Effect of temperature and water stresses on gas exchange, fluorescence kinetics, and solute levels of jojoba

Abstract

Seven year old jojoba, Simmondsia chinensis (Link) Schneid., plants grown under three irrigation treatments, wellwatered, intermediate, and dry, were exposed to controlled temperature treatments of +5, −5, and −10 °C for six hours during February 1991. Following the temperature treatments, gas exchange and fluorescence kinetics were used to evaluate the degree of injury to the plants. Following subfreezing temperatures, gas exchange was depressed, and fluorescence kinetics indicated greater damage to well-watered plants. Amino acid and carbohydrate levels, and osmotic potentials were measured before and after cold treatments to observe the effect of low temperatures on solutes. Freezing temperatures resulted in increased solute concentrations attributed to increases in total carbohydrates and total amino acids. Proline, arginine, aspartate family amino acids, glucose, and fructose increased while phenylalanine, tyrosine/ornithine, glutamate and sucrose decreased in response to freezing temperatures. Lathhouse plants exposed to −5 °C natural frost for seven hours in December 1990 set seed, but, with the exception of dry treatment plants exposed to −5 °C, plants exposed to either −5 or −10 °C in the laboratory in February 1991 did not set seed. Overall, the intermediate irrigation treatment had the least disruption of fluorescence kinetics and photosynthesis, and set the most seed following the controlled low temperature treatments.