Chilling-sensitive Research Articles

SIZ1-Mediated Sumoylation of ICE1 ControlsCBF3/DREB1AExpression and Freezing Tolerance inArabidopsis

SIZ1 is a SUMO E3 ligase that facilitates conjugation of SUMO to protein substrates. siz1-2 and siz1-3 T-DNA insertion alleles that caused freezing and chilling sensitivities were complemented genetically by expressing SIZ1, indicating that the SIZ1 is a controller of low temperature adaptation in plants. Cold-induced expression of CBF/DREB1, particularly of CBF3/DREB1A, and of the regulon genes was repressed by siz1. siz1 did not affect expression of ICE1, which encodes a MYC transcription factor that is a controller of CBF3/DREB1A. A K393R substitution in ICE1 [ICE1(K393R)] blocked SIZ1-mediated sumoylation in vitro and in protoplasts identifying the K393 residue as the principal site of SUMO conjugation. SIZ1-dependent sumoylation of ICE1 in protoplasts was moderately induced by cold. Sumoylation of recombinant ICE1 reduced polyubiquitination of the protein in vitro. ICE1(K393R) expression in wild-type plants repressed cold-induced CBF3/DREB1A expression and increased freezing sensitivity. Furthermore, expression of ICE1(K393R) induced transcript accumulation of MYB15, which encodes a MYB transcription factor that is a negative regulator of CBF/DREB1. SIZ1-dependent sumoylation of ICE1 may activate and/or stabilize the protein, facilitating expression of CBF3/DREB1A and repression of MYB15, leading to low temperature tolerance.

Alteration of oxidative and carbohydrate metabolism under abiotic stress in two rice ( Oryza sativa L.) genotypes contrasting in chilling tolerance

Abiotic stress is a major limiting factor in crop production. Physiological comparisons between contrasting abiotic stress-tolerant genotypes will improve understanding of stress-tolerant mechanisms. Rice seedlings (S3 stage) of a chilling-tolerant (CT) genotype (CT6748-8-CA-17) and a chilling-sensitive (CS) genotype (INIAP12) were subjected to abiotic stresses including chilling (13/12 degrees C), salt (100mM NaCl), and osmotic (200mM mannitol). Measures of physiological response to the stresses included changes in stress-related sugars, oxidative products and protective enzymes, parameters that could be used as possible markers for selection of improved tolerant varieties. Metabolite analyses showed that the two genotypes responded differently to different stresses. Genotype survival under chilling-stress was as expected, however, CT was more sensitive to salt stress than the CS genotype. The CT genotype was able to maintain membrane integrity better than CS, perhaps by reduction of lipid peroxidation via increased levels of antioxidant enzymes during chilling stress. This genotype accumulated sugars in response to stress, but the accumulation was usually less than in the CS genotype. Chill-stressed CT accumulated galactose and raffinose whereas these saccharides declined in CS. On the other hand, the tolerance mechanism in the more salt- and water-deficit-tolerant CS may be associated with accumulation of osmoprotectants such as glucose, trehalose and mannitol.

Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short‐term chilling in the light in four plant species with different chilling sensitivities

Changes in the extent of P700 oxidation (P700+) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m−2 s−1, the decrease in P700+ was observed only in cucumber, but at 150 µmol photons m−2 s−1, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700+ by this short‐term chilling was reversible in the presence of 3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down‐regulation of photosystem II through the accumulation of zeaxanthin and the development of non‐photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700+. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron‐sink pathways such as CO2 assimilation and ascorbate–glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700+ by 20–30% in barley leaves after chilling in the light.

QUALITY CHARACTERISTICS OF 'HORN OF PLENTY' AND 'MEDALLION' YELLOW SUMMER SQUASH AS A FUNCTION OF THE STORAGE TEMPERATURE

QUALITY CHARACTERISTICS OF 'HORN OF PLENTY' AND 'MEDALLION' YELLOW SUMMER SQUASH AS A FUNCTION OF THE STORAGE TEMPERATURE

Recovery from low-temperature photoinhibition is related to dephosphorylation of phosphorylated CP29 rather than zeaxanthin epoxidation in rice leaves

