radish

The plant family of Cruciferae contains many important vegetables of economic importance. Raphanus
sativus L. is originally from Europe and Asia. It grows in temperate climates at altitudes between 190 and
1240 m. It is 30–90 cm high and its roots are thick and of various sizes, forms, and colors (see Fig. 1).
They are edible with a pungent taste. Salted radish roots (Takuan), which are consumed in the amount of
about 500,000 tons/year in Japan, are essentially one of the traditional Japanese foods. The salted radish
roots have a characteristic yellow color, which generates during storage.
This specie is used popularly to treat liver and respiratory illnesses[1]. The antibiotic activity of its
extracts and its time persistence validates its effectiveness in microbial sickness as reported in traditional
medicine. The root’s juice showed antimicrobial activity against Bacillus subtilis, Pseudomonas
aeruginosa, and Salmonella thyphosa. The ethanolic and aqueous extracts showed activity against
Streptococcus mutans and Candida albicans. Aqueous extract of the whole plant presents activity against
Sarcinia lutea and Staphylococcus epidermidis[2]. Aqueous extract of the leaves showed antiviral effect
against influenza virus. Aqueous extract of the roots showed antimutagenic activity against Salmonella
typhimurium TA98 and TA100. In this review, the metabolites produced by R. sativus are presented
according to structural classes. (See also Tables 1 through 10 at the end of this paper.)

Alkaloids and Nitrogen Compounds
Alkaloid and nitrogen compounds present in the roots were pyrrolidine, phenethylamine, Nmethylphenethylamine, 1,2´-pyrrolidin-tion-3-il-3-acid-carboxilic-1,2,3,4-tetrahydro-β-carboline, and
sinapine[3,4,5]. Cytokinin (6-benzylamino-9-glucosylpurine) is a major metabolite of 6-
benzylaminopurine (6-BAP) in the root radish. A minor metabolite of 6-BAP from radish has been
identified as 6-benzylamino-3-β-D-glucopyranosylpurine[6]. Total amino acids were 0.5% of dry wt;
with proline (0.5%) as the major constituent, methionine and cystine were present in traces (0.02%).
Diamines as diaminotoluene (2,4-D), 4,4´-methylenedianiline (4,4-D), and 1,6-hexanediamine (1,6-D)
were isolated in the period of germination of young radish seeds. Production of thiamine is higher during
germination radishes[7].
Total protein was 6.5%[8]. Two chitinases, designated RRC-A and RRC-B, were isolated from radish
roots. Both compounds had a molecular weight of 25 kDa[9]. N-Bromosuccinimide and di-Etpyrocarbonate inhibited the activities of both chitinases.
Arabinogalactan proteins (AGPs) were isolated from primary and mature roots of the radish. These
were composed mainly of L-arabinose and D-galactose. Structures of the carbohydrate moieties of the root
were essentially similar to those isolated from seeds and mature leaves in that they consisted of
consecutive (1→3)-linked β-D-galactosyl backbone chains having side chains (1→6)-linked β-Dgalactosyl residues, to which α-L-arabinofuranosyl residues were attached in the outer regions. One
prominent feature of the primary root AGPs was that they contained appreciable amounts of L-fucose[10].

Two L-arabino-D-galactan–contained glycoproteins were isolated from the saline extract of mature
radish leaves; both contained L-arabinose, D-galactose, L-fucose-4-O-methyl-D-glucuronic acid, and Dglucuronic acid residues. Degradation of the glycoconjugates showed that a large proportion of the
polysaccharide chains is conjugated with the polypeptide backbone through a 3-O-D-galactosylserine
linkage[11].
Arabino-3,6-galactan associated with a hydroxyproline-rich protein portion and carried a unique
sugar residue, α-L-fucopyranosyl-(1-2)-α-L-arabinofuranosyl[12].
Stigma glycoproteins heritable with S-alleles (S-glycoproteins) were detected in R. sativus. Two main
glycoproteins appeared on the SDS-gel electrophoretic pattern. Their molecular weights were established
to be 15,000 and 100,000 Da. The carbohydrate fraction of the glycoprotein consisted of arabinose 17.3%,
galactose 19.1%, xylose 8.1%, mannose 5.4%, glucose 23.7%, and rhamnose or fucose 26.4%. In the
stigma surface diffusate of R. sativus, the content of protein was established to be 16% and that of
carbohydrate was 11%[13].
The R. sativus acanthiformis showed two ferredoxin isoproteins indicating that plants have multiple
genes for ferredoxin. The relative abundance of the isoproteins varied with leaf stage[14]. In the
isoprotein isolated from roots of the radish, the amino acid composition and N-terminal sequence were
different from those of radish leaf ferredoxin.
Polypeptides RCA1, RCA2, and RCA3 were purified from seeds of R. sativus. Deduced amino acid
sequences of RCA1, RCA2, and RCA3 have agreement with average molecular masses from electrospray
mass spectrometry of 4537, 4543, and 4532 kDa, respectively. The only sites for serine phosphorylation
are near or at the C terminal and hence adjacent to the sites of proteolytic precursor cleavage[15].
Cysteine-rich peptides (Rs-AFP1 and Rs-AFP2) isolated from R. sativus showed peptides 6, 7, 8, and
9 comprising the region from cysteine 27 to cysteine 47[16]. Protein AFP1 isolated from radish showed
peptide fragments (6-mer, 9-mer, 12-mer, and 15-mer)[17].
Proteins RAP-1 and RAP-2 were isolated from Korean radish seeds. The molecular mass of the two
purified was established to be 6.1 kDa (RAP-1) and 6.2 kDa (RAP-2) by SDS-PAGE and 5.8 kDa (RAP1) and 6.2kDa (RP-2) by gel filtration chromatography[17].

