Abiotic Stress in Plants

Abstract

Stress in plants refers to external conditions, which drastically affect the growth, development, or productivity of plants. Stress triggers a wide range of plant responses, such as altered gene expression, cellular metabolism, changes in growth rates, and crop yields. Some abiotic stresses, such as low or high temperature, deficient water, and ultraviolet radiation, make plant growth and development unfavorable, leading to a fall in crop yield worldwide. The following writeup incorporated the abiotic stress factors related to the growth and development of plants, such as temperature, drought, heat, cold, and many more. Abiotic stress factors are the nonliving factors influencing the metabolism, growth, and development of the plant tissues at that particular time when such abiotic stress affects them. As a result of such abiotic stresses, the plants have generated many stress tolerance factors. Various stress-responsive genes are thus being formulated in response to the abiotic stresses, so the plants can survive even in such extreme conditions as well. Henceforth, it can be concluded that the abiotic stress factors imposed on the plants adversely impact their growth and developmental procedures, and at the same time, they also produce some stress tolerance factors to minimize the damage.

1. Introduction

Abiotic stress can be defined as the adverse impacts created by the abiotic factors on the plant tissues [1]. Abiotic stress is caused by nonliving factors that are in contrast to biotic stress, which is caused by living organisms. The various factors impacting the plant tissues interrupt their normal metabolism. In response to this stress, the plants adapt newer metabolic reactions to resist the stress. The majority of such reactions aid them to regulate and sustain themselves against various environmental factors [1].

In Figure 1, stresses influencing the growth and developmental patterns of plants are shown. As stated by the figure, plant stress depends upon the stress factors being living or nonliving and thus the stress gets segmented as biotic (living) stress and abiotic (nonliving) stress in plants [2].

Figure 1.

Some of the common plant stresses: both biotic and abiotic stresses have effects on plants.

2. Stress impacts on plants

The consequence of the stress factors on the plant tissue is their influence on their growth and development pattern [2]. As a result of the stresses, various types of plant metabolism get triggered, such as the altered expression of the inherited genes, metabolism of the cells of plants, changed patterns of growth types, crop yields, and much more [2]. However, as stated by Zhang et al. [3], there are two types of stresses—biotic and abiotic that are observed among the plant tissues.

2.1 Biotic stress

Biotic stress is caused by living organisms, such as viruses, bacteria, fungi, nematodes, insects, weeds, and many others [4]. Such stressors deprive the host plants of the growth factors and nutrients within them and eventually the plants die. Thus, biotic stress factors become the major reason for the plants pre-and post-harvest losses.

In Figure 2, the influence of the endophytic fungi on desert plants is. The figure shows how fungi grow with the association of the plants and thus take in salts, water, and other nutrients from the plant roots. In such cases, the growing plants become deprived of salt and water and continuous salt stress and water deficiency are encountered [5]. As a result of all such negative impacts, the deterioration of the inherent metabolism of the plant parts occur. Additionally, in the case of the desert plants, already deserts are known for lower availability of water, thus any such further disturbances by the endophytic fungi have adversely impacted the plant growth [5].

Figure 2.

Biotic stress on the desert plant: the endophytic fungi are taking the natural product of the soil meant for the plant and creating biotic stress.

2.2 Abiotic stress

Abiotic stress factors are the nonliving factors influencing the present metabolism, growth, and development of the plant tissues [6]. As stated by Sharma et al. [7], abiotic stress factors impacting plants are excessive hot temperature, extreme cold temperature, salinity, drought, mineral availability or toxicity, and much more. Such abiotic stress factors have, thus, negatively impacted the overall crop yields, and, thus, there is a need of generating resistant plant varieties that can sustain against abiotic stress factors [6].

