Role of endogenous cytokinin in the development of hollowing in the root of Japanese radish ( Raphanus sativus L.)

Abstract

The size of the hollow cavity increased with time in plants of the early sown plot (ESP), whereas its size remained almost unchanged throughout the growth period in plants of the late sown plot (LSP). The daily maximum soil temperatures in the ESP were 6–12 °C higher than those in the LSP. A much higher level of cytokinin was detected in the ammonia eluate fraction than in the acidic ethyl acetate fraction and none was detected in the effluent and washings. Cytokinin levels in the ammonia eluate fraction and the acidic ethyl acetate fraction were low in roots from the ESP in comparison with those from the LSP. A much larger size of hollow cavity was observed at any days after sowing (DAS) in control roots, that were exposed to temperatures of 30 °C and above for 30 days, than in roots grown at lower soil temperatures between 25 °C and 30 °C throughout the growth period. Cytokinin levels in control roots grown at high soil temperature were consistently lower than those in the roots grown at low soil temperature. The production of endogenous cytokinin in the roots of cvs. Sobuto and Fukumi, cultivars that were prone to hollowness, was reduced at higher soil temperatures, while in cultivars that were resistant to hollowness cytokinin production was higher. The role of endogenous cytokinin in the development of hollowing is discussed.