**1. Introduction**

Root signaling is the response of the plant roots on different stimuli like soil structure, soil nutrients, different chemicals and stress conditions. Root apical meristems are the major sites for different types of activities in response to changes related to roots. Root growth defines the extent to which plant explores soil for water and mineral nutrients. Root systems of individual crop plants may encounter large variations in mechanical impedance to root penetration [1]. Root architecture is a highly plastic and environmentally responsive trait that enables

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

plants to counteract nutrient scarcities with different forging strategies [2]. Root-specific traits such as root system architecture, sensing of edaphic stress and root-to-shoot communication can be exploited to improve resource capture (water and nutrients) and plant development under water-limited conditions [3].

ratio) and grain yield are closely related to soil water status. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions. Therefore objectives of the study were (i) to examine the effect of phosphorus on root signaling of wheat and (ii) to determine the effect of water stress on root signaling. The hypothesis, therefore made, was that there is a significant relationship present between wheat roots and P and also between root and drought stress.

Effect of Phosphorus on Root Signaling of Wheat under Different Water Regimes

http://dx.doi.org/10.5772/intechopen.75806

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Among all essential plant nutrients, phosphorus (P) is the second most abundantly required nutrient element after nitrogen and is an important constituent of many structural components of the plants [19, 20]. In agricultural ecosystems, it determines the soil quality with respect to its production capacity [21]. Being scarce and non-renewable natural resource [22] which is under the threat of rapid depletion as a result of intensive mining across the world more emphasis is being given to increase P use efficiency in soil for successful and sustainable crop production. A field experiment was conducted over 2 years to study the ameliorating effects of P on wheat yield, root cation exchange capacity (CEC) and on different doses of P. Phosphorus was applied as single superphosphate. The application of P increased the root CEC of wheat up to bloom stage only whereas nutrient concentration, uptake and grain and straw yield were found to increase up to maturity [23]. The capacity of plant roots to increase their carboxylate exudation at low plant phosphorus (P) status is an adaptation to acquire sufficient P at low soil P availability. Root mass ratio decreased with increasing P supply for *Triticum aestivum* L. [24]. An experiment was set up to make a critical assessment of the role of organic P in soil solution in the nutrition of wheat plants under sterile conditions. Phosphorus supply had a positive effect on dry matter and P concentration of the plants. Acid phosphatase secretion by plant roots was 5–11 times higher in organic P treatments than in the inorganic P treatments. It was hypothesized that plants secrete phosphatases in response to the presence of organic P in soil solution and organic P might be responsible for the increase in P

Root-soil contact is an important factor for uptake of a less mobile soil nutrient such as phosphorus (P) by crop plants. Root hairs can substantially increase root-soil contact. Identification of crop cultivars with more and longer root hairs can, therefore, be useful for increasing P uptake in low input agriculture. The variation in root hair parameters of the cultivars was related to quantity of P depleted from rhizosphere. These results showed that the variation in root hairs of cereal cultivars can be considerable and it can play a significant role in P acquisition, especially in low-P soils [26]. A field trial was conducted to investigate main morphological and physiological changes of different wheat landraces to low-P stress at the stage of seedling. P-deficiency significantly decreased root volume, total leaf area, and plant dry weight, but greatly increased density of root hairs and root top ratio. In addition, P-deficiency induced the significant enhancement of phosphorus utilization efficiency and the amount of

**2. Root signaling**

influx to wheat plants [25].

**2.1. Phosphorus and root signaling**

The uptake of nutrients depends upon both the supply of available nutrients in the rooting media and the root system [4]. The ability of plants to respond appropriately to nutrient availability is of fundamental importance for their adaptation to the environment. Nutrients such as nitrate, phosphate, sulfate and iron act as signals that can be perceived. These signals trigger molecular mechanisms that modify cell division and cell differentiation processes within the root and have a profound impact on root system architecture. Important developmental processes, such as root-hair formation, primary root growth and lateral root formation, are particularly sensitive to changes in the internal and external concentration of nutrients [5]. There is no doubt that differences occur in response to mineral nutrition both among species and cultivars, that is, genotypes belonging to the same species.

Phosphorus plays a vital role in crop production and is involved in energy transfer in plants. Carbon dioxide fixation by plants is not possible without phosphorus. Many plant physiological functions such as utilization of sugars, starch, photosynthesis, energy storage and transfer are dependent on phosphorus. It is also a constituent of cell nucleus and is essential for cell division and development of meristematic tissues [6]. Phosphorus has been reported to increase the strength of cereal straw, resist abiotic stresses, stimulate root development, promote flowering, fruit production, and formation of seed and hasten maturity of the crops [7]. Phosphorus utilization efficiency can be improved by mixing it with farm yard manure to increase the yield of wheat. Farm yard manure mixed with single superphosphate in 1:2 ratio increases phosphorus efficiency significantly [8]. It would be advantageous if we select, screen or improve plants for higher capacity to adapt to mineral stresses. This approach is beneficial in developing countries like Pakistan where capital input resources are limited. Farmers in these countries require nutrient efficient crop cultivars which perform better or do something better than other cultivars when given a considerable amount of mineral nutrient.

Cereals are facing acute problem of drought and temperature stress [9]. Low water availability is the major environmental factor which limits crop productivity. Root is the place where plants first encounter drought stress, it is likely that roots may be able to sense and respond to stress condition. Drought stress is the most common adverse environmental condition that can seriously reduce crop productivity [10, 11]. The mechanism of drought tolerance and breeding for droughtresistant crop plants has been major goal of plant biologists and crop breeders. Significant progress has been made in understanding root growth under drought stress. However, there has been no genetically defined drought-adaptive response in root development. But inhibition of lateral root development is a typical adaptive response of roots to drought stress. Despite the lack of understanding of drought tolerance mechanisms, physiological and molecular biological studies have documented several plant responses to drought stress [12].

Lack of sufficient water is the most important factor affecting world agriculture. Thus, increasing the efficiency of water and nutrient use is essential in order to improve yield whilst minimizing damage to the environment [13–18]. Plant depends upon the capacity of roots to obtain water and nutrients from the soil. The root respiration, carbohydrates allocation (root: shoot ratio) and grain yield are closely related to soil water status. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions. Therefore objectives of the study were (i) to examine the effect of phosphorus on root signaling of wheat and (ii) to determine the effect of water stress on root signaling. The hypothesis, therefore made, was that there is a significant relationship present between wheat roots and P and also between root and drought stress.
