Growth Responses of Vigna radiata to Arid Land Bacteria Exhibiting Antimicrobial Activity
Twenty-four bacterial strains were isolated from rhizosphere and histoplane of four different arid plants, Trianthema partulacastrum, Rumex dentatus, Chenopodium morale and Coronopus didymus. These bacteria were inoculated to seeds of Vigna radiata var NM-92 which were germinated and grown for 15 days. Majority of strains had inhibitory effect on seed germination (2.2 to 13.0%). The increase in seedling length ranged from 17 to 38% with different inoculations. Bacterial strains TP1, TP3, TP4, RTP4 and RRD1 were the most effective ones for the different growth parameters such as seed length and seed weight whereas the most adverse effects were recorded with the inoculation of TP17 strain. Maximum increase in protein and auxin content was observed with strains TP5 and RCM2, respectively. Peroxidase and acid phosphatase showed maximum activity with the inoculation of strain TP1.
Bacteria are ubiquitous in their distribution and are present in water (Klaus et al., 2007), soil (Sager et al., 2007) and play an important role in soil quality (Hill et al., 2000) by increasing organic carbon and moisture level (Eaton, 2000). They are also essential for various functions such as plant growth promotion (Humphry et al., 2007), inhibition of plant pathogen (antimicrobial activity) (Cho et al., 2007), improvement of soil structures and leaching metal (Van Veen et al., 1997). Tillage reduction in agriculture soil has been reported by microbial mass and microbial density (Lupwayi et al., 2000). The plant species, type and development influenced the variation of microbial communities in soil and association with roots (Wieland et al., 2001). These bacteria produce antimicrobial agents which inhibit/promote the growth of plants in the soil (Casida and Lukezic, 1992). Bacterial strains that enhance plant growth under heavy metal stress have been reported by Faisal et al. (2005) and Faisal and Hasnain (2006). Microbes exhibiting the antimicrobial behavior can effect their host in different ways. Their effect may be stimulatory (Alami et al., 2000) or inhibitory (Li et al., 2007). Vigna radiata is an important cash crop of Pakistan. Keeping the association of antimicrobial activity and plant promoting ability of bacterial strains, twenty-four bacterial strains were used for the present study, to evaluate the impact of antimicrobial activity exhibiting bacterial strains on the growth of V. radiata.
||Bacterial isolates from histoplane and rhizoplane of four
different plants Trianthema partulacastrum, Rumex dentatus,
Chenopodium morale and Coronopus didymus
MATERIALS AND METHODS
Bacterial Strains and Seeds Inoculation
The study was conducted in the University of the Punjab, Lahore, Pakistan
in the year 2005 to 2006. Twenty four different strains were isolated from the
roots of four weeds (Trianthema partulacastrum, Rumex dentatus,
Chenopodium morale and Coronopus didymus) by Ahmed (2000), (Table
1). Bacterial strains were grown in L-agar medium (Gerhardt et al.,
1994) at 37°C for 24 h. Healthy seeds of V. radiata were surface
sterilized by soaking in 0.1% HgCl2 and then washed thrice with distilled
water. Seeds were then soaked in bacterial suspension for 15 to 20 min. For
control, seeds were soaked in sterile glass distilled water for same duration.
Ten milliliter of autoclaved distilled water was poured in labeled petriplate
(lined with double layer of Whattman filter paper No. 1 autoclaved and oven
dried). With the help of sterilized forceps, seeds (control as well as inoculated)
were spread in the respective labeled petri plate (15 seeds of V.
radiata per petri plate) uniformly. Petri plates were kept in dark at 25±1°C
for germination. Germination was recorded daily. After germination, plates were
shifted to light (10D lux and 16 h day length) at 25±1°C after adding
10 mL of Hewitt nutrient solution in each plate (Hewitt, 1963). Seedlings were
grown for 10 days after shifting to light. Experiment was repeated eight times.
Seedlings were removed from the petri plates. Different growth parameters (seed
germination, seedling length, fresh weight of seedlings, dry weight of seedling,
dry weight per gram fresh weight of seedling) were recorded.
For biochemical analysis auxin (Mahadevan, 1984), soluble protein (Bhatti
et al., 1993; Lowry et al., 1951), peroxidase (David and Murray,
1965) and acid phosphatases content (Iqbal and Rafique, 1986) were studied.
