leaf cells, root cells with root cells, and so on. Hidden within these normal groupings are cells called idioblasts.

Scientists believe that idioblasts are the precursors to many specialized cells, such as stomata, glands, and guard cells. When idioblast cells divide, they often create daughter cells different from themselves. These mutations have given rise to much of the diversity within the plant world. At the same time, many idioblasts have remained the same over time, providing important functions within a plant. According to Albert Paul Kausch, in his 1985 doctoral thesis, The development, physiology, and function of selected plant calcium oxalate crystal idioblasts, no one really knows how or why idioblasts form.

Most commonly, idioblasts are storage cells. But some idioblasts hold a defensive arsenal of poisons and pointy crystals! ​

Calcium oxalate needles shooting out from an idioblast - 600x magnification (Agong1) Public Domain

When botanists and scientists talk about idioblasts, they divide them into several groups, depending on function.

Storage idioblasts

Some idioblasts are simply storage cells. They may store pigment, food, waste products, water, resin, latex, oil, or tiny stones of silica (phytolith). Until recently, it was not understood why plants contained silica. Then, some scientists tried growing plants in soil without any silica. Many of these plants flopped over. Mystery solved. Sort of. Then, another group of scientists, led by Fergus P. Massey, proposed that plants evolved to contain silica for more than just structural support. They claim that plants absorb these minerals as a defense mechanism. Massey and his team point out that silica in plants tends to wear down the teeth of those who eat them. There is debate about the truth behind this assumption. You decide.

Idioblasts as manufacturing centers

Other idioblasts do more than just store materials. Some idioblasts actually manufacture important compounds. For example, avocado skins have idioblasts with antifungal properties. Other idioblasts produce mucilage carbohydrates (mucus cells) that store water. Other idioblasts, called phenolic cells produce and store carbolic acid to be used as defensive weapons.

Idioblasts as weapons

While we consider herbivores to be mostly harmless, plants do not share that view. Rooted to one location, and without claws or fangs, plants have to get creative when it comes to defending themselves against grazers and other plant eaters. This is where idioblasts get really interesting. Some idioblasts contain biforine cells. Biforine means having two doors. [Isn’t that a great word?] These cells are oval-shaped with openings at each end. When something (or someone) bites the plant, breaking the cell, crystals of calcium oxalate shoot out, poisoning or irritating the attacker! These oxalates are produced in the vacuoles of the idioblasts. Oxalates are toxic to the plant, too, but the plant protects itself by binding the material up in crystals. These crystals come in many shapes. They may look like a grain of sand, a pencil (styloid), a needle (raphide), or prismatic (isodiametric). Bundles of raphides or prismatics are called a druse.

Plants that use these weapons

Many plant families rely on druses stored in idioblasts for protection. These families include:

• Aeonium - succulents
• Allium - onion, garlic, leeks, chives, and scallions
• Morus - mulberries
• Phaseolus - beans
• Prunus (stone fruits) - plums, peaches, nectarines, cherries, apricots, and almonds
• Rosa - roses
• Vitis - grapes

Botanists believe that plants also use these calcium oxalate-filled idioblasts to provide structure to the plant, and as a way to store calcium.

This information may not help your grow brighter flowers or more delicious tomatoes, but your mind needs to grow, too! And who can resist a word like idioblast?