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Differential in vitro development of inflorescences in long and short day Lemna spp.: involvement of ethylene and polyamines.

In vitro-development of Lemna inflorescences on minimal medium is known to differ in long day (LDP) and short day (SDP) plants (Z. Pfl, physiol. 77, 395). In LDP pistil growth predominates, while in SDP stamen growth predominates. This indicates that LDP and SDP inflorescences differ in endogenous hormones and depend for a balanced male-female development on different plant-supplied factors (Z. Pfl. physiol. 80, 283 and 298). Here inflorescences of the LDP L. gibba and the SDP L. aequinoctialis were tested for differences in ethylene-polyamine (PA) relations, as ethylene and PAs are inversely related (shared precursor, mutual inhibition of synthesis), and exogenous ethylene has been shown previously to restore male-female balance in SDP inflorescences (Z. Pfl. physiol. 80, 283). Promotion of pistil or stamen growth indicates a predominance of ethylene and PAs in LDP and SDP, respectively. Hence, in LDP, exogenous PAs and inhibitors of ethylene synthesis, and in SDP, an inhibitor of PA-synthesis, were applied to restore the male-female balance in vitro. In L. aequinoctialis (SDP), application of methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of spermidine (SD) synthesis, resulted in near normal development via stamen inhibition and/or pistil promotion. In L. gibba (LDP), ethylene inhibition was effective, especially by aminoethoxyvinylglycine (AVG), which reduced pistil growth. Effects of alpha-aminooxyacetic acid (AOA) were less clear. Putrescine (PUT) promoted stamen growth under certain circumstances, perhaps acting as a precursor for the more active SD. SD effects were concentration-dependent for pistil and stamen. Most importantly, increases in SD turned pistil promotion into inhibition and almost normalised floral development. Spermine (SM) enhanced stamen growth. Results are conclusive that PA-ethylene relationships are involved in inflorescence development in a contrasting manner in LDP and SDP. It is apparent that in whole plants the LDP supplies the inflorescences with factors inhibiting ethylene and/or stimulating PA-synthesis. In SDP the converse is true.