Enzymes
A number of enzymes are present in both the cytoplasm and the cell wall, and in some cases it has been
shown that the cell wall isozymes differ from those of the cytoplasmic[19]. When radish seedlings are
grown in the dark, β-fructosidase (βF) first accumulates in the cytoplasm, then slowly increases in the cell
wall. Charge heterogeneity of cytoplasmic enzymes resides in the polypeptides, while the formation of the
basic cell wall occurs as a result of post-translational modifications that can be inhibited by
tunicamycin[20].
Cysteine synthase (EC 4.2.99.8) was purified to near homogeneity (275-fold) in 11.5% yield from
mature roots. It was relatively stable, retaining most of its activity in standing for several days at room
temperature[21].
A basic β-galactosidase (β-Galase) has been purified from imbibed radish. This enzyme, consisting of
a single polypeptide with an apparent molecular mass of 45 kDa and pI values of 8.6 to 8.8, was
maximally active at pH 4.0 on p-nitrophenyl β-D-galactoside and β-1,3-linked galactobiose. Radish seed
and leaf arabino-3,6-galactan-proteins were resistant to the β-Galase[22]. β-Amylase[23], together with
peroxidase c or paraperoxidase[24], which is an isoenzyme, were also isolated from Japanese radish roots.

A hydroxycinnamoyltransferase (EC 2.3.1.-), which catalyzes in vivo the formation of 1,2-di-Osinapoyl-β-D-glucose, was isolated from the radish. Cotyledons exhibited activities of 1-O-acyl-glucose–
dependent acyltransferases, 1-sinapoyl-glucose:L-malate sinapoyltransferase (SMT), and 1-
(hydroxycinnamoyl)-glucose:1-(hydroxycinnamoyl)glucose-hydroxyl cinnamoyl-transferase (CGT),
showing contrary developments depending on light conditions. Light-grown seedlings showed high Lmalate sinapoyltransferase and low 1-(hydroxycinnamoyl)glucose-hydroxyl cinnamoyl-transferase
activities, while dark-grown seedlings showed low L-malate sinapoyltransferase and high 1-
(hydroxycinnamoyl)glucose-hydroxyl cinnamoyl-transferase activities[25].
Catalase and glutathione reductase activities increased considerably in the root and leaves after 24-h
exposure to cadmium, indicating a direct correlation with Cd accumulation. PAGE enzyme activity
staining revealed several superoxide dismutase isoenzymes in leaves. The main response may be via
activation of ascorbate-glutathione cycle for removal of hydrogen peroxide or to ensure availability of
glutathione for synthesis of Cd-binding proteins[26].
A γ-glutamyl transpeptidase was found. It catalyzed the release of CySH-Gly from glutathione, the
release of alanine from γ-glu-Ala, and the formation of γ-glutamyl dipeptides. A dipeptide formed from Smethylcysteine and glutathione or γ-glu-Ala was characterized as γ-glutamyl-S-methylcysteine[27].
Two cationic isoperoxidases (C1 and C3) and four anionic isoperoxidases (A1, A2, A3n, and A3)
were isolated from Korean R. sativus L. root. All the six isoperoxidases are glycoproteins composed of a
single polypeptide chain. The molecular weights of C1, C3, A1, and A2 were ca. 44,000, while anionic
isoperoxidase A3n and A3 have molecular weights of 31,000 and 50,000, respectively. N-terminal amino
acid sequences were determined for A1, A3n, and C3, while A2 was found to have a blocked terminal
residue[28]. Analysis of digested products of the two major N-glycans of C3 suggested that corefucosylated trimannosylchitobiose may contain a different linkage from the typical α-1,6 of native Nlinked oligosaccharide[29].
Thiamin-binding substances were found in the radish. There were two kinds of compounds; one was
heat labile and Pronase sensitive, and the other was heat stable and Pronase resistant. It would be inferred
that the former is protein and the latter is a nonprotein compound[30].
βF is an isozyme (glycoprotein) found in the cytoplasm and cell walls of the radish. The
nonglycosylated cytoplasmic and cell wall βF forms have the same relative molecular mass, but
glycosylated forms have different oligosaccharide side chains with respect to size and susceptibility to αmannosidase and endoglycosidase D digestion[31].
7-Glucoside de zeatin, isolated from radish cotyledons, occurs naturally as glycoside with β-glucose
as substituent. A large number of derivatives of purine are glucosylated, but adenine derivatives with
alkyl side chains at least three carbon atoms in length at position N6 are preferentially glucosylated[20].