{'fraction_non_alphanumeric': 0.02712418300653595, 'fraction_numerical': 0.013818860877684407, 'mean_word_length': 5.330082742316785, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Defensive mechanisms in Plants: The role of component plant cells in defense against biotic and abitic stresses

Plants are often exposed to various environmental stresses such as extreme temperatures, drought, and disease and pest attack. In natural systems, plants face a plethora of antagonists and thus posses a myriad of defense and have evolved multiple defense mechanisms by which they are able to cope with various kinds of biotic and abiotic stresses. In fact plants defense against stresses by different ways. The role of cellular organelles is very important in this way. Cell wall and their derivatives such as oligosaccharins as biochemical defenser or for example trichomes as mechanical defenser is the frontline of the plant defense system. Also Plants have evolved a multi-layered immune system that dynamically responds to pathogens alike cell membrane that is a key mediator of communication between plants and microbes. Cytoplasm and the membrane-bounded structures (organelles) defense against different kind of stresses. The role of cellular organelles in plant defense relate to their enzymes primarily. Enzymes such as proteases, esterases and ribonucleases in cytoplasm, PM H+ATPases in plasma membrane or β glucosidases included cyanogenic glucosides, saponins, glucosinolates or DIMBOA (2,4dihydroxy-7-methoxy-1,4-benzoxazin-3-one) glucoside in ER are responsible for plant defense. Also ROSs plus SA and JA in chloroplast and mitochondria play an important role in immune plant system. In nucleus macromolecules including nucleoporins, importins, and Ran-GTP-related components, are essential to mount an efficient immune response in response to different pathogens. And in Golgi apparatus, peroxysomes and vacuoles, glycosyltransferases, myrosinase and hydrolytic enzymes are liable for plant defense respectively. Keywords— biotic and abiotic stresses; organells; plant defense.


III. DEFENSE BY CELL WALL
The frontline of the plant defense system is cell wall. Cell wall is one of the most distinctive structural features of plant cells is the surrounding wall, characteristically composed of the carbohydrate cellulose deposited in fibrillar form (Dickison 2000).
One of the important ways of plant defense by cell wall are oligosaccharins. Oligosaccharins are fragments of the plant cell wall that serve as regulatory molecules. They help to control such functions as growth, development, reproduction and defense against disease. For example some oligosaccharins, such as oligogalacturonids, act as elicitors and evoke pathogen defense responses. These defense responses include the accumulation of phytoalexins, proteinase inhibitors, lignin, peroxidase, lipoxygenase (LOX) and β-1, 3 glucanases (Ryan, 1988;Hahn et al., 1989;Ebel and Cosio, 1994). These bioactive, are relatively easy to produce and ready to face public acceptance because of their natural origin. Also oligosccharins have practical use in agriculture. So that oligogalacturonides, prepared from citrus pectin, that can partial or totally substitute phytohormones in the culture "in vitro" of sugar cane, citrus, coffee, tomato, rice and banana plants, reducing the time required for plant propagation, avoiding culture-induced genetic changes and increasing field survival percentage of these plants but also inducing rooting and plant growth (Saa Silva et al.. 2013).
It is clear that the shape and integrity of a fungus is also dependent upon the mechanical strength of its cell wall, which performs a wide range of essential roles during its interaction with its environment. The fungal cell wall is a complex structure typically composed of chitin, and glucan, mannan and proteins, although its composition frequently varies between species of fungi (Dhume et al., 1993). Both, plant and fungal cell walls, are a major target of the same type of cell wall degrading enzymes acting in the early stages of the plant-pathogen interaction. Additionally, oligosaccharides released from this degradation of plant or fungal cell walls can play the role of signaling molecules activating defenses responses and enhance growth or development in plants (Sea Silva et al.. 2013).
The role of cell wall in defense mechanisms in plant has been proved by cellulose deficient mutants. These mutants typically exhibit increased lignifications (Malinovsky et al., 2014). Interestingly, these changes appear to have effects beyond the purely structural. Such mutants also display enhanced defense responses (Hamann et al., 2009).
The another outer surface covering of the plant cell is cuticle that is multilayered mass in young stems and foliage consisting an insoluble polyester called cutin (Dickison 2000). Cuticle is a very effective barrier to invasion by pathogenic microbes (Dickison 2000). Not only biotic and abiotic stresses but also water loss is protected by cuticle in plants (Mario et al., 2014). The cuticle is structurally diverse among species but exhibits the organization of a composite material consisting in cutin, a polyester that is partly covered and interspersed with waxes (epicuticular and intracuticular waxes) (Mario et al., 2014). The roles of cuticle function in defensive mechanisms in plants are cleared when we study about mutants with specific defects in cutin. These mutants show an altered ultra structure of the cuticle and an enhanced permeability of the cuticle to solutes In addition, pollen could germinate on fully differentiated leaves of cutinase-expressing plants but not on control leaves. (Patrick et al., 2000). This finding is implied that cutin is important for preventing fusions between different plant organs and is therefore necessary for normal epidermal differentiation and organ formation (Heid 1991; Walker and .Bruck 1985). So the cuticle is the contact zone between the plant and the environment and its physical properties are highly relevant to the functions of the epidermis (Kerstiens 1996a ;1996b).
Some of the epidermal cells of most plants grow out in the form of hairs or trichomes. They may be found singly or less frequently in groups. They may be unicellular or multicellular and occur in various forms. They vary from small protuberances of the epidermal cells to complex branched or satellite multicellullar structures. The cells of the hairs may be dead or living.
In some plants the role of trichomes is minimizing invasion of specific pathogens (Dickison 2000). Actually leaf trichome density is considered a mechanism of defense in plants to prevent or diminish damage by herbivores (Levin, 1973;Johnson, 1975;Rodriguez et al., 1984;Juniper and Southwood, 1986;Marquis, 1992) Evidence from wild and cultivated species gives support to this ecological role (Duffey, 1986;Jeffree, 1986;David and Easwaramoorthy, 1988;Woodman and Fernandes, 1991;Bernays and Chapman, 1994;Peter et al., 1995;Romeis et al., 1999). The most important role of trichomes in plant defense is resistance against natural herbivores. Besides defense, leaf trichomes may serve other physiological functions, hence selection on the antiherbivory role of leaf trichome density can either be constrained or synergistically favored by selection imposed by other environmental stresses (Bell, 1997;Roy et al., 1999).
Alike trichomes thorns are a part of the defensive mechanism in plants. A thorn is a loose term for any sharp, pointed appendage coming off a plant for defensive purposes. Botanically, thorns can also be called spines (modified leaves), prickles (sharpened branches) or trichomes based on their location on the plant. Thorns are essentially defense mechanisms for the plant, The sharp points protect the plant against animals that want to eat it. There is an interesting experiment that have conducted by cut branches of three woody species that had their thorns removed suffered significantly greater herbivory by a tethered goat than did paired intact branches (Milewski et al., 1990).

