http://dx.doi.org/10.11594/jtls.13.03.11
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Research Article
Regular Mechanical Stimuli Enhanced Tolerance to Salinity Stress in Glycine max L. Seedlings
Juhika Patel, Susy Albert, Ravinayak Patlavath *
Department of Botany, The M S University of Baroda, Vadodara -390 002, India
Article history:
Submission September 2022 Revised December 2022 Accepted December 2022
ABSTRACT
Regular touch treatment leads to plant adaptations that enhances mechanical strength. In many crop plants these adaptations result in cross-tolerance to biotic stress caused by bacterial or fungal infection and abiotic stress conditions like salin- ity or drought. In present study, we have explored the effect of mechanical stress on the growth of Glycine max (soybean) seedlings and studied its effect on tolerance to salinity stress. Regular mechanical stress given in the form of touch suppressed over- all growth of the soybean seedlings. Touch pre-treated seedlings were further treated with sodium chloride to test for its tolerance to salinity. Upon salt treatment, we observed comparatively higher survival rate and more growth in the seedlings that received regular mechanical stress during early growth stages. The adaptations to mechanical stress given at the early-stage of growth may have led to the enhanced tolerance to salinity stress experienced in later growth stage.
Keywords: Abiotic Stress, Mechanical Stress, Touch, Salinity, Soybean
*Corresponding author:
E-mail: ravi.nayak-botany@msub- aroda.ac.in
Introduction
Plants have evolved complex survival strate- gies to sense and overcome different biotic and abiotic stress conditions. The plant perceives any changes in mechanical pressure on the plant sur- face and at the cellular level. For example, raindrops, blowing of wind, landing of insects and touch of near-by plants are sensed as mechanical stress [1 - 5]. Mechanical stress in the form of touch by human, animal or insects has been stud- ied in plants since 1880, when Charles Darwin published his research on touch-induced responses in insectivorous plants [6]. Until the early 90s, ex- tensive research was carried out to understand the mechanism by which 'touch me not plant', Mimosa pudica and carnivorous plants like Venus fly-trap perceived touch. Recent research in this area is more diversified and aimed to understand touch induced cellular responses. This gave insight into the molecules involved in touch induced responses [7,8,9]. Mechanical stimuli induce an immediate response like changes in reactive oxygen species (ROS) levels, calcium levels and changes in tran- scriptional profile [10]. In addition, plants also
display anatomical that enhance their mechanical strength. Plants display morphological changes as adaptations in response to regular mechanical stress, termed thigmomorphogenesis [2]. Studies in Arabidopsis indicate that regular human touch delays inflorescence development and further re- duces the diameter size of the leaf rosette [3]. The plant responses to mechanical stress vary from species to species. Regularly touched papaya plants exhibited reduced growth, higher lignin deposition and reduced anthocyanin production in the petiole [11]. However, touch treatment in to- bacco plants increased the crop's vegetation [12].
Here, we have performed a preliminary study to understand the effect of regular mechanical stress on soybean seedlings' growth and further tested the effect of touch on tolerance to salinity stress.
Glycine max L., soybean, is a leguminous (Family Fabaceae) crop grown worldwide for its edible pod [13]. Soybean is cultivated for human as well as for animal consumption. India is fourth largest producer of soybean in the world [14]. Af- ter the green revolution, the extensive use of
inorganic fertilizer has adversely affected the soil health and eventually led to an accumulation of salts [15] that led to gradual decrease in the yield of many crops, including soybean. This crop is partially sensitive to saline soil, and salt stress sub- stantially impacts the production of soybeans, an important cash crop in many countries.
Moreover, high salinity harms growth agron- omy features, like seed quality and quantity and thus affecting the soybean production. Salt stress negatively impacts the regular functioning of pho- tosynthetic enzymes, chlorophylls and carotenoid pigments, which reduces plant's ability to absorb water and causes a decrease in plant growth rate and other metabolic processes [16,17]. Excess salt in soil can cause a 40% reduction in soybean yield.
Soybean plant cell lines have been shown to re- spond to mechanical stress by releasing oxidative burst [18]. However, the effect of mechanical stress on soybean plant growth and morphology has not been reported. The present study indicates that regular mechanical stress suppresses the growth of soybean seedlings and enhances its tol- erance to salt stress.
