A Simple Procedure for Mesophyll Protoplast Culture and Plant Regeneration in Brassica oleracea L. and Brassica napus L.

Abstract

An improved protocol for Brassica protoplast culture and plant regeneration was developed. Isolated protoplasts from four-weeks-old in vitro shoot tip culture of Brassica oleracea var. botrytis cv. Siria F1 and Brassica napus doubled haploid of breeding line OP-1 were cultured at a density of 9.8–11.2 × 10 4 protoplasts/ml in darkness at 25°C in a modified medium containing 2% glucose, 0.25 mg/l 2,4-D, 1 mg/l BAP and 1 mg/l NAA. The first divisions of protoplasts were observed on the third day of culture in B. oleracea and on the fourth day in B. napus. The protoplast cultures were diluted with low osmotic medium on 7 th and 11 th day. The frequency of dividing cells was about 80% in B. oleracea and 50% in B. napus. After one month, the microcalli of approximately 0.5–1 mm in size were transferred into an induction medium with various combinations of growth regulators. Minimum duration of enzyme treatment time and extended dark period in the initial phase of culture increased the survival rate of protoplasts. Organogenesis started when the calli enlarged in size on an induction medium (1 mg/l NAA, 0.02 mg/l GA 3, 1 mg/l 2iP) with 2% sucrose and 0.8% agar. Regeneration frequency of calli was found to be 69–75% in B. oleracea and 2–3% in B. napus. Well-developed shoots were transferred for rooting to a half-strength MS medium without growth regulators. More than 100 B. oleracea regenerants were transferred into soil, and they produced normal heads and set seeds. This very simple procedure is efficient and suitable mainly for B. oleracea var. botrytis and represents a background for fusion experiments.