Degradation of leaf polar lipids during chilling and post-chilling rewarming of Zea mays genotypes reflects differences in their response to chilling stress. The role of galactolipase

Degradation of leaf polar lipids [monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG)] and chlorophyll (Chl) were studied in four Zea mays genotypes differing in chilling susceptibility following dark chilling and post-chilling rewarming at original growth conditions. Assessment of visual chilling injury symptoms during post-chilling rewarming differentiated maize inbred lines into chiling-sensitive (CS) CM7 and Co151 lines and chillingtolerant (CT) S215 and EP1 lines. Severity of chilling injury in CS and CT inbreeds were correlated with the extent of Chl and polar lipids degradation. Chilling for either 4 or 6 days followed by 4 days of rewarming caused more extensive degradation of total polar lipids content in CS than in CT lines. MGDG decreased mostly during chilling whereas DGDG dropped during rewarming only. Chl content was not affected during chilling but its large decrease, greater in CS than in CT lines, was observed upon rewarming. Extent of polar lipids breakdown in CS and CT inbreeds during chilling and post-chilling rewarming is correlated with galactolipase activity in chloroplasts (Kaniuga et al., 1998) and visual assessment of chilling injury. In view of the data it is likely that contribution of galactolipase activity induced during low-temperature stress of CS plants is an important factor responsible for thylakoid lipid degradation and development of chilling injury as postulated previously (Kaniuga 1997). It is suggested that genetically engineered reduction of galactolipase activity or elimination of the factors(s) involved in induction/stimulation of its activity during chilling might increase tolerance of CS species to chilling stress.     

Changes in fatty acids of leaf polar lipids during chilling and post-chilling rewarming of Zea mays genotypes differing in response to chilling

Changes in fatty acids of leaf polar lipids: monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) in maize seedlings of chiling-sensitive (CS) CM 7 and Co 151 lines and chilling-tolerant (CT) S 215 and EP 1 lines upon chilling for either 4 or 6 days in the dark and after rewarming for 4 days at original growth conditions were studied. The content of free fatty acids (FFA) in control leaves as well as alterations in the proportion of major fatty acids, unsaturation ratio (UR), double bond index (DBI) and changes in the proportion of heigh-temperature melting of both phosphatidylglycerol (htm-PG) and sulfoquinovosylglycerol (htm-SQDG) after chilling and rewarming of seedlings were estimated. FFA content in intact leaves was 2–3-fold higher in the chilling susceptible CM 7 line than in the other three inbreeds studied. After chilling for 6 days the level of FFA increased only in CM 7 and S 215 lines by about 30 %. Upon rewarming seedlings chilled for 6 days the level of FFA increased about two-fold in CS Co 151 line and CT EP 1 line and decreased in CS CM 7 line. Limited accumulation of FFAs during chilling and post-chilling rewarming of maize seedlings, did not correspond to the extent of polar lipid breakdown (Kaniuga et al. 1999b) probably due to the contribution of active oxidative systems to the peroxidation of fatty acids under these conditions. During rewarming seedlings chilled for 6 days major changes were observed in decrease of 18:3 and an increase of 16:0 in all four polar lipids studied with more pronounced changes in CS than CT lines. Similarly, in CS inbreeds a decrease in UR of fatty acids in MGDG, DGDG and SQDG after post-chilling rewarming was greater than in CT lines. Proportion of htm-fraction in both PG and SQDG increased after post-chilling rewarming in all four inbreeds, however to a lesser extent in CT than CS lines. A similar pattern of changes in DBI in CS and CT maize seedlings was observed in glycolipid and combine lipid classes. More extensive degradation of polar lipids in CS than CT maize inbreeds following galactolipase action in chloroplasts (Kaniuga et al. 1998) provides FFAs for initiation of peroxidation by LOX which is manifested by decrease of UR and DBI. This sequence of reactions during chilling and post-chilling rewarming appears to be a main route of fatty acids peroxidation responsible for secondary events involved in chilling injury. In addition, the extent of these changes differentiates CS and CT inbreeds. Contribution of esterified fatty acids in thylakoid lipids to direct peroxidation, may be of minor importance.     

