Drought tolerance in barley

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Barley (Hordeum vulgare) is known to be more environmentally-tolerant than other cereal crops, in terms of soil pH, mineral nutrient availability, and water availability. [1] Because of this, much research is being done on barley plants in order to determine whether or not there is a genetic basis for this environmental hardiness. [2]

Contents

Effect of drought on barley plants

Barley is a C4 species and a monocot, and therefore the effects drought has on it can be extrapolated to other plant species. Drought is often the result of increased temperature in a region, which promotes water loss in plants by increased transpirational pull. Lack of water in the soil decreases mineral nutrient availability, as minerals must be dissolved in soil solution in order to enter the roots. Additionally, drought results in decreased photosynthetic rates, decreased biomass, and accelerated leaf senescence.[ citation needed ]

Significance

Barley has been an invaluable crop for humans since the birth of the Fertile Crescent. Prior to the mass cultivation of maize (Zea mays), wheat (Triticum aestivum) and rice (Oryza sativa), barley was the main cereal crop for humans. [3] Today, barley is primarily used for animal feed (55-60%) and malt (30-40%). [4] Many developing countries still rely heavily on barley as a food source, especially in regions of Africa, the Arabian Peninsula, and South America. [5] A decline in barley production would therefore worsen the ongoing food crises in these countries. CO2 levels have increased by 48% since the Industrial Revolution (1760-2019), raising global temperatures. [6] This has resulted in an increase in extreme weather events, such as drought, in many regions of the world which contain valuable farming land. Overall, climates are erratically changing, and one foreseeable way to combat global food insecurity is to breed crops which are tolerant to environmental stresses.[ citation needed ]

Mechanisms

C4 photosynthesis

Barley plants photosynthesize via the C4 pathway, meaning they fix CO2 into a 4-carbon organic acid, which is then shuttled to the bundle sheath, preventing diffusion back into the atmosphere. The C4 pathway uses PEP-carboxylase as a catalyst for carbon fixation, rather than RuBisCO, which is used in the C3 pathway. PEP-carboxylase has a higher affinity for CO2, and does not have affinity for O2, which prevents photorespiration. Overall, the C4 pathway allows barley plants to fix carbon more efficiently, thus allowing them to keep their stomata open for less time, preventing water loss by transpiration.[ citation needed ]

Abscisic acid

Abscisic acid (ABA) is the hormone which plants release in response to stress. [7] It induces stomatal closure in plants, decreasing water loss by transpiration. However, increased stomatal closure results in decreased CO2 assimilation. Perhaps to combat this in the short-term, ABA synthesis also promotes elongation of root cells, which in turn promotes mineral nutrient uptake. [8] Other research has also shown that ABA increases carbonic anhydrase activity under drought conditions. [9]

Increased root growth

Certain varieties of barley plants produce larger root systems. A larger root system improves tolerance to drought by not only increasing the surface area for mineral nutrient absorption, but also by improving the ability of plants to reach deep ground water. [10]

Increased antioxidant production

Barley plants grown under drought stress exhibit higher activity of antioxidant enzymes, which prevent oxidative damage from reactive oxygen species. [11] Plants are at increased risk of cellular damage when exposed to drought stress due to increased production of reactive oxygen species, and therefore this increased antioxidant activity likely aids in protecting the plant under drought stress.[ citation needed ]

Reduced stomatal density

Studies have shown that reduced stomatal density in barley plants does not decrease grain yield despite decreasing gas exchange. [12] A decrease in number of stomata improves drought tolerance by simply inhibiting water escape, thus enhancing water-use efficiency. [12]

Decreased nitric oxide levels

Barley plants grown under drought stress also exhibit decreased levels of nitric oxide, which studies have shown increased polyamine production. [13] Polyamines aid in plant wellbeing during drought stress by stabilizing cellular structures, such as DNA and membranes, [13] thus prolonging survival.[ citation needed ]

