9306521 Bloom In a chilling-sensitive tomato cultivar (Lycopersicon esculentum Mill. cv. T5), short exposures to 5 degree centigrade rapidly and irreversibly inhibited root ammonium influx. By contrast, ammonium efflux and nitrate absorption in this taxon, as well as ammonium and nitrate absorption in a chilling-tolerant congener (Lycopersicon hirsutum LA1778), recovered immediately and fully from such exposures. The research would examine the physiology and genetics of this phenomenon to elucidate the regulation of ammonium transport and the importance of ammonium transport in the chilling response of tomato. The physiological experiments would employ ammonium-selective microelectrodes to localize ammonium absorption in the root and to determine whether resumption of ammonium influx after a chilling episode requires protein synthesis, transcription, or new growth. These characteristics should assist in the identification of root membrane proteins associated with ammonium influx. The genetic studies would involve the screening of 30 plants a day for chilling-sensitive ammonium influx using an automated NH4+ analysis system. Segregation analysis of the chilling-sensitive L. esculentum, the tolerant L. hirsutum, and L. esculentum x L. hirsutum F1 populations should determine the inheritance of this trait. Lastly, we would test backcrosses of the F1 hybrids to L. esculentum that have been selected for chilling-tolerant ammonium influx for their overall chilling tolerance. A better understanding of plant ammonium absorption is critical to the study of plant nitrogen relations in specific, and plant transport processes in general. Moreover, in transferring a specific chilling-tolerant trait to tomato, we should elucidate the role of below-ground processes in the chilling response of plants. ***