IV. DEFENSE BY PLASMA MEMBRANE
Plants have evolved a multi-layered immune system that dynamically responds to pathogens. Most classes of plant pathogens remain outside the host cell membrane during their lifecycle. As a result, the plant plasma membrane (PM) is a key mediator of communication between plants and microbes (James and Gitta 2011). Initial pathogen recognition occurs at the PM and many of the earliest cellular responses to microbial invasion are controlled by PM-localized enzymes and ion channels (Boller and Felix, 2009).
In addition, multiple downstream responses to pathogen stimuli are executed at the plasma membrane. Pathogens must manipulate host cells in order to suppress these defense responses and procure nutrients. It is therefore expected that membrane transport processes have numerous functions in compatible (susceptible) and incompatible (resistant) interactions Also it is noticeable that in plants, PM H+-ATPases are the primary pumps responsible for the establishment of cellular membrane potential. Plant PM H+-ATPases use energy derived from ATP hydrolysis to pump protons from the cytosol to the extracellular space, thus creating and maintaining a negative membrane potential and a transmembrane pH gradient (acidic outside). This proton electrochemical gradient can control multiple aspects of transport across the PM. PM H + -ATPase activity is dynamically regulated during plant immune responses and multiple pathogens target this family of enzymes during infection (James and Gitta 2011).

V. DEFENSE BY CYTOPLASM
The cytoplasm of eukaryotic cells consists of all cell material between the nucleus and the plasma membrane and contains membrane-bounded structures, organelles, which are embedded in the cytosol consisting of water, salts and organic molecules, including sugars, proteins and many enzymes that catalyze reactions. The cytoskeleton of microtubules and actin filaments in the cytosol structures the cell by localizing and transporting the organelles bound to these tubules and filaments. The plasma membrane, enveloping the cytoplasm physically, separates the cell content from the extra-cellular environment, which in plant cells is the cell wall (Esseling-ozdona et al., 2008).
Also cytoplasm is an important barrier for plants defense. The earliest cytoplasmic response to contact between a microorganism and host cell is cyclosis within the protoplast, with a resultant reorganization of cytoplasmic organelles. Infection of tuber tissues and tissue culture cells of Solanum tuberosum by Phytophthora erythroseptica, P. infestans and Fusarium caeruleum caused swelling and disruption of host cytoplasmic particles containing acid phosphatases, esterases and proteases. Heavy diffuse cytoplasmic staining for acid phosphatase was a consistent feature of infection by the three fungi, but staining reactions for esterase and protease showed much less diffuse staining and a lesser degree of particle swelling. An excess recovery of ribonuclease from tissues infected with P. infestans and F. caeruleum was found. An electrophoretic comparison of near isogenic lines of wilt resistant (Fusarium oxysporum f.sp. pisi) or susceptible Pisum sativum was made.

