Exogenous nitric oxide donor sodium nitroprusside enhanced growth attributes of polybagged rubber (Hevea brasiliensis ) seedlings

Shoot die-back condition has been observed in young-budded rubber plants especially under hot and dry weather conditions. This is partly attributed failure of the root system. Therefore, it is imperative to find ways to improve the root system while enhancing other growth attributes of polybagged rubber seedlings. Nitric oxide (NO) func-tions as a signaling molecule as well as a phytohormone in numerous physiological processes in plants from seed germination up to senescence. In the present study, the effect of sodium nitroprusside (SNP) as a NO donor on the root architecture and growth characteristics of polybagged rubber seedlings were investigated. Seven days old rubber seedlings were soaked in 200 μM and 500 μM solutions of SNP for 6 hours and 24 hours respectively prior to transplanting in polybags. Mock treated seedlings were soaked in water. Pretreatment with SNP greatly im-proved the root architecture of rubber seedlings by increasing the number and the length of lateral roots and the dry weight of roots while enhancing other growth parameters viz., stem diameter, shoot height and dry weight, leaf area and chlorophyll content in dose and time-dependant manner. Pretreatment with SNP at 500 μM for 6 hrs was found to be more effective for overall growth improvement in rubber seedlings. The improved growth characteristics of rubber seedlings could be attributed to the beneficial effect of SNP as a NO donor in modifying phytohormone signalling pathways, enhancing antioxidant enzyme activity, increase in nutrient uptake and effec-tive allocation of photoassimilates.