Material and Methods Plant growth
Soybean seeds local variety (native to Gujarat, India) were used for the present study. Seeds were surface sterilized using 90% ethanol with 0.1%
SDS and soaked in a beaker overnight. The soaked seeds were kept for germination over cotton in clean petri plates. Germinated soybean seeds were transferred to pots containing garden soil. The soybean seedlings were watered daily for the first week then on alternate days.
Touch treatment
Touch treatment was initiated on 2-weeks-old seedlings; no tendrils were developed at this stage and the plant stood erect without support (Figure 1d). Seedlings were given a gentle touch, the leaves and the stem tip were bend back and forth ten times with a finger [19]. Seedlings were touched twice for every 24 hours for 15 days. The touched and untouched seedlings were placed apart in same laboratory condition. Plants were observed for morphological changes like shoot length and number of compound leaves.
Figure 1. The experimental setup: a-b shows images of the washed and soaked seedlings, (c) seeds kept for germination, and (d) shows one week old soybean seedlings in soil.
Salt treatment
After two weeks of touch treatment, the seed- lings were given salt treatment. During this period, the seedlings developed tendrils that required erect growth support. Each seedling was supported with the help of a thin wooden stick for climbing (Fig- ure 2 -a). For salt stress, 100 mM of NaCl solution was added to the soil of both touched and un- touched plants. Growth of seedlings in terms of height was measured before salt treatment. The seedlings' growth was measured every seven days and followed till 45th day post salt treatment.
Statistical analysis
All the experiments were repeated in three sets, each with 10-15 seedlings. All the data were analyzed using Student's t-test using Microsoft Excel software.
Results and Discussion
Regular touch treatment suppresses growth of G.
max
For studying the effect of touch on the growth of G. max, healthy uniformly germinated seeds were grown in pots containing garden soil (Figure 1a-d). Two-weeks-old seedlings (n=15-20 seed- lings) were touched twice a day. This was repeated for 15 days and followed for morphological changes. The growth was measured in terms of seedling height after every week. We observed a significant reduction in the shoot height in the touched seedlings as compared to the untouched seedlings (Figure 2 a-b) (p>0.05). Moreover, the average growth rate in touched seedlings was also significantly reduced as compared to the
untouched seedlings. This experiment had three replicates, and similar results were observed in all replicates.
Regular mechanical stress leads to stunted growth in many different plant species. In Cajanus cajan, regular mechanical stress suppressed plant growth in terms of height and number of com- pound leaves [20]. Mechanical stress affects the homeostasis of growth promoting hormones like auxin and gibberellic acid. In tomato plants, me- chanical stress affects the transport and accumula- tion of auxin in the shoot apex [21]. Also, the lev- els of growth suppressing hormones, jasmonic acid and ethylene, are found to be elevated upon mechanical stimuli in Arabidopsis [10, 19,22].
The elevated levels of jasmonic acid promote the catabolism of gibberellic acid, which functions in cell growth and elongation [23]. Similarly, eth- ylene promotes the degradation and modification of plant cell wall components, affecting cell growth [24]. We hypothesis, a similar phenome- non may have led to the suppression of growth in touch treated soybean seedlings.
Regular mechanical stress leads to enhanced tolerance to salinity stress in G. max seedlings
As regular mechanical stress leads to cross tol- erance to abiotic stress, we tested the effect of me- chanical stress in the form of touch on tolerance to salinity stress in G. max. For this, seedlings were given touch treatment for two weeks, followed by salt treatment (100 mM NaCl). The seedling growth (in terms of height) was measured before and after salt treatment for 45 days. The salt treated touched plants displayed healthy leaves as Figure 2. Regular touch treatment suppresses growth of G. max: One-week-old seedlings were regularly touched for three weeks. The growth of seedlings was measured in terms of plant height after seven days. (a-b) shows growth of touched and control soybean plants. The bar in graph represents average height of seedlings(n=20) and error bar represents standard deviation. * Indicates significance value (p<0.05).
compared to the salt treated untouched plants. The salt treated touched plants showed a significant (p<0.05) increase in growth as compared to the salt treated untouched plants (Figure 3a). In addi- tion, the population of salt treated touched plants had a significantly (p < 0.05) higher percentage of survivals as compared to salt treated untouched plants (Figure 3b). Thus, seedlings that received mechanical stress displayed enhanced tolerance to salinity stress. Similar results were observed in three replicates.
