Effects of Abscisin II and Other Plant Growth Substances on Germination of Seeds with Stratification Requirements

Many seeds wvill not germinate uinless they are first stratified, that is, held in cold, moist storage for several months. WVhile these effects are not well understood at a physiological or biochemical level, XVilliers and Wareinig (8) showed that in ash, Fraxinnis excelsior L. both dormant and nondormant seeds have growth-inhibitory activity. However, in the nondormant seeds a growth accelerator was detected which antagonized the activity of the inhibitor. Recently, abscisin II, a new plant growvth regttlator isolated from cotton fruit (5) and driecl leaves of sycamore maple (3) has been identified as 3-methyl-5(1 -hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexene-1-yl)-cis, trans 2,4-pentadienoic acid and shown to bring abouit abscission of young cotton frulit and to possibly play a part in the reguilation of bud dormancv. The term dormin has also been suggested for abscisin II (3). Abscisin II has no activity as an atlxin or gibberellin, but can counteract the action of these hormones in Arena coleoptiles, in the barley endosperm assay and in the growth of dwarf maize or dwarf peas (1, 7). DLAbscisin II and the DL-trans, trans isomer have been synthesized (2). It seemed of interest to determine whether abscisin II woutld act as a germination inhibitor in those seeds that require cold treatment for germination. We now report the effects obtained with DL-abscisin II and other plant growth regulators on excised Ash embryos from Fraximus orntus L. and Fraxinuis anericana L. Depericarped seeds purchased from F. WV. Schumacher, Sandwich, Massachusetts, were imbibed for 24 hours in water, the embryos excised and placed onl WVhatman No. 1 filter paper in 5 cm petri dishes. Ten embryos per dish and 1 ml solution consisting of test substances dissolved in 0.01 m sodium phosphate, pH 6.0, were used. Triplicate plates were held at 220 tinder normal laboratory light and the formation of a geotropic bend at the basal end was interpreted as a positive germination response. Following the recommendations of Timson (6) we are reporting ouir germination (lata as the suim of the dlaily percentage of germiinatioin for a 10 clay period starting at the dav of excision. Thus, z 10 = 1000 would mean 100 % germination during the first day and , 10 = 0, Ino germination during the 10 day period. Depericarped seeds were stratified at 50 on moist filter paper in petri dishes for 3 months. Chlorophyll contenit was dletermineid spectrophotometrically from acetonie extracts by the proceduire of Maclachlan and( Zalick (4). DL,-Abscisin II and the DL-trans, trans-isomer were prepared by the proceduire of Cornforth et al (2). Excised F. ornuis embryos germinated well even without stratification (table I). The small enhancement obtained with gibberellin A. (gibberellic acid) is duie primarily to earlier germination. Embryos from F. amtericana gave good germination only when stratified, or treated with gibberellins A3 or A1. Gibberellin A, may be somewhat less effective than gibberellin A2, buit the differences are small. Contrary to Vlilliers and W;\areing (8, 9) who worked with F. excelsior, we foulnd no enhancement of germination on soaking of the excised F. orutlis and F. amiiericanaia embryos in water.