Internode length in Pisum. Further studies on the ‘micro’ gene, lm

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Reid, J. B. and Ross, J. J. 1988. Internode length in Pisum. Further studies on the ‘micro’ gene, lm. ‐ Physiol. Plant. 72: 547–554.In the garden pea, Pisum sativum L., gene lm confers the micro phenotype. The shoots of lm plants may be described as scaled‐down versions of comparable Lm plants, with reduced internode length, leaflet size and rate of leaf expansion. However, the first phenotypic effect of gene lm is on root morphology. The gene results in curling and reduced elongation of the roots and, eventually, degeneration of the root cortex. These changes commence prior to any major visible effects in the shoot. The primary action of the lm gene does not appear to be confined to the root system, however, since epicotyl grafts between Lm and lm plants showed no graft‐transmissible effects. The effects of gene lm are also apparent in dark‐grown plants. Microdwarf plants (lm le) respond well to gibberellin A1 (GA1), but do not elongate to the same extent as dwarf (Lm le) plants. The two genotypes contain the same complement of GA‐like substances. It is argued that gene lm is unlikely to be directly involved with GA‐metabolism or the reception of the GA signal, but rather reduces the GA response by influencing some aspect of normal cell development, which results in the wide range of pleiotropic effects observed. Consequently, it may be misleading to continue to classify this gene simply as an internode length mutant.