Carbon utilization in tobacco cells adapted to sodium-chloride

Sherry Rae Schnapp, Purdue University

Abstract

Carbon utilization was evaluated in tobacco (Nicotiana tabacum L. var. Wisconsin 38) cell suspensions adapted to 0 and 428 mM NaCl in order to test the hypotheses that there are additional metabolic carbon costs associated with adaptation to salinity and that these costs may contribute to reduced cell expansion under saline conditions by imposing carbon limitations. Carbon use efficiency was defined as organic dry weight accumulation per unit sugar removed from the medium. Carbon use efficiency of salt adapted cells increased from.422 to.618 when sucrose was supplied at 10 and 50 g L$\sp{-1}$, respectively. However, the carbon use efficiency of unadapted cells decreased from.495 when supplied with 5 g L$\sp{-1}$ to.361 when supplied with 50 g L$\sp{-1}$. These results indicate that there is no net increase in carbon costs associated with survival and growth in saline environments. Results demonstrated that cell expansion was not carbon limited. In fact, at higher levels of sugar supplied, salt adapted cells were more carbon use efficient than unadapted cells. However, the possibility remained that costs of some processes increased while others decreased to compensate. Carbon utilization can be divided into two components expressed in terms of energy and carbon skeletons used for growth (growth yield = Yg) and for maintenance of viability in existing biomass (maintenance coefficient = m). These parameters were assessed according to the equation q = (1/Yg) $\mu$ + m where q = specific rate of sugar uptake and $\mu$ = specific growth rate. Initial attempts to determine growth yield and maintenance coefficients in batch culture were unsuccessful due to problems with the underlying assumptions and technical difficulties. We therefore developed a semi-continuous culture system for the establishment of cells growing at different specific growth rates. Mathematical simulations were used to verify the validity of this approach. Results indicate that the growth yield and maintenance coefficient of the two cell types do not differ, suggesting that the ability to invoke metabolic homeostasis may be an important component of the adaptation to salinity. These results corroborated the carbon use efficiency data indicating that there are not additional carbon costs associated with adaptation to salinity.

Degree

Ph.D.

Advisors

Hasegawa, Purdue University.

Subject Area

Botany

COinS