Characterization of the main lipid components of chloroplast membranes and cold induced changes in Coffea spp.

Low temperatures affect many plant physiological and biochemical components, amongst them the lipid phase of membranes. The present work aimed to characterize the lipid composition of chloroplast membranes of three Coffea genotypes, representing three agronomic valuable species (Coffea arabica cv. Icatu, Coffea canephora cv. Conilon clone 02 and Coffea dewevrei), under adequate environmental conditions and to relate its cold tolerance ability to the adjustments triggered during a gradual temperature decrease, after chilling exposure and upon a recovery period. Under adequate temperature (25/20 °C, day/night) the lipid composition of chloroplast membranes was fairly similar amongst the genotypes concerning the total fatty acid (TFA) content and individual FAs (both globally or within the classes), suggesting a close lipid composition amongst Coffea species, which can be considered as “C18:3” plants. Under cold exposure and subsequent recovery the genotypes undergo adjustments, some of them with acclimation potential. The genotypes displayed some ability to increase lipid synthesis, increasing their FA content. However, under cold exposure (even at 4 °C), Icatu and C. dewevrei plants performed qualitative adjustments, including preferential synthesis of phospholipids (especially PG) instead of galactolipids and increases in the unsaturation degree of DGDG and phospholipid classes (PG, PC and PI). Clone 02 maintained almost all lipid characteristics, what explains its higher cold sensitivity. Furthermore, differences that contribute to explain contrasting cold sensitivity in Icatu (more tolerant) and C. dewevrei emerged when analyzing PA content (taken as a stress metabolite) and the FA composition within MGDG and PG classes. C. dewevrei presented the higher increase, absolute value and relative weight of PA, while Icatu was the solely genotype to show a rise in the unsaturation degree of MGDG and PG, displaying as well the highest DBI values for these classes. We conclude that lipid qualitative and quantitative adjustments constitute a flexible mechanism that decisively contributes to cold acclimation in Coffea spp., working in tandem with others that minimize oxidative stress damages.     

Physiological and biochemical impacts of magnesium-deficiency in two cultivars of coffee

Aim

To evaluate biochemical and physiological impacts of magnesium-deficiency on seedlings of two cultivars (Catuaí and Acaiá) of Coffea arabica L..

Methods

Six month old seedlings from both cultivars were transferred to plastic receptacles containing solutions with different concentrations of magnesium (Mg). Fully expanded leaves and roots were evaluated at the beginning of treatment and after 10, 20 and 30 days for chlorophyll and carotenoid content, biomass allocation, partitioning of carbohydrates and antioxidant metabolism.

Results

Mg-deficiency was characterized by an increase in the shoot/root dry weight ratio, which may be related to accumulation of carbohydrates in leaves. This accumulation is probably responsible for triggering a reduction in the consumption of reducing equivalents, providing favorable conditions for the formation of reactive oxygen species (ROS). The increase in ROS production was accompanied by increases in ascorbate concentration and enzyme activity of the antioxidant metabolism.

Conclusions

The Catuaí cultivar is more sensitive to Mg-deficiency than the Acaiá cultivar. When exposed to magnesium deficiency the Catuaí cultivar had reduced growth and its antioxidant metabolism was less efficient at removing ROS.     

The impact of cold on photosynthesis in genotypes of Coffea spp.--photosystem sensitivity, photoprotective mechanisms and gene expression

Environmental constraints disturb plant metabolism and are often associated with photosynthetic impairments and yield reductions. Among them, low positive temperatures are of up most importance in tropical plant species, namely in Coffea spp. in which some acclimation ability has been reported. To further explain cold tolerance, the impacts on photosynthetic functioning and the expression of photosynthetic-related genes were analyzed. The experiments were carried out along a period of slow cold imposition (to allow acclimation), after chilling (4 °C) exposure and in the following rewarming period, using 1.5-year-old coffee seedlings of 5 genotypes with different cold sensitivity: Coffea canephora cv. Apoatã, Coffea arabica cv. Catuaí, Coffea dewevrei and 2 hybrids, Icatu (C. arabica × C. canephora) and Piatã (C. dewevrei × C. arabica). All genotypes suffered a significant leaf area loss only after chilling exposure, with Icatu showing the lowest impact, a first indication of a higher cold tolerance, contrasting with Apoatã and C. dewevrei. During cold exposure, net photosynthesis and Chl a fluorescence parameters were strongly affected in all genotypes, but stomatal limitations were not detected. However, the extent of mesophyll limitation, reflecting regulatory mechanisms and/or damage, was genotype dependent. Overnight retention of zeaxanthin was common to Coffea genotypes, but the accumulation of photoprotective pigments was highest in Icatu. That down-regulated photochemical events but efficiently protected the photosynthetic structures, as shown, e.g., by the lowest impacts on A_max and PSI activity and the strongest reinforcement of PSII activity, the latter possibly reflecting the presence of a photoprotective cycle around PSII in Icatu (and Catuaí). Concomitant to these protection mechanisms, Icatu was the sole genotype to present simultaneous upregulation of caCP22, caPI and caCytf, related to, respectively, PSII, PSI and to the complex Cytb₆/f, which could promote better repair ability, contributing to the maintenance of efficient thylakoid functioning. We conclude that Icatu showed the best acclimation ability among the studied genotypes, mostly due to a better upregulation of photoprotection and repair mechanisms. We confirmed the presence of important variability in Coffea spp. that could be exploited in breeding programs, which should be assisted by useful markers of cold tolerance, namely the upregulation of antioxidative molecules, the expression of selected genes and PSI sensitivity.     