VI. DEFENSE BY ENDOPLASMIC RETICULUM
The endoplasmic reticulum (ER) is a network-like structure that is bound by a single membrane. The ER is a dynamic organelle composed of various functional domains (Staehelin 1996). It includes the rough ER (rER), smooth ER (sER) and nuclear envelope. The rER is a well-understood organelle that is coated by ribosomes and is responsible for the synthesis of secretory proteins. The sER has no ribosomes but instead accumulates a series of lipid biosynthesis enzymes. In addition, the ER accumulates specific types of seed storage proteins, such as prolamin or zein, to produce protein bodies (PBs) in the endosperm of some plants. (

VII. DEFENSE BY NUCLEUS
Communication between the cytoplasm and the nucleus is a fundamental feature conserved among eukaryotic systems. Transport of macromolecules across the nuclear envelope occurs through nuclear pore complexes (NPCs), which are composed of nucleoporins, and depends on import and export receptors, importins and exportins that respectively recognize nuclear localization signals (NLSs) and nuclear export signals on cargo proteins (Meier and Brkljacic, 2009). The Ras-related nuclear (Ran) protein provides the directionality of transport through its binding to GDP (cytoplasmic side) or GTP (nuclear side). Several cellular factors involved in the transport of macromolecules through the nuclear envelope, including nucleoporins, importins, and Ran-GTP-related components, are essential to mount an efficient immune response in response to different pathogens ( ). In addition, several reports strongly suggest that components of the NPC specifically mediate the transport of R proteins, immunity components, as well as TFs (transcription factors) and regulators that are necessary for activation of disease resistance ). These and other findings support the notion that specific modulation of the nuclear concentration of a set of defense regulators is crucial for the fine tuning of plant immunity (Susana 2012). A significant number of effectors proteins from different pathogens, including nematodes, fungi, viruses, bacteria, and oomycetes, are targeted to the nucleus by co-opting the host nuclear import machinery (Deslandes and Rivas 2011). This means that effectors may manipulate host transcription or directly target nuclear essential host components for the benefit of the pathogen. It has been additionally proposed that some effectors may affect histone modification and chromatin remodeling. Alternatively, nuclear translocation of effectors may affect sub cellular localization of their cognate R proteins in a process that is essential for R-protein-mediated plant immunity. (Susana 2011

VIII. DEFENSE BY CHLOROPLAST
It is nice to know that chloroplasts are a key defense organelle. Indeed The chloroplast is a vital component of photosynthetic cells in algae, and higher plants, since it is the organelle in which photosynthesis takes place (Cooper 2000). Photosynthesis is the major function of the chloroplast, but its roles clearly extend further than converting light energy into chemical energy. Actually the chloroplast, together with the nucleus, cell membrane, and endoplasmic reticulum (ER), plays a critical role during the establishment of plant immunity against microbial attack (Padmanabham and Dinesh-Kumar, 2010). It implies that during plant defense, interorganellar signaling to achieve a synchronized whole-cell response occurs (Serano et al.,  2016).
Among cellular organelles chloroplast is an integrators for environmental signals and, more particularly, as mentioned earlier is a key defensive organelles (Serano et al., 2016) The role of chloroplast in plant defense have been proved by evidence that show plants undergo an increased demand for photosynthesis during the interaction with pathogens, as the biosynthesis of pro-defense molecules and, more generally, the induction of defense responses requires energy that is provided through photosynthesis (Hammerschmidt 1999 Page | 20

