The Effects of 1-Naphthylacetic Acid on the Growth of Excised Tomato Roots

1-naphthylacetic acid (NAA) enhances main axis extension and lateral initiation of excised tomato roots cultured in 0.5 per cent sucrose medium. NAA has a qualitatively similar effect upon the growth of root tips cultured in glucose medium or transferred after 2 days' previous growth in standard (1.5 per cent sucrose) medium to a glucose medium containing NAA. NAA does not raise the growth-rate of roots cultured in glucose medium to that occurring in presence of sucrose as carbon source. The enhanced growth resulting from addition of NAA to glucose medium is not dependent upon enhanced glucose uptake. The unique role of sucrose in the growth of excised tomato roots is discussed in the light of the above observations and of studies on the ability of glucose to maintain the growth of excised roots previously established by a period of culture in sucrose medium.