Photosynthetic performance of two coffee species under drought

Coffea arabica cv. Red Catuaí and C. canephora cv. Kouillou were grown in pots beneath a plastic shelter. When they were 14 months old, irrigation was withheld until the leaf pre-dawn water potential was about -1.5 and -2.7 MPa (designated mild and severe water stress, respectively). Under mild stress, net photosynthetic rate (PN) decreased mainly as a consequence of stomatal limitations in Kouillou, whereas such decreases were dominated by non-stomatal limitations in Catuaí. Under severe drought, further decreases in PN and apparent quantum yield were not associated to any changes in stomatal conductance in either cultivar. Decreases were much more pronounced in Catuaí than in Kouillou, the latter maintained carbon gain at the expense of water conservation. In both cultivars the initial chlorophyll (Chl) fluorescence slightly increased with no changes in the quantum efficiency of photosystem 2. In response to rapidly imposed drought, the Chl content did not change while saccharide content increased and starch content decreased. Photoinhibition and recovery of photosynthesis, as evaluated by the ratio of variable to maximum fluorescence and by the photosynthetic O2 evolution, were unaffected by mild drought stress. Photoinhibition was enhanced under severe water deficit, especially in Catuaí. In this cultivar the O2 evolution did not resume upon reversal from photoinhibition, in contrast to the complete recovery in Kouillou.     

Foliar cuticular waxes of cultivated species and varieties of Coffea

The cuticular waxes of leaves of Coffea arabica cv. ‘Catuaí Vermelho’, C. arabica cv. ‘Obatã’, Coffea canephora cv. ‘Apoatã’, Coffea racemosa and two hybrids between C. arabica and C. racemosa were extracted by rapid washing of the surface with chloroform. The waxes were fractionated by thin layer chromatography over silicagel. The fractions of the constituent classes were characterized by infrared spectroscopy and the distribution of the homologs of the n-alkanes and n-primary alcohols was determined by GC/MS and GC/FID. Among the samples analyzed, leaves of C. racemosa have the highest content of foliar wax (22.9 μg cm⁻²). Most samples contain either n-alkanes (C. canephora and C. racemosa) or n-primary alcohols (C. arabica) as predominant wax constituents. The distribution of n-alkanes allowed the distinction of C. racemosa from the other samples; the distribution of alcohols allowed the distinction of the three species. The two hybrids have waxes similar to the wax of C. arabica.     

Photosynthetic performance of two coffee species under drought

Coffea arabica cv. Red Catuaí and C. canephora cv. Kouillou were grown in pots beneath a plastic shelter. When they were 14 months old, irrigation was withheld until the leaf pre-dawn water potential was about -1.5 and -2.7 MPa (designated mild and severe water stress, respectively). Under mild stress, net photosynthetic rate (PN) decreased mainly as a consequence of stomatal limitations in Kouillou, whereas such decreases were dominated by non-stomatal limitations in Catuaí. Under severe drought, further decreases in PN and apparent quantum yield were not associated to any changes in stomatal conductance in either cultivar. Decreases were much more pronounced in Catuaí than in Kouillou, the latter maintained carbon gain at the expense of water conservation. In both cultivars the initial chlorophyll (Chl) fluorescence slightly increased with no changes in the quantum efficiency of photosystem 2. In response to rapidly imposed drought, the Chl content did not change while saccharide content increased and starch content decreased. Photoinhibition and recovery of photosynthesis, as evaluated by the ratio of variable to maximum fluorescence and by the photosynthetic O2 evolution, were unaffected by mild drought stress. Photoinhibition was enhanced under severe water deficit, especially in Catuaí. In this cultivar the O2 evolution did not resume upon reversal from photoinhibition, in contrast to the complete recovery in Kouillou. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photoprotective mechanisms in cold-acclimated and nonacclimated needles of <Emphasis Type="Italic">Picea glehnii</Emphasis>

