HETEROTROPHIC NUTRITION OF SEED PLANTS WITH PARTICULAR REFERENCE TO LEMNA MINOR L.

Abstract

Lemna minor L. was grown aseptically in darkness for 189 days in a modified Hoagland's solution, containing 1% sucrose, acid-hydrolyzed casein 800 mgm., and yeast extract 40 mgm. per liter as essential ingredients. Etiolated fronds, with root primordia that failed to elongate, were produced at about one-sixth of the rate in light. Lemna could not utilize nitrate, ammonium, or urea as heterotrophic nitrogen sources, nor were supplements of acetate, pyruvate, malate, fumarate, succinate, or citrate beneficial in the presence of sucrose. No single amino acid, of 23 tested in a medium containing sucrose plus yeast extract, was as effective as casein hydrolyzate. At suitable concentration, DL-phenylalanine, β-alanine, DL-isoleucine, DL-methionine, and DL-aminobutyric acid were utilized for growth without harmful effects, but other amino acids were either injurious or without effect. Frond development was more normal at low nitrate concentration, but potassium concentration had to be proportionately reduced to avoid inhibition. Growth was not limited by the concentration of other major elements, minor elements, or the degree of aeration. Sucrose feeding and increased photosynthesis had additive rather than competitive effects upon accumulation of growth factors in plants transferred from light to darkness. Spirodela oligorrhiza Kurtz, utilized nitrate heterotrophically to a limited extent. Albino maize was grown to the stage of ear formation by feeding sucrose to the leaves and nitrate to the roots. Growth was not promoted, however, by corn seed diffusate, coconut milk, or ammonium plus casein hydrolyzate supplied to the leaves. Albino barley fed sucrose through the leaves did not grow beyond the seedling stage. The heterotrophic requirements reported for various plants, plant organs, and tissues are compared, and the existence of two mechanisms of nitrate assimilation, one of which requires light, is discussed.