Perspective Chapter: Effect of Low-Temperature Stress on Plant Performance and Adaptation to Temperature Change

*Veena Devi, Amanpreet Kaur, Mehak Sethi and Gosangi Avinash*

## **Abstract**

Low-temperatures (LT) stress is one of the abiotic stresses in plants that affect cell survival, cell division, photosynthesis, and water transport, negatively affecting plant growth, and eventually constraining crop productivity. LT stress is categorized as, (i) chilling stress where low temperature (0–15°C) causes injury without ice crystal formation in plant tissues, and (ii) freezing stress (<0°C), where ice formation occurs within plant tissues. Both stresses are together termed low temperature or cold stress. In general, plants originating from tropical and subtropical regions are sensitive to LT, whereas temperate plants showed chilling tolerance to variable degrees. Low-temperature stress negatively impacts plants, may affect the survival rate of crop plants, and also affect various processes, including cell division, photosynthesis, plant growth, development, metabolism, and finally reduce the yield of crop plants, especially in the tropics and subtropics. To overcome stress generated by low-temperature exposure, plants trigger a cascade of events that enhance their tolerance by gene expression changes and activation of the ROS scavenging system, thus inducing biochemical and physiological modifications. In this chapter, a detailed discussion of different changes in plants and their tolerance mechanism is done to understand the plant's response under LT stress.

**Keywords:** low-temperature stress, oxidative stress, resilience, stress tolerance

## **1. Introduction**

Low-temperature (LT) stress is one of the abiotic stresses [1] in plants that affect cell survival, cell division, photosynthesis, and water transport with a negative effect on plant growth, eventually constraining crop productivity [2, 3]. LT stress is categorized as, (i) chilling stress, where low temperature (0–15°C) causes injury without ice crystal formation in plant tissues, and (ii) freezing stress (<0°C), where ice formation occurs within plant tissues. Both stresses are termed low temperature or cold stress [4]. In general, plants originating from tropical and subtropical regions are sensitive to LT, whereas temperate plants showed chilling tolerance to variable degrees [2]. Low temperature

negatively impacts plants, may affect the survival rate of crop plants, and also affect various processes including cell division, photosynthesis, plant growth, development, metabolism, and finally reduce the yield of crop plants, especially in the tropics and subtropics [5, 6]. To overcome stress generated by LT exposure, plants trigger a cascade of events that enhance their tolerance by changes in gene expression and activation of the ROS scavenging system and thus inducing biochemical and physiological modifications [7, 8]. This review is a detailed discussion of different changes in plants and their tolerance mechanism in order to understand the plant's response under LT stress.

### **2. Morpho-physiological changes in crop plants in response to LT stress**

Morphological changes are the change that is visible on the plants during the early stage of LT stress. These are the primary signs of the plants, indicating adverse effects of stress on plants. Stress reduces leaf expansion, causes chlorosis, wilting of leaves and necrosis, and accelerates senescence in crop plants [9, 10]. Various metabolic reactions were inhibited by LT exposure, consequently preventing the plant's full genetic expression potential expressed by diverse phenotypic symptoms [11]. Low temperature is a limiting factor for seed germination and plant growth [12–14]. Under LT stress in *Elymus nutans* Griseb, the shoot and root lengths in tolerant seedlings were longer than the susceptible ones. Low temperatures also increased the mortality percentage of seedlings [15]. LT dramatically affects photosynthesis as well [16]. The negative impact of abiotic stress on the photosynthetic process in plants has been extensively studied and measurement of chlorophyll fluorescence (Fv/Fm) has proven as an effective, reproducible, and nondestructive tool for evaluating the susceptibility index of plants subjected to LT stress [3, 17]. Under LT stress, photosynthesis is impaired, resulting in a lower amount of carbohydrates for grain production and reducing growth, adding to indirect yield loss [3]. In rice seedlings, LT stress affected total chlorophyll (Chl) content and thus photosynthetic efficiency [18, 19]. Proteomic analysis in a semihardy winter wheat cultivar under natural field conditions indicated a down-regulation of several photosynthesis-related proteins (such as oxygen-evolving enhancer protein, NADH dehydrogenase, and dehydroascorbate reductase) during the initiation of cold acclimation [16]. Low temperature decreases photosynthesis due to partial stomatal closure, slowdown of electron transport, inhibits metabolism of carbohydrates, and interferes with phloem loading [13]. In plants, the content of both total Chl and chlorophyll b (Chl b) decreased and the Chl a/b ratio increased under low night temperature stress [17]. Low night temperature probably enhanced the activity of chlorophyllase enzyme in leaves and hence resulted in reduced Chl synthesis. Most of the Chl a, all the Chl b, and other pigments absorb light. They transfer that light energy to the reaction center but only a part of Chl a molecule can utilize that energy to perform the charge separation process. Plants maintain a relatively higher level of Chl a content, so that they can perform the process of photosynthesis normally and adapt themselves to cold stress. The cessation of growth ensuing from cold stress decreases the capacity of utilizing the energy and hence results in feedback inhibition of photosynthesis. In cold-acclimated winter annuals, Calvin cycle enzymes accumulate in higher amounts and effectively maintain the photosynthetic activity of plants. The Chl content and photosynthetic parameters like Fv/Fm had a positive correlation with chilling injury indices and have been utilized as a marker of cold tolerance in sugarcane [20]. Under dark chilling treatment, Fv/ Fm significantly decreased in plants and after the recovery period, the Fv/Fm ratio

*Perspective Chapter: Effect of Low-Temperature Stress on Plant Performance and Adaptation… DOI: http://dx.doi.org/10.5772/intechopen.110168*

recovered to nearly that of the control levels [21, 22]. A greater decrease in Chl content in the cold-sensitive rice genotype was reported as compared to the cold-tolerant genotype under cold stress [23]. LT tolerant lines of rice, after stress, seedling height in both the lines remained unchanged over time; however, more tolerant seedlings (M202) exhibited a small increase in the root-to-shoot ratio [23].

