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.