The response of Picea glehnii, a cold-tolerant species in the boreal zone, to air temperature (T) was investigated for its cold-acclimated needles (i.e. the ones subjected to gradual decrease in T) and nonacclimated needles (i.e. the ones subjected to a sudden decrease in T) were compared under low temperature. Cold-acclimated needles showed a greater increase of zeaxanthin and lutein contents than nonacclimated ones, whereas the nonacclimated needles showed a greater increase of thylakoid-bound ascorbate peroxidase (tAPX) activity than cold-acclimated ones under chilling conditions (after cold acclimation). These results suggest that: (1) low T induces the increase of zeaxanthin and lutein content, and tAPX activity; (2) accumulated zeaxanthin and lutein protect needles from photooxidative stress by dissipating excess energy before the reactive oxygen species (ROS) are formed in response to a gradual decrease in T (with cold acclimation and subsequent chilling condition), and by tAPX scavenging ROS formed in the case of a sudden decrease in T (without cold acclimation and chilling condition).     

Electrolyte leakage and lipid degradation account for cold sensitivity in leaves of Coffea sp. plants

Five Coffea genotypes differing in their sensitivity to low positive temperatures were compared with regard to the effects of chilling on membrane integrity, as well as their ability to recover from cold-induced injury upon re-warming. Membrane damage was evaluated through electrolyte leakage, changes in membrane lipid composition and malondialdehyde (MDA) production in control conditions (25/20 degrees C, day/night), after a gradual temperature decrease period to 15/10 degrees C, after chilling treatment (3 nights at 4 degrees C) and upon re-warming to 25/20 degrees C during 6 days (recovery). C. dewevrei showed the highest electrolyte leakage at 15/10 degrees C and after chilling. This was due mainly to lipid degradation observed at 15/10 degrees C, reflecting strong membrane damage. Furthermore, MDA production after chilling conditions indicated the occurrence of lipid peroxidation. A higher susceptibility of C. dewevrei to cold also was inferred from the complete absence of recovery as regards permeability, contrary to what was observed in the remaining plants. Apoat? and Piat? presented significant leakage values after chilling. However, such effects were reversible under recovery conditions. Exposure to cold (15/10 degrees C and 3 x 15/4 degrees C) did not significantly affect membrane permeability in Catuaí and Icatú. Furthermore, no significant MDA production was observed even after chilling treatments in Apoat?, Piat?, Catuaí and Icatú, suggesting that the four genotypes had the ability to maintain membrane integrity and/or repair membrane damage caused by low temperatures. Apoat?, Piat? and, to a lower extent, Catuaí, were able to cope with gradual temperature decrease through an enhanced lipid biosynthesis. After acclimation, Piat? and Catuaí showed a lowering of digalactosyldiacylglycerol to monogalactosyldiacylglycerol ratio (MGDG/DGDG) as a result of enhanced DGDG synthesis, which represents an increase in membrane stability. The same was observed in Apoat? after chilling, in spite of phospholipids decrease. The studied parameters clearly indicated that chilling induced irreversible membrane damage in C. dewevrei. We also concluded that increased lipid synthesis, lower MGDG/DGDG ratio, and changes in membrane unsaturation occurring during acclimation to low temperatures may be critical factors in maintenance of cellular integrity under chilling.     

Cold-induced changes in mineral content in leaves of Coffea spp. Identification of descriptors for tolerance assessment

Temperature and mineral nutrition are major environmental factors regulating plant growth and development. Yet, cold impact on mineral contents and the ability of the plants to perform changes in specific elements as a part of the acclimation process received little attention. Using five Coffea genotypes previously characterized concerning their cold sensitivity, a mineral analysis was performed considering macro (N, P, K, Ca, Mg, and S) and micro (Na, Fe, Mn, Zn, Cu, and B) nutrients in order to predict their importance in cold tolerance. The results showed a cold-induced dynamics of mineral nutrients in recently mature leaves. The less cold sensitive Icatu, and partially Catuaí, accumulated N, Ca, Mn, Cu, and Zn with potential implications in the maintenance of photosynthetic performance, the reinforcement of the antioxidative defense system, lipid metabolism, and the expression of cold regulated genes, thus constituting interesting traits to evaluate the cold acclimation ability. After a principal component analysis (PCA), N, Fe, Mn, and Cu were further confirmed as strong candidates for an early cold tolerance evaluation due to their dynamics and to specific roles in the activities of Cu/Zn-SOD (Cu), APX (Fe), and PSII (Mn).     

