Standardization of Explant Surface Sterilization Technique for Micropropagation in

Andrographis paniculata Nees.

Haripriya.S and M.Kannan

Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore – 3

ABSTRACT

Surface sterilization with 70 % ethanol washing for 10 seconds followed by

0.1 % mercuric chloride (HgCl2) sterilization for two minutes proved to be optimum for maximum

survival percentage in juvenile phase explants (shoot tip and nodal segment) whilst 70 % ethanol

washing for 25 seconds followed by 0.1 % HgCl2 sterilization for two minutes proved to be

optimum for vegetative phase explants (shoot tip and nodal segment) of Andrographis paniculata.

The tissue response of the explant varied with treatment duration depending on the type and

physiological stages of the same plant resulting in establishment of aseptic culture.

Key words: Ethanol , mercuric chloride , shoot tip, nodal segment, juvenile phase, vegetative

phase.

INTRODUCTION

Andrographis paniculata Nees. (Acanthaceae), is an erect annual herb extremely bitter in

taste in each and every part of the plant body. The plant is known in

north-eastern India as ‘Maha-tita’, literally ‘king of bitters’ and it is also acknowledged as ‘Bhui-

neem’, since the plant, though much smaller in size, shows similar appearance and has bitter taste

as that of Neem (Azadirachta indica). Since time immemorial, Andrographis was used as a wonder

drug in traditional Siddha and Ayurvedic systems of medicine as well as in tribal medicine in India

and in some other countries for multiple clinical applications. A study was carried out to

standardize the protocol for micropropagation in Andrographis paniculata. The most decisive step

in explant preparation while standardizing micropropagation techniques is that of keeping the

explant alive overcoming the problems of conamination. The explant or the piece of the plant

tissue to be cultured is often the major source of contamination. The contaminant may be on the

surface of the explant, between the cells or within the plant cells. In order to surmount such

tribulations detrimental to the culture, the explants ought to be surface-sterilized before inoculation

in sterile growth medium. This paper details the research undertaken to standardize expalnt surface

sterilization techniques for micropropagation in Andrographis paniculata Nees.

MATERIALS AND METHODS

The experiment was conducted at the Plant Tissue culture laboratory, HC & RI, TNAU,

Coimbatore. The stock plant, Andrographis was maintained in pot culture at Botanic Gardens,

TNAU, Coimbatore for supply of explants i.e., shoot tip (1.5 - 2 cm) and nodal segment (2 -2.5 cm)

throughout the experiment period. The explants were collected at two physiological stages of interest

viz., juvenile phase (30-45 days old seedlings) and vegetative phase (60-90 days old plants) for

micropropagation. Initially the freshly collected explants were washed thrice under running tap

water. The explants were then prewashed with Tween 20 emulsifier (2-3 drops in 100 ml sterile

distilled water) for one minute followed by rinsing three times in sterile distilled water. Prior to

surface sterilization, antibrowning treatment was given to control phenol exudation from the cut

end of the tissues. Before disinfection, the explants were washed with 70 % ethanol (v/v) for 10-25

seconds and surface sterilized with 0.1 % ( w/v) mercuric chloride (HgCl2 ) for 2-6 minutes. For

better contact of the sterilant (0.1 % HgCl2 ) with the explants, they were stirred for few minutes

while disinfesting. The surface sterilized explants were finally rinsed in sterile distilled water

under laminar airflow chamber to remove all traces of sterilizing agent (1) and placed on a

sterilized petridish covered with sterilized filter paper to remove excess moisture present on the

surface of the explant. Data on contamination, mortality and survival percentage were recorded.

The contamination percentage was calculated using the following formula,

Number of cultures contaminated

Contamination (% ) = X 100

Total number of cultures inoculated

RESULTS AND DISCUSSION

Surfaces of plant carry a wide range of microbial contaminants. To avoid this source of

infection, the explant tissues must be thoroughly surface sterilized before inoculating it on the

nutrient medium. Explants treated with Tween 20, a wetting agent improved the disinfestation by

acting as a surfactant thereby removing the surface contaminants like soil and dust. While

trimming the explants, phenols ooze out from the cut tissues, resulting in explant browning. In

order to control the phenol exudation, the explants were given antibrowning treatment. 70 %

ethanol washing was given prior to disinfection, apart from a surface sterilant by itself, it enhances

the contact of the disinfectant (0.1 % HgCl2 ) efficiently (4). After rinsing in ethanol, the explants

were left exposed until the alcohol evaporates (3). Generally, to disinfect the plant tissues various

sterilizing agents have been used. Mercuric chloride was found to be a very effective sterilizing

agent at 0.1 % concentration in Andrographis. The chlorine gas released from HgCl2 was very

penetrating that it destroyed the microorganisms present in most tissues of the explant (2). It is also

important to be cautious that a surface sterilant is also toxic to the explant tissues. Therefore

concentration of the sterilizing agent and duration of the treatment should be optimum to minimize

tissue mortality of the explants due to over sterilization.

Table 2. Standardization of surface sterilization for vegetative phase explants in

Andrographis paniculata Nees.

Duration of

exposure

Shoot tip Nodal segment

Treatment

70 %

Alcohol

(sec)

0.1%

HgCl2

(mins)

%

CON

%

SUR

%

MOR

%

CON

%

SUR

%

MOR

T1 10 1 60.00 20.00 20.00 40.00 10.00 45.00

T2 10 2 40.00 30.00 30.00 40.00 20.00 40.00

T3 10 3 30.00 40.00 30.00 30.00 25.00 45.00

T4 10 4 20.00 40.00 40.00 20.00 30.00 50.00

T5 10 5 25.00 30.00 45.00 15.00 15.00 70.00

T6 25 1 25.00 60.00 15.00 55.00 20.00 25.00

T7 25 2 5.00 85.00 10.00 10.00 80.00 10.00

T8 25 3 10.00 70.00 20.00 15.00 25.00 20.00

T9 25 4 10.00 60.00 30.00 20.00 80.00 15.00

T10 25 5 10.00 50.00 40.00 30.00 70.00 10.00

% CON - % Contamination, % SUR - % Survival, % MOR - % Mortality (Browning or blackening

of explants).

Statistically not analysed.

Incase of Andrographis paniculata, surface sterilization with 70 % ethanol washing for 10

seconds followed by 0.1 % HgCl2 sterilization for two minutes proved to be optimum for

maximum survival percentage in juvenile phase explants (Table.1) whilst 70 % ethanol washing

for 25 seconds followed by 0.1 % HgCl2 sterilization for two minutes proved to be optimum for

vegetative phase explants (Table.2). The treatment duration varied with the physiological stage of

the explant. The morphogentic growth pattern of the cell changes according to the physiological

age of the plant material, resulting in direct correlation between the sensitivity of the tissues to the

sterilizing agent and the ontogenic age of the explants. Juvenile phase explants consisted mostly of

newly formed delicate tissues than the matured tissues of the vegetative phase explants. Thus

juvenile phase explants require lesser time to surface disinfect than vegetative phase explants

resulting in establishment of aseptic cultures.

REFERENCES

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