Distribution and utilization of chlorogenic acid in Coffea seedlings

Ripe coffee seeds (Coffea arabica L.) contain large quantitiesof the purine alkaloid caffeine and the depside chlorogenicacid (5-O-caffeoyl-quinic acid). Directly after germination,both compounds were recovered almost exclusively in the cotyledonsand surrounding endosperm and hardly at all in the hypocotyland root of coffee seedlings. During the first 10 weeks of development,the cotyledons invaded the endosperm and expanded. The caffeinecontent in the developing cotyledons changed little, but thechlorogenic acid content dropped to one-third of the originallevel. The loss of chlorogenic acid was not recovered in theother organs of the seedling. The drop in chlorogenic acid contentcoincided with an increase in the amount of cell wall-boundphenolic polymers in the developing cotyledons, which couldbe extracted after thioglycolic acid derivatization. In thedeveloping cotyledons, phenylalanine ammonia lyase (PAL) activitywas hardly detectable. These results suggest that the chlorogenicacid stored in coffee seeds is used for the deposition of phenolicpolymers, presumably lignin, in cotyledonary cell walls duringexpansion. The situation in cotyledons was found to be in markedcontrast to that in foliage leaflets, in which PAL activitywas 900-fold higher than in cotyledons. In the leaflets, bothchlorogenic acid and caffeine accumulated continuously duringleaf expansion. Key words: Coffea arabica, seedling, chlorogenic acid, caffeine     

Degradation of the endosperm cell walls of Lactuca sativa L., cv. Grand Rapids

The timing of mobilisation of lipid, sucrose, raffinose and phytate in lettuce seeds (achenes) (cv. Grand Rapids) has been examined. These reserves (33%, 1.5%, 0.7%, 1.4% of achene dry weight, respectively) are stored mostly in the cotyledons. Except for a slight degradation of raffinose and increase in sucrose, there is no detectable reserve mobilisation during germination. The endosperm (8% of seed dry weight), which has thick, mannan-containing cell walls (carbohydrate, 3,4% of seed dry weight), is completely degraded within about 15h following germination. Mannanase activity increases about 100-fold during the same period and arises in all regions of the endosperm. Also during this period sucrose and raffinose are degraded and fructose and glucose accumulate in the embryo. The endosperm hydrolysis products are taken up by the embryo, and are probably used as an additional reserve to support early seedling growth. However, endosperm cell-wall carbohydrates, such as mannose, are not found as free sugars. Lipid and phytate are degraded in a later, second phase of mobilisation. Low levels of sucrose are present in the embryo, mostly in the cotyledons, and large amounts of fractose and glucose (14% of seedling dry weight at 3 days after sowing) accumulate in the hypocotyl and radicle. It is suggested that sucrose, produced in the cotyledons by gluco-neogenesis, is translocated to the axis and converted there to fructose and glucose.     

Mobilisation of the major stored reserves in the embryo of fenugreek (Trigonella foenum-graecum L., Leguminosae), and correlated enzyme activities

Changes in total nitrogen, soluble amino nitrogen, lipid and phytate contents, and in the activities of proteinase (pH 7.0), isocitrate lyase and phytase were followed in the endosperm, cotyledons, and axis during germination of fenugreek seeds and subsequent growth of the seedlings. The endosperm is comprised largely of cell-wall galactomannans: the majority of the seed total nitrogen, lipid and phytate (5%, 8%, 0.44% of seed dry weight respectively) is localised within the cotyledons as stored reserves. Germination is completed after 10–14 h from the start of imbibition, but the major reserves are not mobilised during the first 24 h. Then the total nitrogen content of the cotyledons starts to decrease and that of the axis increases; there is a concomitant accumulation of soluble amino nitrogen in both cotyledons and axis. An increase in proteinase activity in the cotyledons correlates well with the depletion of total nitrogen therein. Depletion of lipid and phytate reserves in the different seed tissues constitutes a late event, occurring after 50 h from the start of imbibition, and is coincident with the final disintegration of the endosperm tissue. The depletion of phytate and stored lipids is accompanied by an increase in phytase and isocitrate lyase activity. It appears that the products of lipid hydrolysis are converted by gluconeogenesis to serve as the major source of sugars for the growing axis after the endosperm galactomannan has been completely mobilised.     

Dynamics of Water and Abscisic Acid During Embryogeny and Embryo Drying in the Recalcitrant Seeds of Vateria indica L.

