Promotion of Callus Formation by Abscisic Acid in Citrus Bud Cultures

Abstract

Abscisic acid is known to control different phases of plant growth processes, and its physiological effects have been recently reviewed (1, 12). Although its inhibitory effects are numerous (1), cases of growth promotion by ABA are scarce (10,11). Some interactions of ABA with other growth substances, mainly with gibberellic acid, in promoting growth of cucumber hypocotyls (2), and with kinetin, in the growth of soybean callus (3), were also reported.While studying the development of citrus buds in vitro, we noticed a formation of callus in bud cultures which was induced specifically by ABA. The effects of ABA alone, and in combination with IAA and 6-benzylaminopurine are reported.MATERIALS AND METHODS Plant Material. Typical branchlets of spring flush, bearing 5 to 7 leaves and their axillary buds, were cut from 40-year-old Shamouti orange trees (Citrus sinensis [L.] Osbeck), washed with tap water and detergent, rinsed with distilled water, dipped momentarily in 80% ethanol, and surface-sterilized by immersing for 30 min in a filtered calcium hypochlorite solution (90 g/liter) with 0.1% Tween-20. Explants were prepared aseptically: the petiole was excised and then the explant was removed from the branchlet by a shallow longitudinal excision penetrating somewhat into the wood. These explants therefore consisted of the whole bud, portions of bark and wood from the branchlet, and the stump end of the petiole (Fig. 1A). In some experiments portions of the leaf petiole and blade, with or without the bud, were also examined. Bud explants were planted in 25-x 95-mm culture tubes containing 10 ml of nutrient medium with the stem end in the agar.Nutrient Media. The Murashige and Skoog medium as adapted for citrus tissues (6, 7) was used throughout the experiments. The medium, in addition to the original inorganic salt composition, contained the following (mg/liter): glycine, 2.0; nicotinic acid, 0.5; pyridoxine-HCl, 0.5; thiamine-HCl, 0.1; and myoinositol, 100.0, together with 5% sucrose and 1% Difco Bacto-agar. To this basal medium were further added varying concentrations of ABA, IAA, and BA.' The pH of the medium was adjusted to 5.7, and sterilization was accomplished by autoclaving for 25 min at 124 C (1.4 kg/cm2).Cultures were allowed to develop for up to 2 weeks in a controlled growth chamber at 25 + 1 C and under a 16-hr photoperiod in weak white light (400 ft-c). Explants were then removed for examination and fresh weight determination. Each experiment consisted of 10 separate cultures and was repeated at least three times.

Role of Ethylene in Abscisic Acid-induced Callus Formation in Citrus Bud Cultures

“…In addition it was shown (Table III) that ABA promoted the formation of ethylene, as known in other systems (9). Based on several lines of evidence (1)(2)(3)5) and the (1,2) or ethylene (present study), by sugar starvation (5) and, to a certain extent, by wounding (as evidenced by the controls). The subsequent proliferation of the callus is dependent on the hormonal balance of the explant, it can be promoted by the addition of GA to the medium (2), and suppressed by high sugar levels (5).…”

Effects of light on somatic embryo development and abscisic levels in carrot suspension cultures

“…The callus then became a renewed cell source for embryogenesis. Contradictory evidence exists concerning whether ABA can be promotive [2,7] or inhibitory to callus production [11,34] which may be an important factor in this case.…”

Influence of Phytohormones on the Response of Cultured Cotton Ovules to (2‐chloroethyl)phosphonic Acid

“…However, the observed ABA stimulation of growth is not unprecedented. Altman and Goren (1971) found that ABA alone induced callus growth from an abscission zone on citrus bud explants. Takahashi (1973) found that ABA stimulated the elongation of rice mesocotyl but that synergistic elongation occurred when ethylene and ABA were both present.…”