Environmental Parameters Affecting Dark Response of Rice Seedlings (Oryza sativa L.) to Triacontanol

Abstract

(9). Triacontanol was first identified in alfalfa in 1933 (2), and it occurs in smali quantities in the waxes of many plant species (6) including wheat and triticale (1 1).Triacontanol applied in nutrient solutions to rice seedlings at 23 nm (10 ,ug/l) caused an increase in dry wt and leaf area of rice seedlings within 3 hr. The response was independent of light conditions. However, the response in the dark was eliminated by removing CO2 from the atmosphere. Triacontanol also increased Kjeldahl-N content up to 30%o after 6 hr in the dark (10).The present study considers the growth response of rice seedlings to triacontanol, in the dark, under various CO2 and 02 levels, different N sources, and the kinetics of the response using presentation experiments. Hoagland solution. The seedlings were supported in the solution by sponge rubber discs at the top of the cups.Prior to an experiment the seedlings were blocked by size, and a randomized complete block design with at least two blocks was used in each experiment. The experimental unit was one cup containing four seedlings. A random number table was used to assign treatments in all experiments, including those harvested when the test was initiated (zero time). Data were analyzed by analysis of variance or linear regression-correlation.Triacontanol dissolved in chloroform or chloroform alone (control), was applied to 2-cm2 filter paper squares, dried, and placed in nutrient solutions the night before an experiment. Unless otherwise specified, all treatments were made in 150 ml of 6 mM NO3-and 0.5-strength Hoagland solution with 10 ,ug/l triacontanol under dark conditions at 30 C for 6 hr.For gas treatments and respiration measurements, the seedlings were placed in 1.8-liter glass bottles with air-tight lids fitted with air inlets and outlets. Air flow was controlled by calibrated capillary flow meters and CO2 was measured with a Beckman IR-ISA CO2 analyzer. Flow rates of 100 ml min-' were used in the air versus COrfree air experiments, 50 ml min-' for the 02 concentration experiment, and 300 ml min-' for the CO2 concentration experiment. The higher flow rate was necessary to maintain similar influent and effluent CO2 levels in the atmosphere for the CO2 concentration experiment.Fixation of CO2 was further investigated by pulsing (160 ml min-' for 10 or 20 sec) radioactive "CO2 (322 ,tl/l, 0.53 ,uCi 1-') to intact leaves in a portable leaf chamber (1-cm diameter) under dark conditions after 4-hr exposure to triacontanol in the nutrient solution. After exposure to C02, the leaf sections (two/seedling) were removed, solubilized with NCS (Amersham/Searle), and the radioactivity determined by liquid scintillation procedures (7). For the NO3-versus NH4' experiment, plants were grown on NH4+ for at least I week prior to treatment. The pH of the NH4' nutrient solution was adjusted daily to that of the NO3-solution.Five ,ug/l 2-chloro-6-(trichloromethyl) pyridine was added to the NH4' and N03-nutrient solutions (N-serve, Dow Chemical Co.) to prevent nitrification of ...

Regulation of plant growth with triacontanol

“…The response in the dark occurred within 3 hr of treatment, but was eliminated by removing COi from the atmosphere. 73 After 6 hr in the dark TRIA had increased the Kjeldahl nitrogen concentrations resulting in 30% more N per plant than controls. 72 When lettuce seedlings were grown in the dark and treated with very high concentrations of TRIA (10 to 1000 mg/l), seedling growth was inhibited much more in the light than in the dark.…”

Rapid Growth and Apparent Total Nitrogen Increases in Rice and Corn Plants following Applications of Triacontanol

“…TRIA-induced growth increases in rice proved to be independent of light conditions, and CO2 concentration appeared to play a regulatory rather than a substrate role (2). Six-h dark responses were characterized by increases in dry weight, soluble and insoluble Kjeldahl N, and soluble carbohydrates.…”

Effect of triacontanol on photosynthesis, alkaloid content and growth in opium poppy (Papaver Somniferum L.)

“…on vegetables [18], cereals [19,5] and horticultural crops [8] are well documented . These are associated with increased protein content, water uptake [10], uptake of elements [17] and photosynthetic CO 2 fixation [8] .…”