Vateria indica L. is a critically endangered tree species in South-Western Ghats of India, commercially exploited for its valuable resins. Seed recalcitrance is a major problem hindering the natural regeneration of this species and it poses a great challenge in seed storage and conservation. There was a continuous import of water from the maternal tissues to seed tissues till maturity and the seeds were released in a fully hydrated state. Differential accumulation of water has been noticed in the cotyledons and embryonal axis. There was a positive correlation between seed moisture content and rate of germination which is a character of recalcitrant seeds. The critical moisture content was found to be 40% in the axis and 23.5% in the cotyledons, below which the embryo will not germinate. Loss of germination ability as a result of desiccation was attributed to the cell membrane damage, expressed as the electrolyte leakage exceeding 0.79 μS/cm. ABA peaked in the mid embryogenesis, then dropped drastically and maintained a lower level till seed maturity. On desiccation, ABA started to increase but gradually dropped down. Both cotyledons and embryonal axis had differential ABA content but exhibited a general pattern of ABA level during embryogeny. Due to the thin seed coat/embryo ratio and low investment in the seed coat, this recalcitrant seed could not hold water as efficient as orthodox seeds. Thus, it germinated as soon as it was shed from the mother plant. On desiccation, ABA shot up and moisture content decreased along with electrolyte leakage and cell membrane damage. All these hindered germination of the seed. Thus, we can see a clear interplay between moisture content and ABA levels during embryogeny and desiccation. Since the seed biology of this species has not been well documented, the present work is mainly intended to study the dynamics of water and ABA during embryogeny and embryo drying. This study can surely contribute to the long-term storage and conservation of recalcitrant seeds which is a less explored area.

     

Seed of Cercis siliquastrum L (Leguminosae,Caesalpinioideae): Reserves and their Utilization after Germination

An ultrastructural study on the reserves stored in cotyledons and endosperm and on their utilization after germination has been carried out in Cercis siliquastrum seeds. The observations have shown that all the cotyledonal reserves of proteins and lipids are used during seedling growth. However, inside the endosperm cells only the protein reserves are depleted, and large quantities of lipids remain undigested. In both cell walls and intercellular spaces of the endosperm cells huge masses of polysaccharide reserves are stored. However, only the polysaccharides inserted in the cell walls are dismantled, while those located in the intercellular spaces are not attacked by the lytic enzymes. Some hypotheses regarding the possible roles of those endospermic non-nutritional materials in the strategies of seed germination and seedling growth are suggested.     

An Intermediate Category of Seed Storage Behaviour?II. EFFECTS OF PROVENANCE, IMMATURITY, AND IMBIBITION ON DESICCATION-TOLERANCE IN COFFEE

Seeds of four cultivars of arabica coffee (Coffea arabica L.)received from three continents survived desiccation to between7-2% and 11-3% moisture content (wet basis), i.e. to seed waterpotentials of –90 MPa to –150 MPa, but further desiccationreduced germination (criterion, normal seedling development)in all seed lots. Only a few individuals from four of the lotsgerminated after being dried to 4–5% moisture content.Differences in desiccation sensitivity were apparent among lotswithin each cultivar. Desiccation sensitivity in these lotswas similar to that observed in seeds of orthodox species whichhave begun to germinate. Seeds extracted from fruits of intermediatematurity (yellow) were able to tolerate greater desiccationthan those from either ripe (red) or immature (green) fruits.Imbibed storage increased desiccation sensitivity. The resultsare compatible with the view that arabica coffee seeds are unableto tolerate extreme desiccation because germination has beeninitiated before harvest.     

Changes in developing pea (Pisum sativum) seeds in relation to their ability to withstand desiccation

In two separate experiments in 1970 and 1971 the germination ability of seeds that had been rapidly desiccated following harvesting from glasshouse-grown pea plants improved with time after fertilization. In 1970 the germination of seeds directly after harvesting also improved with time. In both years the readiness with which electrolytes were leached from dried seeds decreased with seed age, measured as time after fertilization. The germination ability of desiccated seeds, and of undried seeds in 1970, improved after the cessation of seed moisture increase on the parent plant. This improvement coincided, in 1970, with a fall in the readiness with which electrolytes could be leached from seeds and with a decline in the rate of oxygen uptake of seeds directly after harvest. Vital staining of dried seeds from harvest samples indicated the viability of the samples as determined by germination tests. In both years, when the cotyledons first showed complete staining, the staining was very intense; in 1970 this occurred in a harvest sample with a greater than 50% germination level, but in 1971 it occurred in a sample that showed incomplete staining in the embryo axis and less than 5 % germination. In 1971 the comparative rates of moisture loss from seeds, measured with a sensor element diffusion porometer, were very low at 25 days after fertilization, increased up to a peak at 35 days and fell to a rate at the final harvest (44 days) which was nearly three times faster than the initial rate. Thus, during the period of dehydration, after 37 days, the seeds were able to lose moisture. When seeds were allowed to lose moisture slowly after harvest, before being desiccated rapidly, their eventual condition as measured by leaching improved. Also, the faster the initial water loss preceding rapid desiccation the more readily were the dried seeds leached. It is suggested that seeds can only withstand rapid desiccation after the cessation of moisture increase and after some slow dehydration, which is accompanied by a slowing down in physiological activity.     

