Effect of aluminum on growth of root tips of honey locust and loblolly pine

Honey locust ( Gleditsia triacanthos L.) and loblolly pine ( Pinus taeda L.) were grown in solution culture with 150–1500 μM Al. In both species Al reduced primary root elongation, but more severely in honey locust. The decrease was most evident in the 2nd mm root segment after 24 hr. The decrease in elongation was not accompanied by a decrease in cell size. Al drastically reduced mitotic activity in honey locust which was not reversed with time. A less marked decline was noted in loblolly pine and mitotic activity returned to control levels after 72 hr. These observations plus the appearance of necrotic lesions in honey locust suggest (1) that honey locust is more sensitive to Al than loblolly pine and (2) that Al more probably exerts its growth effect through a nuclear rather than cell wall synthesis mechanism.