A Cobalt Requirement for Symbiotic Growth of Azolla filiculoides in the Absence of Combined Nitrogen

Abstract

lReceixved Nonemnber 15, 1965 .S'uummu,ary. Cobalt wx-as shown' to be essenitial for the syvnbiotic growtl of Asolla filiciiloi(des and Aniabacii,, a_zollac in the absence of fixed nlitrogeni. Addition of 0.01 ,ug/liter cobalt resulted in large inicreases in vield, chlorophyll conitent ani(l nitrogeln fixationi as compared to conltrol cuilttires without cobalt. Cobalt was not require(l for the growth of Az4olla when nitrate nitrogen was supl)l)liedl. The numbler of .4la(biciuia azollac cells in the froln(ds of .41oll(i appeared to be dlecrease(l by oimmiiiissioln of cobalt from1 the ctlltnire imie(diuimi containing nitrate nitrogen. It is con1cEt(lu(d that col)alt i., essential for the symbiotic growth of .4-olla in the al)sence of combined nitrogen andcl it is suggested tlhat the co)alt re(utiiremlent is associate(l with the growth of .AInabacoa a-ollae. The aqtuatic fern Alolla filicniloi(dcs clharacteristic-ally occurs with the blue green alga. Anab a ao.vla(c, enclosed within cavities in the (lorsal lobes of the leaves of the fern (12). Atmospheric niitro-gen is fixed svibiotically by Avolla anid the associated Anabacuia (4). 4o/la(ctlltured in the ab)sence of the symlbiotic alga requiiires a source of comhbined nitrogeni (11). Accordingg to Bortels (4) AiabaLia azol/ac isolated fronm Afolla plants. faile(d to grow alonie. \Venkataraman (13) however. hals reported that the alga grew independently ai(i fixed atmios-pheric nitrogeni in pure ctiltuire. This report hias niot been conifirme(l. Since cobalt is requliredl for certaini free-living blue-green algae (7) for symbiotic niitrogeni fixation by leg-umes (1. 2) and(i for certaini nionilegLliumes (3). it was of interest to investigate the inifltienice of cobalt on1 the growth of .4-oll(a in the l)resence an(l absence of fixed nitrogeni. A prelimiina,iry relport on this researclh has a)l)peare(l (6). Materials and Methods 'I'lTe milacrointitrienlt salts and(l nAInS()4 4H.,() tise(l in cobalt (leficiencv sttu(lies with Az-olla were purified by extraction of the 1-nitroso-2-napthol complex of heavy imietals wvitlh redistille(d chloroformi as described byv Kliewer et al. (9). Calcium sulfate was crvs