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.     

Proteomic Analysis of Developing Somatic Embryos of Coffea arabica

Differential protein profiles of three stages of somatic embryogenesis, including globular, torpedo, and cotyledonary somatic embryos, of Coffea arabica cv. Catuaí Vermelho were analyzed in an attempt to better understand somatic embryogenesis in coffee plants. Somatic embryos at these different stages of development were collected from in vitro-grown cultures, and then macerated in liquid nitrogen. Proteins were extracted with phenol and further quantified using the Bradford method. The bidimensional electrophoresis analysis revealed a wide range of proteins ranging between 10 and 160?kDa and of pH values ranging from 3 to 10. Several differentially expressed proteins were identified by mass spectrometry, and some were found to be specific to these different stages of somatic embryogenesis in coffee. The enolase and 11S storage globulin proteins, for example, could be used as molecular markers for somatic embryo development stages and for embryogenic and non-embryogenic genotype differentiation, respectively.     

Effects of long-term chilling on growth and photosynthesis of the C4 gramineae Paspalum dilatatum

Dallis grass (Paspalum dilatatum Poir.) is a C₄/NADP‐ME gramineae, previously classified as semi‐tolerant to cold, although a complete study on this species acclimation process under a long‐term chilling and controlled environmental conditions has never been conducted. In the present work, plants of the variety Raki maintained at 25/18°C (day/night) (control) were compared with plants under a long‐term chilling at 10/8°C (day/night) (cold‐acclimated) in order to investigate how growth and carbon assimilation mechanisms are engaged in P. dilatatum chilling tolerance. Although whole plant mean relative growth rate (mean RGR) and leaf growth were significantly decreased by cold exposure, chilling did not impair plant development nor favour the investment in biomass below ground. Cold‐acclimated P. dilatatum cv. Raki had a lower leaf chlorophyll content, but a higher photosynthetic capacity at optimal temperatures, its range being shifted to lower values. Associated with this higher capacity to use the reducing power in CO₂ assimilation, cold‐acclimated plants further showed a higher capacity to oxidize the primary stable quinone electron acceptor of PSII, Q_A. The activity and activation of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were not significantly affected by the long‐term chilling. Cold‐acclimated P. dilatatum cv. Raki apparently showed a lower transfer of excitation energy from the light‐harvesting complex of photosystem II to the respective reaction centre and enhancement of radiationless energy‐dissipating mechanisms at suboptimal temperatures. Overall, long‐term chilling resulted in several effects that comprise responses with an intermediate character of both chilling‐tolerant and –sensitive plants, which seem to play a significant role in the survival and acclimation of P. dilatatum cv. Raki at low temperature.     

Phosphatidylglycerol and chilling sensitivity in plants

The hypothesis that molecular species of thylakoid phosphatidylglycerol containing two saturated fatty acids (disaturated phosphatidylglycerol) confer chilling sensitivity upon plants was tested by analyzing the fatty acid composition of phosphatidylglycerols isolated from leaves of a range of plants expected to have different sensitivities to chilling temperatures.

`Saturated' fatty acids (palmitate plus stearate plus hexadeca-trans-3-enoate) as a proportion of total phosphatidylglycerol fatty acids varied from 51 to 80 mole per cent in the plants analyzed but appeared to be rigidly fixed for a given plant species, being unaffected by leaf maturity or by environment.

Hexadeca-trans-3-enoate occurred only at the sn-2 position, whereas C-18 fatty acids occurred only at the sn-1 position of thylakoid phosphatidylglycerol. Therefore, the proportion of disaturated molecular species could be predicted accurately from the total fatty acids of phosphatidylglycerol.

Disaturated molecular species accounted for <25% of the total phosphatidylglycerol from leaves of chilling-resistant plants and for 50 to 60% of the phosphatidylglycerol in leaves from some of the most chilling-sensitive plants. However, not all chilling-sensitive plants contained high proportions of disaturated phosphatidylglycerol; solanaceous and other 16:3-plants and C₄ grasses may be important exceptions. Nonetheless, proportions of disaturated phosphatidylglycerol increased concomitantly with increasing chilling sensitivity of plants within a genus.

