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.
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). A little more explanation of functions and tissue breakdown here.(St Louis University,Bioweb)
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)
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.)
The root normally comprises 6 elements:
The root cap
Conical covering of the tip of the root which covers the apical meristem (undifferentiated cells). It protects against scratches while moving through the soil and excretes a mucus like substance called mucigel that allows the root to move through the soil easily.
Is the hard outer layer on a root absorbing water from surrounding soil through
Produces root hairs
Also known as the Peel, or periderm - Roots take water from the capillary spaces between soil particles. This function is carried out by the young portions of the roots at the location of minimal cutinisation of the epidermis and at maximum surface area. This location is found in the root-hair zone just proximal from the growing root tip. Thus roots take in their water through very fine roots located at the drip-line of the plant's canopy.
These are small, microscopic hairs on the outside of the epidermis and serve to increase the surface area of the root. They only survive for only a few days
Is located below the epidermis. Makes up the bulk of the primary root. Main purpose is to store starches. The sugar and carotene are contained in the Cortex.
The Cortex is comprised of the phloem, or nutrient conducting tissue - phloem
conducts photosynthate from the leaves to the root tips. The metabolism of roots
growing in the dark of the soil is essentially dependent upon respiration. This
process requires carbohydrate or other organic molecules as fuel. It also
requires a supply of oxygen, which is why soil needs to drain well for good
This is the thin layer of cells in the center of the cortex surrounding the xylem and phloem . It forces minerals into the xylem and phloem
The Central Core comprised of xylem (a water conducting tissue, transporting water from root to leaf) All Roots contain xylem to conduct water from the soil up the plant and out through the leaves. These xylem tracheids and/or vessels are connected to others in an end-to-end design allowing soil water and minerals to be lifted up to the leaves. The evaporation of water from the leaves is the major pull of water through the xylem, but roots can also develop "root pressure" osmotically when the soil is well-watered and the plant has sufficient reserves.
The US Department of Agriculture circular dated March 1950 listed 389 names that have been applied to orange-fleshed carrot varieties or strains. This gave a thorough classification of all varieties of orange rooted carrots found in the US at the time.
On the basis of their general or outstanding characteristics these varieties or strains were classified in 9 major groups, as follows:
I, French Forcing; II, Scarlet Horn ; III, Oxheart ; IV, Chantenay ; V, Danvers ; VI, Imperator; VII, James' Intermediate; VIII, Long Orange; and IX, Nantes.
Type was determined mainly by root size and shape ; but other root characteristics, such as those of the flesh (phloem) and core (xylem), the shape and colour of the shoulder, the size and degree of indentation of the collar, the nature of the surface, the shape of the base, and the kind of top, were also taken into consideration. (Source -Synonymy of Orange-Fleshed Varieties of Carrots M F Babb 1950).
Right shows the longitudinal section of a carrot illustrating the terms used in the 1950 circular for varietal descriptions.
For information here is the full botanical classification of a carrot:
Kingdom Plantae – Plants; Subkingdom Tracheobionta – Vascular plants
Superdivision Spermatophyta – Seed plants; Division Magnoliophyta – Flowering plants
Class Magnoliopsida – Dicotyledons; Subclass Rosidae
Order Apiales; Family Apiaceae – Carrot family
Genus Daucus L. – wild carrot P; Species Daucus carota L. ssp. sativus- domestic carrot
(It is generally accepted that domesticated carrot is drawn from the wild variety)
Note - Some classifications show Umbelliferae rather than Apiaceae
Important Note - The chemical constituents of carrot are not there by chance, but perform a function. Many constituents of the orange carrot we now cultivate are also in the white root of the wild carrot, Queen Anne's lace, from which our carrot was developed. This is true of falcarinol, falcarindiol and myristicin. Carotene (present in small amounts in Queen Anne's lace) has been increased by centuries of selection. Volatile oils have been decreased in this process. Plant scientists must continue to monitor all known constituents nutritive and non-nutritive as new cultivars of the carrot are developed to keep our vegetables nutritious and safe. Plant breeding for the sake of high yields, appearance, and keeping quality will not be sufficient.
Carotenoid pigments provide red, yellow and orange colours and antioxidant protection to a wide variety of plants, animals, bacteria, and fungi. In plants, carotenoids play a protective role in photosynthesis by dissipating excess light energy absorbed by the photosynthetic mechanism.
What it means is that carotenoids are good antioxidant compounds which effectively prevent damage to DNA or other important parts of cells. This damage can be caused by ‘free radicals’ which are very reactive molecules generated through the normal living processes of a cell (the release or generation of energy).
In plants, the carotenoids protect the plant cells from damage caused by energy from the sun in the same way. Carotenoids are also a starting point for the construction of other useful compounds, so their function is not always protective. There are possibly more important parts of the plant containing carotenoids (eg the leaves) where they are less obvious because they are masked by the green colour of chlorophyll. We can see their presence more easily in the parts of the plant which don’t photosynthesize, .
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