Cellular mechanisms of salinity tolerance in plants

Marla Lynn Binzel, Purdue University

Abstract

Cell lines of tobacco (Nicotiana tabacum L var Wisconsin 38) were adapted to varying levels of NaCl (up to 600 mM). Adaptation to NaCl led to reduced cell expansion and fresh weight gain, while dry weight remained unaffected. This reduction in cell expansion was not due to a failure of the cells to maintain turgor since cells adapted to NaCl underwent osmotic adjustment in excess of the change in water potential caused by the addition of salt to the medium. Although tobacco is considered to be a glycophyte, when grown in culture the cells respond in a manner similar to halophytes, utilizing Na$\sp+$ and Cl$\sp-$ as primary osmotica and exhibiting a positive correlation between tolerance and intracellular (Na$\sp+$) and (Cl$\sp-$). The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation, however, the levels of these solutes did not approach those observed for Na$\sp+$ and Cl$\sp-$. The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 mM in cells adapted to 428 mM NaCl and representing about 80% of the total free amino acid pool as compared to an average of 0.29 mM and about 4% of the pool in unadapted cell. X-ray microanalysis of frozen hydrated samples of salt adapted cells revealed that the Na$\sp+$ and Cl$\sp-$ accumulated was predominantly localized in the vacuole, concentrations of Na$\sp+$ and Cl$\sp-$ in the vacuole were approximately 800 mM and 600 mM, respectively, while cytoplasmic concentrations were near 100 mM for both ions. Steady state efflux analyses of cells preloaded with either $\sp{22}$Na$\sp+$ or $\sp{36}$Cl$\sp-$ corroborated that Na$\sp+$ and Cl$\sp-$ were compartmentalized in the vacuole. While adaptation to NaCl did not appear to enhance tolerance to Na$\sb2$SO$\sb4$, NaCl adapted cells were more tolerant of KCl than unadapted cells. However, our results did indicate some degree of cation specificity which was particularly apparent when cells were subjected to an osmotic downshock and then exposed to moderate levels of NaCl or KCL.

Degree

Ph.D.

Advisors

Hasegawa, Purdue University.

Subject Area

Botany

COinS