Chilling response of plants: importance of galactolipase, free fatty acids and free radicals

The chilling response of plants is complex and based on the interplay of two important metabolic processes--lipolytic degradation of membrane lipids and a set of oxidative reactions leading to lipid peroxidation and membrane damage evoked in chilling-sensitive (CS) plants subjected to low temperature and light. The effects of chilling of detached leaves and intact plants differ and are often neglected during experiments. In closely-related species, the activity of several constitutive enzymes (i.e. superoxide dismutase, ascorbate peroxidase and glutathione reductase) appears to be higher in chilling-tolerant (CT) than in CS species; while in several native, closely-related CS species, lipid acyl hydrolase (galactolipase) activity is higher than in CT species. Moreover, in chilling-insensitive (CI) plants, galactolipase activity is very low and is neither activated by detachment of leaves nor under stress conditions in growing plants. Dark and low-temperature treatments of detached leaves of CS species and post-chilling recovery of growing plants in the light activate galactolipase, which is responsible for the release of free fatty acids (FFA), the main substrates of peroxidation by lipoxygenase and free radicals. In several CS species, increased galactolipase activity is an important factor contributing to chilling susceptibility. Thus, it seems likely that enhancement of chilling tolerance may be achieved by genetically suppressing galactolipase in order to reduce both the degradation of chloroplast lipids and the level of released FFA, and thereby avoiding the deleterious action of their peroxidation products on plant tissues.     

The effect of low oxygen concentration on the acyl-lipid and fatty-acid composition of the C4 plant Amaranthus paniculatus L.

Acyl lipids and their constituent fatty acids were studied in leaves, chloroplasts and bundle-sheath strands of the C₄ plant Amaranthus paniculatus L. grown under normal and 4%-oxygen-containing atmospheres. In all fractions the major lipids were found to be monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulphoquinovo-syldiacylglycerol and phosphatidylglycerol. Significant quantities of phosphatidylcholine and phosphatidylethanolamine were restricted to leaves and bundle-sheath strands. All lipids, except phosphatidylglycerol where 3-trans-hexadecenoic acid was also present, contained palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. On a chlorophyll basis and compared with whole leaves, the amounts of phosphatidylcholine and phosphatidylethanolamine in bundle-sheath strands were considerably reduced. Three weeks after the change from a normal to a 4% atmospheric O₂ level, the galactolipid content, particularly in the bundlesheath strands, was enhanced. There were no significant differences in the degrees of saturationunsaturation of total acyl lipid for the plants grown in the low oxygen and normal atmospheres, although under 4% O₂ the phosphatidylglycerol contained an increased proportion of 3-trans-hexadecenoic acid at the expense of palmitic acid.Abbreviations DGDG digalactosyldiacylglycerol - MGDG monogalactosyldiacylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - SQDG sulphquinovosyldiacylglycerol     

Galactolipase activity and free fatty acid levels in chloroplasts of domestic and wild tomatoes with different chilling tolerance

In order to establish differences in the chilling sensitivity of domestic and wild Lycopersicon species, galactolipase (EC 3.1.1.26) activity, free fatty acid (FFA) level and Hill reaction activity were measured in chloroplasts isolated from control and cold treated leaves of L. esculentum Mill., cv. Norton, L. hirsutum Humb. and Bonpl., L. peruvianum var. glandulosum Mill. Galactolipase activity was higher in chloroplasts from Lycopersicon species with high chilling sensitivity than in chloroplasts of more chilling-resistant ones. A similar relationship was observed for FFA level in chloroplasts from both cold-stored and control leaves. Decrease in Hill reaction activity due to cold stress was greater in chloroplasts of more chilling-sensitive species. The changes are accompanied by a decline of photochemical activity. Considering the changes in the three parameters noted above, an increasing order of chilling tolerance was established: L. esculentum < L. hirsutum (700 m) < L. hirsutum (3100 m) < L. peruvianum (3400 m). It is suggested that measurements of galactolipase activity and FFA may be useful in an evaluation of differences in resistance to chilling injury of closely related species.     

