In-vitro-cultured subclover root can develop Fe-deficiency stress response

The Fe-deficiency stress response is induced in most plants under Fe-deficient conditions, but whether the shoot and/or the root control development of the stress response is not known. The objectives of the present study were to determine whether in-vitro-cultured subclover roots can develop Fe-deficiency stress response and to examine this approach as a possible screening technique for Fe-deficiency resistance. One-cm long root tips of subclover seedlings were cultured in modified White's medium without (-Fe) or with (+Fe) 100 μM Fe³⁺EDTA. Root Fe³⁺ reduction and H⁺ release were evaluated. On the first day after transfer to the -Fe medium, the Fe-deficiency-resistant cultivar Koala (Trifolium brachycalycinum Katzn. and Morley) started to release H⁺, resulting in a decrease in pH of the culture medium, while the susceptible cultivar Karridale (T. subterraneum L.) did not release H⁺ until the second day. The H⁺-release rate of the -Fe Koala was approximately twice as high as that of the -Fe Karridale for the first 4 days of -Fe treatment. Both Koala and Karridale reached their highest H⁺-release rates on the fourth day after -Fe treatment initiation. The +Fe Koala released H⁺ after several days of culture, but the H⁺ release of the -Fe Koala was severalfold greater than that of the +Fe Koala. The implicit correlation between H⁺ release and Fe-deficiency resistance was substantiated by using a series of subclover cultivars with a range of susceptibilities to Fe deficiency. The pH of the -Fe culture media of the series of cultivars was positively correlated to their Fe-chlorosis scores reported in previous research. The results of the present study indicate that root itself has the full ability to develop Fe-deficiency stress response and the response is dependent on the root Fe status. The results also suggest that root culture could be used as a simple and efficient alternative technique for screening germplasm for Fe-deficiency resistance.