Investigations on the growth and metabolism of cultured explants of Daucus carota : I. Effects of iron, molybdenum and manganese on growth.

The effects of Fe, Mo and Mn on the growth of explants drawn from different carrot clones were investigated. The explants were cultured aseptically on purified basal media supplemented with coconut milk. The two components of growth, i.e. cell division and cell enlargement, seem to respond differentially to the trace elements in question. Fe plays the key role and acts as a "trigger" of the action of coconut milk in stimulating cell division. Neither Mo nor Mn could replace iron in this respect. Mo and Mn acting separately tend to foster growth by cell enlargement to a different degree and at different concentrations. However, when Mo and Mn were added together to a medium containing iron, they seem to interact and stimulate growth by cell division and cell, enlargement still further. The suggestion is made that the behavior of the explants from different clones may have been responsive to differences in the functional Fe/Mn ratio which also involves endogenous levels of trace elements as well as the exogenous levels furnished in the medium.Thus, the element Fe emerges as the key trace element which interacts with the factors present in coconut milk to induce growth in the otherwise quiescent carrot tissue.