Comparison of galactolipase activity and free fatty acid levels in chloroplasts of chill-sensitive and chill-resistant plants

Galactolipase activity in chloroplasts of several chill-resistant plants was found to be very low [0.02-0.13 mumol free fatty acid (FFA) liberated min-1 mg protein-1] or not detected. The same phenomenon was observed for soybean and members of the Cucurbitaceae such as cucumber, pumpkin, melon and squash. Since, following cold storage of cucumber leaves, the levels of monogalactosyl-diacylglycerol and digalactosyl-diacylglycerol in chloroplasts decrease while those of FFA accumulate it seems likely that in these typical chill-sensitive plants galactolipase is present but inactivated during isolation procedure. The low galactolipase activity in chloroplasts was accompanied by a relatively low FFA content ranging from 0.05 mumol to 0.30 mumol FFA mg chlorophyll (Chl)-1. However, both pea and horse bean chloroplasts (with low galactolipase activity) exhibit about 0.45 mumol FFA mg Chl-1. Elevated galactolipase activity was observed in chloroplasts of most chill-sensitive species (ranging from 0.31 mumol to 1.32 mumol FFA liberated min-1 mg protein-1) as well as in chloroplasts from broad bean, a member of a chill-resistant species (1.26 mumol FFA liberated min-1 mg protein-1). In addition in this latter group of plants FFA level in chloroplasts often did not fit the galactolipase activity. The results suggest that there exists a tendency for chilling tolerance of plants to decrease both galactolipase activity and FFA level. However, in some plant species with elevated galactolipase activity the chloroplast FFA level does not correlate with enzyme activity.     

Lipids in Cruciferae IX. The Effect of Growth Temperature and Stage of Development on the Fatty Acid Composition of Leaves, Siliques and Seeds of "Zero-erucic-acid" Breeding Lines of Brassica napus

Two breeding lines of “zero-erucic-acid” rapeseed (Brassica napus) were grown in climate chambers at a constant night temperature (12°C) and constant photoperiod (16 hours) but with different day temperatures (15, 20 and 25°C). Samples of leaves, siliques and immature seeds were analysed for total fatty acid pattern. The content of different acyl lipids and the fatty acid pattern of these lipids were also determined in some of the samples by use of preparative TLC followed by GLC of the fatty acids. The mature seeds produced by ten plants of each selection in each climate were analysed separately for total fatty acid composition. Mono- and digalactosyl diglycerides (MGDG, DGDG) were the predominant acyl lipids in leaves and siliques. In developing seeds they also were more abundant than the phospholipids, but in this case the neutral lipids, mainly triacylglycerols, contained about 95% of the total fatty acids. Large variations were found in the fatty acid composition of monogalactosyl diglyceride and digalactosyl diglyceride, isolated from leaves, siliques and immature seeds. The palmitic acid content of leaf MGDG was about 15 %, atypically high for MGDG from photosynthetic tissue. The linolenic acid content of the MGDG was about 45 %, 30 % and 10 % in the leaf, silique and seed tissues respectively. A hexadecatrienoic acid (16: 3) was found almost exclusively in the MGDG samples of leaves, siliques and immature seeds (about 25 %, 10 % and 3 % 16:3 respectively). The lipids of siliques — mainly photosynthetising tissue — were different from those of leaves and had especially high contents of stearic acid (6–12 % in the different lipids). For all lipid classes studied, leaves grown at the lowest day temperature had a slightly lower oleic and higher linolenic acid content than those grown at the highest temperature. On the other hand, increasing the day temperature caused a decreased level of oleic, an increased level of linoleic and an essentially unchanged level of linolenic acids in the mature seeds from both selections.     

