Glycine Betaine (GB) is an amphoteric quaternary amine that plants produce as an adaptive response to water stress. It increases resistance of crops to drought, extreme temperatures and salinity, thus enhancing crop yield.
GB mitigates the yield-declining impacts of HS in several crops [160]. GB significantly reduces MDA accumulation and lipid peroxidation caused by Cd toxicity in cotton [161]. It also enhances salt tolerance in mung bean.
Increases Photosynthetic Activity
Glycine betaine (GB) is a non-toxic, organic, class IV compound that promotes plant growth by improving photosynthetic efficiency. It can also be absorbed into the meristematic tissues of plants, such as buds and stem tips, where it is able to promote growth and flowering.
GBP can be used to mitigate the effects of abiotic stresses such as salt, drought, heavy metals and chilling stress. In addition to enhancing photosynthetic activity, it can also help reduce stomatal limitations and improve plant morphology.
GB also enhances seed germination and improves seedling growth. It has been shown to increase the expression of genes involved in producing antioxidant enzymes and thereby lowers ROS accumulation. In addition, GB can inhibit lipid membrane oxidation, improve chlorophyll content and increase protein contents in two Zea mays L. cultivars under salt stress.
Reduces Stomatal Closure
Heavy metal (HM) pollution is a widespread phenomenon and limits the profitable yield of different plant species. HMs can cause several detrimental effects such as biomagnifications, oxidative stress and stomatal closure. However, the application of osmoprotectants can mitigate these abiotic stresses and increase plant productivity.
The osmoregulator Glycine Betaine (GB) is a natural compound that is derived from betaine aldehyde dehydrogenase (BADH). BADH is an enzyme with a multifunctional role in fragrance production, resistance against abiotic and osmotic stresses and antibiotic-free selection of transgenic plants [31].
Exogenous GB increased the leaf gas exchange attributes, photosynthetic pigments and antioxidant activities of salt-stressed Gossypium hirsutum seedlings [32]. Exogenous GB at high concentration also significantly reduced stomatal closure and increased stomatal conductance under 150 mM salinity. Moreover, the increase of stomatal opening was more pronounced in plants treated with a higher concentration of GB compared to the control.
Reduces Malondialdehyde (MDA) Accumulation
Glycine Betaine (GB) is a natural antioxidant that protects plants from the damaging effects of stress. It reduces oxidative damage by inhibiting the production of ROS. It also enhances the activity of phenol oxidases and antioxidative enzymes.
In the field, GB has been shown to promote flowering and growth in plants. The increase in growth is mainly due to the upregulation of morphological parameters and the activation of meristem-related genes.
GB has been shown to mitigate the adverse effects of heavy metals (HMs) on plant growth. HMs induce the production of ROS, which damages the cellular compartments and hinders the photosynthetic machinery. GB acts as an osmolyte, and prevents the accumulation of ROS in plants under HMs stress.
In addition, GB enhances the antioxidant system in plants by triggering gene expression and increasing the activities of CAT, POX, and SOD enzymes. This leads to a reduction in the accumulation of MDA, an indicator of oxidative stress.
Increases Leaf Turgidity
Glycine betaine (GB) is a naturally occurring class IV organic compound that accumulates in plants and animal cells and serves as their main osmolyte. Its accumulation alleviates abiotic stress condition such as drought, salt and heavy metals by increasing the number of photosynthetic pigments and machinery in plants, plant height and root and stem growth, as well as chlorophyll content.
Exogenous application of GB enhances the ability of plants to resist the deleterious effects of cadmium (Cd) stress by regulating gene expressions to create additional antioxidant enzymes and reducing unwarranted ROS in perennial ryegrass (Lemna gibba L.) plants [82].
GB also promotes plant growth under salt stress by increasing the number and activity of nodules in rapeseed mustard (Brassica oleracea) and the biological process of nitrogen fixation in rice (Oryza sativa L.) plants [163]. It is also effective in enhancing the tolerance of chickpea (Cicer arietinum L.) plants to chilling stress by increasing pollen germination, sperm viability, and flowering [176].
Increases Leaf Growth
Glycine Betaine significantly enhances the growth of leaves, roots, stems, and flowers in fenugreek (Trigonella foenum-graecum L.) under salt stress, particularly at a low concentration of 50 mM. In addition, it increases photosynthetic pigments, relative water content, protein contents, and antioxidant activity.
GB also alleviates the negative effects of salinity on fenugreek plants by increasing photosynthesis and chlorophyll fluorescence parameters, such as Fv/Fm, in the absence of stomatal closure, whereas it decreases the photosynthetic efficiency when stomata are closed. This effect is mediated by the inhibition of the oxidation of thiols in the chloroplasts, which causes photorespiration and energy loss in the cells.
Exogenous GB also increases the contents of amino acids, including glutamate, proline, aspartate, serine, arginine, threonine, leucine, valine, isoleucine, methionine, and tryptophan, although it decreases their conversion and utilization rates.