EFFECT OF TEMPERATURE AND WATER STRESSES ON GAS-EXCHANGE, FLUORESCENCE KINETICS, AND SOLUTE LEVELS OF JOJOBA

Seven year old jojoba, Simmondsia chinensis (Link) Schneid., plants gr own under three irrigation treatments, well-watered, intermediate, and dry, were exposed to controlled temperature treatments of +5, -5, and -10 degrees C for six hours during February 1991. Following the tempe rature treatments, gas exchange and fluorescence kinetics were used to evaluate the degree of injury to the plants. Following subfreezing te mperatures, gas exchange was depressed, and fluorescence kinetics indi cated greater damage to well-watered plants. Amino acid and carbohydra te levels, and osmotic potentials were measured before and after cold treatments to observe the effect of low temperatures on solutes. Freez ing temperatures resulted in increased solute concentrations attribute d to increases in total carbohydrates and total amino acids. Proline, arginine, aspartate family amino acids, glucose, and fructose increase d while phenylalanine, tyrosine/ornithine, glutamate and sucrose decre ased in response to freezing temperatures. Lathhouse plants exposed to -5 degrees C natural frost for seven hours in December 1990 set seed, but, with the exception of dry treatment plants exposed to -5 degrees C, plants exposed to either -5 or -10 degrees C in the laboratory in February 1991 did not set seed. Overall, the intermediate irrigation t reatment had the least disruption of fluorescence kinetics and photosy nthesis, and set the most seed following the controlled low temperatur e treatments.