RESUMEN
Adventitious root development in lamina and midrib-petiole junction expiants of sugar beet cv. Primo was investigated using scanning electron microscopy and light microscopy. Primordia developed close to the vascular strands and areas of newly dividing cells (meristematic centres) were seen adjacent to the intrafascicular cambium after 2 d incubation on medium containing 30 mg 1(-1)1-naphthalene acetic acid. Clearly defined primordia were visible at 4 d and the first roots had emerged by 6 d. A minimum of 24 h exposure to NAA was necessary for root induction. Four days on NAA caused twice as many roots to be initiated but more prolonged exposure (5 and 10 d) inhibited root development. Root initiation continued after transfer to medium containing no plant growth regulators, new primordia appearing as the older ones extended as roots. Attempts were made to modify the development of primordia by sequential culture on cytokinin after induction by auxin. Incubation on N6-benzylaminopurine within 48 h of exposure to NAA disrupted the development of primordia and roots but did not induce shoot formation.
RESUMEN
A simple assay for phytotoxicity, using small scale cultures of Chlorella vulgaris, is described. Growth after 3 days' incubation in 0.5 cm(3) medium is assessed by DMSO-acetone extraction and chlorophyll determination. The method is sensitive enough to detect phytotoxicity in small samples of material and this is illustrated by the inhibitory effects of microgram additions of copper, cadmium and zinc.