During recovery from chilling-induced photoinhibition in rice leaves, we compared the reactivation kinetics of PSII photochemical efficiency (Fv/Fm) with that of zeaxanthin (Z) epoxidation and the dephosphorylation of CP34 (i.e., the phosphorylated form of CP29). The latter two processes were kinetically similar to the slow increase in Fv/Fm measured in our control leaves. However, the rate of Z epoxidation was significantly retarded by an epoxidase inhibitor, 5 mM salicylaldoxime (SA), without any significant changes in the processes of PSII reactivation and CP34 dephosphorylation. When chilled leaves were incubated at 10°C in the dark, both reactivation and dephosphorylation were significantly blocked, but Z epoxidation was not. Finally, we observed that the kinetics of CP34 dephosphorylation matched very well with those of PSII recovery in two rice cultivars with different chilling sensitivities. These results suggest that PSII reactivation from low-temperature photoinhibition is more closely related to CP34 dephosphorylation than to Z epoxidation.

Fatty acid composition of lipids in immature cattle, pig and sheep oocytes with intact zona pellucida

Cattle, pig and sheep oocytes isolated from healthy cumulus-oocyte complexes were pooled, within species, to provide samples of immature denuded oocytes with intact zona pellucida (n = 1000 per sample) for determination of fatty acid mass and composition in total lipid, constituent phospholipid and triglyceride. Acyl-containing lipid extracts, transmethylated in the presence of a reference penta-decaenoic acid (15:0), yielded fatty acid methyl esters which were analysed by gas chromatograph. Mean (+/- SEM) fatty acid content in samples of pig oocytes (161 +/- 18 micrograms per 1000 oocytes) was greater than that in cattle (63 +/- 6 micrograms; P < 0.01) and sheep oocytes (89 +/- 7 micrograms; P < 0.05). Of 24 fatty acids detected, palmitic (16:0; 25-35%, w/w), stearic (18:0; 14-16%) and oleic (18:1n-9; 22-26%) acids were most prominent in all three species. Saturated fatty acids (mean = 45-55%, w/w) were more abundant than mono- (27-34%) or polyunsaturates (11-21%). Fatty acids of the n-6 series, notably linoleic (18:2n-6; 5-8%, w/w) and arachidonic acid (20:4n-6; 1-3%), were the most abundant polyunsaturates. Phospholipid consistently accounted for a quarter of all fatty acids in the three species, but ruminant oocytes had a lower complement of polyunsaturates (14-19%, w/w) in this fraction than pig oocytes (34%, w/w) which, for example, had a three- to fourfold greater linoleic acid content. An estimated 74 ng of fatty acid was sequestered in the triglyceride fraction of individual pig oocytes compared with 23-25 ng in ruminant oocytes (P < 0.01). It is concluded that the greater fatty acid content of pig oocytes is primarily due to more abundant triglyceride reserves. Furthermore, this species-specific difference, and that in respect of polyunsaturated fatty acid reserves, may underlie the contrasting chilling, culture and cryopreservation sensitivities of embryos derived from pig and ruminant (cattle, sheep) oocytes.

Fatty acid composition of lipids in immature cattle, pig and sheep oocytes with intact zona pellucida

Cattle, pig and sheep oocytes isolated from healthy cumulus-oocyte complexes were pooled, within species, to provide samples of immature denuded oocytes with intact zona pellucida (n = 1000 per sample) for determination of fatty acid mass and composition in total lipid, constituent phospholipid and triglyceride. Acyl-containing lipid extracts, transmethylated in the presence of a reference penta-decaenoic acid (15:0), yielded fatty acid methyl esters which were analysed by gas chromatograph. Mean (+/- SEM) fatty acid content in samples of pig oocytes (161 +/- 18 micrograms per 1000 oocytes) was greater than that in cattle (63 +/- 6 micrograms; P < 0.01) and sheep oocytes (89 +/- 7 micrograms; P < 0.05). Of 24 fatty acids detected, palmitic (16:0; 25-35%, w/w), stearic (18:0; 14-16%) and oleic (18:1n-9; 22-26%) acids were most prominent in all three species. Saturated fatty acids (mean = 45-55%, w/w) were more abundant than mono- (27-34%) or polyunsaturates (11-21%). Fatty acids of the n-6 series, notably linoleic (18:2n-6; 5-8%, w/w) and arachidonic acid (20:4n-6; 1-3%), were the most abundant polyunsaturates. Phospholipid consistently accounted for a quarter of all fatty acids in the three species, but ruminant oocytes had a lower complement of polyunsaturates (14-19%, w/w) in this fraction than pig oocytes (34%, w/w) which, for example, had a three- to fourfold greater linoleic acid content. An estimated 74 ng of fatty acid was sequestered in the triglyceride fraction of individual pig oocytes compared with 23-25 ng in ruminant oocytes (P < 0.01). It is concluded that the greater fatty acid content of pig oocytes is primarily due to more abundant triglyceride reserves. Furthermore, this species-specific difference, and that in respect of polyunsaturated fatty acid reserves, may underlie the contrasting chilling, culture and cryopreservation sensitivities of embryos derived from pig and ruminant (cattle, sheep) oocytes.

