ULTRAVIOLET MICROBEAM IRRADIATION OF CHROMOSOMAL SPINDLE FIBERS IN HAEMANTHUS-KATHERINAE ENDOSPERM .1. BEHAVIOR OF THE IRRADIATED REGION

We used an ultraviolet microbeam to irradiate chromosomal spindle fibr es in metaphase Haemanthus endosperm cells. An area of reduced birefri ngence (ARB) was formed at the position of the focussed ultraviolet li ght with all wavelengths we used (260, 270, 280, and 290 nm). The chro mosomal spindle fibre regions (kinetochore microtubules) poleward from the ARBs were unstable: they shortened (from the ARB to the pole) eit her too fast for us to measure or at rates of about 40 mum per minute. The chromosomal spindle fibre regions (kinetochore microtubules) kine tochore-ward from the ARBs were stable: they did not change length for about 80 seconds, and then they increased in length at rates of about 0.7 mum per minute. The lengthening chromosomal spindle fibres someti mes grew in a direction different from that of the original chromosoma l spindle fibre. The chromosome associated with the irradiated spindle fibre sometimes moved off the equator a few micrometers, towards the non-irradiated half-spindle. We discuss our results in relation to oth er results in the literature and conclude that kinetochores and poles influence the behaviour of kinetochore microtubules.