Seed Germination and Physiological Behavior of Maize (cv. Nac-6002) Seedlings under Abiotic Stress (Pendimethalin) Condition
T.C. Shivashankara Murthy
In the present investigation five treatments with pendimethalin concentrations namely 0.5, 1.0, 2.5, 5.0 and 10.0 ppm were given to maize cv. NAC-6002 grains to evaluate herbicidal toxicity on germination and early growth. The seedlings were maintained upto 15 days. Embryonic axis and endosperm of 4, 6, 8, 10 and 15 days old germinated soybean seedlings were used for bioassay on biochemical parameters viz., total protein, total carbohydrate, starch and reducing sugar were carried out. Germination percentage, length of radical and plumule were decreased significantly with increase in concentration of pendimethalin. The germinating seedlings of treated set showed high content of seed serves viz., total protein, total carbohydrate, starch and reducing sugar in the endosperms, whereas it was low in the shoot-root axis at all the days of observation over control. With increase in the days of germination the seed serves (protein, carbohydrate, starch and reducing sugar) showed a drastic decrease in control, whereas in treated sets the rate of seed reserves degradation was slow in the endosperm. On the contrary, in shoot-root axis a reverse trend was recorded in response to pendiemthalin treatment. The effect was more pronounced at higher herbicidal concentration. These results reveal that the mobilization of seed reserve was suppressed by pendimethalin, as result of impaired degradation of seed reserve, during germination and early growth.
Received: August 05, 2011;
Accepted: November 29, 2011;
Published: January 21, 2012
Agricultural research till now has been primarily concerned how yield can be
increased by the use of fertilizers, pesticides, irrigation etc. Pesticide form
an essential part of the crop production technology that makes it possible for
the farmers to feed the ever growing population. Crops differ in their responses
to various biotic and abiotic stresses. Among the abiotic stresses, chemical
stress is known to affect all the metabolic processes resulting in reduced crop
growth and yield. The herbicide pendimethalin N-(1-ethyl proply)-2,6-dinitro
3,4 xylidine belongs to di-nitroaniline group is a highly volatizing chemical
and it may cause injury or damage to the non-target plant species in addition
to the weeds (Ashok et al., 1995; Madhu
et al., 1996; Pahwa et al., 1988).
Ashok et al. (1995) have reported in their findings
that pendimethalin residue reduced the root and shoot dry weight of sorghum
after 200 days of application. Madhu et al. (1996)
observed adverse effect of pendimethalin on dry weight of succeeding crop viz.,
maize, soybean and cucumber in puddle seeded rice. The effect of herbicides
on the growth and metabolism of crop plants whether beneficial or detrimental
is the subject of interest to the scientist since long ago. Hence, the present
investigation aims at a detail evaluation on the biochemical changes during
germination and early growth of maize cv. NAC-6002, under varied concentration
MATERIALS AND METHODS
Maize (Zea mays L.) NAC-6002 variety was obtained from the University
of Agricultural Science, Nagenahalli, Mysore. The herbicide Pendimethalin (TATA
PANIDA) was obtained from The Rallies India Ltd., Peenya, Bangalore. The present
study was taken up with commercial grade of (pendimethalin) TATA PANIDA at 0.5,
1.0, 2.5, 5.0 and 10.0 ppm along with control using maize cv. NAC-6002. Hundred
healthy grains of NAC-6002 variety of maize were surface sterilized with 2%
sodium hypochloride for 5 min and rinsed with distilled water for 10-12 times
to remove excess chloride. Ten grains (grain sample of 100 seeds for each replicate)
were placed on a 9 cms petriplates containing 8 mL of Hoaglands nutrient
media (Hoagland and Arnon, 1938) supplemented with a
range of concentrations namely 0.5, 1.0, 2.5, 5.0 and 10.0 ppm of herbicide
Pendimethalin along with control in dark at 28±2°C for four days.
Later, on 5th day onwards, the germinated seedlings were exposed to 12 h light
intensity and the seedlings were further grown up to 15-days.
The data of seed germination, length of radicle and plumule were recorded according
to ISTA standard (Anonymous, 1985) and the biochemical
assay were conducted separately for shoot-root axis and cotyledons from the
4, 6, 8, 10 and 15 days old seedlings. According to the standard protocol prescribed,
the estimation of protein (Lowry et al., 1951),
total carbohydrate (DuBois et al., 1956), reducing
sugar (Miller, 1959) and total starch (Clegg,
1956) were calculated and the data obtained were subjected to statistical
analysis, using SPSS package version-10.2 with Tukeys significant test
RESULTS AND DISCUSSION
Seed germination and associated biochemical changes decreased significantly,
during germination and early growth of treated sets when compared to control.
Seed germination in the control was maximum, i.e., 95.31%. The germination percentage
decreased drastically in the treated sets with increasing concentrations of
pendimethalin. A severe decrease of about 69% was observed at high concentration
of pendimentalin-10.0 ppm when compared to control. Similarly, the length of
plumule decreased by 77% and the length of radicle decreased upto 90% at high
concentration of herbicide pendimethalin (10.0 ppm) (Table 1).
The present investigation has shown a significant decline in seed germination
and its subsequent growth by herbicide-pendimethalin indicating that some of
the biochemical processes taking place during germination and early growth are
|| Effects of pendimethalin on percent germination, length of
radicle and plumule
|Note: Mean±SD followed by same letter are not statistically
significant between the concentration, when subjected to SPSS package ver.
