Does triacylglycerol (TAG) serve a photoprotective function in plant leaves? An examination of leaf lipids under shading and drought

Abstract

Plant survival in many ecosystems requires tolerance of large radiation loads, unreliable water supply, and suboptimal soil fertility. We hypothesized that increased production of neutral lipids (triacylglycerols, TAGs) in plant leaves is a mechanism for dissipating excess radiation energy. In a greenhouse experiment, we combined drought and shade treatments and examined responses among four species differing in life form, habitat, and drought- and shade-tolerance. We also present a lipid extraction protocol suitable for sclerophyllous leaves of native Australian trees (e.g. Acacia, Eucalyptus). Fluorescence measurements indicated plants exposed to full sunlight experienced mild photoinhibition during our experiment. Accumulation of TAGs did not follow photosynthetic capacity, but instead, TAG concentration increased with non-photochemical quenching. This suggests plants under oxidative stress may increase biosynthesis of TAGs. Moderate drought stress resulted in a 60% reduction in TAG concentration in wheat (Triticum aestivum). Shading had no effect on TAGs, but increased concentrations of polar lipids in leaves; for example, acclimation to shade in Austrodanthonia spp., a native Australian grass, resulted in a 60% increase in associated polar lipids and higher foliar chlorophyll concentrations. Shading also reduced the digalactosyldiacylglycerol: monogalactosyldiacylglycerol (DGDG:MGDG) ratio in leaves, with a corresponding increase in the degree of unsaturation and thus fluidity of thylakoid membranes of chloroplasts. Our results suggest prevention of photodamage may be coordinated with accumulation of TAGs, although further research is required to determine if TAGs serve a photoprotective function in plant leaves.

Fatty Acid Profile Changes During Gradual Soil Water Depletion in Oats Suggests a Role for Jasmonates in Coping With Drought

“…This might explain the effects of the substantial FFA accumulation at the latest sampling time of the drought time-course in Flega which could cause an unbalance between the increase of PLs released from the membrane and the capacity to esterify the resulting FFA to TAG. Alternatively, the accumulation of TAG is a mechanism for dissipation of excess radiation energy in leaves that is induced at increased levels of photoinhibition ( Marchin et al, 2017 ). The rationale of this hypothesis is that the production of the energy-rich reduced carbon compounds requires about twice the energy of carbohydrate biosynthesis ( Solovchenko, 2012 ).…”

A novel glycerophosphodiester phosphodiesterase improves phosphate deficiency tolerance in rice

“…Lipid extracts were dried and stored at −80°C till further analysis. Quantitation of lipids was performed with a triple quadrupole ion trap mass spectrometer, 4000 QTRAP (Applied Biosystems) as described earlier (Marchin, Turnbull, Deheinzelin, & Adams, ). Acyl chain length (ACL) and double bond index (DBI) were calculated as previously described (Zheng, Li, & Li, ) with the following formulas:…”

Adjustment of Photosynthetic and Antioxidant Activities to Water Deficit Is Crucial in the Drought Tolerance of Lolium multiflorum/Festuca arundinacea Introgression Forms

“…Accumulation of hydrogen peroxide observed in the LTD introgression form under advanced drought could be associated with a synthesis of TAG lipids that are suggested to play an important role in the neutralization of oxidized FA [80]. It was hypothesized that the accumulation of TAG may function as a mechanism for dissipation of excess radiation energy in leaves [27], and can be associated with a stabilization of membranes during dehydration [81,82]. Moreover, accumulation of TAG lipids could help to accommodate a shrinking organelle during osmotic stress by removing excess lipids from the membranes [81] and protecting cells against lipid peroxidation and ROS-induced oxidative damage by converting free FA and damaged lipids into TAG [34,83].…”

“…Under drought conditions, cellular processes involved in photoprotection play fundamental roles in plant metabolism. These processes involve the activity of the antioxidant system, dissipation of absorbed light energy as a heat, the photorespiration pathway [ 26 ], and utilization of excess light energy for the production of reduced-carbon compounds, including storage lipids [ 27 ]. A relationship between drought tolerance and the abundance and activity of antioxidant enzymes has been observed in different plant species [ 4 , 28 ].…”

“…It has been demonstrated that abscisic acid (ABA)-inducible accumulation of triacylglycerol lipids (TAG) in the vegetative tissues represents a common mechanism of plant adaptation to different abiotic stresses, including long-term stress acclimation [ 29 , 30 ]. In plants, TAG accumulation has been observed under heat stress [ 31 ], drought [ 29 , 32 , 33 ], prolonged darkness [ 34 ], and excess light [ 27 ]. It was demonstrated that the accumulation of TAG can protect cells against oxidative stress by limiting ROS generation and inhibiting lipid peroxidation of polyunsaturated fatty acids [ 30 ].…”