Endogenous Growth Substances in Normal and Dwarf Mutants of Cortland and Golden Delicious Apple Shoots

Endogenous growth substances in the shoots of dwarf mutants of Cortland (Cortland 65–6 and Cortland 65–7) and Golden Delicious (Golden Auvil Spur and Yellow Spur) were investigated in relation to dwarfism. The shoots were extracted at three stages of growth, namely: 1) rapid elongation growth, 2) formation of terminal bud, and 3) cessation of cambial growth. The growth substances were partially separated by thin layer chromatography and bioassayed using the Avena first internode and Lepidium seed germination tests. Shoot extracts from the normal Cortland and Golden Delicious plants contained higher levels of auxins at all stages of growth than those from dwarf mutants. Growth-promoting activity was found in two zones on chromatograms developed with isopropanol: ammonia: water (10:1:1 v/v/v):R_f 0.4 to 0.5 and R_f 0.8 to 0.9. The Lepidium seed germination test showed the presence of a highly inhibitory zone between R_f 0.3 and 0.4 in the extracts of dwarf and normal plants. However, the peak of germination inhibition activity was sharp for dwarf mutants and less for extracts of normal growing plants at 3 stages of growth. The inhibitory substance(s) was further purified on TLC plates by successive separations in different solvent systems. Two substances which inhibited the Lepidium seed germination were found, one close to the R_f value of synthetic abscisic acid and the other appeared to be similar to xanthoxin in R_f value, biological activity and UV absorption spectra.     

Efficiency of Filter Feeding in Two Species of Tetrahymena*

SYNOPSIS. Rates of removal of suspended India ink particles from the surrounding medium by 2 ciliates, Tetrahymena pyriformis strain GL and Tetrahymena vorax strain V₂S, have been measured. It is evident from the results that the food vacuoles concentrate the suspended particles, clearing a volume of the surrounding suspension fluid 500 × greater than the total volume of food vacuoles made during the same period of time.