The effects of nitric oxide (NO) on caulogenesis, shoot organogenesis and rhizogenesis from hypocotyl explants of Linum usitatissimum were investigated. Exogenously supplied NO donors, 5 lM sodium nitroprusside (SNP), 2 lM S-nitroso-N-acetylpenicillamine (SNAP) and 2 lM 3-morpholinosydnonimine (SIN-1), significantly promoted shoot differentiation from the hypocotyl explants of L. usitatissimum excised from its in vitro raised seedlings. Potassium ferrocyanide, a structural analogue of SNP, lacking NO group, did not promote shoot organogenesis. Likewise, products of NO, NO À 2 and NO À 3 supplied as 5 lM NaNO 2 and 5 lM NaNO 3 did not enhance shoot differentiation. Another source of NO, a mixture of sodium nitrite (SN) provided along with ascorbic acid (AsA), also caused significant promotion in the average number of shoots per responding explant. SNP also augmented the rhizogenic response of the microshoots in terms of percentage of responding explants, number of roots per responding explant and average root length. The NO scavengers, 2-(4-carboxy-phenyl)-4, 4, 5, 5-tetramethylimideazoline-1-oxyl-3-oxide (cPTIO) or methylene blue (MB), provided along with SNP, SNAP, SIN-1 or SN ? AsA, at concentrations equimolar to the optimum concentration of the donors, reversed the promotory influence, thereby, confirming the role of NO in promotion of in vitro morphogenesis. However, NO scavengers individually did not affect the observed morphogenic processes. Morphological and histological studies of hypocotyl segments cultured on BM or BM ? SNP for 4, 8 and 12 days demonstrated that SNP enhanced shoot differentiation by inducing a higher number of shoot primordia, each of which develops into a single shoot.

The paper reports stimulatory effect of nitric oxide (NO) on in vitro caulogenesis in Albizzia lebbeck, a tree legume. Exogenously supplied NO donor, sodium nitroprusside (SNP) stimulated shoot differentiation from hypocotyl explants of Albizzia lebbeck, excised from its in vitro seedlings. Potassium ferrocyanide, a structural analog of SNP incapable of releasing NO, did not promote shoot organogenesis. Likewise, metabolic products of NO, NO 2 -and NO 3 -, provided as NaNO 2 and NaNO 3 did not enhance shoot differentiation. The NO scavenger, 2-(4-carboxy-phenyl)-4, 4, 5, 5-tetramethylimideazoline-1-oxyl-3-oxide (cPTIO), supplemented along with SNP, at equimolar concentration, reversed the stimulatory effect of the latter, thus, confirming the role of NO in promotion of in vitro caulogenesis. The transfer of explants cultured on the basal medium (BM) to the same containing SNP and vice versa after different time intervals revealed that for its enhancing effect, SNP was required only during the initial phase (5 days) of culture. Its presence or administration beyond 5 days neither promoted nor inhibited the caulogenic response.

The present investigation was carried out to decipher the interplay between paraquat (PQ) and exogenously applied nitric oxide (NO) in Azolla microphylla. The addition of PQ (8 µM) increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) by 1.7, 2.7, 3.9 and 1.9 folds respectively than that control in the fronds of Azolla. The amount of H2O2 was also enhanced by 2.7 times in the PQ treated plants than that of control. The supplementation of sodium nitroprusside (SNP) from 8-100 µM along with PQ, suppressed the activities of antioxidative enzymes and the amount of H2O2 compared to PQ alone. The drop in the activity of antioxidative enzymes -SOD, GPX, CAT and APX was highest (39.9%, 48.4%, 41.6% and 41.3% respectively) on the supplementation of 100 µM SNP with PQ treated fronds compared to PQ alone. The addition of NO scavengers along with NO donor in PQ treated fronds neutralized the effect of exogenously supplied NO. This indicates that NO can effectively protect Azolla against PQ toxicity by quenching reactive oxygen species. However, 200 µM of SNP reversed the protective effect of lower concentration of NO donor against herbicide toxicity. Our study clearly suggests that (i) SNP released NO can work both as cytoprotective and cytotoxic in concentration dependent manner and (ii) involvement of NO in protecting Azolla against PQ toxicity.