Journal of Plant Growth Regulation

The effects of salinity on growth and fatty acid composition of borage (Borago officinalis L.) leaves and seeds grown in hydroponic medium were investigated. Three different levels of NaCl (25, 50, and 75 mM) were applied. The first results showed that salinity significantly reduced plant growth by 56.5 % at 75 mM compared with the control, suppressed seed yield at 50 and 75 mM, and increased lipid peroxidation. Raising NaCl concentrations led to an important decrease in total fatty acid (TFA) content by 77 % at 75 mM NaCl. Moreover, the polyunsaturated fatty acid (PUFA) content decreased, whereas the saturated fatty acids increased with respect to increasing salinity. The 25 mM NaCl level did not modify the fatty acid composition of seeds and their contents.

Factors affecting somatic embryogenesis induction and conversion in paradise tree (Melia azedarach) were evaluated. Somatic embryogenesis was influenced by plant growth regulators, explant stage, carbohydrate source and concentration, gelling agents, light, and induction times. MS medium with 4.54 μM thidiazuron (TDZ) was optimal for the induction of embryogenic tissue. Zygotic embryos that were 1-1.5 mm long (torpedo and early cotyledonal stage) had a greater embryogenic response than smaller or larger embryos and better conversion of somatic embryos into plants. In general, embryos that formed in medium containing 1% or 5% carbohydrate were hyperhydrics or fused, respectively, whereas those that formed in medium with a carbohydrate concentration of 3% had better morphology. Raffinose at 3% yielded satisfactory somatic embryo induction with good morphology and the best values of conversion into plants. Induction and conversion of somatic embryos were superior on medium solidified with agar A-1296. The explants maintained under 160 μmol m−2 s−1 or 1 week in darkness and later 160 μmol m−2 s−1 produced a significantly higher embryogenic index. Only 4 days of treatment on induction medium, with either raffinose or sucrose at 3% as a carbohydrate source, were required to induce somatic embryogenesis, but longer exposure, until 18 days, increased the yield and improved the morphology of somatic embryos.

A rapid, sensitive, and economical chemical analysis of the triazole, gibberellin-inhibitor, paclobutrazol (PP333, [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4 triazol-1-yl) pentan-3-ol]) was sought, featuring high-performance liquid chromatography (HPLC) as the final quantitation step. Three C18-reverse phase columns (conventional, 250×4.6 mm; cartridge type, 125×4.6 mm; and minicolumn, 33×4.6 mm) were evaluated for their performance in HPLC separation and quantitation of PP333 applied to soil and plant foliage. The 125-mm Whatman Partisil 5 ODS-3 cartridge column was superior to the standard 250-mm DuPont Zorbax ODS unit, and provided enhanced resolution and reduced solvent consumption, analysis time, and cost. A Perkin-Elmer Pecosphere 3×3C-C18 cartridge system was also superior to the 125-mm column with respect to these parameters. Although this minicolumn necessitated an additional purification step prior to HPLC analysis, its exceptionally fast analysis time and recovery period coupled with a high degree of sensitivity rendered it the most superior unit. This HPLC technology provided an efficient means of assaying for PP333 in large-scale experiments dealing with the chemical's absorption, translocation, and physiological response.

A gibberellin 2β-hydroxylase has been purified from mature seeds ofPhaseolus vulgaris. The enzyme is of molecular weight 36,000 and has the characteristics of a dioxygenase; the cofactors areα-ketoglu-tarate, Fe2+ and ascorbate, and activity is stimulated by catalase. The Vmax of the enzyme is 6.86 nmole h−1 mg−1, and the Km values for [1,2-3H2]GA1 andα-ketoglutarate are 0.085 μM and 21 μM, respectively. The purified enzyme preparation catalyzes hydroxylation of GA1, GA4, GA9, and GA20 but exhibits a marked preference for the 3-hydroxylated gibberellins as substrate.

