Cotyledonary node explants of Acacia nilotica subspecies indica Brenan, differentiated multiple shoots on Gamborg et al.' s medium (B5, Gamborg et al. 1968) supplemented with cytokinins like N(6)-benzyladenine, 6-(γ, γ-Dimethylallylamino)-purine, kinetin or zeatin. Of the four, BA supported maximum multiple shoot differentiation; the highest average number of shoots (6.3) per expiant was in 1.5 mg/l. The number of shoots was further enhanced by (i) using nodal explants of in vitro regenerated shoots as microcuttings, and (ii) repeated subculture of the original expiants (stumps) on the same medium after excising the shoots. Thus, over seven hundred shoots could be obtained from a single cotyledonary node explant. Individual shoots, when transferred to 2 mg/l indole-3-acetic acid augmented medium organised healthy roots in 100% cultures. Such test tube grown plantlets have been successfully transferred to soil, where they grow well up to eight weeks.
Stem cuttings of Populus nigra were Ircated with 10 and 100 mg/1 each of IAA, IBA, 2,4-D and NAA at one month intervals and observations were recorded for the morphophysiological status of the liranches, their starch content and their rooting response. -The first phase characterized by delayed, sbort and scarce roots and the high starch content of cuttings coincided with Ibe onset of winter dormancy in November lasting througb February. It was followed by a pbase of vigorous rooting and low starch content of cuttings coinciding with the renovation of growth activity in February lasting tbrongh October, except in April and May when rooting was more or less completely nullified. -Tbe ])oor rooting in winter was caused by low activity of bydrolyzing enzymes not mobilizing starch into soluble sngars; and profuse rooting during active growth period by high activity of hydrolyzing enzymes caused by endogenous anxin, resulting in mobilization of reserved food materials necessary for the initiation and development of roots. The low rooting in Aprit and May is ascribed to the fact tbat l)ulk of tbe mobilized food was nsed up in tbe growtti of sprouted branches leaving very little for rooting wtien tbese cuttings were planted. -The seasonal changes in the effectiveness of exogenonsty applied auxins also appear to be related with tbe level of endogenous auxin. In June endogenous auxin was high dne to high meristematic activity, tbe exogenously ajiplied auxins raising it lo supra-optimal levels that were inhibitory. On the other hand, in October exogenously applied auxins enbanced rooting by raising it to an o])timal level as the jjroduclion of endogenous auxin had been decreasing gradually due lo lowering temperatures. -The results demonstrate that anxin effect on differential rooting with season in this plant is determined by the physio-morphological status of the brandies tbat govern the prodnction of endogenous auxin and is mediated primarily through its effect on mobilization of reserve food materials caused by enhanced activity of liydrolytic enzymes.• i. u .-«"
Multiple shoots were induced from the cotyledonary nodes derived from seedling of Sesbania rostrata on Nitsch (1969; N) medium supplemented with various concentrations of benzyladenine (BA). 1 mg dm -3 BA proved to be the best, eliciting 5.8 ± 1.0 shoots per explant in 100 % cultures. The elongation of shoots was best at 2.0 mg dm -3 BA. The shoot proliferation capacity increased to 7.5 shoots per explant following transfer of explants to the fresh shoot multiplication medium (MS + 1.0 mg dm -3 BA), after an initial incubation of 30 d. To further enhance number of shoots per explant an alternative strategy of cultivation of mother explant on fresh shoot multiplication medium after excision of shoots was adopted. Following the repeated harvesting of shoots an average of 33 shoots per explant could be obtained. The in vitro regenerated shoots produced roots when transferred to half-strength MS medium supplemented with 3 % sucrose and 1 mg dm -3 IBA. The developed plantlets were planted in the soil and transferred to the field after an acclimatization period of 3 -4 months. These plants produced flowers and fruits in the field and exhibited the development of prominent and more organized stem nodules as compared to the in vivo raised plants of the same age.
2.5 cm long stem segments of Populus nigra L. did not root when cultured in water or in auxins alone but rooted in glucose. The number of rooted segments and roots produced on them increased with rising glucose concentrations up to 0.5 "le, but decreased with higher concentrations. An addition of 1.0 mg/l IAA inhibited rooting at 0.01 "/o glucose, was ineffective at 0.1 "/o and stimulative at higher concentrations of glucose which were inhibitory when used alone. The results show that the auxin effects on rooting are influenced by the nutritional status of the stem cutting of a species, and that a proper balance of the two is necessary for root development.
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