Improving the Efficiency of Adventitious Shoot Induction and Somatic Embryogenesis via Modification of WUSCHEL and LEAFY COTYLEDON 1

The induction of adventitious organs, such as calli, shoots, and somatic embryos, in tissue culture is a useful technique for plant propagation and genetic modification. In recent years, several genes have been reported to be adventitious organ inducers and proposed to be useful for industrial applications. Even though the Arabidopsis (Arabidopsis thaliana) WUSCHEL (WUS) and LEAFY COTYLEDON 1 (LEC1) genes can induce adventitious organ formation in Arabidopsis without phytohormone treatment, further improvement is desired. Here, we show that modifying the transcriptional repression/activation activities of WUS and LEC1 improves the efficiency of adventitious organ formation in Arabidopsis. Because WUS functions as a transcriptional repressor during the induction of adventitious organs, we fused it to an artificial strong repression domain, SUPERMAN REPRESSION DOMAIN X (SRDX). Conversely, we fused the strong transcriptional activation domain VP16 from herpes simplex virus to LEC1. Upon overexpression of the corresponding transgenes, we succeeded in improving the efficiency of adventitious organ induction. Our results show that the modification of transcriptional repression/activation activity offers an effective method to improve the efficiency of adventitious organ formation in plants.

VEGETATIVE PROPAGATION OF CONIFERS: XII. EFFECTS OF MEDIA, TIME OF COLLECTION, AND INDOLYLACETIC ACID TREATMENT ON THE ROOTING OF WHITE PINE AND WHITE SPRUCE CUTTINGS

Semimonthly collections of white pine and white spruce cuttings were taken from July to October, 1939, and propagated in several media. Collections of both species were taken in late October to examine the effect of type of cutting and of planting in media involving different proportions of two sands and two different peats. Cuttings were dusted with a series of concentrations of indolylacetic acid in talc. The season of collection and the medium used for propagation were the factors of main importance. Phytohormone treatment failed to demonstrate appreciable effect, no difference in rooting response could be attributed to the kind of sand used, but there were indications that response increased with the amount of sedge peat in the medium.Rooting of white pine cuttings collected in late August and propagated in a sedge peat medium was 62%, earlier and later collections gave substantially less rooting. Sand only and the sphagnum peat media were generally inferior to the sedge type of peat. At the optimum season of collection the sphagnum peat effected 50% rooting.The late July collection of white spruce cuttings effected rooting of 90% of the plain cuttings when propagation occurred in a sedge peat medium. Low percentages rooted in sand or sphagnum peat media. Cuttings with a heel of old wood tended to be superior to plain cuttings in respect to survival and rooting.Preliminary experiments with spring and early summer collections of both species resulted in slight rooting. Likewise, greenhouse propagations of dormant material gave very poor results.

EFFECTS OF TALC AND PHYTOHORMONE TREATMENT ON THE ROOTING OF DAHLIA CUTTINGS

Groups of Dahlia cuttings, untreated, talc treated, and treated with talc containing various concentrations of naphthylbutyric acid, were propagated in sand in a greenhouse. All the untreated cuttings died; those treated with talc alone suffered only 4% mortality. Although phytohormone treatment increased the number of roots per rooted cutting, it increased the average mortality to 23%. There were no significant differences in the effects of the various concentrations of phytohormone. Reduction of mortality by talc treatment was the chief feature of the results.

VEGETATIVE PROPAGATION OF CONIFERS: VII. OUTDOOR PROPAGATION OF A NOVEMBER COLLECTION OF NORWAY SPRUCE CUTTINGS TREATED WITH PHYTOHORMONES, CANE SUGAR, AND AN ORGANIC MERCURIAL DISINFECTANT

Dormant Norway spruce cuttings were collected in mid-November and treated with talc dusts containing two separate phytohormone chemicals, indolylacetic and naphthylacetic acids, in three concentrations, 0, 1000, and 5000 p.p.m., alone, and in combination with cane sugar and an organic mercurial disinfectant. Treated cuttings were planted immediately in outside frames in sand and a mixture of sand and peat in equal proportions. They were removed for examination 10 months later. Phytohormone treatment, except with the 5000 p.p.m. concentration of naphthylacetic acid, which was injurious, increased the number of cuttings rooted, the number and length of roots, the number of surviving cuttings, and the number of rooted cuttings with new growth. There were also marked effects on the initiation and development of new growth. The admixture of peat in the propagation medium improved rooting and development of new growth, particularly in certain of the phytohormone treatments. Only about 50% of the controls rooted in both sand and sand-peat, while the 5000 p.p.m. concentration of indolylacetic acid effected 68% rooting in sand and 82% in sand-peat.Both cane sugar and organic mercury significantly affected a number of the responses. However, the effects were comparatively small and depended, for the most part, on interactions with phytohormone treatments and media. Organic mercury increased the number of cuttings rooted by about 6%.