Exogenously applied sodium nitroprusside improves physiological attributes and essential oil yield of two drought susceptible and resistant specie of Thymus under reduced irrigation

This research was conducted to address the influence of foliage-applied sodium nitroprusside (SNP; 0, 50, 100 and 150 mu M) on resistance against reduced irrigation by 80, 60 and 40% Field Capacity (FC), in two drought tolerant thyme (Thymus serpyllum Serpolet) and drought susceptible thyme (T. Vulgaris L). Non-SNP treated resistant specie showed 55.17% higher plant growth rate than drought susceptible thyme under severe water deficit (40% FC). However, SNP treatment caused drought susceptible specie to show higher growth rate compared with those of resistant one under non- water stressed conditions (80% FC). Intensified drought, while significantly enhancing malondialdehyde (MDA), H2O2 and electrolyte leakage of both specie, caused marked reduction in chlorophyll content, ratio of variable to maximum fluorescence (Fv/Fm) and relative water content. The essential oil yield of both specie increased with the decrease in irrigation from 80 to 60% FC, and decreased with the water deficit increase to 40% FC. Spraying Thymus specie with all three levels of SNP further increased the essential oil yield and improved physiological attributes of both specie, being more pronounced in drought resistant one. The compensatory effect of SNP in mitigating the negative impact of reduced irrigation was due to increase of proline accumulation and reduction of some antioxidant activities which increased drought tolerance of Thymus.