Lipid composition of envelopes,prolamellar bodies and other plastid membranes in etiolated,green and greening wheat leaves

Summary Comparative studies of lipid composition were made on prolamellar bodies, envelopes and other plastid membranes separately extracted from etiolated, green or greening (intermittent or continuous light) wheat (Triticum sativum L.) leaves. The different membrane fractions were examined by electron microscopy.The major lipid was digalactosyldiglyceride in the envelopes and prolamellar bodies and monogalactosyldiglyceride in stroma lamellae and grana. Phosphatidylcholine represented 60% of total phospholipids in the envelopes, 30% in prolamellar bodies and 14% in grana. All types of envelopes had the same lipid proportions.For all lipids the lowest fatty acid unsaturation was always found in the envelope membranes. The relative amount of {ie193-1} acid in the phosphatidylglycerol of envelopes increased from 4% (etioplasts) to an average of 15% (etiochloroplasts and chloroplasts).Abbreviations DGDG digalactosyldiglyceride - MGDG monogalactosyldiglyceride - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - PI phosphatidylinositol - PS phosphatidylserine - SL sulfolipid     

The action of lipases on chloroplast membranes I. The release of plastocyanin from galactolipase-treated thylakoid membranes

Bean chloroplasts treated with galactolipase (lipolytic acyl hydrolase) isolated from bean leaves showed an inhibition of photosystem I activity as measured by methyl viologen-mediated oxygen uptake and NADP⁺ photoreduction. This inhibition was partially reversed by exogenous plastocyanin added to galactolipase-treated thylakoid membranes. Galactolipase released substantial amounts of endogenous plastocyanin (about 40%) from bean chloroplasts. The results are discussed with regard to the localization of plastocyanin in thylakoid membranes.Abbreviations chlf chlorophyll - DCMU 3-(2,4-dichlorophenyl)-1,1-dimethylurea - DGDG digalactosyldiacylglycerol - MGDG monogalactosyldiacylglycerol - MV methyl viologen - NADP⁺ nicotinamide dinucleotide phosphate - PC phosphatidylcholine - PG phosphatidylglycerol - PE phosphatidylethanolamine - PI phosphatidylinositol - SQDG sulphoquinovosyldiacylglycerol - SDS sodium dodecyl sulphate - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - Tricine N-Tris-(hydroxymethyl)-methylglycine - Tris Tris-(hydroxymethyl)-aminomethane     

Introduction of the cDNA for shape Arabidopsis glycerol-3-phosphate acyltransferase (GPAT) confers unsaturation of fatty acids and chilling tolerance of photosynthesis on rice

The chilling sensitivity of several plant species is closely correlated with the levels of unsaturation of fatty acids in the phosphatidylglycerol (PG) of chloroplast membranes. Plants with a high proportion of unsaturated fatty acids, such as Arabidopsis thaliana, are resistant to chilling, whereas species like squash with only a low proportion are rather sensitive to chilling. The glycerol-3-phosphate O-acyltransferase (GPAT) enzyme of chloroplasts plays an important role in determining the levels of PG fatty acid desaturation.A cDNA for oleate-selective GPAT of Arabidopsis under the control of a maize Ubiquitin promoter was introduced into rice (Oryza sativa L.) using the Agrobacterium-mediated gene transfer method. The levels of unsaturated fatty acids in the phosphatidylglycerol of transformed rice leaves were found to be 28% higher than that of untransformed controls. The net photosynthetic rate of leaves of transformed rice plants was 20% higher than that of the wild type at 17°C. Thus, introduction of cDNA for the Arabidopsis GPAT causes greater unsaturation of fatty acids and confers chilling tolerance of photosynthesis on rice.     

