INVOLVEMENT OF NITRIC OXIDE IN ABA-INDUCED STIMULATION OF ADVENTITIOUS ROOT FORMATION IN DEROOTED MUNG BEAN [Vigna rsdists (L.) WILCZEK] SEEDLINGS

The present study aimed to investigate whether nitric oxide (NO) is involved in the ABA-induced adventitious root formation (ARF) in derooted Vigna radiata seedlings due to its nature as a second messenger In stress responses. 7 -day-old derooted mung bean seedlings were treated with the plant growth regulator ABA, NO donor sodium nitroprusside (SNP), and ABA in combination with the specific NO scavenger 2-(4-carboxyphenyl)- 4,4,5;5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) or the nitric oxide synthase (NOS) inhibitor N^ω-nitro-I-arglnine (l-NNA). Results showed that application of ABA and SNP significantly stimulated ARF in a concentration dependent manner. However, the NO specific scavenger carboxy- PTIO and the NOS-inhibitor L-NNA suppressed the stimulatory effect of ABA on ARF in derooted V. radiata seedlings, indicating that endogenous NO plays a vital role in the ABA induced ARF; and it can be Implied that the generation of NO catalyzed by NOS-like enzyme. In addition, data showed that ABA-treated cuttings had higher levels of NO, hydrogen peroxide (H2O2), and lower levels of superoxide anion (O2^0-) than those of untreated ones. Further, ABA-treated cutting also contained higher activities of the antioxidant enzymes, i.e. [superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX)], than those of the control treatment; however, carboxy-PTIO + ABA-treated cuttings had lower activities of such enzymatic activities at 120 h of ABA treatment. These results suggest that NO Is Involved In the ABA-induced stimulation of mung bean ARF most prt bably mediated via creating optimal levels of O2 ^0-, and H2O2 and enhancement of antioxidant enzymatic activities. It may be concluded that endogenous NO plays a vital role In ABA-induced de novo root formation in derooted V. radiata seedlings.