Root
In response to the concentration of nutrients, roots also synthesise cytokinin, which acts as a signal as to how fast the shoots can grow.
This system can be extremely complex and is dependent upon multiple factors such as the species of the plant itself, the composition of the soil and the availability of nutrients.
[10] Root architecture plays the important role of providing a secure supply of nutrients and water as well as anchorage and support.
[13] Extrinsic factors affecting root architecture include gravity, light exposure, water and oxygen, as well as the availability or lack of nitrogen, phosphorus, sulphur, aluminium and sodium chloride.
In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root.
As a result, tissues beyond the secondary phloem including the epidermis and cortex, in many cases tend to be pushed outward and are eventually "sloughed off" (shed).
[15] The suberin thickenings functions by providing a physical barrier, protection against pathogens and by preventing water loss from the surrounding tissues.
[citation needed] The xylem vessels are dead at maturity (in some) but are responsible for most water transport through the vascular tissue in stems and roots.
Tree roots usually grow to three times the diameter of the branch spread, only half of which lie underneath the trunk and canopy.
[24] Different types of roots such as primary, seminal, lateral and crown are maintained at different gravitropic setpoint angles i.e. the direction in which they grow.
Recent research show that root angle in cereal crops such as barley and wheat is regulated by a novel gene called Enhanced Gravitropism 1 (EGT1).
[25] Research indicates that plant roots growing in search of productive nutrition can sense and avoid soil compaction through diffusion of the gas ethylene.
[27] Research instead found that shoot localized PhyA is the phytochrome responsible for causing these architectural changes of the lateral root.
Research has also found that phytochrome completes these architectural changes through the manipulation of auxin distribution in the root of the plant.
In an attempt to discover the role that phytochrome plays in lateral root development, Salisbury et al. (2007) worked with Arabidopsis thaliana grown on agar plates.
To do this, Salisbury et al. used GFP fluorescence along with other forms of both macro and microscopic imagery to observe any changes various mutations caused.
To do this, they took Arabidopsis plants, grew them in agar gel, and exposed the roots and shoots to separate sources of light.
To identify the function of specific photoreceptors, proteins, genes, and hormones, they utilized various Arabidopsis knockout mutants and observed the resulting changes in lateral roots architecture.
The majority of roots on most plants are however found relatively close to the surface where nutrient availability and aeration are more favourable for growth.
The fossil record of roots—or rather, infilled voids where roots rotted after death—spans back to the late Silurian, about 430 million years ago.
Studies of Arabidopsis in the 1990s showed negative phototropism and inhibition of the elongation of root hairs in light sensed by phyB.
Owing to the high energy required to fix nitrogen from the atmosphere, the bacteria take carbon compounds from the plant to fuel the process.
Needs vary by plant species, but in temperate regions cool temperatures may limit root systems.
Researchers have found that plants like cotton develop wider and shorter taproots in cooler temperatures.
Perennial grasses that grow wild in rangelands contribute organic matter to the soil when their old roots decay after attacks by beneficial fungi, protozoa, bacteria, insects and worms release nutrients.
[47] Researchers found that partial deficiencies of K or P did not change the fatty acid composition of phosphatidyl choline in Brassica napus L. plants.
Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish.
Specialized bald cypress roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art.
Hundreds of millions of plants are propagated via cuttings annually including chrysanthemum, poinsettia, carnation, ornamental shrubs and many houseplants.
