Relationship between concentration of cytokinin for efficient shoot regeneration and seed coat color in leaf lettuce

Lettuce (Lactuca sativa L.) is an economically important leafy vegetable crop around the world. Recently, transgenic lettuce has been developed to improve agronomic traits. Although plant regeneration is a key step in plant genetic transformation, it depends strongly on the cultivar. In this study, shoot regeneration efficiency was measured by using two leaf lettuce cultivars, Chima-sanchi, white seed cultivar, and Chirimen-chisya, brown seed cultivar, a basal salt mixture, and a combination of the cytokinin, 6-benzylaminopurine (BAP), and an auxin, 1- naphthaleneacetic acid (NAA). Efficient shoot regeneration in Chima-sanchi was thus obtained on 1 x Murashige and Skoog medium (MS) with 0.05 mg L-1 BAP and 0.1 mg L-1 NAA. However, the highest efficiency was obtained in Chirimen-chisya on 1 x MS with 0.5 mg L-1 BAP and 0.1 mg L-1 NAA. Therefore, the BAP concentration for efficient shoot regeneration differs significantly between the two cultivars. These cultivars also have different seed coat colors. Due to the similar results obtained from analyzing 4 additional cultivars, 2 white seed cultivars and 2 brown seed cultivars, we demonstrated a strong correlation between the BAP concentration for efficient shoot regeneration and the seed coat color in leaf lettuce.