Brassica napus and B. campestris are grown in Western Canada in areas subject to unseasonable frosts. At the seedling stage, cultivars of Brassica are very sensitive to frosts of -2° to-5°C, which are either lethal or delay the development of the plant. Seedlings of B. napus and B. campestris, germinated and grown at 10°C (16-h photoperiod), were treated with a foliar spray of either 100 μM racemic abscisic acid (ABA), 100 μM of various ABA analogs, 0.1% acetone, or were untreated. Freeze tests indicated 2°C of frost tolerance could be gained in B. napus following an application of three ABA analogs. In B. campestris, three analogs also increased freezing tolerance approximately 1.5°C. The analogs 2′,3′ dihydro ABA and acetylenic divinyl methyl-ABA were effective in both species. Plant fresh weight and dry weight increased in treated plants relative to control or acetone-treated plants after 3 weeks at 10°C. The effect of frost and/or analog treatment on flowering was determined in both species. In B. campestris and B. napus, a mild frost advanced flowering by approximately 2 days compared with nonfrozen control plants. The promotive effect of frost on flowering decreased with increasing severity of the frost. Several of the analog treatments, particularly 2′,3′ dihydro ABA and acetylenic divinyl ABA, advanced flowering by 2–3 days in both species. The benefit of these ABA analog treatments on flowering was enhanced additionally by a mild frost. Plants treated with either ABA, 2′,3′ dihydro ABA, 2′,3′ acetylenic dihydro ABA, or acetylenic divinyl ABA flowered up to 5 days earlier than control plants.

Transcriptional reprogramming is a central feature of senescence regulation, implying an essential role for transcription factors. A regulatory function has already been attributed to different members of the plant-specific NAC and WRKY families in Arabidopsis but also in other plant species. WRKY53 is one important senescence regulator of the Arabidopsis WRKY family that is tightly regulated on different levels. In this study we show that WRKY18, which was formerly characterized as a downstream target of WRKY53 in the WRKY network, also regulates the expression of WRKY53. WRKY18 is able to bind directly to different W-boxes in the WRKY53 promoter region and to repress expression of a WRKY53 promoter-driven reporter gene in a transient transformation system using Arabidopsis protoplasts. Consistent with its repressing function on WRKY53 as a positive senescence regulator, WRKY18 overexpression led to delayed senescence, whereas wrky18 mutant plants exhibited a clearly accelerated senescence. In addition, a direct interaction between WRKY53 and WRKY18 proteins could be detected in yeast using the split ubiquitin system and in planta in transiently transformed tobacco epidermal cells via FRET-FLIM. In contrast to WRKY18/18 homodimers, WRKY18/53 heterodimers positively influenced WRKY53 promoter-driven reporter gene expression but appear to act only on a shorter 1.1 kbp promoter fragment but not on a 2.8 kbp longer fragment, indicating a more complex protein-protein-DNA interaction on the longer WRKY53 promoter, most likely also triggered by the accessibility of the promoter on the chromatin level.

Thirty-eight N-substituted-N′-(2-thiazolyl and furfuryl)ureas and thioureas were prepared by reaction of 2-aminothiazole and 2-furfurylamine with the appropriate iso(thio)cyanate. All compounds were tested for herbicidal activity and selectivity on seedlings of wheat (a monocotyledonous plant) and cucumber (a dicotyledonous plant). Only one compound (1) out of 14 ureas was characterized by considerable herbicidal activity against the wheat seedlings and two compounds (1 and 2) - towards the cucumber seedlings. The phenylurea derivative of 2-aminothiazole (1) was 1.7-fold more and the 3-chlorophenylurea derivative of 2-furfurylamine (23) was equally as active as the standard diuron with respect to selective herbicidal activity. Among 24 thioureas, four compounds (15,16,17, and 18) to displayed the highest selective herbicidal activity and two other compounds (19 and 33) were almost equal to diuron activity. Selective herbicidal ratio (SHR) represents the degree of herbicidal effect of the investigated compounds compared to diuron at both test objects. Four compounds (16,17,18, and 23) possessed SHR << 100 in the wheat seedlings while in the cucumber seedlings they had SHR >> 100. Therefore these compounds were substantially more active herbicides to the wheat seedlings as compared to diuron. The cytokinin-like activity of the synthesized compounds was also investigated in terms of betacyanin synthesis and radish cotyledon enlargement. The urea derivatives exhibited mostly high cytokinin-like activity but their activity remained lower than those of kinetin and N-phenyl-N′-(4-pyridyl)urea. The N-(3-fluorophenyl)-N′-(2-thiazolyl)urea (2) possessed the greatest activity at 10 μM while the corresponding compound with 3-chlorophenyl (4) was the most active cytokinin-like substance in the whole concentration range tested. Attention was also given to structure-activity relationships for the screened compounds. In general, the ureas and thioureas containing a 2-thiazole ring were more active than those containing a 2-furfuryl residue.