Plastid differentiation, acyl lipid, and Fatty Acid changes in developing green maize leaves

Plastid differentiation, acyl lipid, and fatty acid composition have been followed in successive 2-cm sections from the base (youngest tissue) to the tip (oldest tissue) of green Zea mays (maize) leaves grown under a normal diurnal light regime. Although the youngest cells (0-4 cm from the leaf base) had only proplastids with one or two grana, they contained chlorophylls a and b, monogalactosyldiglyceride, digalactosyldiglyceride, sulfolipid, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol. In the more mature sections, the plastids increased in size 5-fold, and differentiation into mesophyll and bundle-shealth chloroplasts had occurred. Concomitantly, the levels of all the lipids increased with the exception of phosphatidylcholine and phosphatidylethanolamine which decreased. With increasing cell maturity, the percentage of linolenic acid increased in all the individual acyl lipids, but palmitic acid remained constant in phosphatidylcholine, phosphatidylethanolamine, and sulfolipid. The Δ^3t-hexadecenoic acid was only detectable in the phosphatidylglycerol of the most mature maize tissue.     

The action of lipases on chloroplast membranes. III. The effect of lipid hydrolysis on chlorophyll-protein complexes in thylakoid membranes

Bean thylakoid membranes treated with various lipolytic enzymes (bean galactolipase, phospholipases A₂, C, D) showed marked changes in their acyl lipid composition. As a consequence of acyl lipids hydrolysis, destruction of some chlorophyll a-protein complexes (CP1a, CP1, CPa) or monomerization of the oligomeric of light harvesting chlorophyll a/b protein complex (LHCP) was observed. It is concluded that galactolipids and phosphatidylcholine are responsible for the stability of CP1a, CP1 and CPa, respectively. Phosphatidylglycerol and to some extent monogalactosyldiacylglycerol are essential for the stabilization of oligomeric structures of light harvesting chlorophyll a/b protein complex.Abbreviations chl chlorophyll - CP1a, CP1 chl a-protein complexes, of PSI - CPa chl a-protein complex of PSII - DGDG diagalactosyldiacylglycerol - FC free chl - GL galactolipase - LHCP^1–3 light harvesting chl a/b protein complex - MGDG monogalactosyldiacylglycerol - PAGE polyacrylamide gel electrophoresis - PC phosphatidylcholine - PG phosphatidylglycerol - PLA₂ phospholipase A₂ - PL phospholipase C - PLD phospholipase D - PSI photosystem I - PSII photosystem II - SDS sodium dodecyl sulphate - SQDG sulfoquinovosyl-diacylglycerol - TCA trichloroacetic acid - Tricine N-tris-(hydroxymethyl)-methylglycine - Tris Tris-(hydroxymethyl)-aminomethan     

Effect of cadmium on lipid composition of pepper

Seedlings (2 weeks old) of pepper (Capsicum annum) were grown in nutrient solution with added CdCl(2) (10 or 50 microM) for 7 days. In Cd-treated plants, changes in acyl lipids and fatty acid composition were investigated. Cd particularly lowered the amount of monogalactosyldiacylglycerol (MGDG) and enhanced accumulation of phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine and phosphatidylglycerol] in leaves. In contrast, content of PC and galactolipids (MGDG and digalactosyldiacylglycerol) decreased in roots. Fatty acid composition of leaves was also changed by Cd addition to external medium, but no important changes occurred in roots. Levels of leaf polyunsaturated fatty acids, especially 18:3 and 16:3, were reduced. Lipid and fatty acid composition changes in roots are discussed in relation to Cd tolerance in pepper.     

