Cucurbit Genetics Cooperative Report 22:11-13 (article 5) 1999
Huanwen Meng, Hongwen Cui, Yanfeng Zhang, Jing Su and Meng Zhang
Horticultural Department, Northwest Agricultural University, Yang Ling, Shaanxi, P.R. China
With the world wide development of salinizing soil, more attention has been paid to increasing a plant’s ability to undergo osmotic change (resistance) and withstand salinizing stress. Under such stress conditions, growth and development of the plant are hindered, and some physiological metabolic processes are affected (1,2). There is little information on effects of salt stress on cucumber growth and metabolism. Therefore, seed vigor, seedling growth, and other physiological and biochemical indices were studied under different concentrations of salt to: (1) characterize the salt injury and salt tolerant mechanisms, and (2) provide a theoretical basis for salt tolerance breeding and cultivation in cucumber.
Methods
The cucumber cultivar 3511 was selected and stressed during germination and the cotyledon and second-leaf stage. At these growth stages plants were treated with 5 NaCl concentrations (0. 100, 200, 300 and 500 mmol/L) in a random block design with 4 replications.
Exp.1 Treatment in germination stage. After soaking in distilled water for 8 hours, 100 seeds (per block) were germinated under different liquid salt concentrations at 28 C. New salt liquid for each concentration was added every 24 hours. The number of germinated seeds whose sprout length was half of seed length were counted after 24 hours. This procedure was carried out once every 12 hours. The sprouts were weighed after 8 days, and then the germination rate, germination viability and seed vigor index were calculated for each treatment.
Exp. 2. Treatment in cotyledon stage. Ten dry seeds were sown in every seedling bowl with vermiculite (diameter 7.5 cm) nd each experimental unit was irrigated with a nutrient solution containing different salt concentrations depending on the treatment. All treatments were held at 28 C in the dark. The seedlings were cultured in a growth chamber at 28 C (d)/18 C (n) [d = 16 hr]. Salt liquid irrigation occurred two times from sowing to the cotyledon stage. Sprouting seed, tissue water, and amount of seedling growth were calculated at the end of experimentation for each treatment.
Exp. 3 Treatment in the second-leaf stage. Five seeds were sown in the culture medium. Different kinds of irrigation were used. Water was applied before sprouting, and the nutrient solution (0.09 lg urea+0.045g KH2PO4+ 0.5 MgSO4+ 1.215g Ca (No3)2/L) was used from sprouting to second-leaf stage. Then the seedlings were treated two times with an NaCl salt solution. Amount of growth and several physiological and biochemical indices were evaluated on the 8th day after treatment. The following data were taken: (1) chlorophyll content was measured using a spectrophotometer (3); (2) MDA content was measured by the method of Lin Guifang; (3) proline content measured by inhydrin colormetry (3); (4) soluble protein content was determined by the method of Coomassie brilliant blue G-250, and (5) cell membrane permeability was determined by electrical conductivity (3).
Results
Exp. 1. The effect NaCl stress on seed germination. Germination rate, germination viability and seed vigor index decreased with increasing NaCl concentrations (Table 1). No significant differences in germination rates were detected among of 0, 100, and 200 mmol/L treatments. Germination rates at these concentrations were significantly higher than seeds held at 300 and 500 mmol/L, and germination at these concentrations was significantly higher than those under 200, 300, 500 mmol/L. The seed vigor index under 0 mmol/L was significantly higher than those held at 200, 300, and 500 mmol/L.
Exp.2. The effect of NaCl stress on sprouting and seedling growth in cotyledon stage: effect on the speed of sprouting. The speed of sprouting and the germination rate decreased with increasing salt concentration (Table 2). The sprouting rate of seed held at the concentration from 0 to 200 mmol/L reached 96.3% five days after sowing, and the sprouting rate of seed held at 300 and 500 mmol/L ranged between 77.5% and 5.0% eight days after sowing.
The effect on seedling growth. Seedling height, stem diameter, leaf area, ratio of root and crown, root length and fresh weight of seedling decreased with increasing NaCl concentration, and decreased by 1.9-42.9%,1.5-12.4%, 15.4-79.5%, 32.7-64.9%, 9.4-60.4$ and 8.1-89.5% respectively, when compared to contrasting treatments (Table 2).
The effect of water content in tissue. Water content in seedlings increased slightly under lower 100 mmol/L salt concentration, decreased when seedlings were held from 100 to 300 mmol/L, and decreased slightly when seedlings were held in from 300 to 500 mmol/L salt concentrations.