Figure 3 showcases the various abiotic stress impacting plant parts and their relative outcomes. As stated in the figure, sunlight, cold weather, salinity, and mineral availability or deficiency are the major abiotic stress factors for a plant [8]. As a result of various stress factors, multiple responses can be seen. For example—the amount of ROS (reactive oxygen species) can be increased, plant growth and yield reduced, and simultaneously photosynthetic activity can be reduced. The adverse environmental temperatures deteriorated the plants’ growth and developmental patterns [8].

Figure 3.

Abiotic stress factors in plants: major abiotic stress factors for a plant deficiency are sunlight, cold weather, salinity, and mineral availability or deficiency. They are the major abiotic stress factors for plant deficiency.

3. Mechanism of abiotic stress

The abiotic stress is known to impact the internal metabolism of the plant parts, and, thus, the overall productivity of the plants gets reduced [9]. This could be the major adverse impact as the abiotic stress factors are widely known to cause mostly negative impacts only [9]. The several abiotic stress factors and their simultaneous mechanisms are being discussed as follows:

3.1 Cold

Every plant is known to survive at a particular temperature only. The alteration of the required temperature changed the overall sustenance patterns of the individual plants [10]. In case of plants growing in cold temperatures, cold temperature would result in disruption of the plant tissues, as a result, it would lead to deterioration of the life cycle of plants.

Figure 4 explains the various mechanisms adopted by the plants to mitigate the cold stress factors against the sustenance of plants [10]. As seen from the figure, the incorporation of such stress factors aids the plants to generate signals and further transcriptional control so that the genes of stress signaling could be simultaneously activated. This will ultimately lead to re-establishment of the cellular homeostasis and functional and structural protection of protein and membranes [10]. All such optimistic sequential steps impacted positively internal cellular membranes and, thus, lead to stress tolerance or resistance against abiotic stress factors by plants [10].

Figure 4.

Mechanism of abiotic stress factors on plants: genes of abiotic stress signaling could be simultaneously activated. This will ultimately lead to re-establishment of the cellular homeostasis, functional and structural stress tolerance, or resistance protection of proteins and membranes.

3.2 Salt

The salt concentration is one of the major factors impacting plants’ growth and development [11]. Higher amounts of salt lead to the re-release of genes for minimizing stresses against salt concentration and thus optimizing the plants to survive in such hazardous situations as well.

Figure 5 illustrates the fact that accumulation of solute concentration leads to mineral absorption in an excessive amount and simultaneously it leads to cell wall modification and incorporation of transporters that lead to re-transportation of salts to mesophyll, homeostasis of potassium, and nitrate ions and thus generating optimistic stress responses [12].

Figure 5.

Factors impacting salt stress in plants: excessive amount of mineral absorption leads to cell wall modification and incorporation of transporters that lead to re-translocation of salts to mesophyll, homeostasis of potassium and nitrate ions, and thus generating optimistic stress responses.

3.3 Toxin

Toxins are chemicals released by the plant tissues in response to several abiotic stress factors [13]. Toxins are also considered to be the surrounding stress factors adversely impacted by the environment, and, thus, the plants are getting negatively impacted by such abiotic stress factors.

Figure 6 illustrates the toxins released by the cell wall, cell membranes, cytoplasm, chloroplast, mitochondrion, endoplasmic reticulum, peroxisome, and nucleus [14]. Signal integration of the stress factors occurs now and the stress response genes are activated and released. These responses lead to the sustenance of the overall growth and development of the plant parts [14].

Figure 6.

Mitigation strategies against toxins: signal integration of the stress factors occurs and the stress response genes are activated and released. These responses lead to the sustenance of the overall growth and development of the plant parts.

4. Mitigation strategies adopted by plants for overcoming abiotic stress factors

The abiotic stress factors are the ones that cannot be sustained and mitigated by the plants externally, henceforth plants are known for developing fresh mechanisms within their inner metabolism to balance the excessive adverse impacts created by the outside environment [7]. Many such mitigation strategies are adopted by plants to overcome such abiotic stress factors [7].

