**7. Proline content**

All plants are capable of detecting and responding to [16, 17]. To overcome the effect of stress, plants have advanced using adaptive mechanisms which may be classified into four categories. Three of these adaptations are developmental traits (e.g., time of flowering), structural traits (e.g. leaf waxiness) and physiological mechanisms (e.g. ability to exclude salt while maintaining the absorption of water and the capacity to sort ions with in vacuoles) involve complex interaction. The fourth one is the metabolic responses such as alteration in photosynthetic metabolism and accumulation of organic osmolytes, most commonly proline. One mechanisms utilized by the plants for overcome the water stress effects might be via accumulation of compatible osmolytes, such as proline and soluble sugars. Production and accumulation of free amino acids, especially proline by plant tissue during drought, salt and water stress is an adaptive response. Proline has been proposed to act as a well-suited solute that regulates the osmotic potential in the cytoplasm. Thus, proline can be used as a metabolic marker in relation to stress. Moreover, under drought stress, the accumulation of total soluble sugars in different plant parts would be increased. However, the rate of additional production or accumulation of proline and soluble sugar is different in different plant parts. Proline content increases in a large variety of plant under stress up to 100 times the normal level, which makes up to 80% of the total amino acid pool. Proline accumulation is maximum during the flowering stage and minimum at vegetative stage. Proline source can be either from the synthesis from glutamate or hydrolysis of proteins. The proline accumulated in response to drought stress or salinity stress in plants is primarily restricted in the cytosol (**Figure 3**) [18–20].

Proline biosynthesis path way undergoes by plant in drought stress condition.

#### **Figure 3.**

*Flow chart showing proffered rout of proline biosynthesis in plant in stress full condition [21, 22].*

#### **7.1 Estimation of proline**

Proline content was assessed for the leaves exposed to control and waterstressed conditions. Leaves (100 mg) from control and water-stressed plants were separately standardized in 10 mL of 3% sulphosalicylic acid using mortor and pestle and centrifuged at 5000 rpm for 10 min and the supernatant was collected to estimate the Proline. Ninhydrin (1.25 g) was liquified in 30 mL of glacial acetic acid and then 20 mL of 6 M phosphoric acid was added and kept for 24 h at 40°C. To 2 mL of plant extract, 2 mL of acid Ninhydrin and 2 mL of glacial acetic acid were added and the mixture was boiled at 100°C for 1 h in a water bath. At that time, the solution continued to cool and the reaction was completed. About 4 mL of toluene was added to the contents and mixed vigorously for few sec and OD values for the colored component was restrained at 520 nm using toluene as the blank. From the OD values, proline content (μmoles/g fresh wt.) was calculated individually.

### **8. Conclusion**

Finally, studying all traits related to shoot and root its morphological, physiological, biochemical, phenological, anatomical or responses to environment shows additional opportunities to increase drought resistance in crops. The characters of the plant have to be synchronized with the suitable agronomical practices or better expression of diverse characters. This is a best approach to plant breeding for drought resistance.

### **Conflicts of interest**

The authors have no conflict of interest to declare.

*Breeding for Drought Resistance DOI: http://dx.doi.org/10.5772/intechopen.97276*