Exp. 3. The effect of NaCl stress on seedling growth and some physiological and biochemical index in the second leaf stage: effect on seedling growth. The seedling growth index has a tendency to decrease with increasing NaCl concentration (Table 3). Seedling height, stem diameter, leaf area, ratio of root and crown, and fresh weight of seedling were decreased by 6.6-14.1%, 3.9-14.3%, 7.2-15.8%, 26.3-60.5% and 28.8-50.6%, respectively, when compared with contrasting treatments. The seedlings died when salt concentration reached 500 mmol/L.
The effect of NaCl stress on some physiological and biochemical index of cucumber seedling. The chlorophyll, proline, MDA and injury rate of cell membrane has a tendency to increase with the increasing NaCl salt concentration, while soluble protein content had a tendency to decrease (Table 4). The injury rate of the cell membrane reflected the widest difference of effects when all salt concentration were considered. Proline content also showed wide differences among treatments. The difference in MDA contents and soluble protein content under different treatments was not significant. It is concluded that cell membrane injury rate and proline content were the most sensitive variables to salt stress of those variables considered.
Table 1. The effect of NaCl stress on seed germinating in cucumber.
| NaCl (mmol/L) | Germination rate (%) | Germination viability (%) | Vigor index |
| 0(ck) | 99.0 aA | 99.0 aA | 2.98 aA |
| 100 | 98.0 aA | 98.0 aA | 1.23 bB |
| 200 | 90.3 aA | 79.0 bB | 0.31 cC |
| 300 | 18.0 bB | 73.0 cC | 0.14 cC |
| 500 | 0.0 cC | 0.0 cC | 0.00 cC |
Table 2. The effect of NaCl stress on sprouting and seedling growth at the cotyledon stage in cucumber.
| NaCl (mmol/L) | Sprouting rate (%) | Cotyledon stage | |||||||
| 3d | 5d | 8d | Seedling height (cm) | Stem diameter (mm) | Leaf area (cm2) | Rate of root and crown | Root length (cm) | Fresh weight of seedling (g) | |
| 0(ck) | 91.5 | 98.75 | 98.75 | 3.17 | 2.02 | 5.47 | 0.171 | 6.61 | 0.694 |
| 100 | 76.25 | 98.75 | 98.75 | 3.11 | 1.99 | 4.63 | 0.115 | 5.99 | 0.638 |
| 200 | 23.75 | 96.25 | 96.25 | 2.75 | 1.97 | 3.54 | 0.085 | 4.47 | 0.520 |
| 300 | 1.25 | 66.25 | 77.50 | 1.87 | 1.85 | 2.35 | 0.064 | 3.58 | 0.343 |
| 500 | 0.00 | 1.25 | 5.00 | 1.81 | 1.77 | 1.12 | 0.060. | 2.62 | 0.073 |
Table 3. The effect of NaCl stress on cucumber seedling growth at the second-leaf stage.
| NaCl (mmol/L | Seedling height
(cm) |
Stem diameter
(mm) |
Leaf area
(cm2) |
Rate of root and crown | Fresh weight of seedling
(g) |
| 0(ck) | 6.23 | 2.59 | 19.93 | 0.19 | 12.03 |
| 100 | 5.82 | 2.49 | 18.50 | 0.14 | 8.56 |
| 200 | 5.53 | 2.36 | 17.04 | 0.10 | 6.77 |
| 300 | 5.46 | 2.22 | 16.78 | 0.08 | 5.94 |
| 500 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Table 4. The effect of NaCl stress on some physiology and biochemical indices in cucumber seedlings.
| NaCl
(mmol/L) |
Injury rate of cell membrane (%) | Proline
(%) |
MDA
(-mol/l.g{Fw*} |
Chlorophyll
(%) |
Soluble protein
(mg/g []w) |
| O(ck) | 0.0 dD | 4.55×10-3 cC | 7.6×10-3 aA | 0.304 bB | 3.24 aA |
| 100 | 7.0 cD | 5.68×10-3 bcBC | 7.8×10-3 aA | 0.361 aA | 2.94 aA |
| 200 | 13.8 bB | 7.21×10-3 bB | 8.1×10-3 aA | 0.395 aA | 2.75 aA |
| 300 | 22.5 aA | 9.20×10-3 aA | 10.5×10-3 aA | 0.403 aA | 2.33 aA |
*Fw = Fresh weight.
Figure 1. The effects of NaCl stress on water contents of cucumber seedlings.
Literature Cited
- Youliang Liu., 1987. Recent study developments on plant salt tolerance. Plant Physiol. Comm. 4:1-12.
- Wenhua Zhasng. 1997. The effects of NaCl on root protein and free amino acid contents of barley seedling. Acta Botanical Boreali-Occidentalia Sinica 17:439-445.
- Chief edited by Northwestern Agricultural University. 1985. Guide tobasic biochemical experiments. Shaanxi Science and Technology Publishing House.