The soybean crop is partially sensitive to soil salinity. Salt treatment affects plants' regular growth and development as salt accumulation in the cytoplasm inhibits cell's biochemical enzymes and protein functions. Similar effects may have led to high mortality and poor growth in the un- touched salt treated plants. Salt treatment further enhances jasmonic acid production, suppressing plant growth under stress [25]. Mechanical stress given during the initial growth period may bring changes in the cellular transcriptional profiling, the effect of which will be retained even after the removal of the mechanical stress. Eric Brenya et al. (2022) have proposed that the initial regular treatment of mechanical stress builds up a somatic memory, which helps the plant to acclimatize to abiotic and biotic stress experienced in later stages of growth [26]. This can be correlated to the ob- servation made in the present study, where touch treatment given at the initial growth period led to enhanced tolerance to salinity stress given in the later growth stage of soybean seedlings. The plant's adaptation in response to mechanical stress perceived at early stages of growth may have led to enhanced tolerance to salinity stress
experienced in the later growth stage. Overall, the observations presented here open new areas of re- search which can be explored to develop new methods of crop improvement.
Conclusion
Mechanical stress given to soybean seedlings at the early growth stage led to enhanced tolerance to salinity stress. Observations of this study can be used in developing new agricultural strategies for growing crops on lands with high salt content. Fur- ther field studies in adult soybean plants will im- provise this technique for large scale field applica- tion.
Acknowledgment
We acknowledge the M. S. University's re- search consultancy cell for the grant given to Ravi- nayak Patlavath.
References
1. Biro RL, Jaffe M (1984) Thigmomorphogenesis: ethylene evolution and its role in the changes observed in mechan- ically perturbed bean plants. Physiologia Plantarum 62 (3): 289-296. doi: 10.1111/j.1399-3054.1984.tb04575.x 2. Braam J (2005) In touch: plant responses to mechanical
stimuli. New Phytologist 165 (2): 373-389. doi:
10.1111/j.1469-8137.2004.01263.x
3. Chehab EW, Eich E, Braam J (2009) Thigmomorphogen- esis: a complex plant response to mechano-stimulation.
Journal of Experimental Botany 60 (1):43-56. doi:
10.1093/jxb/ern315
4. Li ZG, Gong M (2011) Mechanical stimulation-induced cross-adaptation in plants: an overview. Journal of Plant Biology 54(6):358.
5. Dimitrije M, Colzi I, Taiti C, Ray S, Scalone R, Ali JG, Mancuso S, Ninkovic V (2019) Airborne signals synchro- nize the defenses of neighboring plants in response to Figure 3. Regular touch treatment leads to enhanced tolerance to salt stress in G. max: Seedlings that were given
touch treatment for two weeks and untouched plants were treated with 100 mM salt. The plant growth was monitored for 45 days (a) shows the average plant height in presence of salt. The error bar repre- sents standard deviation. * Indicates significance value (p < 0.05) (b) shows percentage survival after salt treatment.
touch. Journal of Experimental Botany 70: no. 2: 691- 700. doi: 10.1093/jxb/ery375
6. Darwin C (1880) The Power of Movement in Plants; Lon- don: William Clowes and Sons, Ltd. doi:
10.1017/CBO9780511693670
7. Braam J, Davis RW (1990) Rain-, wind- and touch-in- duced expression of calmodulin and calmodulin-related genes in Arabidopsis. Cell 60: 357–364.doi:
10.1016/0092-8674(90)90587-5
8. Botella JR, Arteca JM, Somodevilla M, Arteca RN (1996) Calcium-dependent protein kinase gene expression in re- sponse to physical and chemical stimuli in mungbean (Vigna radiata); Plant Molecular Biology 30:1129–1137.
doi: 10.1007/BF00019547
9. Botella JR, Arteca RN (1994) Differential expression of two calmodulin genes in response to physical and chemi- cal stimuli. Plant Molecular Biology 24:757–766. doi:
10.1007/BF00029857
10. Lee D, Polisensky DH, Braam J (2005) Genome‐wide identification of touch‐and darkness‐regulated Arabidop- sis genes: a focus on calmodulin‐like and XTH genes.