Galactolipase activity but not the level of high-melting-point phosphatidylglycerol is related to chilling tolerance in differentially sensitive Zea mays inbred lines.

Galactolipase activity, the level of high-melting-point phosphatidylglycerol (HMP-PG) as well as degradation of lipids during chilling and rewarming were studied in seedlings of maize inbred lines with different chilling responses. In aged chloroplasts of chilling-sensitive (CS) lines, galactolipase activity was considerably higher than that determined in aged chloroplasts isolated from chilling-tolerant (CT) ones. Chilling of seedlings at 5 °C for 6 days induced neither loss of chlorophyll content nor visible changes in the leaves, while a slight decline in total acyl lipid content by about 15.5% and 12.5% in CS and CT lines, respectively, was observed. Among total acyl lipids, only monogalactosyldiacylglycerol (MGDG) levels were decreased significantly upon chilling. Following return to the original growth conditions for 4 days, visible chilling injury in seedlings as well as essential differences in the decrease in total acyl lipids by about 53% and 20% in CS and CT lines, respectively, were found. These changes were accompanied by more extensive degradation of MGDG, digalactosyldiacylglycerol and phosphatidylglycerol in CS than in CT lines. As the levels of HMP-PG in fresh leaves were the same in all four lines of maize, it seems that galactolipase activity and not the level of HMP-PG is related to chilling response in maize.

Antioxidant Enzyme and Compound Responses to Chilling Stress and their Combining Abilities in Differentially Sensitive Maize Hybrids

Chilling sensitive species often have lower antioxidant capacities than do tolerant species. This study was conducted to determine if antioxidant capacities and carbohydrate concentrations would be useful in a proposed screening technique for chilling sensitivity in maize (Zea mays L.). Leaves of 12 maize hybrids exhibiting differential sensitivity to chilling were harvested at the third‐leaf stage under either (i) a constant 25°C control regime or (ii) the control regime plus a short‐term chilling shock of 11°C for 1 d prior to harvesting. Catalase (CAT; EC 1.11.1.6), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and ascorbate peroxidase (ASPX; EC 1.11.1.11) activities were assessed. Carbohydrate levels were determined as general metabolic indicators of chilling stress. The chill/control ratios of CAT, MDHAR, and ASPX were lowest and concentrations of carbohydrates highest in the most chilling sensitive hybrids. Differences between hybrids in antioxidant capacities to detoxify toxic oxygen compounds may be important in differential chilling sensitivity. The higher chili/control ratios of carbohydrates in the sensitive hybrids after chilling indicated that their rate of assimilate utilization was reduced by the chilling treatment more so than those of the chilling tolerant hybrids. Activities of CAT, MDHAR, and ASPX and concentrations of carbohydrates would thus make excellent indicators of chilling stress in a screening technique for chilling sensitivity of maize.

