Herself’s Houston Garden

Plants grown in soils low in phosphates grow hairy roots in the search for nutrients. Now scientists have discovered the gene that turns on hairy roots and hope to use it to develop food crops that will grow in poor soils or with less fertilizer.

When crops such as barley and wheat are grown on soils containing small amounts of phosphate it is known that those plants with long hairs on their roots give higher yields than those with short hairs. Similarly, long-haired beans grown on the nutrient-poor tropical soils of Central America do much better than short haired varieties.

Root hairs burrow into the soil like tiny ‘mining machines’ releasing acids and other scouring chemicals that crack open rocky minerals releasing valuable nutrients, such as iron and phosphate, that are necessary for plant growth.

Now, for the first time, scientists have found the mechanism that controls the growth of these specialised nutrient-excavating cells. They discovered that a master regulatory gene called RSL4 acts like a switch; hair cells grow when the gene is turned on and growth stops when it is off. read more

More information:
A basic helix-loop-helix transcription factor controls cell growth and size in root hairs
Discovery of nutrient mining machine in plants

It is well known that some animal species use camouflage to hide from predators. Individuals that are able to blend in to their surroundings and avoid being eaten are able to survive longer, reproduce, and thus increase their fitness (pass along their genes to the next generation) compared to those who stand out more. This may seem like a good strategy, and fairly common in the animal kingdom, but who ever heard of a plant doing the same thing?

In plants, the use of coloration or pigmentation as a vital component of acquiring food (e.g., photosynthesis) or as a means of attracting pollinators (e.g., flowers) has been well studied. However, variation in pigmentation as a means of escaping predation has received little attention. In the December issue of the American Journal of Botany, Matthew Klooster from Harvard University and colleagues empirically investigated whether the dried bracts on a rare woodland plant, Monotropsis odorata, might serve a similar purpose as the stripes on a tiger or the grey coloration of the wings of the peppered moth, namely to hide.

“Monotropsis odorata is a fascinating plant species, as it relies exclusively upon mycorrhizal fungus, that associates with its roots, for all of the resources it needs to live,” notes Klooster. “Because this plant no longer requires photosynthetic pigmentation (i.e., green coloration) to produce its own energy, it is free to adopt a broader range of possibilities in coloration, much like fungi or animals.”

read more Rare woodland plant uses cryptic coloration to hide from predators

More information
Cryptic bracts facilitate herbivore avoidance in teh mycoheterotrophic plant Monotropsis odorata (Ericaceae) ( pdf )

American Journal of Botany article

When spider mites attack a bean plant, the plant responds by producing odours which attract predatory mites. These predatory mites then exterminate the spider mite population, thus acting as a type of ‘bodyguard’ for the plant. However, if the plant is simultaneously attacked by whiteflies, insects that are related to aphids, the plant becomes less attractive to the predatory mites and therefore more vulnerable to spider mites.

The research team studied the strength of the plant’s “cry for help” through a chemical analysis of the plant odour blend and found that one of the odour components (beta-ocimene) is produced in much lower quantities if the plant is not only attacked by spider mites, but also by whiteflies. The production of the odour decreases because of a lower expression rate of the plant gene that codes for a crucial enzyme in the production chain. When the researchers added ocimene to the odour of plants which were attacked by both species, the attraction of predatory mites was restored.

This recent breakthrough demonstrates that there are also herbivores that can interfere with a plant’s “cry for help”, possibly because the whiteflies attempt to interfere with the plant’s defence system. Spider mites also produce more offspring on a plant under attack by whiteflies. For a spider mite, there are therefore two reasons why a bean plant which is being attacked by whiteflies is better than a bean plant that is not being attacked: more offspring and fewer bodyguards. It is therefore no surprise that the researchers found that the spider mite preferred plants infested with whiteflies above plants without them.

Read more Whiteflies sabotage alarm system of plants in distress

More information:
Whiteflies interfere with indirect plant defense against spider mites in Lima bean