X. DEFENSE BY GOLGI APPARATUS
Glycosylation is a posttranslational modification reaction which is related to protein activity and protein secretory pathway in eukaryotic cells (Roth 2002). This essential reaction occurs in the endoplasmic reticulum and Golgi apparatus ( Kang et al., 2015). Although the glycosylation in the endoplasmic reticulum and Golgi apparatus has been known to regulate protein quality control, salt stress and cellulose biosynthesis, few evidences related to the roles of glycosylation in plant immunity have been reported (Kang et al., 2015). The role of Golgi apparatus in plant defense or plant immunity that is a pivotal role has been proved by studying about Arabidopsis thaliana mutants defective in glycosylation. The results showed that Arabidopsis mutants was more susceptible against Pseudomonas syringae pv. tomato DC3000 and Erwinia carotovora subsp. Carotovora compared to the wild type plant (Kang et al 2015). As mentioned above glycosylation occurs in endoplasmic reticulum and Golgi apparatus. In fact The glycosylated protein in the ER is translocated via vesicle to target or Golgi apparatus. In Golgi apparatus, the glycoprotein contains modification of N-glycan chain by various glycolytic enzyme and glycotransferase. In contrast of mammals that complex N-glycan are involved in different processes, including molecular recognition and signaling events, in plants complex N-glycan function is still largely unknown (Strasser 2014). In spite of the fact that complex N-glycans are ubiquitously present in plants (Wilson et al., 2001), their biological function is virtually unknown. The first mutant lacking complex N-glycans was isolated more than two decades ago from Arabidopsis. These mutant showed that n-glycan mutants did not caused a substantial change in Arabidopsis growth or development when grown under long day conditions (16 h-light/8 h-dark) at 22°C (Strasser et al., 2007b). Up to now, the only evidence for a biological function of complex N-glycans in Arabidopsis was found when cgl1 and other mutants were subjected to osmotic and salt stress (Kang et al., 2008). Reduced root growth on media containing high NaCl concentrations indicated that complex N-glycans are implicated in tolerance to salt stress. However, a deeper understanding of complex N-glycan function in Arabidopsis and studies that associate distinct complex N-glycan structures on individual glycoproteins with the enhanced salt sensitivity are completely missing (Strasser 2014).

XI. DEFENSE BY PEROXYSOMES
As mentioned repeatedly, plants suffer from infections caused by fungi, bacteria, viruses and nematodes. Peroxysoms are one of the sub cellular organelles that play a substantial role in disease resistance. Peroxysomes are single membrane bound cellular organelles, present in almost all eukaryotic cells, which have an essentially oxidative metabolism (del Rio et al. 2002 ;Kaur et al. 2009). Peroxysomes contains a variety of enzymes that primarily function together to detoxify the toxins present in the cell and most notably hydrogen peroxide, which is the most common by product of cellular metabolism in living systems. These organelles contain enzymes that convert the hydrogen peroxide to water, rendering the potentially toxic substance safe for release back into the cells (del Rio et al. 2002 ;Nyathi and Baker 2006).
The roles of peroxysomes in plant biotic and abiotic defenses are becoming clearer (del Rio et al. 2006 ;Reumann et al. 2007;Palma et al. 2009;Corpas et al. 2010). About role of peroxysomes in plant defense for example we can express that plant peroxysomes contribute to extracellular defense mechanisms against fungi by preventing colonization. Upon fungal invasion peroxysomes migrate toward the site of invasion (Lipka, 2005). Under these conditions the myrosinase which is bound to the peroxysomal membrane, hydrolyzes indolic glucosinolates to antifungal defense compounds protecting plants against fungal entry (Bednarek 2009). Furthermore, certain benzylglucosinolates play a role in pathogen defense and are found in developing seeds and germinating seedlings (Graser et al., 2001). These active defense molecules are synthesized in the cytosol by transferring a benzoyl moiety from benzoyl-CoA to a hydroxylated aliphatic glucosinolate, though the precursor benzoyl-CoA is primarily produced from cinnamic acid via peroxysomal beta-oxidation (

XII. DEFENSE BY VACUOLES
The central vacuole is one of the unique features of mature plant cells and presents the largest intracellular compartment in many higher plant tissues. Numerous studies carried out over the last twenty years have provided evidence that this organelle really behaves as a multifunctional compartment of plant cells. One of the roles of vacuoles in cells is plant defense response under condition of environmental stresses (Andreev 2001

XIII. CONCLUSION
Photosynthesis is one of the most important processes that occur in green plants, alges and prokaryotic living organisms named cyanobacteria. In this pivotal process sunlight turn into chemical energy (food). In fact life on earth depends on this important process that the highest percentage of it's occurring in green plants. Briefly only plants can produce food for animals and humans. These supporter living organisms are sessile but they have to suffer from an extensive range of biotic or abiotic stresses. So they must equipped against injurious agents. Plants, unlike animals, which have specialized defender cells and an adaptive immune system, have an innate immunity of each cell and produce systemic signals emanating from the infection site. Generally plants campaign against harmful factors with different forms. Sometimes a plant is in contact with a pathogen to which is not a host, this form of defense is the most common form of resistance in nature, sometimes the host can to hinder the growth and/or the development of the pathogen. But this is important that Plant defense systems against pathogen invasion consist of multiple layers that means all of plant cell component such as: cell wall, plasma membrane, cytoplasm, endoplasmic reticulum, chloroplast, mitochondria, Golgi apparatus, peroxysomes and vacuoles.