     

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.     

Relationship of cold acclimation,total phenolic content and antioxidant capacity with chilling tolerance in petunia (Petunia × hybrida)

Extracts from Petunia × hybrida plants, which had been subjected to cold pretreatment to induce chilling tolerance, were analyzed for specific phenolic acids, such as gentisic acid, and assessed for their antioxidant capacity by their ability to reduce (decolorize) the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt radical (ABTS^*). Gentisic acid was induced in significant quantities by the third week of cold acclimation and levels remained constant up to the fourth week. Cold acclimation induced accumulation of total phenolics, which was positively related to antioxidant capacity. Petunia plants recovered from chilling injury following 3 weeks of cold pretreatment with an increase in total phenolics, which suggested some form of antioxidant protection. However, antioxidant capacity was only moderately related to chilling tolerance, which indicated that factors other than total phenolics may play a role in the chilling tolerance in petunia. These data suggest that the 5 °C cold pretreatment may have initially caused injury that impeded acclimation at the outset, and that subsequent phenolic metabolism was related to protective functions in petunia.     

Plasma Membrane Lipid Alterations Associated with Cold Acclimation of Winter Rye Seedlings (Secale cereale L. cv Puma)

Highly enriched plasma membrane fractions were isolated from leaves of nonacclimated (NA) and acclimated (ACC) rye (Secale cereale L. cv Puma) seedlings. Collectively, free sterols, steryl glucosides, and acylated steryl glucosides constituted >50 mole% of the total lipid in both NA and ACC plasma membrane fractions. Glucocerebrosides containing hydroxy fatty acids constituted the major glycolipid class of the plasma membrane, accounting for 16 mole% of the total lipid. Phospholipids, primarily phosphatidylcholine and phosphatidylethanolamine with lesser amounts of phosphatidylglycerol, phosphatidic acid, phosphatidylserine, and phosphatidylinositol, comprised only 32 mole% of the total lipid in NA samples. Following cold acclimation, free sterols increased from 33 to 44 mole%, while steryl glucosides and acylated steryl glucosides decreased from 15 to 6 mole% and 4 to 1 mole%, respectively. Sterol analyses of these lipid classes demonstrated that free β-sitosterol increased from 21 to 32 mole% (accounting for the increase in free sterols as a class) at the expense of sterol derivatives containing β-sitosterol. Glucocerebrosides decreased from 16 to 7 mole% of the total lipid following cold acclimation. In addition, the relative proportions of associated hydroxy fatty acids, including 22:0 (h), 24:0 (h), 22:1 (h), and 24:1 (h), were altered. The phospholipid content of the plasma membrane fraction increased to 42 mole% of the total lipid following cold acclimation. Although the relative proportions of the individual phospholipids did not change appreciably after cold acclimation, there were substantial differences in the molecular species. Di-unsaturated molecular species (18:2/18:2, 18:2/18:3, 18:3/18:3) of phosphatidylcholine and phosphatidylethanolamine increased following acclimation. These results demonstrate that cold acclimation results in substantial changes in the lipid composition of the plasma membrane.     

Photoinhibition and recovery of photosynthesis in Coffea arabica and C. canephora

Photosynthetic parameters were determined in disks from leaves of C. arabica cv. Red Catuaí and C. canephora cv. Kouillou grown in the field. Kouillou showed a relatively higher irradiance requirement for saturating photosynthesis, lower chlorophyll (Chl) content, and higher Chl a/b ratio than Catuaí. Photoinhibition of photosynthesis under bright irradiance was manifested by decreases in maximum photochemical efficiency (evaluated by the variable to maximum fluorescence ratio, Fv/Fm), as a consequence of an increased initial and a quenched maximum fluorescence. Restoration of Fv/Fm following photoinhibition in low irradiance was faster in Kouillou than in Catuaí. Chloramphenicol both accelerated photoinhibition (mainly in Kouillou) and blocked its recovery for at least 190 min in either cultivar. Photosynthetic oxygen evolution under photoinhibitory conditions was decreased by chloramphenicol; in control leaf disks this decrease was only observed in C. arabica, but with a rapid recovery within 90 min of low irradiance exposure. In both coffee cultivars, the depressed photochemical efficiency of photosystem 2 was not accompanied by a concomitant lowering in oxygen evolution during reversal from photoinhibition.     

