Differential responses of the enzymes involved in proline biosynthesis and degradation in drought tolerant and sensitive cotton genotypes during drought stress and recovery

The relative water content (RWC), free proline levels and the activities of enzymes involved in proline metabolism were studied in drought tolerant (Ca/H 680) and drought sensitive (Ca/H 148) genotypes of cotton (Gossypium hirsutum L.) during induction of water stress and posterior recovery. Water stress caused a significant increase in proline levels and P5CS activity in leaves of both tolerant and sensitive genotypes, whereas the activity of P5CR increased minimally and the activity of OAT remains unchanged. The activity of PDH decreased under drought stress in both the genotypes. The leaf of tolerant genotype maintained higher RWC, photosynthetic activity and proline levels, as well as higher P5CS and P5CR activities under water stress than that of drought sensitive genotype. The drought induced proline levels and activities of P5CS and P5CR declined and tend to be equal to their respective controls, during recovery, whereas the PDH activity tends to increase. These results indicate that induction of proline levels by up regulation of P5CS and down regulation of PDH may be involved in the development of drought tolerance in cotton.