Standard errors of the means and LSD were calculated following Steel and
Seed germination of V. radiata was affected with the inoculation of
bacterial strains. The germination was increased over control with few bacterial
strains such as TP17 (4.5%), RTP4, RCD1, RCD2, RD3 (4%). Majority of strains
had inhibitory effects on this parameter and 1.04 to 2.7% reductions in germination
of seeds were recorded (Table 2). Inoculation of TP2, TP9,
RCD3 and RD4 and RCM2 did not cause any change in germination parameter. Seedling
length was increased with inoculation of bacterial strains except TP17 where
slight decrease (2.5%) over control was recorded (Table 2).
||Effects of bacterial inoculations on seed germination, seedling
length, fresh weight, dry weight and dry weight g-1 fresh weight
of V. radiata seedlings
||Effects of bacterial inoculation on the soluble protein, auxin,
peroxidase and acid phosphatase activity of in V. radiata
Maximum increase in the seedling was observed with inoculation of RRD1 (38.0%).
Fresh weight of V. radiata was increased in the presence of bacterial
strains TP1, TP2, TP3, TP4, TP8, TP9, TP17, RCD1, RCD2, RD3, RRD1, RCM2 and
RTP2, when compared with non-inoculated control (Table 2).
The maximum increase in this parameter was observed with the inoculation of
RTP2 (19.0%). Dry weight and dry weight per gram fresh weight increased with
bacterial inoculation as compared to non-inoculated control.
Protein content was increased with the inoculation of majority of bacterial strains while TP7, TP14, TP16, TP17, RCD2, RD8 and RRD1 caused reduction in the soluble protein content over non-inoculated seedlings (Table 3). The maximum increase was observed with the inoculation of RCM2 (79.0%). The maximum increase in auxin content was observed with inoculation of RCM2 (26.7%). Peroxidase activity of V. radiata seedlings were increased with the inoculation of bacterial strains TP9 (44.0%). The activity of acid phosphatases increased with the inoculation of majority of bacterial strains. The maximum increase in the acid phosphatases activity was observed with the inoculation of TP1 (153.2%).
Microorganisms of soil are sensitive indicator of soil health because of the relationships between microbial diversity, soil quality and ecosystem sustainability (Doran et al., 1994). Hence the microorganism plays important roles in soil quality and plant productivity (Hill et al., 2000). The rhizospheric bacteria promote plant growth by inducing systemic resistance in host plant and protect plant from pathogens (Zheng et al., 2000). The strains used in present work were characterized and screened for antimicrobial activity against Saccharomyces cervisae, E. coli and Bacillus subtilis by Ahmed (2000). Majority of them showed antimicrobial activity against yeast but none of them showed any activity against E. coli. Strains TP13 and RD8 produce certain substances that inhibit Bacillus subtilis growth.
Germination of V. radiata was adversely affected by the inoculation of bacterial strains excluding TP13 and RTP4 (Table 2). The increase in fresh weight might be due to rise in water content (Hashim et al., 1996). Enhanced dry weight could be attributed to the accumulation of salts and nutrients, enhanced ion uptake and increased level of organic salts in cytoplasm (Sudhakar et al., 1993). Improved seedling length coupled with increased dry weight, which is clear indication of growth stimulation by bacteria. Decrease in fresh weight of seedlings may be due reduce water uptake under stress condition. Soluble protein content was also affected with the inoculation of bacterial strain. Maximum increase in this parameter was caused by the inoculation of RCM2 (79.01%). According to Staples and Dacher (1986) auxin and protein are formed from tryphtophan molecules with different molecular arrangement, so the amount of the auxin is directly related to the amount of soluble protein content. Auxin is the master hormone, exercising regulatory action over many different sorts of plant process. Campbell (1985) reported that bacterial strains stimulate plant growth by synthesizing and liberating growth hormone. Enhancement in the auxin contents with the inoculation of bacterial strains was reported in the present study. Enzymes are biochemical catalyst, which play important role. Two enzymes, acid phosphatases and peroxidase were studied for their activity vis-à-vis treatments. Activities of these enzymes were also improved with bacterial inoculation as compared to non-inoculated treatments (Table 3). Majority of bacterial strains caused improvements in the activity of peroxidase and acid phosphatase. The increase in antioxidant enzyme activity in plants under stress provides better protection against reactive oxygen activities (Meloni et al., 2003).
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