In Figure 7, the sequential steps adopted by plants to overcome the abiotic stress impacts are shown. The figure states that with abiotic stresses, the plants tend to develop excessive ROS. Such an excessive production leads to the further incorporation of 3 steps—activation of oxygen antioxidants, up-regulation of osmolytes, and activation of stress-responsive genes [15]. The activation of the stress-responsive genes makes the plants much tolerant and thus they can survive against such hazardous temperatures as well. So identification of targeted genes is necessary as the overall mechanism depends upon such gene regulations only [3]. Henceforth it can be concluded that oxidative stress reduction results in an increase in the stress tolerance factors and long-term sustainability of the plants in such adverse conditions as well [3].

Figure 7.

Steps for overcoming abiotic stress by plants: in abiotic stresses, the plants tend to develop excessive ROS in oxidative stress reduction, which results in increase of stress tolerance factors and long-term sustainability of the plants.

5. Conclusion

The research on abiotic stress factors on plant growth and development reveals that they are the major factors that influence and lead to the deterioration of the plant species. Heat, cold, drought, salinity, and toxins are various abiotic stressors impacting adversely the overall development of plants. Various stress-responsive genes are formulated in response to abiotic stresses so that the plants can survive extreme conditions as well. Rapid population growth, economic development, and international economic integration have intensified resource use in every sector of the world. The human population is expected to increase to a total of 9 billion by 2050. So production of more food from the same area of land will be needed and this can happen only by reducing the adverse environmental impacts on plants. This is what has been called sustainable intensification, for feeding, clothing, and providing energy to such a large population. Transgenic approaches have been proven to show as powerful tools to help understand and manipulate the responses of plants to stress. Global research analyses indicate that transcription to proteins and metabolites occurs during abiotic stress. These findings will advance our understanding of major metabolic pathways and provide direction for achieving abiotic stress-tolerant plants. The viable evaluation of transgenes that enhance crop performance under both stress and optimal conditions is a prolonged, tedious, and expensive process. It is being proposed that the current stance on plant stress tolerance can be significantly polished by thorough characterization of individual genes and evaluating their contribution to stress tolerance.

The molecular mechanisms of plants to create stress tolerance against salt, drought, and temperature involve a number of regulatory proteins, such as transcription factors. The study of such mechanisms enabled us to increase our knowledge of enhanced plant survival and increased crop yields in spite of abiotic stresses. Further research is needed for accurate evaluation in the field of genotypes for abiotic stress resistance, a deeper understanding of the transcription factors that regulate major stress-responsive genes, and cross-talks between divergent signaling components. We are to advance our knowledge on traits that are associated with root architecture and plasticity, especially in agronomically superior genotypes under abiotic stress conditions. Crop tolerance to various abiotic stresses is a matter of continued research to increase our knowledge further and to help plants from deterioration and extinction. The stress biotechnology research in the recent future will emphasize on strength and stress-induced expression of the transgenes, combined with the regulatory machinery involving transcription factors as a new genetic manipulation tool for controlling the expression of many different stress-responsive genes.

In conclusion, plant sciences currently achieve good models of how model plants react to environmental factors by transcriptional and metabolic reprogramming. However, especially molecular research efforts in crops have to be strengthened considerably. Plant stress physiology is a very complex matter and needs future biocomputational integration of multiple omics and meta-omics to understand it properly. This needs further effort in developing innovative research tools and fundamental resources for crop plant research, such as reference genomes, proteomes, and metabolomes with comprehensive annotations and structure-function relationships, respectively. Even for the model Arabidopsis, these resources are not fully available. Nevertheless, in several cases, Arabidopsis and other model plants have already been proved suitable for the translation of fundamental research into agronomically relevant crop traits. This is encouraging but requires further and significant investment into translational research. Besides this, it remains indispensable to investigate abiotic stress resistance mechanisms directly in elite crop plants and in the genetic resources available for breeding.