IN-VITRO-CULTURED SUBCLOVER ROOT CAN DEVELOP FE-DEFICIENCY STRESS-RESPONSE

The Fe-deficiency stress response is induced in most plants under Fe-d eficient conditions, but whether the shoot and/or the root control dev elopment of the stress response is not known. The objectives of the pr esent study were to determine whether in-vitro-cultured subclover root s can develop Fe-deficiency stress response and to examine this approa ch as a possible screening technique for Fe-deficiency resistance. One -cm long root tips of subclover seedlings were cultured in modified Wh ite's medium without (-Fe) or with (+Fe) 100 mu M Fe(3+)EDTA. Root Fe3 + reduction and H+ release were evaluated. On the first day after tran sfer to the -Fe medium, the Fe-deficiency-resistant cultivar Koala (Tr ifolium brachycalycinum Katzn. and Morley) started to release H+, resu lting in a decrease in pH of the culture medium, while the susceptible cultivar Kamidale (T. subterraneum L.) did not release H+ until the s econd day. The H+-release rate of the -Fe Koala was approximately twic e as high as that of the -Fe Karridale for the first 4 days of -Fe tre atment. Both Koala and Karridale reached their highest H+-release rate s on the fourth day after -Fe treatment initiation. The +Fe Koala rele ased H+ after several days of culture, but the He release of the -Fe K oala was severalfold greater than that of the +Fe Koala. The implicit correlation between Ht release and Fe-deficiency resistance was substa ntiated by using a series of subclover cultivars with a range of susce ptibilities to Fe deficiency. The pH of the -Fe culture media of the s eries of cultivars was positively correlated to their Fe-chlorosis sco res reported in previous research. The results of the present study in dicate that root itself has the full ability to develop Fe-deficiency stress response and the response is dependent on the root Fe status. T he results also suggest that root culture could be used as a simple an d efficient alternative technique for screening germplasm for Fe-defic iency resistance.