Population structure and genetic diversity of coffee progenies derived from Catuaí and Híbrido de Timor revealed by genome-wide SNP marker

The use of single nucleotide polymorphism (SNP) molecular markers has provided advances in selection methodologies used in breeding programs of different crops, reducing cost and time of cultivar release. Despite the great economic and social importance of Coffea arabica, studies with SNP markers are scarce and a small number of SNP are available for this species, when compared with other crops of agronomic importance. Thus, the objective of this study was to identify and validate SNP molecular markers for the species Coffea arabica and to introduce these markers to genetic breeding by means of an accurate analysis of the diversity and genetic structure of breeding populations of this species. After quality filtering, 11,187 SNP markers were selected from the coffee population obtained from crosses between the genotypes Catuaí and Híbrido de Timor. A great number of markers were distributed in the 11 chromosomes, within transcribed regions, and were used to estimate the genetic dissimilarity among the individuals of the breeding population. Dendrogram analysis and a Bayesian approach demonstrated the formation of two groups and the discrimination of all genotypes evaluated. The expressive number of SNP molecular markers distributed throughout C. arabica genome was efficient to discriminate all the accessions evaluated in the experiment, clustering them according to their genealogies. This work identified mixtures within the progenies. The genotyping data also provided detailed information about the parental genotypes and led to the identification of new candidate parents to be introduced to the breeding program. The study discussed population structure and its consequence in obtaining improved varieties of C. arabica.     

Cold Acclimation Ability and Photosynthesis among Species of the Tropical Coffea Genus

Abstract: Three Coffea species (C. arabica cv. Icatu, C. canephora cv. Apoatã and C. dewevrei) were tested in order to identify and study the mechanisms of tolerance to low, non‐freezing temperatures. Several photosynthesis‐related parameters were monitored during a 20‐day period of gradual temperature decrease, from 25/20 °C (day/night) down to 15/10 °C, during chilling treatments (15/4 °C), and upon rewarming (25/20 °C). Differences were found among species, both during low temperature exposure and during rewarming. In general, Coffea species showed cold‐induced photoinhibition of photosynthesis, which was attributable to biochemical (in vivo ribulose‐1,5‐bisphosphate carboxylase/oxygenase activity and carbohydrate synthesis) and biophysical (antennae functioning, photosystem II efficiency and linear electron transport) inactivation, rather than to stomatal constraints. The moderately low temperature of 15/10 °C was enough to cause a negative impact on net photosynthesis (A), mostly due to low (initial) rubisco activity in all species. However, C. arabica cv. Icatu showed a higher tolerance to chilling and recovered quickly and completely upon rewarming, as assessed from the impacts on the photosynthetic machinery (e.g. A_max, F_o, F_v/F_m, F_v′/F_m′, q_P, ?_e, rubisco activity) and on carbohydrate metabolism. Such lesser effects are likely to be related to the strong increases and higher contents of zeaxanthin, lutein and β‐carotene that presumably increased the ability to dissipate excitation energy and contributed to protect the photosynthetic apparatus. During cold exposure, a significant reduction of the α/β carotene ratio, which is considered an acclimation feature, was observed solely in C. arabica cv. Icatu. However, C. canephora cv. Apoatã and, especially, C. dewevrei showed to be highly cold‐sensitive. In these latter species, the photoinhibitory impairments to photosynthesis were stronger, probably due to the lower contents of protecting pigments during chilling conditions that lead to a higher vulnerability to excess excitation energy. Moreover, the mesophyll impairments (e.g. A_max, F_v/F_m, ?_e) became significant even at moderately low temperatures of 15/10 °C, and a lower ability to recover after chilling exposure was observed. The limitation of in vivo rubisco activity and A_max may have been due to substrate limitation, but disturbances in sugar metabolism could also play an important role in the expression of chilling sensitivity in C. canephora cv. Apoatã and C. dewevrei.     

Modulation of membrane fluidity by catalytic hydrogenation affects the chilling susceptibility of the blue-green alga, Anacystis nidulans

All the changes, i.e. the phase separation temperature of thylakoid lipids, shift in the chilling induced increase of K⁺ permeability and decline in photosynthetic O₂-production, respectively, brought about by temperature acclimation in Anacystis nidulans, can be accomplished by homogeneous catalytic hydrogenation of the fatty acids, as well, using a new water-soluble Pd(II) complex, hitherto unknown in biological applications. Since the thermo-adaptation replaced by proper hydrogenation conducted under isothermal condition results in a similar modification of chilling susceptibility, it afforts direct evidence that chilling response is mediated by changing the degree of fatty acid unsaturation in Anacystis nidulans.