Individual Study 2019. Low Nitrogen Availability in Plant: Transport Mechanism and its Effects in Root Shape and Leaf Composition Adillatul Lathiifatun Jannah. 6100412723 Abstractitrogen is a essensial macronutrient which is required for plant growth and development. Mostly plant absorb nitrogen from soil in form of nitrat and ammonium. Since the concentration of nitrogen in the soil is heterogen, plants do some mechanism to confront this problem. Some mechanism that plants do are through the regulation of nitrogen acquisition efficiency and changing in morphology and physiology process. This review provides information about some plant responses in low nitrogen availability: (i) nitrogen transporter and transport mechanism in low nitrogen availability, (ii) low nitrogen effect in root shape, (iii) low nitrogen effect in leaf component. Keywords leaf, nitrogen, root, transporter. Introduction Nitrogen is being a major food for plants and it plays the most important role in plant. This is because all processes in plants are associated with protein, where nitrogen is the important constituent of protein. Mitrogen also the major constituent of nucleotides, chlorophyll and many cellular component (Lawlor, 2002). Some function of nitrogen in plant are imparting the green colour (Sorin et al. 2016), promoting the growth and root morphology (Razaq et al. 2017), promote young leave and stem (Oskarsson et al., 2006), increasing biomass and crop productivity (Massignam et al., 2009), and also being found as component of secondary metabolites in plant (Cartelat et al., 2005). The distribution of nitrogen in the soil is heterogen, in response to this heterogenous distribution plants do nitrogen use efficiency that is defined into two ways, that are omponents, Nitrogen utilization efficiency and N acquisition (uptake) efficiency, this mechanism is facilitated by influx transporters located on ………………………………………………. the plasma membrane, and the latter by alterations in growth and development in response to local and systemic nitrogen signals (Forde, 2014 and Krapp et al. 2014). Another mechanism that plants do are trough changing in morphology such as root architecture and in physiology process such as producing secondary metabolite. This review aims to summarize some plant responses in low nitrogen availability. This review mostly focus on plant transport mechanism, effect in root shape and leaf component. Nitrogen Transporter and Transport Mechanism in Low Nitrogen Availability Plants acquire nitrogen from the soil through their roots in inorganic form such as nitrate (NO3-) and ammonium (NH4+). Ammonium and nitrate are taken up into root cells activelly by different transporters which is localized in different sets of plasma membrane. Ammonium is transported by AMMONIUM TRANSPORTER (AMT) (Ludewig et al. 2007), while nitrate is transported by two families of transporters, Individual Study 2019. NITRATE TRANSPORTER 1 family (NRT 1 family) and NRT 2 family (Krapp et al. 2014) Nitrate consentration in the soil can be vary from micromolar to millimolar, to confront with low condition of nitrogen in soil plant have evolved nitrate transport system called High Affinity Transport System (HATS), in Arabidopsis thaliana the gene that contribute in this sytem are NRT 2 family (Orsel et al., 2002) and AMT 1.1 (Yuan et al. 2007), that system is opponent of Low Affinity Transport System (LATS) which active in high consentration of Nitrogen using NRT 1.2 gene (Huang et al. 1999). And also NRT 1.1 which have role in both of types of transport system (Ho et al.2009). According to the study by Riveras et al. (2015), one of mechanism that activates NRT 2.1 is through [Ca2+]cyt signal (Figure 1), increasing of calcium activates gene expression of AtNRT 2.1 via TGA1/TGA4 which is triggered by Phospholipase C (PLC). They also found that AtNRT 1.1 is the first regulator of that mechanism, which activates PLC. Contribution of AtNRT 1.1 in that pathway is because AtNRT has a role as nitrate sensor. Ho et al. (2009) found that AtNRT 1.1 is involved in primary nitrate response of AtNRT 2.1 gene and serves as a nitrate sensor by evaluating CHL1 deletion mutant (chl1-5) and single amino acid substitution mutant (chl1-9). Study by Ma et al. (2015) also found another way which activate another HATS genes (NRT 2.4 and NRT 2.5) through the calcium sensor CLB7. This is realated to that Ca2+ is one of second messenger in nitrate signaling pathway, their study found that in the mutation of cbl7 significantly decreased the expression of NRT2.4 and NRT2.5 under low N ………………………………………………. availability (Figure 1). Another study that indicate the activates of HATS gene is found by Tabata et al. (2014), which found that under low nitrogen availability, C-TERMINALLY ENCODED PEPTIDEs (CEPs) is translocated to the shoot, then CEPs are perceived by CEP RECEPTOR1/2 (CEPR1/2) that increase AtNRT2.1 gene (Figure 1), but the way of CEPR1/2 activates AtNRT2.1 is not described in the study. Figure 1. Three kind of pathway that activate High Affinity Transport System (HATS) gene in low nitrogen availability. Low Nitrogen Effect in Root Shape Low concentration of nitrogen in soil can make change in root. This is because root is the first organs that senses mineral starvation in the soil. One of consequence is the change of root shape. Ma et al. (2014) indicate that low nitrogen availability reduce auxin content in the aerial organs and stimulate accumulation of auxin in lateral root primordia, this stimulation is promoted by expression of TAR2 which expressed in the pericycle and vascular of the Individual Study 2019. root maturation zone, this case stimulate the development of lateral root emergence, make the root has more branch (Figure 2). TAR2 Figure 2. Illustration of low nitrogen concentration effect in root. Source: Zhang et al, 2007 Low Nitrogen Effect in Leaf Composition. Beside changing root shape, low nitrogen condition in plant also have effect in leaf composition. One of physiological effect is decreasing the chlorophyll content that cause chlorosis that accelerated leaf senescence. Wei, Meng (2015) indicate that nitrogen deficiency decrease chlorophyll, essential amino acids, such as Lys, Phe, isoleucine (Ile), tryptophane (Trp), leucine (Leu), and valine (Val) content, and nonessential amino acids, consisting of glutamic acid (Glu), aspartic acid (Asp), Gly, arginine (Arg), and proline (Pro) content. Differently with chlorophyll and amino acids, in low nitrogen availability another leaf component such as some secondary metabolites content will increase. Benard et al. (2011), found that phenolic compounds including chlorogenic acid and rutin is increasing in Tomato leaf. But in different plant the type of compunds that accumulated will be different. The change of chlorophyll and leaf polyphenolics content can be used as indicator of plant nitrogen status (Cartelat et al., 2005). ………………………………………………. References : Benart, Camille., Frédéric Bourgaud and Hélène Gautier. 2011. Impact Temporary Nitrogen Deprivation on Tomato Leaf Phenolic. Int. J Mol. Sci. 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