Photosynthesis in Salt-Adapted Heterotrophic Tobacco Cells and Regenerated Plants

Abstract

Tobacco (Nicofiana tabacum L.) cells growing heterotrophically in the light on supplied sucrose (SO) have previously been adapted to grow in 428 mM NaCl (S25). Among the changes occurring in salinity-adapted cell cultures are (a) elevated levels of chlorophyll compared to unadapted cells; (b) decreased levels of starch; (c) alterations in chloroplast ultrastructure, including loss of starch grains, increased thylakoid membrane structure, and the presence of plastoglobules; and (d) increased rates of O, evolution, CO, fixation, and photophosphorylation relative to SO cells. These latter changes apparently derive from the fact that thylakoid membranes in S25 cells contain higher levels of photosystem I-and 11-associated proteins as well as thylakoid ATPase components. S25 chloroplasts contain immunologically detectable levels of ribulose-1 ,S-bisphosphate carboxylase/oxygenase, whereas SO completely lack the enzyme. These changes taken together suggest that even in the presente of sucrose, S25 cells have acquired a significant degree of salt-tolerant photosynthetic competence. This salt-tolerant photoysynthetic capability manifests itself in plants backcrossed with normal plants for three generations. These plants contain chloroplasts that demonstrate in vitro more salt-tolerant CO, fixation, O, evolution, and photophosphorylation than do backcross progeny of plants regenerated from SO cultures.Numerous cell-suspension culture lines able to grow in the presence of salt-induced osmotic stress have been established (Dix and Street, 1975;Nabors et al., 1975;Tyagi et al., 1981;Kochba et al., 1982; Rangan and Vasil, 1983;Watad et al., 1983;Pandey and Ganapathy, 1984; Binzel et al., 1985;Rains, 1989;Plaut et al., 1991) for the purpose of studying cellular adaptation to salinity stress, and these cell lines have provided much information about salinity tolerance at the cellular level. The tobacco cell line chosen for the present study has been widely studied in this regard. Binzel et al. (1985) established a heterotrophically growing, salt-adapted cell line of tobacco (Nicotiana tabacum L. var Wisconsin 38) by gradually adapting cells to increasing concentrations of NaC1. The adapted cell line showed substantially greater growth in salt-containing media than did previously unadapted cells. However, adapted cells growing in salt showed reduced cell expansion and fresh weight gain but equivalent dry weight gain ' This is publication No. 6-955101 of the Alabama Agricultura1 (Binzel et al., 1985;Bressan et al., 1990) when compared to unadapted cells growing without salt.Adaptation of tobacco cells to salt has also been shown to involve the accumulation of a 26-kD, thaumatin-like protein, called osmotin (Ericson and Alfinito, 1984;Singh et al., 1985Singh et al., , 1987; alterations in the cell wall and extracellular polysaccharides (Iraki et al., 1989a(Iraki et al., , 1989b; the accumulation of various osmolytes, including Suc and Pro (Binzel et al., 1987); and the accumulation and partitioning of inorganic ions such as p...

Tocopherol Cyclase (VTE1) Localization and Vitamin E Accumulation in Chloroplast Plastoglobule Lipoprotein Particles

“…Under high light stress conditions, levels of tocopherols increase (72), and VTE1 is up-regulated (45). The presence of VTE1 and tocopherols (this paper) together with the reported increase in size and number of plastoglobules (33)(34)(35) provides a molecular explanation for the role of plastoglobules under conditions resulting in oxidative stress.…”

“…At least two PAP/fibrillins were localized at the periphery of plastoglobules (3,26), and purified fibrillin was able to promote carotenoid fibril assembly in vitro (1), suggesting a structural function (29). Upregulation of several PAP/fibrillins has been correlated with various treatments generating reactive oxygen species (20, 24, 30 -32), and enlarged plastoglobules have been described in chloroplasts under abiotic stress such as drought (33), nitrogen starvation (34), or hypersalinity (35). Taken together, these observations implicate plastoglobules in stress tolerance.…”

A mechanism implicating plastoglobules in thylakoid disassembly during senescence and nitrogen starvation

“…Conditions provoking oxidative stress such as high light, nitrate starvation, drought, high saline concentration, viral infection, chilling and ozone (Nordby and Yelenosky 1985;Locy et al 1996;Rey et al 2000;Oksanen et al 2001;Gaude et al 2007;Lichtenthaler 2007) or developmental stages such as senescence and fruit development (Kaup et al 2002) result in the dismantling of thylakoid membrane. In parallel, the number and the size of lipid droplets increase, due to the accumulation of lipids in their hydrophobic core.…”

Plastid Localization of the Key Carotenoid Enzyme Phytoene Synthase Is Altered by Isozyme, Allelic Variation, and Activity

“…Fibrillins, the major proteins of plastoglobuli (Singh and McNellis, 2011), maintain the structure of the globules and assist in the globular-fibril transition to store high amounts of carotenoids synthesized during chromoplast development (Bréhélin and Kessler, 2008). Plastoglobuli also enlarge and proliferate in response to abiotic stress (e.g., high light, drought, salt, heat, and nitrogen starvation) (Locy et al, 1996;Eymery and Rey, 1999;Bondada and Syvertsen, 2003;Szyma nska and Kruk, 2010;Zhang et al, 2010). These stress conditions induce accumulation of carotenoids and/or their apocarotenoid products (Li et al, 2008a(Li et al, , 2008b, and the expression of core plastoglobuli protein genes correlates with the expression of several enzymes from the carotenoid pathway (Lundquist et al, 2012).The importance of plastoglobuli in modulating plant metabolism is beginning to gain attention.…”