Adventitious bud formation in culture of Douglas fir (Pseudotsuga menziesii (MIRB.) Franco)

The histological events associated with shoot primordium formation in cultured excised cotyledons from germinated seed of radiata pine (Pinus radiata D. Don) were examined. Cytological changes in the explants were observed by day 1 in culture. Mitotic activity, initially random, became restricted to the epidermal and subepidermal cell layers closest to the medium. This led to the formation of meristematic tissue along the entire length of the cotyledon during the first 3 wk in culture. Within this meristematic zone, meristemoids, shoot primordia, and finally shoots with well-developed apical meristems, needles, and needle primordia were formed.

Shoot Histogenesis in Cotyledon Explants of Radiata Pine

Stimulation of embryogenesis in citrus ovular callus by ABA, ethephon, CCC and alar and its suppression by GA3

All tissue and organ culture systems used with forest species make use of natural or artificial plant growth regulators. Without added hormones, most tissues do not remain viable, much less grow in the manner we wish. Unfortunately, few studies have dealt with the mechanism of hormone action; instead, effective hormones and their concentration have been derived empirically. We are therefore left with a wide range of hormones that have been applied to a number of species with sometimes conflicting results. The purpose of this chapter is to summarize some of these results, particularly those from recent papers, and arrive at generalizations where possible. Since extensive reviews are available elsewhere (9, 13, 89), no attempt will be made here to list every paper which has reported use of a growth regulator in an aseptic culture system of a forest species.

Action of Growth Regulators

Plant growth regulators include naturally occurring plant hormones such as indoleacetie acid (IAA), gibberellins, zeatin, abscisic acid (ABA) and ethylene, etc., and also a number of synthetic chemicals that affect or control growth and development in plants. Each type of plant growth regulator has a wide range of physiological effects in different plants. These effects are determined by the kind of the growth regulator, its concentration, the presence or absence of other growth regulators, and by the genetic makeup and the physiological status of the target tissue. The same physiological response in different tissues even of the same plant may require different growth regulator(s) or different combinations of growth regulators. Synergism and quantitative interaction of two or more growth regulators are of common occurrence. Finally, a growth regulator that elicits a positive response in a given tissue at a given concentration may inhibit the same physiological response when used at higher concentrations.

Plant Growth Regulators and Morphogenesis in Cell and Tissue Culture of Forest Trees

Initiation of adventitious buds on cultured callus tissue, hypocotyl and young stem cuttings have been reported on hardwood trees, but similar reports on conifers have been meagre. The present paper deals with conditions which control generation of adventitious buds from Cryptomeria hypocotyl cuttings in vitro with actions of abseisie acid (ABA), 6-benzylaminopurine (BAP) and potassium naphthalene-l-acetate (NA). Cryptomeria hypocotyl cuttings were obtained from 2-week-old seedlings grown from seeds sown under aseptic conditions. The seeds were sterilized by a 0.2% aqueous solution of Uspulun* in a beaker on a slowly moving magnetic stirrer for 17 hr. In the first set of trials, basal medium 1 (Wolter and Skoog, 1966; Wolter, 1968) was tested. As for growth substances 0.02 mg/l NA or 1.0 mg/1 NA plus 0.1 mg/1 BAP was added. Even the basal medium 1 without any growth substances initiated adventitious buds at the rate of 12% per treatment (Fig. 1). By outward appearance, it was observed that buds were generated without internal callus formation, at least in this treatment. The medium containing 0.02 mg/l NA also induced bud formation and growth of buds (Fig. 2) at the rate of 17% per treatment. Root-like excrescences (Fig. 3) were initiated only in the medium in which the basal medium 1 was supplemented with 1.0 mg/1 NA plus 0.1 mg/1 BAP. Basal medium 2 used in the second set of trials consisted of the inorganic medium similar to the former supplemented with organic substances of Grinblat's medium (Grinblat, 1972). In addition, the growth substances BAP, ABA* or NA in malt extract (ME) were added in the concentrations listed in Table 1. Table 1 shows results of bud formation from upper segments of hypocotyl cuttings 3.5 months after explantation in the second set of trials. Explants were placed in a growth chamber at 25 C under light on a 14-hr day with fluorescent lamps at 1,900 lux or in the continuous dark. As shown in Table 1, an appreciable number of adventitious buds were generated under the illuminated conditions, especially on the medium containing ABA 1.0 mg/l, and according to the analysis of variance, a remarkable difference was obtained

Hirotaka Isikawa

Papers

In vitro formation of adventitious buds and roots on the hypocotyl ofCryptomeria japonica

In vitro formation of adventitious buds and roots on the hypocotyl of Cryptomeria japonica(Short communication)