Carotenoids are not considered photosynthetic pigments, but play important role in protecting the photosystems from damage. They have structural roles and act as natural antioxidants, quenching triplet Chl and singlet oxygen species, which are potentially harmful to the chloroplast [24, 25]. Carotenoids also maintain and stabilize thylakoid membranes from the damage caused by lipid peroxidation and cold stress [26]. In *Elymus nutans* seedlings, carotenoid content was decreased when exposed to cold stress at 5°C. The decrease in carotenoid content was higher in GN (more sensitive) than DX (tolerant) seedlings [15].

In conclusion, under LT stress plants showed various phenotypic symptoms, these are the primary symptoms of stress. Photosynthetic pigments and photosynthetic parameters like Fv/Fm ratio are altered under LT stress and showed a positive correlation with the chilling injury indices and potential to be used as a marker for cold resistance.

### **3. Oxidative stress**

Plants exposed to LT stress undergo various metabolic and physiological changes and chilling stress ultimately leads to oxidative stress in plants, a physiological condition, where an imbalance occurs between the generation of reactive oxygen species [27] and their metabolism *via* enzymatic and nonenzymatic antioxidants [28]. Different types of reactive oxygen species (ROS) are accumulated under LT stress, which includes (a) singlet oxygen (1 O2), (b) superoxide radical (O2 •–), (c) hydrogen peroxide (H2O2), and (d) hydroxyl radical (OH• ) [29]. In plant cells, ROS are continuously produced as a

consequence of aerobic metabolism in all the intracellular organelles, particularly in the chloroplast, mitochondria, and peroxisomes [30]. Chloroplast is considered the main source of ROS in plants. Other ROS-producing sources include NADPH oxidases, cell wall-bound peroxidases, and amine oxidases (**Figure 1**).

### **4. Other biochemical changes**

Under normal physiological conditions, ROS levels are maintained low by the action of various enzymatic and nonenzymatic antioxidants, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione (GSH), and vitamin C [31]. Accumulation of ROS accelerated under extremely cold conditions, beyond the plant's tolerant level due to less activity of antioxidant enzymes, which are responsible for detoxification of ROS. Higher content of ROS causes oxidative stress which is manifested as peroxidation of membrane lipids, damage to proteins, carbohydrates, and DNA, etc. [28, 32, 33]. They also alter enzyme activities, biochemical reactions, and plant processes, such as photosynthesis and respiration, which negatively affect the plant's survival percentage [12].

ROS alters the activities of enzymes and affects various biochemical reactions and physiological processes, including nutrient movements, respiration, photosynthesis, and transpiration, thus having a negative impact on a plant's survival percentage. Higher H2O2 accumulation in cold-stressed leaves of chickpea plants resulted in membrane injury [34]. Oktem *et al.* [35] also stated that an increase in oxidative damage caused by cold stress in lentils resulted due to high H2O2 production. Higher MDA content and higher electrolyte leakage from cell membranes of sensitive plants indicate injury caused by LT stress [36, 37]. Increased content of ROS and malondialdehyde (MDA) under LT stress probably impair metabolism in rice seedlings [38]. A significant increase in lipid peroxidation, membrane leakage, and hydrogen peroxide levels was observed in wheat seedlings subjected to chilling stress [39]. Apostolova *et al.* [40] reported a 40 and 100% increase in the content of H2O2 in the leaves of winter wheat and spring wheat, respectively under cold stress. Janmohammadi *et al.* [41] reported that during cold stress less cold-hardy spring wheat cultivar had a higher accumulation of hydrogen peroxide than the winter wheat cultivar. LT stress resulted in increased electrolyte leakage in the leaves of *Avena nuda* L. (naked oats) seedlings. Electrolyte leakage also increased with the prolongation of the stress period [42]. Membranes are a primary site of cold-induced injury because of their central role in the regulation of various cellular processes [43, 44]. LT stress leads to the destruction of cell membrane structure in maize plants [45], change the permeability of membranes, and causes leakage of cell electrolytes [5] and thus damages the plants. It has been demonstrated that LT responses are triggered by membrane rigidification, coupled with calcium influxes, cytoskeletal rearrangements, and the activation of MAPK cascades [46]. ROS are not only the toxic by-products of metabolism but also act as signaling molecules that transform the expression of different genes, for example, genes encoding for antioxidant enzymes and modulators of H2O2 production. ROS plays a vital role in plant stress acclimation [47, 48].

In conclusion, ROS are accumulated under LT, which alter the activities of enzymes, affect various biochemical, and physiological processes, and thus affect the plant's survival. Enzymatic and nonenzymatic antioxidants enhance their content under LT stress and are involved in the detoxification of ROS, thus increasing the resistance against the stress condition.

*Perspective Chapter: Effect of Low-Temperature Stress on Plant Performance and Adaptation… DOI: http://dx.doi.org/10.5772/intechopen.110168*