Genetic basis

Recent research has shown that barley is highly variable in its genotypes concerning drought tolerance, in both wild and cultivated varieties. [14] Indeed, quantitative trait loci (QTLs) have been associated with barley seed germination in drought conditions. [15] As well, varieties grown in more arid climates exhibit better regulation of reactive oxygen species than varieties grown in cooler climates. [16] Traits which would be favourable and unfavourable in drought conditions have been found to exist in barley plants, [17] suggesting that the agricultural industry could plausibly select for drought-resistant traits in barley plants to grow in warmer regions, and the opposite for cooler regions in order to maximize yield.[ citation needed ]

Identifying the genes responsible for drought tolerance in barley plants and applying them to other plant species or other barley varieties via transgenics has also shown promising results. One study expressed the hva1 gene from barley in creeping bentgrass, and found that it improved drought tolerance by lessening the effects of water-deficit damage. [18] Similarly, transgenic Basmati rice plants containing an hva1 gene from barley exhibited higher drought tolerance than control plants. [19] Other research finds that expression of the HvMYB1 gene in barley is increased under drought stress, and when over-expressed in transgenic barley plants, was found to increase drought tolerance. [20] Induced over-expression of K+ transporters in barley plants has also been found to increase drought tolerance, due to the many roles K+ plays in plant metabolism and physiology, such as stomatal aperture. [21]

See also

Related Research Articles

Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.

<span class="mw-page-title-main">Stoma</span> In plants, a variable pore between paired guard cells

In botany, a stoma, also called a stomate, is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spaces of the leaf and the atmosphere. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that regulate the size of the stomatal opening.

<span class="mw-page-title-main">Plant hormone</span> Chemical compounds that regulate plant growth and development

Plant hormones are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, including embryogenesis, the regulation of organ size, pathogen defense, stress tolerance and reproductive development. Unlike in animals each plant cell is capable of producing hormones. Went and Thimann coined the term "phytohormone" and used it in the title of their 1937 book.

C<sub>4</sub> carbon fixation Photosynthetic process in some plants

C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.

<span class="mw-page-title-main">Photorespiration</span> Process in plant metabolism

Photorespiration (also known as the oxidative photosynthetic carbon cycle or C2 cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in C3 plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.

C<sub>3</sub> carbon fixation Series of interconnected biochemical reactions

C3 carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, the other two being C4 and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into two molecules of 3-phosphoglycerate through the following reaction:

<span class="mw-page-title-main">Abscisic acid</span> Plant hormone

Abscisic acid is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to environmental stresses, including drought, soil salinity, cold tolerance, freezing tolerance, heat stress and heavy metal ion tolerance.

Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure. Moisture stress is described by two main metrics, water potential and water content.

<span class="mw-page-title-main">Guard cell</span> Paired cells that control the stomatal aperture

Guard cells are specialized plant cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are largest when water is freely available and the guard cells become turgid, and closed when water availability is critically low and the guard cells become flaccid. Photosynthesis depends on the diffusion of carbon dioxide (CO2) from the air through the stomata into the mesophyll tissues. Oxygen (O2), produced as a byproduct of photosynthesis, exits the plant via the stomata. When the stomata are open, water is lost by evaporation and must be replaced via the transpiration stream, with water taken up by the roots. Plants must balance the amount of CO2 absorbed from the air with the water loss through the stomatal pores, and this is achieved by both active and passive control of guard cell turgor pressure and stomatal pore size.

In botany, drought tolerance is the ability by which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions, surviving with protection mechanisms such as desiccation tolerance, detoxification, or repair of xylem embolism. Other plants, specifically crops like corn, wheat, and rice, have become increasingly tolerant to drought with new varieties created via genetic engineering. From an evolutionary perspective, the type of mycorrhizal associations formed in the roots of plants can determine how fast plants can adapt to drought.

A xerophyte is a species of plant that has adaptations to survive in an environment with little liquid water. Examples of xerophytes include cacti, pineapple and some gymnosperm plants. The morphology and physiology of xerophytes are adapted to conserve water during dry periods. Some species called resurrection plants can survive long periods of extreme dryness or desiccation of their tissues, during which their metabolic activity may effectively shut down. Plants with such morphological and physiological adaptations are said to be xeromorphic. Xerophytes such as cacti are capable of withstanding extended periods of dry conditions as they have deep-spreading roots and capacity to store water. Their waxy, thorny leaves prevent loss of moisture.

