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Articles

Rapid Growth and Apparent Total Nitrogen Increases in Rice and Corn Plants following Applications of Triacontanol ¹

Department of Horticulture, Michigan State University, East Lansing, Michigan 48824

Triacontanol (TRIA) increased fresh and dry weight and total reducible nitrogen (total N) of rice (Oryza sativa L.) seedlings within 40 minutes. Increases in total N in the supernatants from homogenates of corn (Zea mays L.) and rice leaves treated with TRIA for one minute before grinding occurred within 30 and 80 minutes, respectively. The source for the increase was investigated utilizing atmospheric substitution and enrichment and depletion studies with ¹⁵N. The increase in total N in seedlings was shown to be independent of method of N analysis and the presence of nitrate in the plants. Automated Kjeldahl determinations showing apparent increases in N composition due to TRIA were shown to be correlated with hand Kjeldahl, elemental analysis, and chemiluminescent analysis in three independent laboratories. TRIA did not alter the nitrate uptake or endogenous levels of nitrate in corn and rice seedlings. Enrichment experiments revealed that the total N increases in rice seedlings, in vivo, and in supernatants of corn leaf homogenates, in vitro, are not due to atmospheric N₂. TRIA increased the soluble N pools of the plants, specifically the free amino acid and soluble protein fractions. No differences in depletion or enrichment of ¹⁵N incorporated into soluble and insoluble N fractions of rice seedlings could be detected on an atom per cent ¹⁵N basis. The apparent short-term total N increases cannot be explained by current knowledge of major N assimilation pathways. TRIA may stimulate a change in the chemical composition of the seedlings, resulting in interference with standard methods of N analysis.