Tocopherols Play a Crucial Role in Low-Temperature Adaptation and Phloem Loading in Arabidopsis  

Abstract

To test whether tocopherols (vitamin E) are essential in the protection against oxidative stress in plants, a series of Arabidopsis thaliana vitamin E (vte) biosynthetic mutants that accumulate different types and levels of tocopherols and pathway intermediates were analyzed under abiotic stress. Surprisingly subtle differences were observed between the tocopheroldeficient vte2 mutant and the wild type during high-light, salinity, and drought stresses. However, vte2, and to a lesser extent vte1, exhibited dramatic phenotypes under low temperature (i.e., increased anthocyanin levels and reduced growth and seed production). That these changes were independent of light level and occurred in the absence of photoinhibition or lipid peroxidation suggests that the mechanisms involved are independent of tocopherol functions in photoprotection. Compared with the wild type, vte1 and vte2 had reduced rates of photoassimilate export as early as 6 h into low-temperature treatment, increased soluble sugar levels by 60 h, and increased starch and reduced photosynthetic electron transport rate by 14 d. The rapid reduction in photoassimilate export in vte2 coincides with callose deposition exclusively in phloem parenchyma transfer cell walls adjacent to the companion cell/sieve element complex. Together, these results indicate that tocopherols have a more limited role in photoprotection than previously assumed but play crucial roles in low-temperature adaptation and phloem loading.

Genetic Control of Carbon Partitioning in Grasses: Roles of Sucrose Transporters and Tie-dyed Loci in Phloem Loading

“…It is not understood how a lack of tocopherol leads to ectopic callose deposition. However, this function is conserved in potato (Solanum tuberosum) and Arabidopsis (Arabidopsis thaliana), as plants deficient for the Sxd1 orthologous gene show a similar callose-deposition and carbohydrateaccumulation phenotype (Hofius et al, 2004;Maeda et al, 2006).…”

Collection and Analysis of <em>Arabidopsis</em> Phloem Exudates Using the EDTA-facilitated Method

“…While EDTA can lead to cell damage 30 , several groups have used this method and observed no adverse effect of EDTA concentrations from 10 mM to 20 mM on the cell ultrastructure or on phloem loading and transport 5,24 . To reduce any damaging effect as well as interference of EDTA with chromatography and gel electrophoresis, plants are moved into water after 1 h and only the later part of the exudate is used 14 .…”

Zeaxanthin Has Enhanced Antioxidant Capacity with Respect to All Other Xanthophylls in Arabidopsis Leaves and Functions Independent of Binding to PSII Antennae

“…Protection of thylakoid membrane lipids against peroxidative damage is a function that is traditionally attributed to vitamin E (Fryer, 1992), although alternative functions have been suggested for vitamin E (Maeda et al, 2006;Munné-Bosch et al, 2007). Thus, unbound zeaxanthin in ch1 thylakoid membranes could fulfill a protective function similar to that of vitamin E. A previous study has shown that zeaxanthin and vitamin E are functionally redundant (Havaux et al, 2005), and this is supported here by the similarity of the phenotypes obtained by suppression of zeaxanthin or tocopherols in ch1.…”

“…The vte1 Arabidopsis mutant is deficient in tocopherol and accumulates the tocopherol precursor 2,3-dimethyl-phytyl-1,4-benzoquinol (DMPBQ; Maeda et al, 2006). We designed a double mutant, ch1 vte1, deficient in vitamin E, and a triple mutant, ch1 vte1 npq1, deficient in both vitamin E and zeaxanthin.…”