Sugar Uptake and Translocation in the Castor Bean Seedling II. Sugar Transformations During Uptake

Changes in the dry weights of various parts of the castor bean seedling showed that the rates of transfer of material through the cotyledons to the embryonic axis exceeded 2 mg/hour after 5 to 6 days of germination. The sugar present in the endosperm was predominantly, and in the cotyledon almost exclusively, sucrose. Anatomical features were described which contribute to the efficiency of the cotyledons as organs of absorption and transmittal of sucrose to the embryonic axis, where hexoses are much more prevalent.     

Sugar uptake and translocation in the castor bean seedling I. Characteristics of transfer in intact and excised seedlings

Changes in the dry weights of various parts of the castor bean seedling showed that the rates of transfer of material through the cotyledons to the embryonic axis exceeded 2 mg/hour after 5 to 6 days of germination. The sugar present in the endosperm was predominantly, and in the cotyledon almost exclusively, sucrose. Anatomical features were described which contribute to the efficiency of the cotyledons as organs of absorption and transmittal of sucrose to the embryonic axis, where hexoses are much more prevalent.The ability of the cotyledons to absorb sucrose survived removal of the endosperm from the seedling. A series of experiments is described in which the cotyledons of such excised seedlings were immersed in sucrose-(14)C and measurements made of uptake and of translocation to various parts of the seedling. Increasing rates of absorption were observed as the sucrose concentration was raised to 0.5 m and these rates were maintained for several hours. Removal of the embryonic axis (hypocotyl plus roots) drastically altered both the response to sucrose concentration and the time course of absorption by the cotyledons.More than 80% of the sugar normally entering the cotyledons from the endosperm is transmitted to the embryonic axis and this extensive turnover was seen also in pulse/chase experiments with excised seedlings. The cotyledons of excised seedlings absorbed sucrose against high apparent concentration gradients. The absorption was stimulated by phosphate and had a pH optimum at about pH 6.4. It was inhibited by arsenate, azide and 2,4-dinitrophenol.     

Mechanism and control of Solanum lycocarpum seed germination

BACKGROUND AND AIMS: Solanaceae seed morphology and physiology have been widely studied but mainly in domesticated crops. The present study aimed to compare the seed morphology and the physiology of germination of Solanum lycocarpum, an important species native to the Brazilian Cerrado, with two species with endospermic seeds, tomato and coffee. METHODS: Morphological parameters of fruits and seeds were determined by microscopy. Germination was monitored for 40 d under different temperature regimes. Endosperm digestion and resistance, with endo-beta-mannanase activity and required force to puncture the endosperm cap as respective markers, were measured during germination in water and in abscisic acid. KEY RESULTS: Fruits of S. lycocarpum contain dormant seeds before natural dispersion. The best germination condition found was a 12-h alternating light/dark and high/low (20/30 degrees C) temperature cycle, which seemed to target properties of the endosperm cap. The endosperm cap contains 7-8 layers of elongated polygonal cells and is predestined to facilitate radicle protrusion. The force required to puncture the endosperm cap decreased in two stages during germination and showed a significant negative correlation with endo-beta-mannanase activity. As a result of the thick endosperm cap, the puncture force was significantly higher in S. lycocarpum than in tomato and coffee. Endo-beta-mannanase activity was detected in the endosperm cap prior to radicle protrusion. Abscisic acid inhibited germination, increase of embryo weight during imbibition, the second stage of weakening of the endosperm cap and of endo-beta-mannanase activity in the endosperm cap. CONCLUSIONS: The germination mechanism of S. lycocarpum bears resemblance to that of tomato and coffee seeds. However, quantitative differences were observed in embryo pressure potential, endo-beta-mannanase activity and endosperm cap resistance that were related to germination rates across the three species.     

