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.
A 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.
Temperatures above 70°F 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.
Examples of typical carrot root shapes here. (Biology web - Carrots are didcots)
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:
Is the hard outer layer on a root absorbing water from surrounding soil through
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
|In the US Department of Agriculture circular dated March
1950 are 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 indentationcof the collar, the nature of the surface, the shape of the base, and theckind 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 classification of a carrot:
Kingdom Plantae – Plants
Subkingdom Tracheobionta – Vascular plants
Superdivision Spermatophyta – Seed plants
Division Magnoliophyta – Flowering plants
Class Magnoliopsida – Dicotyledons
Family Apiaceae – Carrot family
Genus Daucus L. – wild carrot P
Species Daucus carota L. ssp. sativus- domestic carrot
(It is generally accepted that 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. In the parts of the plant which don’t photosynthesize, we can see their presence more easily.
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