INFLUENCE OF NUTRIENTS ON THE DEVELOPMENT OF GIBBOSITY IN FRONDS OF THE DUCKWEED LEMNA-GIBBA L

The duckweeds Lemna gibba L. and Lemna minor L. only grew well in undi sturbed culture under axenic conditions in low light intensity when pr ovided with a suitable energy source such as glucose. In media contain ing NO3-N gibbosity (a convex ventral surface) was induced in the pres ence of the chelating agent ethylene-diamine-di-o-hydroxyphenylacetic acid (EDDHA). In nutrient solutions containing NO3-N as the only N sou rce, but without EDDHA, L. gibba occasionally exhibited gibbosity in c ulture solutions of 40 cm(3) volumes. More fronds were induced to exhi bit gibbosity when the volume of the culture medium was increased from 40 cm(3) to 200 cm(3). Gibbosity was never induced in L. minor, neith er was it induced in L. gibba in media containing NH4-N, even in the p resence of NO3-N. There was no direct correlation between the occurren ce of gibbosity and frond growth rate, but gibbosity occurred only whe n there was good frond growth. In the absence of a sugar, frond growth was enhanced by bubbling air through the culture solution in the ligh t. Increasing the CO, concentration in the air up to 1% enhanced growt h and induced gibbosity. Carbon dioxide did not induce gibbosity in me dia containing NH4-N.