Sensitivity of Maize Hybrids to Chilling and Their Combining Abilities at Two Developmental Stages

Maize (Zea mays L.), one of the most economically important plants grown in North America, is often subjected to cool conditions soon after sowing which can disrupt development. No studies on chilling sensitivity of maize at both germination and early growth developmental stages have been reported. To discern differences in chilling sensitivity between the germination and early growth phases, twelve hybrids originating from a complete diallel of four inbreds which differed in their sensitivity to chilling were subjected to laboratory screening tests at both these stages. Corresponding field trials were sown and parameters reflecting those evaluated in the laboratory were assessed. Estimates of general combining abilities and specific combining abilities were performed. Some lines that were initally chilling sensitive or tolerant at the germination stage altered their sensitivity to chilling at the early growth stage. This suggests that it is only possible to accurately evaluate chilling tolerance of maize by examining plants at both the germination‐emergence and early growth stages as these two stages may be under the control of different genetic factors. Furthermore, based on the physiological growth parameters assessed both in the laboratory and in the field, it is not possible to reliably predict hybrid maize cold tolerance from knowledge of the inbreds' responses.

Methods of Selection for Chilling Tolerance in Nepalese Rice by Chlorophyll Fluorescence Analysis

Rice (Oryza sativa L.) yields are frequently low in the high hills of Nepal because of chilling temperatures throughout the growing season. Conventional screening for chilling sensitivity of different rice genotypes in breeding programs relies on visual observations in the field. The screening is subjective, time consuming, and subject to genotype × environment, interactions (e.g., stage of development when chilled). In this study, chlorophyll fluorescence analysis (CFA) was used to test its value in assessing chilling tolerance. Landraces and cultivars with known chilling sensitivities, including chilling‐tolerant landraces and cultivars from Nepal, were compared. Detached leaves from plants of 16 rice genotypes at the tillering stage were chilled in growth cabinets before their photochemical efficiencies (Fv/Fm) were measured by CFA. Genotype differences were examined by three methods: absolute Fv/Fm ratios of excised leaves chilled for 24 to 72 h at 10°C, decline in Fv/Fmratios of excised leaves chilled for 24 to 72 h at 10°C in comparison to unchilled checks, and absolute Fv/Fm ratios of chilled leaves after recovery of up to 72 h at 25°C in the dark. Altitudes of the site of genotype adaptation correlated well with Fv/Fm ratios after chilling for 48 h, whether Fv/Fm values were the absolute values or percentages of corresponding unchilled checks. The absolute Fv/Fm ratios of the chilled plants after 48 h recovery at 25 °C gave the highest correlation with altitude but that correlation was not significantly better than the correlation obtained with the absolute Fv/Fm ratios determined in the absence of a recovery period.

130 SUPEROXIDE PRODUCTION BY MITOCHONDRIA ISOLATED FROM CHILLING-SENSITIVE PLANT TISSUE

An emerging theory contends that chilling injury is due to oxidative damage resulting from the metabolic generation of active oxygen species. Mitochondria were isolated from chilling-sensitive (CS) and from conditioned chilling-resistant (CR) bell pepper fruit and their ability to generate superoxide determined by measuring the formation of adrenochrome from epinephrine. Mitochondria from CS fruit were sensitive to cyanide and produced superoxide when supplied with NADH, succinate, or malate-pyruvate. Mitochondria from CR fruit were insensitive to cyanide and sensitive to SHAM and produced little superoxide when supplied with respiratory substrates. ATP enhanced the production of superoxide and ADP reduced the production. Results suggest that the mitochondria are a major source of superoxide in CS plant tissue and the presence of the alternative pathway reduces the production of superoxide.

Discrimination between chilling-sensitive and chilling-resistant plants based on measurements of free fatty acid accumulation and inactivation of oxygen evolution in aged chloroplasts.

The effect of aging of isolated chloroplasts of two chilling-sensitive (CS) and three chilling-resistant (CR) plants on the inactivation of oxygen evolution and accumulation of free fatty acids (FFA) was studied at 30 degrees C, pH 5.5 or 7.0, in the absence or presence of either sorbitol or NaCl. Considerable accumulation of FFA in aged chloroplasts of CS plants: bean and maize line F7-RpIII was accompanied by a marked inactivation of oxygen evolution. This relation was not, however, found in chloroplasts of CR species: pea, wheat and maize line EP1-RpI, in which the accumulation of FFA upon aging was very low whereas the decline of the rate of oxygen evolution was pronounced. In contrast to changes observed at pH 5.5, the inactivation of oxygen evolution in chloroplasts of CR species aged at pH 7.0 was dependent on the composition of the medium, especially in wheat chloroplasts. Thus, for the evaluation of chilling sensitivity based on the measurements of oxygen evolution activity solely, either aging of chloroplasts at pH 5.5 or possibly at pH 7.0 with NaCl included into the incubation medium may be recommended. It is concluded that determination of both the extent of FFA accumulation and inactivation of oxygen evolution in aged chloroplasts might be applied as chilling tolerance indexes.

