Effect of paclobutrazol on abscisic acid levels in wheat seedlings

Abstract

Abstract. Contradictory results have been reported for the effects of triazoles on abscisic acid (ABA) levels in plants. Paclobutrazol reduced the height, fresh weight, and ABA levels of wheat seedlings. The magnitude of the inhibitory effect of paclobutrazol on ABA levels was dependent on the length of time after application. ABA levels in plants as determined by gas chromatographyselected ion monitoring-mass spectrometry (GC-SIM-MS) were reduced by 50-60% 2 days after soil application. A further 15% reduction occurred by the seventh day after treatment. ABA level analyses began at the time of treatment with 4-day-old seedlings and continued until 21 days after treatment when only a 20% reduction was detected. These determinations using GC-SIM-MS should increase the understanding of triazole effects on ABA levels.Paclobutrazol (PP 333) is one of a group of triazole fungicides, which have been under intensive investigation as crop plant growth regulators . The principal plant response reported has been the inhibition of internode growth of plants as seen in cereal grains due to a reduction of gibberellic acid biosynthesis (Dalziel and Laurence 1984, Hedden andGraebe 1985). Recently, however, the levels of cis-abscisic acid (ABA), another plant hormone, were found to be affected by triazole applications to plants. Results have been reported that include increases in ABA levels (Lurssen 1987), a transient rise in ABA levels (Asare-Boamah et al. 1986), no change (Izumi et al. 1988), and decreases in ABA levels (Grossman et al. 1987, Wang et al. 1987. The measurements of ABA levels were reported on different species of plants and at different plant growth stages after treatment. Little information has been reported concerning ABA levels in triazole-treated plants over a period of time other than the effect of triadimefon on beans for 8 days (Asare-Boamah et al. 1986).Since the growth-retarding effects of triazoles on cereal grains are seen within 1 week after treatment, this study was done to determine whether ABA levels in young wheat seedlings might also be affected during the early periods of growth. An examination of the relationship between growth retardation and ABA levels should provide further information on the importance of time of measurement after treatment or plant species studied in understanding the effect of triazole treatment on ABA levels. Materials and MethodsWheat seeds (Triticum aestivum L.), "Purple Straw" (5 g), were sown in soil, and seedlings were treated 4 days later by soil application with paclobutrazol formulations: Rl = 0.3 mg/pot and R2 = 3.0 mg/pot (11 cm diameter). Each treatment was replicated three times. The plants were grown in a greenhouse during the month of May and watered uniformly as needed. Whole plant samples were taken at 0, 2, 5, 7, 9, 14, and 21 days after treatment. Plant heights (tip of the most expanded leaf) were measured for each of the 10 plants randomly selected per replicate at each sampling date. Top fresh weights for 30 plants were obtained after the plants we...

Abscisic acid increases in non-growing and paclobutrazol-treated fruits of seedless mandarins

“…Tafazoli and Beyl 1993. However, paclobutrazol suppressed the water stress-induced ABA increase in apple leaves (Wang et al 1987), and reduced the ABA level in intaet wheat and soybean seedlings (Grossmann 1990, Buta andSpaulding 1991). Although these effects may reflect tissue and species specificity, or a different mode of action of the growth retardant in the developmental process under study, bioehemical data have been obtained supporting both kind of results.…”

GROWTH RETARDANTS: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways

“…Other growth retardants of the group of monooxygenase inhibitors affect ABA metabolism in a similar fashion in other plant species. However, this effect is clearly not achieved by all retardants of this type in all plant species (20,134,139). It rather appears that the right compound has to match the right species.…”

Influence of the Triazole Growth Retardant Uniconazole on Phytohormone Levels in Wheat Plants.

“…A similar increase has been reported in rape, wheat, and rice (Hauser et al, 1990;Liao et al, 1990 andTang et al, 1992). On the other hand, reduction of ABA level was found in treated soybean plants (Grossman et al, 1987 andButa andSpaulding, 1991). However, no change in ABA content was noticed in treated Pennisetum purpureum (Rajasekaran, et al, 1987).…”