10.2, according to Tukeys mean range test
The impaired metabolism consequently leads to reduced growth. Several reports
have demonstrated the adverse effects of herbicide on seed germination. Delvin
and Cunningham (1970), Dhillonand Anderson (1972),
Schultz et al. (1967), Nehru
et al. (1999) and Delvin and Cunningham (1970)
have reported the adverse effects of alachlor and propachlor herbicides which
severely reduced the germination of barley by interfering with the metabolic
activities related to it. Similarly Schultz et al.
(1967) and Nehru et al. (1999) observed the
adverse effect of herbicide pendimethalin and trifluralin on seed germination
and early growth in corn, mungbean and maize, respectively. Our results also
indicate that higher concentrations of herbicide-pendimethalin inhibited the
germination of maize grains at varying degree. This may be attributed to the
adverse effect of the herbicide on degradation and mobilization of seed reserves.
The external morphology of development is often marked by biochemical changes
of seed reserves and enzymes of the internal tissues and is considered as markers
of growth and development. During seed germination and seedling growth, the
seed reserve gets hydrolyzed and a change in the cellular and organellar constituents
such as proteins, lipids and carbohydrates takes place. However, the rate of
change varies from crop to crop and species to species (Ching,
1972; Ashton, 1976; Osborne,
Protein is a major storage reserve in many plant seeds. This protein is hydrolyzed
during seed germination by proteolytic enzymes. Its metabolism has been implicated
in the breaking of seed dormancy as seed storage proteins plays a pivotal role
providing reducing nitrogen, carbon and amino acids to growing tissues (Staswick,
1988, 1990). In cotyledons, there was 65% decrease
in total protein content from 4 to 15 days in control and it was only 25-35%
in different treatments. On other hand, the total protein content (55%) increased
from 4 to 15 days in both control and 0.5 ppm treatment, while it varied between
32-37% among other treatments of shoot-root axis (Table 2).
The slow degradation of protein in treated cotyledons over control may be attributed
to the inhibition of proteolytic activity of these enzymes (Mann
et al., 1965; Moreland et al., 1969),
whereas significant decrease of protein content in treated shoot-root axis over
control indicates that it may be due to the inhibition of dipeptidase activity
(Tsay and Ashton, 1971). The rate of protein synthesis
and degradation in treated seedlings showed slowing down in the rate of protein
synthesis and increase in the rate of protein break down which may be responsible
for the observed rapid protein loss. These results are in line with Lorenzo
et al. (1985) which demonstrates that pendimethalin might interfere
with protein metabolism during germination and its early growth.
Carbohydrates are important components of storage and structural material in
plants. They are the energy rich sources and are essential for germination of
seeds. Germinating seeds are dependent on starch for their energy supply which
is degraded into soluble forms by a-amylase enzyme. During germination the carbohydrate
reserve of seed i.e., principally the starch gets degraded to provide sugars
either via amylolytic or phosphorolytic pathways. They exist as free sugar and
polysaccharides (Hedge and Hofreiter, 1962; Swain
and Dekker, 1966). In cotyledons of soybean the reduction in total carbohydrate
content from 4 to 15 days was 52% in control and 0.5 ppm treatment, while it
varied between 32-46% in other treatments. On the other hand, higher content
of total carbohydrate was recorded (61-67%) in the embryonic axis of the treated
seedlings, when compared to control (42%) from 4 to 15 days. Similarly, the
decrease in reducing sugar with time interval was 90% in control and varied
between 66-80% in different treatments in cotyledons, while in shoot-root axis
the increase in the reducing sugar from 4 to 15 days was 44% in control and
it ranges between 54 to 66% among treatments.
||Effects of pendimethalin on total protien, carbohydrate, starch
and reducing sugar content in Maize
|Mean±SD followed by same letter are not statistically
significant between the concentration, when subjected to SPSS package ver.
10.2, according to Tukey’s mean range test
On the other hand, the decline in total starch content with time interval was
62% in control and it was varied from 33 to 43% in different treatments in cotyledons
of soybean, while in shoot-root axis the total starch content with time interval
was 37% increase in control and in different treatments it ranged from 41 to
47% (Table 2).
Penner (1968) reported that the reduction in degradation
of total carbohydrate and starch content in barley seedlings by herbicides bromoxylin
and amiben. He also reported that these herbicides interfere in the processes
of hydrolytic enzymes synthesis, which are involved in the degradation of food
reserves. And more pronounced inhibition of amylase activity by several herbicides
has been reported by Jones and Foy (1971) which impair
the degradation and mobilization of seed serves. Our results are in accordance
with the above findings in case of total carbohydrate and starch content which
showed reduced content in the shoot-root axis and a higher content in the cotyledon
of all treatment at five different time interval over control. Felipe
et al. (1988) reported that decline in RuDP carboxylase activity
results in reduction in reducing sugar content in wheat after isoproturon treatment.
Similarly, the decline in reducing sugar in shoot-root axis and a higher content
in the cotyledons in all treatments and at different time intervals in our study
may also be due to lower activity of RuDP carboxylase enzyme.
In short, pendimethalin bears adverse effects on the seed germination and early growth of developing maize seedlings. Each concentration affected the parameters studied at different point of observation. The herbicidal action of this degradation of reserve materials and on the control of these processes during germination may be one of the factors responsible for greater susceptibility of seedlings to the herbicide pendimethalin than that observed in mature plant. However, further studies are needed to strengthen this conclusion.
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