New Phytologist 165 (2): 429-444. doi: 10.1111/j.1469- 8137.2004.01238.x
11. Chehab EW, Yao C, Henderson Z et al. (2012) Arabidop- sis touch-induced morphogenesis is jasmonate mediated and protects against pests. Current Biology 22(8):701- 706. doi: 10.1016/j.cub.2012.02.061.
12. Porter B W, Yun JZ, David TW, David AC (2009) Novel thigmomorphogenetic responses in Carica papaya: touch decreases anthocyanin levels and stimulates petiole cork outgrowths. Annals of botany 103: 847-858. doi:
10.1093/aob/mcp009
13. Anten NPR, Raquel CG, Hisae N (2005) Effects of me- chanical stress and plant density on mechanical character- istics, growth, and lifetime reproduction of tobacco plants The American Naturalist 166:650-660. doi:
10.1086/497442
14. Malukani B (2016) Export potential of soybean from In- dia: a trend analysis. Prestig eJ Manag Res 3:pp.43-53.
15. Badrakia J, Patel KB, Dhandhukia P, Thakker JN, (2021) Mycoparasitic Pseudomonas spp. against infection of Fusarium chlamydosporum pathogen in soybean (Gly- cine max) plant. Archives of Phytopathology and Plant Protection 54 (19-20): 2160-2170. Doi:
10.1080/03235408.2021.1925433
16. Pillai SE, Patlavath R, (2020) Organic Farming: A new way to increase the Basmati Rice production.
Environment at Crossroads Challenges and Green Solu- tions p.128.
17. Stepien P, G Klobus (2006) Water relations and photo- synthesis in Cucumis sativus L. leaves under salt stress.
Biologia Plantarum 50 (40): 610-616.
doi:10.1007/s10535-006-0096-z
18. Munns R, (2002) Comparative physiology of salt and wa- ter stress. Plant, Cell, and Environment 25 (2): pp.239- 250. doi: 10.1046/j.0016-8025.2001.00808.x
19. Yahraus T, Chandra S, Legendre L, Low PS (1995) Evi- dence for a mechanically induced oxidative burst. Plant Physiology 109 (4): 1259-1266. doi:
10.1104/pp.109.4.1259
20. Patlavath R, Pillai SE, Gandhi D, Albert S. (2022) Ca- janus cajan shows multiple novel adaptations in response to regular mechanical stress. Journal of Plant Research 135 (6):809-821. doi: 10.1007/s10265-022-01414-8 21. Nakayama N, Smith RS, Mandel T et al. C (2012) Me-
chanical regulation of auxin-mediated growth. Current Biology 22 (16): 1468-1476. doi:
10.1016/j.cub.2012.06.050
22. Okamoto T, Takatani S, Motose H, Iida H, Takahashi T (2021) The root growth reduction in response to mechan- ical stress involves ethylene-mediated microtubule reor- ganization and transmembrane receptor-mediated signal transduction in Arabidopsis. Plant Cell Reports 40 (3):
575-582. doi: 10.1007/s00299-020-02653-6.
23. Lange MJP, Lange T (2015) Touch-induced changes in Arabidopsis morphology dependent on gibberellin break- down. Nature Plants 1 (3): 1-5. doi:
10.1038/nplants.2014.25
24. Wu Q, Li Y, Lyu M et al. (2020) Touch-induced seedling morphological changes are determined by ethylene-regu- lated pectin degradation. Science advances 6(48):
eabc9294. doi: 10.1126/sciadv.abc9294
25. Pillai SE, Kumar C, Patel HK, Sonti RV (2018) Overex- pression of a cell wall damage induced transcription fac- tor, OsWRKY42, leads to enhanced callose deposition and tolerance to salt stress but does not enhance tolerance to bacterial infection. BMC Plant Biology 18(1):1-15.
doi: 10.1186/s12870-018-1391-5.
26. Brenya E, Pervin M, Chen ZH et al. (2022) Mechanical stress acclimation in plants: Linking hormones and so- matic memory to thigmomorphogenesis. Plant, Cell and Environment 45 (4): 989-1010. doi: 10.1111/pce.14252
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