Effect of light intensity on pigments and main acyl lipids during ‘natural’ chloroplast development in wheat seedlings

The content and composition of pigments and acyl lipids (monogalactosyl diacylglycerol, digalactosyl diacylglycerol and phosphatidyl glycerol) have been investigated in developing chloroplasts isolated from successive 2-cm sections along the leaves of wheat seedlings grown either under 100, 30 or 3 W·m^-2. In all examined stages of plastid development chlorophyll a/b and chlorophyll/carotenoid ratios were higher with increasing irradiance, whereas chlorophyll content expressed on fresh weight basis gradually decreased.Concentrations of monogalactosyl diacylglycerol, digalactosyl diacylglycerol and phosphatidyl glycerol decreased per chlorophyll unit with increasing plastid maturity. The higher was the light intensity applied during plant growth, the higher were galactolipid and phosphatidyl glycerol contents in developing chloroplasts. During plastid development the percentage of -linolenic acid markedly increased in total and individual acyl lipids. Under high light conditions, the accumulation of this fatty acid proceeded more rapidly. Significantly higher proportion of -linolenic acid was found in acyl lipid fraction of chloroplasts differentiating in high light grown plants, than in those from plants exposed to lower light intensities. The differences in the double bond index may indicate higher fluidity of thylakoid membranes in sun-type chloroplasts.Trans-3-hexadecenoic acid, virtually absent in the youngest plastids, was found in much higher concentration (per chlorophyll unit and as mol % of phosphatidyl glycerol fatty acids) in chloroplasts developing at high light conditions.Abbreviations MGDG monogalactosyl diacylglycerol - DGDG digalactosyl diacylglycerol - PG phosphatidyl glycerol - PC phosphatidyl choline - DBI double bond index - PS I photosystem I - PS II photosystem II - PSU photosynthetic unit - LHCP light harvesting chlorophyll-protein complex     

Effect of Leaf Detachment on Chlorophyll Fluorescence during Chilling Experiments

The effect of leaf detachment on chlorophyll fluorescence was analyzed for Zea mays, Cucumis sativus, Phaseolus vulgaris, and Echinochloa crus-galli. Results clearly indicate that detachment hastens the decrease in chlorophyll fluorescence during the course of chilling experiments. For maize and bean, the activity of photosystem II of chloroplasts isolated from detached leaves is lower than that of chloroplasts isolated from attached leaves. There are also large differences in ionic loss between detached and attached leaves of barnyard grass which could correlate with changes in leaf water status. The detached leaves lost some 50% of their total ionic content. Finally, detachment alters the ranking of the species with regard to their chilling tolerance.     

Lipid response to short-term chilling shock and long-term chill hardening in Jatropha curcas L. seedlings

Low non-freezing temperature is one of the major environmental factors that affect metabolism, growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas, a chilling-sensitive plant, which is considered as a sustainable energy plant with great potential for biodiesel production. Our previous studies showed that short-term chilling shock at 5 °C for 4 h and long-term chill hardening at 12 °C 1 or 2 days could improve chilling tolerance of J. curcas seedlings, but lipidomic response to chilling shock and chill hardening has not been elucidated. In this study, membrane lipid composition change in J. curcas seedlings during chilling shock and chill hardening was investigated by liquid chromatography-electrospray ionization-mass spectrometry (LC–ESI–MS) approach. The results indicated that the relative abundances of nine classes and 72 species of membrane lipids, such as phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylinositol (PI), lysophosphatidylcholine (lysoPC) and lysophosphatidylglycerol (lysoPG), two glycolipids digalactosyldiacylglycerol (DGDG) and monogalactosyldiacylglycerol (MGDG) and a sulfoquinovosyldiacylglycerol (SQDG), were significantly changed, and the degree of unsaturation of above-mentioned cellular membrane lipids with fatty acid differing in chain lengths and the number of double bonds also increased in varying degrees during chilling shock and chill hardening. These results suggested that remodeling and increase in the degree of unsaturation of membranes lipids may be a common physiological basis for short-term chilling shock- and long-term chill hardening-induced chilling tolerance of J. curcas seedlings.     

Glycerolipid acyl hydrolase activity in the brown alga Cladosiphon okamuranus TOKIDA

The brown alga, Cladosiphon okamuranus TOKIDA, was found to contain a large amount of free fatty acid (45% of the total lipids). A crude enzyme preparation from the alga showed activity for hydrolyzing the acyl groups of various glycerolipids. The results suggest that the free fatty acid in C. okamuranus was released mainly from glycoglycerolipids, which were the major lipid components in the alga, by such glycerolipid acyl hydrolases as galactolipase.     