<span class="mw-page-title-main">Transpiration</span> Process of water moving through a plant parts

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a passive process that requires no energy expense by the plant. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients. When water uptake by the roots is less than the water lost to the atmosphere by evaporation plants close small pores called stomata to decrease water loss, which slows down nutrient uptake and decreases CO2 absorption from the atmosphere limiting metabolic processes, photosynthesis, and growth.

Dehydrin (DHN) is a multi-family of proteins present in plants that is produced in response to cold and drought stress. DHNs are hydrophilic, reliably thermostable, and disordered. They are stress proteins with a high number of charged amino acids that belong to the Group II Late Embryogenesis Abundant (LEA) family. DHNs are primarily found in the cytoplasm and nucleus but more recently, they have been found in other organelles, like mitochondria and chloroplasts.

<span class="mw-page-title-main">Photosynthesis system</span> Instruments measuring photosynthetic rates

Photosynthesis systems are electronic scientific instruments designed for non-destructive measurement of photosynthetic rates in the field. Photosynthesis systems are commonly used in agronomic and environmental research, as well as studies of the global carbon cycle.

Water-use efficiency (WUE) refers to the ratio of plant biomass to water lost by transpiration, can be defined either at the leaf, at the whole plant or a population/stand/field level:

Stomatal conductance, usually measured in mmol m−2 s−1 by a porometer, estimates the rate of gas exchange and transpiration through the leaf stomata as determined by the degree of stomatal aperture.

Breeding for drought resistance is the process of breeding plants with the goal of reducing the impact of dehydration on plant growth.

Hydraulic signals in plants are detected as changes in the organism's water potential that are caused by environmental stress like drought or wounding. The cohesion and tension properties of water allow for these water potential changes to be transmitted throughout the plant.

<span class="mw-page-title-main">Alarm photosynthesis</span> Variation of photosynthesis

Alarm photosynthesis is a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO2) to photosynthetic cells when stomata are partially or totally closed. This biochemical appendance of the photosynthetic machinery is a means to alleviate the perpetual plant dilemma of using atmospheric CO2 for photosynthesis and losing water vapor, or saving water and reducing photosynthesis. The function of alarm photosynthesis seems to be rather auxiliary to the overall photosynthetic performance. It supports a low photosynthetic rate, aiming at the maintenance and photoprotection of the photosynthetic apparatus rather than a substantial carbon gain.

Chemical defenses in <i>Cannabis</i> Defense of Cannabis plant from pathogens

Cannabis (/ˈkænəbɪs/) is commonly known as marijuana or hemp and has two known strains: Cannabis sativa and Cannabis indica, both of which produce chemicals to deter herbivory. The chemical composition includes specialized terpenes and cannabinoids, mainly tetrahydrocannabinol (THC), and cannabidiol (CBD). These substances play a role in defending the plant from pathogens including insects, fungi, viruses and bacteria. THC and CBD are stored mostly in the trichomes of the plant, and can cause psychological and physical impairment in the user, via the endocannabinoid system and unique receptors. THC increases dopamine levels in the brain, which attributes to the euphoric and relaxed feelings cannabis provides. As THC is a secondary metabolite, it poses no known effects towards plant development, growth, and reproduction. However, some studies show secondary metabolites such as cannabinoids, flavonoids, and terpenes are used as defense mechanisms against biotic and abiotic environmental stressors.