Correlation between chilling sensitivity of plant tissues and fatty acid composition of phosphatidylglycerols

Seedlings of 13 species of Leguminosae were grown and rated for severity of chilling injury after two low-temperature treatments. The fatty acid composition of three polar lipids, phosphatidylinositol (PI), phosphatidyl-glycerol (PG) and sulphoquinovosyldiacylglycerol (SQDG), was determined by GC in leaves of the seedlings with different chilling sensitivities. The sum of the amounts of palmitate (16:0), stearate (18:0) and trans-3-hexadecenoate [16:1 (3 t)], as a percentage of the total fatty acids was different, depending on the polar lipid. Comparison with the chilling sensitivity ratings indicated a high correlation only with PG, but not with PI and SQDG. Fatty acid composition of these polar lipids was also determined by GC in flower petals of 11 species with different geographical origins, probably also related to their chilling sensitivities. The sum of the fatty acids [16:0 + 18:0 + 16:1(3 t)] was correlated with the latitude of plant origin. Our results confirm that the chilling sensitivity of higher plants is affected by the content of saturated fatty acids of PG in chloroplasts and chromoplasts.

Seedling Growth and Chilling Stress Effects on Photosynthesis in Chilling-Sensitive and Chilling-Tolerant Cultivars of Zea mays

Summary Distinct differences were observed between chilling-sensitive (CS) and chilling-tolerant (CT) maize cultivars with respect to early seedling growth strategies and response to chilling at 5 °C. The CT cultivar exhibited more rapid emergence and growth rates and an earlier depletion of seed reserves. During early growth, both cultivars partitioned more biomass to their roots ( ~ 57 %) than to their leaves or stems. Following depletion of seed reserves, the CT cultivar increased its partitioning to the leaves (40 % of new biomass). Prior to short-term chilling, both cultivars had identical net photosynthetic and relative growth rates. The chilling-induced decrease in photosynthesis per unit leaf area was twice as large in the CS cultivar as in the CT cultivar. These decreases were not accompanied by changes in leaf chlorophyll content and could not be primarily attributed to stomatal limitations. Analysis of chlorophyll fluorescence suggested that photoinhibition did not occur in either cultivar and that decreased photosynthesis in the CS cultivar resulted from inhibition of the dark reactions. Stress responses were reversed within 48 h after return to control conditions in both cultivars.

CHANGE IN THE FATTY ACID COMPOSITION OF AVOCADO FRUIT DURING ONTOGENY, COLD STORAGE AND RIPENING

The ratio of saturated fatty acids to unsaturated fatty acids has been implicated in the sensitivity of plant materials to chilling injury. Chilling sensitive plant materials have been reported to have a higher mole percent of saturated fatty acids than plant materials not sensitive to chilling injury. Changes in the fatty acid composition have also been reported for chilling sensitive crops during and following exposure to chilling temperatures and that these changes may be related to chilling sensitivity. The fatty acid composition of ‘Fuerte' and 'Hass' avocados was determined during ontogeny, cold storage, and ripening. During ontogeny, oleic acid increased, linoleic and linolenic acids decreased and palmitic and palmitoleic remained essentially constant relative to the percentage of total fatty acids. The fatty acid composition did not change significantly during 2, 4 and 6 weeks storage at 0°, 5° and 10°C or after ripening at 20°C subsequent to the cold storage treatments.

