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In higher plants, proline is a candidate biochemical solute, being well known as a stress indicator, especially of water deficit stress. (Yoshiba et al., 1997). The proline biosynthesis pathway in plant s has been well established via glutamate intermediate, using P5CS (...1 pyrroline- 5 -carboxylate synthetase) to P5C (...1 -pyrroline-5-carboxylate), subsequently oxidized to the final product proline by P5CR (...1-pyrroline- 5-carboxylate reductase). Also, proline degradation has been discovered through ProDH (proline dehydrogenase) from proline to P5C (...1-pyrroline-5- carboxylate) and then P5CDH (...1-pyrroline-5- carboxylatedehydrogenase) (Verslues and Sharma, 2010). The function of proline in plant defence responses to water deficit stress has been reported, including signal transduction, osmoregulation and antioxidant systems (Dalauney and Verma, 1993).
Poly Phenol Oxidaseis a copper-containing enzyme and is responsible for the enzymatic browning reaction occurring in many fruits and vegetables. In the presence of molecular oxygen, PPO catalyzes the o-hydroxylation of monophenols to o-diphenols (monophenolase activity) and oxidation of the o-diphenols to o-quinones (diphenolase activity) (Chararra et al., 2001). The synthesis of phenolic compounds is often enhanced in plant tissues under oxidative stresses such as drought and mechanical damage (Reyes and Cisneros-Zevalloss, 2003). Bananas are quite sensitive to drought; however, genotypes with "B" genome are more tolerant to abiotic stresses than those solely based on "A" genome. In particular, bananas with "ABB" genomes are more tolerant to drought and other abiotic stresses than other genotypes (Ravi et al., 2013). Salekdeh et al. (2009) mentioned that the reduction in banana growth and yield may be due to the shortage of water in the root zone.
Drought is one of the important abiotic constraints restricting banana cultivation and its further adoption into non- conventional growing areas. Drought has rarely been addressed in the past, but is gaining importance in the face of depleting natural resources (Ravi et al., 2013). The results of successful cultivation, especially of the water loving Cavendish clones, in drought prone areas with protected irrigation have provided the required momentum to perform research on drought in bananas (Ravi et al., 2013). In subtropical and semi- arid banana cultivation zones have very limited rainy days and also had uneven distribution of rainfall, new crop management practices in terms of varieties selected, soil improvement (in terms of physical properties and nutrient enrichment), water...