Lipid Compositions of Photomixotrophic Green Calluses and Chlorophyll Deficient Leaves of Tobacco

Among photomixotrophic green calluses tested (N. rustica. N. tobacum L. cv. BY-4 and Samsun), the callus of Samsun had the highest contents of chlorophyll and chloroplast lipids, such as monogalactosyldiglyceride (MGDG), digalactosyldiglyceride (DGDG), sulfoquinovosyldigly-ceride (SQDG) and phosphatidylglycerol (PG). However, the chlorophyll and chloroplast lipids in the green callus of Samsun were still 1/6 and 1/3 of that in the parent leaves, respectively. The relative content of a-linolenate in MGDG, DGDG and SQDG of the green calluses were higher than that of the white calluses. The ratios of hexadecatrienoate in MGDG and hexadeceno-ate (Δ³-trans) in PG in the green calluses were trace or less compared with that of the parent leaves. The crude lipids and total fatty acid contents of the chlorophyll deficient leaves (N. taba-cum L. cv. Consolation 402 and Dominant Aurea Su/su) were almost the same as those of the normal leaves (cv. BY-4 and Samsun), although the chlorophyll contents of the chlorophyll deficient leaves were 1/3 ~ 1/4 of that of the normal leaves. The ratios of chloroplast lipids in the total polar lipids in the chlorophyll deficient leaves were a little lower than that in the normal green leaves, but the former had a slightly higher ratio of phospholipids such as phosphatidylcholine and phosphatidylethanolamine than the latter. There were few differences in the fatty acid compositions of each individual lipid betweeen both types of leaves.     

Ultrastructure and Dimensions of Chloroplasts in Leaves of Three Maize (Zea mays L.) Inbred Lines and their F1 Hybrids Grown Under Moderate Chilling Stress

Influence of moderate chilling stress on vascular bundle sheath cell (BSC) and especially mesophyll cell (MC) chloroplasts of mature maize leaves was studied by electron microscopy and stereology. Plants of two inbred lines of maize, differing in their photosynthetic activity, and their F₁ hybrids were cultivated during autumn in heated or unheated glasshouse. Generally, chilling temperatures resulted mainly in the decrease in stereological volume density (VD) of both granal and intergranal thylakoids of MC chloroplasts, while the ratio of granal to all thylakoids (granality) was less affected. The VD of peripheral reticulum and plastoglobuli usually increased after cold treatment of plants. The volume of MC chloroplasts usually increased under chilling stress, the shape of the chloroplasts changed only slightly. The ultra-structure of chloroplasts differed between individual genotypes; chilling-stressed hybrid plants showed positive heterosis particularly in the granal thylakoids' VD of MC chloroplasts.     

膜脂对菠菜细胞色素b6f复合体电子传递活性的影响

利用从菠菜(Spinacia oleracea L.)叶绿体分离、纯化出的缺失膜脂的细胞色素b6f蛋白复合体(Cyt b6f)制剂与从菠菜类囊体分离、纯化的膜脂进行体外重组,检测了不同膜脂对Cyt b6f催化电子传递活性的影响.结果表明:被检测的5种膜脂,即单半乳糖基甘油二酯(MGDG)、双半乳糖基甘油二酯(DGDG)、磷脂酰胆碱(PC)、磷脂酰甘油(PG)和硫代异鼠李糖基甘油二酯(SQDG)对Cyt b6f催化电子传递的活性均有明显的促进作用,但促进的程度各不相同,这可能与这些膜脂分子的带电性质密切相关.不带电荷的MGDG和DGDG及分子整体呈电中性的PC对促进Cyt b6f催化电子传递的活性非常有效,可分别使其活性提高89%、75%和77%;而带负电荷的PG和SQDG对活性的促进作用则相对较弱,仅可使其活性分别提高43%和26%.