A Chilling Sensitive Mutant of Arabidopsis with Altered Steryl-Ester Metabolism

A chilling-sensitive mutant of Arabidopsis thaliana was isolated and subjected to genetic, physiological, and biochemical analysis. The chilling-sensitive nature of the mutant line is due to a single recessive nuclear mutation at a locus designated chs1. In contrast to wild-type plants, which are not adversely affected by low temperatures, the chs1 mutant is killed by several days of exposure to temperatures below 18 degrees C. Following exposure to chilling temperatures, the mutant displays two common symptoms of chilling injury-leaf chlorosis and electrolyte leakage. In these respects, the physiological response of the mutant to low temperatures mimics the response observed in some naturally occurring chilling sensitive species. The biochemical basis of chilling sensitivity was explored by examining the pattern of incorporation of (14)CO(2) into soluble metabolites and lipids in wild-type and mutant plants. The only difference observed between the mutant and wild type was that following low temperature treatment, the mutant accumulated 10-fold more radioactivity in a specific class of neutral lipids which were identified by a variety of criteria to be steryl-esters. The accumulation of radioactivity in the steryl-ester fraction occurs 24 hours before there is any visible evidence of chilling injury. These results suggest one of two possible explanations: either the mutation directly affects sterol metabolism, which in turn leads to chilling sensitivity, or the mutation affects another unidentified function and the accumulation of radioactivity in steryl-esters is a secondary consequence of chilling injury.

Cold-Induced Sudden Reversible Lowering of in Vivo Chlorophyll Fluorescence after Saturating Light Pulses

In chilling-sensitive plants (Glycine max, Saintpaulia ionantha, Saccharum officinarum) a sudden reversible drop in chlorophyll fluorescence occurs during photosynthetic induction immediately following saturating light pulses at low temperatures in the range 4 to 8 degrees C. A comparison of two soybean cultivars of different chilling sensitivities revealed that this phenomenon, termed lowwave, indicates specific thresholds of low temperature stress. Its occurrence under controlled chilling can be regarded as a quantitative marker for screening chilling susceptibility in angiosperms.

The Influence of Dark Adaptation Temperature on the Reappearance of Variable Fluorescence following Illumination

The effect of chilling temperatures (5 degrees C) on chlorophyll fluorescence transients was used to study chilling-induced inhibition of photosynthesis in plant species with differing chilling sensitivities. A Brancker SF-20 fluorometer was used to measure induced fluorescence transients from both attached and detached leaves of chilling-sensitive cucumber (Cucumis sativus L. cv Ashley) and chilling-resistant pea (Pisum sativum L. cv Alaska). The rate of reappearance of the variable component of fluorescence (F(v)), following a period of illumination at 25 degrees C, was dependent on the temperature at which the leaf was allowed to dark adapt in chilling-sensitive cucumber, but not in chilling-resistant pea. In cucumber, dark adaptation at 25 degrees C following illumination resulted in a much faster return of F(v) than dark adaptation at 5 degrees C following illumination. However, F(v) reappearance during the dark adaptation period in chilling-resistant pea was temperature independent. The difference in the temperature response of F(v) following illumination correlated with temperature sensitivity of these two species. The process responsible for the difference in F(v) may represent a site of chilling sensitivity in the photosynthetic apparatus.

Fatty Acid Specificity and Selectivity of the Chloroplast sn-Glycerol 3-Phosphate Acyltransferase of the Chilling Sensitive Plant, Amaranthus lividus

Chilling sensitivity of plants is strongly correlated with the presence of high levels of a species of chloroplast phosphatidylglycerol that contains two saturated fatty acids. The most straightforward synthetic pathway for this lipid would require the primary acylation of sn-glycerol 3-phosphate (G3P) with a saturated fatty acid (palmitic acid) rather than with oleic acid, an unsaturated acid. This selective incorporation would differ markedly from the reported properties of the chloroplast G3P acyltransferases of pea and spinach, two chilling resistant plants and thus we have studied the chloroplast G3P acyltransferase of Amaranthus lividus, a chilling sensitive plant. In contrast to our results and those of others (M. Frentzen et al. 1983 Eur J Biochem 129: 629-636 and previous work) with the pea and spinach enzymes, the amaranthus chloroplast G3P acyltranferase did not select oleic acid donors from a mixture of oleic and palmitic acid donors (either coenzyme A or acyl carrier protein thioesters). Instead the fatty acid composition of the synthesized 1-acyl G3P faithfully reflected the composition of the acyl donor mixture. However, the amaranthus enzyme did strongly select against incorporation of stearic acid. The properties of the amaranthus G3P acyltransferase are consistent with this enzyme having the major role in synthesis of the disaturated phosphatidylglycerol species.