ZINC TREATMENT RESULTS IN TRANSPIRATION RATE DECREASES THAT VARY AMONG SOYBEAN GENOTYPES

Zinc (Zn) pollution of croplands can have negative impacts on yields through its effects on key physiological functions such as transpiration rate (TR). Previous long-term experiments indicated that differential tolerance among soybean genotypes following exposure to high Zn levels existed in the shoots. There are, however, no studies of the possibility that short-term responses to Zn directly limit shoot TR. Measurements of TR of eight soybean genotypes were measured over 220 minutes after placing de-rooted shoots in 500 mu M Zn solution. Six genotypes exhibited TR that decreased slowly in a linear fashion over time while two genotypes ('PI 416937' and 'N01-11136') exhibited very rapid decrease in TR following a Boltzmann sigmoid response. One possibility to explain these results is that there exists a Zn-sensitive AQP population in the leaves of 'PI 416937' and 'N01-11136' with abundance or activity that is much higher than in the leaves of the remaining six lines.