References

  1. ↑ Goyal, A.; Ahmed, M. (November 2012). "Barley: Production, Improvement, and Uses". Crop Science. 52 (6): 2852–2854. doi:10.2135/cropsci2012.12.0003bra. ISSN   0011-183X. S2CID   252135699.
  2. ↑ Varshney, Rajeev (2013). Translational Genomics for Crop Breeding : Volume 2 - Improvement for Abiotic Stress, Quality and Yield Improvement. Wiley-Blackwell. ISBN   978-1-299-87149-6. OCLC   858653470.
  3. ↑ Verstegen, Harold; Köneke, Otto; Korzun, Viktor; von Broock, Reinhard (2014), Kumlehn, Jochen; Stein, Nils (eds.), "The World Importance of Barley and Challenges to Further Improvements", Biotechnological Approaches to Barley Improvement, vol. 69, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 3–19, doi:10.1007/978-3-662-44406-1_1, ISBN   978-3-662-44405-4 , retrieved 2022-12-05
  4. ↑ Swanston, J. Stuart (2011-07-29). "Barley: Production, Improvement and Uses. Edited by S. E. Ullrich, Chichester, UK: Wiley-Blackwell (2011), pp. 637, £170.00. ISBN 978-0-8138-0123-0". Experimental Agriculture. 47 (4): 733. doi:10.1017/s0014479711000615. ISSN   0014-4797. S2CID   83513924.
  5. ↑ Wiegmann, Mathias; Maurer, Andreas; Pham, Anh; March, Timothy J.; Al-Abdallat, Ayed; Thomas, William T. B.; Bull, Hazel J.; Shahid, Mohammed; Eglinton, Jason; Baum, Michael; Flavell, Andrew J.; Tester, Mark; Pillen, Klaus (December 2019). "Barley yield formation under abiotic stress depends on the interplay between flowering time genes and environmental cues". Scientific Reports. 9 (1): 6397. Bibcode:2019NatSR...9.6397W. doi:10.1038/s41598-019-42673-1. ISSN   2045-2322. PMC   6484077 . PMID   31024028.
  6. ↑ Walker, A.; et al. (2021). Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2. Umeå universitet, Institutionen för medicinsk kemi och biofysik. OCLC   1234762992.
  7. ↑ Finkelstein, Ruth (2013-11-01). "Abscisic Acid Synthesis and Response". The Arabidopsis Book. 11: e0166. doi:10.1199/tab.0166. ISSN   1543-8120. PMC   3833200 . PMID   24273463.
  8. ↑ Muhammad Aslam, Mehtab; Waseem, Muhammad; Jakada, Bello Hassan; Okal, Eyalira Jacob; Lei, Zuliang; Saqib, Hafiz Sohaib Ahmad; Yuan, Wei; Xu, Weifeng; Zhang, Qian (2022-01-19). "Mechanisms of Abscisic Acid-Mediated Drought Stress Responses in Plants". International Journal of Molecular Sciences. 23 (3): 1084. doi: 10.3390/ijms23031084 . ISSN   1422-0067. PMC   8835272 . PMID   35163008.
  9. ↑ Popova, L. P.; Lazova, G. N. (1990), "Carbonic Anhydrase Activity in Barley Leaves After Treatment with Abscisic Acid and Jasmonic Acid", Current Research in Photosynthesis, Dordrecht: Springer Netherlands, pp. 3273–3277, doi:10.1007/978-94-009-0511-5_737, ISBN   978-94-010-6716-4 , retrieved 2022-12-05
  10. ↑ Chloupek, O.; Dostál, V.; Středa, T.; Psota, V.; Dvořáčková, O. (December 2010). "Drought tolerance of barley varieties in relation to their root system size: Drought tolerance and roots size of barley". Plant Breeding. 129 (6): 630–636. doi:10.1111/j.1439-0523.2010.01801.x.
  11. ↑ Matamoros, M. A.; Loscos, J.; Dietz, K.-J.; Aparicio-Tejo, P. M.; Becana, M. (2010-01-01). "Function of antioxidant enzymes and metabolites during maturation of pea fruits". Journal of Experimental Botany. 61 (1): 87–97. doi:10.1093/jxb/erp285. ISSN   0022-0957. PMC   2791115 . PMID   19822534.
