Betaine, a non-toxic osmoprotectant, is believed to accumulate considerably in plants under stress conditions to maintain the osmotic pressure and promote a variety of processes involved in growth and development. Phosphoethanolamine N-methyltransferase (PEAMT), a key enzyme for betaine synthesis, is reported to be regulated by its upstream promoter. In the present investigation, by using the transgenic approach, a 1048 bp long promoter region of ZmPEAMT gene from Zea mays was cloned and functionally characterized in tobacco. Computational analysis affirmed the existence of abiotic stress responsive cis-elements like ABRE, MYC, HST, LST etc., as well as pathogen, wound and phytohormone responsive motifs. For transformation in tobacco, four 5′-deletion constructs of 826 bp (P2), 642 bp (P3), 428 bp (P4) and 245 bp (P5) were constructed from the 1048 bp (P1) promoter fragment. The transgenic plants generated through a single event exhibited a promising expression of GUS reporter protein in the leaf tissues of treated with salt, drought, oxidative and cold stress as well as control plants. The GUS expression level progressively reduced from P1 to P5 in the leaf tissues, whereas a maximal expression was observed with the P3 construct in the leaves of control plants. The expression of GUS was noted to be higher in the leaves of osmotically- or salt-treated transgenic plants than that in the untreated (control) plants. An effective expression of GUS in the transgenic plants manifests that this promoter can be employed for both stress-inducible and constitutive expression of gene(s). Due to this characteristic, this potential promoter can be effectively used for genetic engineering of several crops.

Experiments, both pot and field trial, were conducted to examine the effects of exogenously applied IAA and GA3 (at 0, 10, 20 and 30 days after topping) individually or in combination, on growth and C and N metabolisms of tobacco (Nicotiana tabacum L.). Application of IAA or GA3, at low concentrations had a promising effect in terms of promoting the yield and quality of tobacco. The key enzymes' activities were also enhanced by low PGRs concentrations, which is known to be involved in the C and N metabolisms. The combined treatment of the two PGRs was more effective than the PGRs applied individually in improving the activities of nitrate reductase (NR), invertase (INV) and amylase (AMY) finally resulting in improved soluble sugars, reducing sugars, starch, total C and N, soluble proteins and nicotine content. The optimum levels for improvement of C and N metabolites were found to be GA3 at 50 mg/L and IAA at 30 mg/L.

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