The Main Parts and Functions of the Carrot Root
The roots of certain vegetable crops are important as food. Roots typically originate from the lower portion of a plant or cutting. They possess a root cap, have no nodes and never bear leaves or flowers directly. The principal functions of roots are to absorb nutrients and moisture, to anchor the plant in the soil, to furnish physical support for the stem, and to serve as food storage organs. The purpose of a root is to anchor the plant to the ground and to absorb water and nutrients diagrams below. Examples of typical carrot root shapes here. Botanical Classification here.
Plants have two different types of transport tissue: the Xylem (core) transports water and solutes from the roots to the leaves, and the Phloem (flesh) transports food from the leaves to the rest of the plant. Transpiration is the process by which water evaporates from the leaves, which results in more water being drawn up from the roots. The majority of the carotenoid content is contained in the Phloem (outer flesh).
Source Distribution of Caretenoids in Different Parts of the Carrot by V H Booth 1951, J. Sci. Food Agric., 2, August, 1951
The tap root system develops from the hypocotyl with secondary lateral roots branching from the xylem. Together, the hypocotyl and the tap root form the ‘Carrot Root'. At the center of the root is the light coloured and more woody xylem surrounded by the deep orange and sugar loaded phloem.
The periderm skin is composed of suberin and other waxy substances. Optimum root growth occurs at 60-70°F. Temperatures into the 50’s will affect the colour development and favour longer, more slender roots.
Factors affecting root shape and size - The shape and size of carrot roots are influenced by soil type, temperature etc. branching in carrot due to hereditary, and presence of under composted organic matter or injury to the cap root system or check in heavy soil at lower temperature. Roots are longer and slender at 13 to 20 0 C than at higher temperature. High temperature and irregular results in rough root surface.
Temperatures above 20°C will cause shorter, thicker roots with a stronger flavour, but less sugar. During flower initiation, the hypocotyl crown shrinks as carbohydrates and water content is shifted to support flower development and the overall root diameter becomes slender.
Management of plant spacing and density influences root size distribution within the crop. Carrot root shape at harvest is principally determined during the crop establishment phase. Factors that influence the rate of growth of the taproot during early plant development determine the length and shape of the root at maturity. The final length of the carrot appears to be determined during the early growth phase, with conditions promoting rapid taproot growth and initiation of secondary growth down the length of the root resulting in greater potential root length.
Summary of "Some factors affecting carrot root shape and size" R Thompson - Euphytica September 1969, Volume 18, Issue 2, pp 277–285
Measurements were made of the shape and size of roots of the carrot varieties Amsterdam Forcing and Autumn King. The roots changed during growth from a near conical to a more cylindrical shape. The change was especially rapid in the first half of the growing period. In both varieties, plant density influenced the change in shape with age.
Thus in young carrots, cylindricality was associated with high plant density, whereas in older carrots it was associated with low plant density. With at least the lower densities of Amsterdam Forcing the range in root length for a given range in root diameter increased at first, later becoming constant. For roots of a given age, increasing plant density was accompanied by a decrease in the range of root lengths for a given range in diameter. Relationships between root shape and certain biochemical constituents are discussed on the basis of data presented by Barnes (1936). It is concluded that plant density as well as age can influence carrot root shape so much as to make unsuitable a variety normally suited to a particular requirement.
Examples of typical carrot root shapes here. (Biology web - Carrots are dicots)
Right - Colour of prime marketable root (A) and foliage (B) of the Imperator variety of carrot. Cross sections of roots (C to E) show stages in the development of interior colour from poor (E) to fair (D) to good (C). Colour designations (11) as follows: Local colour on A, root 10F 10, petiole base 21 L5 and lighter; B foliage 23 L6; C, phloem 10 C 10, xylem 10 1 9: D phloem 9 K 10, xylem 9 K 8; E phloem 9 J 7, xylem 9 K 5. (Source - United States. Department of Agriculture. Descriptions of Types of Principal American Varieties of Orange-fleshed Carrots. By Roy Magruder. Vol. 361. Washington, D.C.: United States Department of Agriculture, 1940. Print. full copy here)
Why and how do carrots make sugar - Carrots make natural sugar to make energy for the plant to reproduce. A carrot is biennial and therefore when the root is left in the ground for a further year it produces a long stalk and a mass of flower and then seeds. All this needs energy.
Carrots send sugar to their storage organs (the root). This is easy to do as it is sent in a dissolved form and will therefore travel easily along conducting vessels. For storage purposes the sugar is converted into starch; being non-soluble it is convenient to store in this way. When the plant requires the energy in the form of sugar it uses an enzyme to do the conversion. The sweetness of carrots and related plants depends on the proportion of sugar still present.
This photo (below) is a good representative sample of carrots, used in the 2014 research study entitled - New insights into domestication of carrot from root transcriptome analyses (Rong et al.: New insights into domestication of carrot from root transcriptome analyses. BMC Genomics 2014 15:895