Penetration of Dry Seeds with Chemicals Applied in Acetone

Abstract

Acetone is able to carry chemicals through the seed coats to reach the embryo. The amount of chemical penetrating into the seeds depends on the seed type, permeation time, and the concentration of solution. The chemicals reaching the embryo are biologically effective. trate into the embryonic tip (Fig. 1). However, in the nontip area of the embryo (cotyledons), the radioactive IAA appeared to be located on the surface. The reason for this difference is uncertain. It may be due to the fact that the embryonic tip is in close proximity to the micropyle or that the cotyledon is less porous than the embryonic tip. The technique to introduce chemicals into dry seeds by means of organic solvents and its significance has been discussed (2. 3, 5, 7). Although the seeds respond to chemicals permeated in this fashion, the extent and manner of permea-tion of various chemicals has not yet been established. The present studies show that chemicals penetrate the seed coat. reach the embryo, and elicit physiological responses. RESULTS AND DISCUSSION Various seeds were permeated with "4C-IAA in acetone. Radioactivity was detected even after removing the seed coats (Table 1). The contamination of radioactivity in the embryo during suLrgical removal of the seed coat is negligible because only 0.2% of radioactivity was associated with lima bean embryo when the seed was permeated for only 1 sec. The amount of IAA reaching the embryo varied considerably, both on per seed and per gram tissue basis. Seed size appeared to be an important factor. The percentage of IAA reaching the embryo varied depending on the seed type. The amount of chemical penetrating the seeds depended on the chemical used. This was tested using seeds of various plant species. A larger amount of IAA penetrated into the seed compared with GA:. The ratios of IAA to GA, penetrating the seeds varied from 1.5 to 3.5 depending on the seed type (Table II). This might be expected because of the higher mol wt of GA:. The extent of penetration of chemicals into various embryos was tested by means of autoradiography. The autoradiograms of squash (Cucurbitai mnaixina Du(chesne) embryo from the seed permeated with "C-IAA showed that IAA was able to pene-1 Table I. Amoiiiit of IAA Permeated itito Seed aind Embryo Uniform seed samples (number of seeds actually used varied from 2 to 20 depending on the species) were treated with 14C-IAA in acetone (1 mNi, 2.5 ,uCi ,umole) for 2 hr, seeds were vacuum dried, and the coats were removed from half of the seeds in each sample. The embryos (minus seed coat) or intact seeds (plus seed coat) were ground in a mortar and extracted with 2 ml of acetone.