  12. 1 2 Hughes, Jon; Hepworth, Christopher; Dutton, Chris; Dunn, Jessica A.; Hunt, Lee; Stephens, Jennifer; Waugh, Robbie; Cameron, Duncan D.; Gray, Julie E. (June 2017). "Reducing Stomatal Density in Barley Improves Drought Tolerance without Impacting on Yield". Plant Physiology. 174 (2): 776–787. doi:10.1104/pp.16.01844. ISSN   0032-0889. PMC   5462017 . PMID   28461401.
  13. 1 2 Montilla-Bascón, Gracia; Rubiales, Diego; Hebelstrup, Kim H.; Mandon, Julien; Harren, Frans J. M.; Cristescu, Simona M.; Mur, Luis A. J.; Prats, Elena (2017-10-17). "Reduced nitric oxide levels during drought stress promote drought tolerance in barley and is associated with elevated polyamine biosynthesis". Scientific Reports. 7 (1): 13311. Bibcode:2017NatSR...713311M. doi:10.1038/s41598-017-13458-1. ISSN   2045-2322. PMC   5645388 . PMID   29042616. S2CID   205612254.
  14. ↑ Cai, Kangfeng; Chen, Xiaohui; Han, Zhigang; Wu, Xiaojian; Zhang, Shuo; Li, Qi; Nazir, Muhammad Mudassir; Zhang, Guoping; Zeng, Fanrong (2020). "Screening of Worldwide Barley Collection for Drought Tolerance: The Assessment of Various Physiological Measures as the Selection Criteria". Frontiers in Plant Science. 11: 1159. doi: 10.3389/fpls.2020.01159 . ISSN   1664-462X. PMC   7403471 . PMID   32849716.
  15. ↑ Thabet, Samar G.; Moursi, Yasser S.; Karam, Mohamed A.; Graner, Andreas; Alqudah, Ahmad M. (2018-11-02). "Genetic basis of drought tolerance during seed germination in barley". PLOS ONE. 13 (11): e0206682. Bibcode:2018PLoSO..1306682T. doi: 10.1371/journal.pone.0206682 . ISSN   1932-6203. PMC   6214555 . PMID   30388157.
  16. ↑ Wendelboe-Nelson, Charlotte; Morris, Peter C. (November 2012). "Proteins linked to drought tolerance revealed by DIGE analysis of drought resistant and susceptible barley varieties". Proteomics. 12 (22): 3374–3385. doi:10.1002/pmic.201200154. PMID   23001927. S2CID   29301162.
  17. ↑ Shakhatreh, Y.; Kafawin, O.; Ceccarelli, S.; Saoub, H. (2001-04-22). "Selection of Barley Lines for Drought Tolerance in Low-Rainfall Areas". Journal of Agronomy and Crop Science. 186 (2): 119–127. Bibcode:2001JAgCS.186..119S. doi:10.1046/j.1439-037x.2001.00459.x. ISSN   0931-2250.
  18. ↑ Fu, Daolin; Huang, Bingru; Xiao, Yanmei; Muthukrishnan, Subbaratnam; Liang, George H. (2007-04-01). "Overexpression of barley hva1 gene in creeping bentgrass for improving drought tolerance". Plant Cell Reports. 26 (4): 467–477. doi:10.1007/s00299-006-0258-7. ISSN   1432-203X. PMID   17106681. S2CID   494394.
  19. ↑ Rohila, Jai S; Jain, Rajinder K; Wu, Ray (2002-09-01). "Genetic improvement of Basmati rice for salt and drought tolerance by regulated expression of a barley Hva1 cDNA". Plant Science. 163 (3): 525–532. doi:10.1016/S0168-9452(02)00155-3. ISSN   0168-9452.
  20. ↑ Alexander, Ross D.; Wendelboe-Nelson, Charlotte; Morris, Peter C. (2019-09-01). "The barley transcription factor HvMYB1 is a positive regulator of drought tolerance". Plant Physiology and Biochemistry. 142: 246–253. doi:10.1016/j.plaphy.2019.07.014. ISSN   0981-9428. PMID   31374377. S2CID   199387889.
  21. ↑ Feng, Xue; Liu, Wenxing; Qiu, Cheng-Wei; Zeng, Fanrong; Wang, Yizhou; Zhang, Guoping; Chen, Zhong-Hua; Wu, Feibo (August 2020). "HvAKT2 and HvHAK1 confer drought tolerance in barley through enhanced leaf mesophyll H + homoeostasis". Plant Biotechnology Journal. 18 (8): 1683–1696. doi:10.1111/pbi.13332. ISSN   1467-7644. PMC   7336388 . PMID   31917885.
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