(Megaspore germination and initial sporophytic development of the fern Regnellidium diphyllum (Marsileaceae) under mineral deficiencies). Regnellidium diphyllum Lindm. is a heterosporous fern in the Marsileaceae family with restricted distribution to Southern Brazil and some adjoining localities in Uruguay and Argentina. The species has been listed as vulnerable in the endangered species list of the State of Rio Grande do Sul. In the present study we verified the effect of absence of mineral nutrients on megaspore germination and initial development of R. diphyllum sporophytes in vitro. The effect of Meyer's nutrient solutions modified by the absence of NH4NO3, NaCl, FeCl3·6H2O, MgSO4·7H2O, KH2PO4 or CaCl2 was analyzed in the germination and sporophyte formation of R. diphyllum. Megaspore germination decreased in absence of CaCl2 (52%) when compared to the control (77.3%). A low percentage of gametophytes gave rise to sporophytes in the absence of MgSO4·7H2O (38.6%) and KH2PO4 (33.8%). Without CaCl2 in the solution, no sporophytes were formed. The length of the primary root and of the primary and secondary leaves was significantly reduced without MgSO4·7H2O and KH2PO4. Without KH2PO4 in the solution, no secondary leaf was formed after five weeks of culture. The other treatments did not inhibit the megaspore germination process and the initial development of sporophytes, showing that the species may establish itself even under low levels of these nutrients.
aquatic macrophyte; ecophysiology; mineral nutrition; pteridophytes; reproduction
