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Observations have been made on the effect of synthetic, (±)‐abscisin II (dormin), alone and in combination with gibberellin, kinetin and indoleacetic acid, on seed germination and seedling growth of two strains of lettuce, cv. Attraktion and cv. Hohlblättriger Butter. (±)‐Abscisin II inhibited seed germination and seedling growth in both strains. The inhibitory effect of abscisin II on seed germination as well as seedling growth was completely overcome by kinetin in both dark and light. Gibberellic acid, on the other hand, proved ineffective in exerting its influence on seed germination in presence of abscisin II but affected subsequent seedling growth as usual. Indoleacetic acid was found to be least potent in reversing abscisin II caused inhibition of seed germination and seedling growtb. It is concluded, that like its effect on certain other naturally occurring inhibitors of seed germination, kinetin can effectively undo the inhibitory effects of abscisin II in these growth processes.

Seedlings of silktree (Albizzia julibrissin Durrazz .) were grown in vitro on MS-media containing B5 vitamins, 3% sucrose, 0.25% phytagel and various concentrations (0 .1-10 µM) of thidiazuron (TDZ) . Addition of TDZ to the culture medium greatly reduced shoot and root elongation but did not influence shoot production from the cotyledonary node or apex . Within 8-10 days the seedling roots split open, formed large masses of callus, and developed green patches which eventually grew into normal shoots while still within the culture medium containing TDZ at 0.1-1 .0 µM . Such callus and shoot formation did not occur in control cultures lacking TDZ . At higher TDZ concentrations (2 .5-10 ,tiM), the green patches formed in the callus did not further develop into shoots . Addition of other cytokinins (kinetin, benzylaminopurine, zeatin) to the culture medium also induced some shoot formation from the roots, but higher concentrations than TDZ were required to induce regeneration . Isopentenyladenine failed to induced shoot formation . Following excision and transfer to MS media with or without 4 .9 pM IBA, the shoots induced by kinetin or benzylaminopurine rooted 4-7 days earlier than those induced by TDZ, but all excised shoots developed into normal rooted plantlets within 3 weeks.Abbreviations : TDZ = thidiazuron

Hybrid poplar clone NC–5339 (Populusalba × Populusgrandidentata cv. Crandon) was genetically modified for glyphosate (N-(phosphonomethyl)glycine) tolerance by Agrobacterium-mediated transformation with genetic constructs (pPMG 85/587 and pCGN 1107) that included the mutant aroA gene for 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase (EC 2.5.1.19) and the neomycin phosphotransferase selectable marker gene. pCGN 1107 also harbored the coding sequence for a chloroplast transit peptide and the CaMV 35S promoter fused to the mutant aroA gene. Transformants were selected for kanamycin tolerance, and integration of the aroA gene was verified by Southern blot analysis. Cuttings of NC-5339 and the derived transformants were rooted and grown in glasshouses at separate locations, with maximum photosynthetic photon flux density of 1600 and 750 μmol•m−2•s−1. Productivity was assessed by growth studies and photosynthesis measurements at both locations. Glyphosate tolerance was tested by (i) measurement of chlorophyll concentration in herbicide-treated leaf discs and (ii) whole-plant spray tests. Plants transformed with construct pCGN 1107 were the most herbicide tolerant. Perhaps high-level expression of the aroA gene by the CaMV 35S promoter, transport of mutant EPSP synthase into the chloroplasts, or both facilitated glyphosate tolerance. Plants grown at higher photosynthetic photon flux densities (1600 vs. 750 μmol•m−2•s−1) had significantly higher maximum net photosynthesis (19.8 vs. 16.2 μmol•m−2•s−1) and more biomass accumulation (47.6 vs. 33.7 g). However, there were no significant differences between NC-5339 and transformants within location for net photosynthesis or any growth parameter. Genetic modification of hybrid poplar NC-5339 for glyphosate tolerance did not adversely affect plant productivity at either location.