Amino Acids Content in Germinating Seeds and Seedlings from Castanea sativa L

During germination the chestnut (Castanea sativa L.) var ecotype 33 accumulates a large amount of asparagine in the cotyledons. This compound also accumulates in the growing axis:shoots and roots. In the cotyledons, γ-aminobutyrate (GABA) represents a major amino compound during germination and early seedling growth. In young seedlings, 35 days old, arginine predominates over the other soluble amino acids, particularly in roots. Five enzymic activities involved in arginine and GABA have been measured in the storage organ of the seed: arginase and ornithine carbamyltransferase decrease during germination indicating the slowing down of the urea cycle. In contrast, ornithine aminotransferase increases. Glutamate decarboxylase is particularly active about 21 days after imbibition and GABA aminotransferase activity decreases during germination. These two activities are in good agreement with the likely transport of GABA from cotyledons to growing axis. Asparagine, arginine, and GABA are the three amino compounds obviously involved in the mobilization of nitrogen reserves in the germinating chestnut seeds Castanea sativa.     

Utilization of Seed Reserves and Currently Produced Photosynthates by Embryonic Tissues of Pine Seedlings

The importance of seed reserves for growth of Pinus resinosaAit. during and shortly after seed germination was studied undercontrolled conditions. Tissues in the resting embryo were notcompletely differentiated. Many small, presumably reserve particleswere present in the embryo in addition to reserves in the megagametophyte.During seed germination, procambia in the embryo first differentiatedprotophloem 2 days after seeds were sown. The radicle beganto emerge from the seed coat at 5 days, at which time initialxylem formation was observed. Also, at approximately the sametime, primordia of primary needles were forming in the peripheralzone of the apex. Elements of the photosynthetic apparatus,including stomata and mesophyll with chloroplasts, were differentiatedfirst in the hypocotyl and then in cotyledons between 5 and8 days after seeds were sown. Photosynthetic rates of youngseedlings were correlated with rates of cotyledon expansion.During early developmental stages, reserve particles in megagametophytecells and embryo cells gradually disappeared. Surgical removalof megagametophytes at various stages of seed germination resultedin subsequent growth inhibition of the hypocotyl-radicle axis,with early removal of cotyledons suppressing most growth. Growthof primary needles appeared to be influenced indirectly by megagametophytereserves, probably by changes in amount of photosynthetic tissue.The embryo alone possessed capacity to differentiate such tissuesas primary needle primordia, stomata, and primary and secondaryvascular systems. Megagametophyte reserves appeared to contributeto growth of embryonic tissues only after the embryo itselfinitiated growth. Both current photosynthesis of seedlings andseed reserves contributed importantly to seedling development.     

桃儿七种子解剖结构及其萌发生长期形态特征

为探明种皮和胚乳是否是限制桃儿七种子萌发的主要因素,利用组织切片和显微技术,对桃儿七种子及其不同萌发期（1、7、14、21、28 d）解剖结构和播种后一定时期内（7~210 d）的植株生长形态进行观察。桃儿七种子由种皮、胚乳和胚构成。种皮包括外种皮和内种皮,外种皮致密规整,由外至内分别为栅状石细胞和表皮层细胞,内种皮由5~6层海绵细胞组成。胚乳占种子体积的绝大部分,包括珠孔胚乳和外胚乳。胚由胚根、胚轴和子叶组成,被致密种皮、多层珠孔胚乳和外胚乳包围。萌发期1~7 d胚根和胚轴开始伸长,7~14 d两片子叶分离,14~21 d胚根突破珠孔胚乳和种皮,21~28 d胚根、胚轴和子叶继续扩张伸长。种子播种210 d后可平均形成3片功能真叶和5条不定根。致密种皮（物理休眠）和多层胚乳（机械休眠）是限制桃儿七种子萌发的两个主要因素。     

Studies on Desiccation and Storage of Mango Seeds

Mango (Mangifera indica L.) seed is recalitrant which taken from ripened fruits con,ained as high as 69.2'–75.5% moisture content (The moisture content of embryonic axis is 73.8–86.3%). When seeds were naturally dried for 8 days, the moisture content declined to 39.1% (in embryonic axis the moisture content declined to 46.5%) and the viability of seeds completely lost. Embryonic axis lost water slower than whole seed because of the prevention of desiccation by the large cotyledons. During natural desiccation, the conductivity of leachate increased rapidly from 2.2 μΩ·cm-1·g-1 (the same unit below) to 56.7, whereas the activities of dehydrogenase and acid phosphatase decreased drastically. When seeds were rapidly dried for 42 hours, the moisture content declined from 75.5 to 29.9%, the conductivity of leachate increased from 1.8 to 36.9 and the percentage germination changed from 100% to 10%. Desiccation damaged the cell membrane and decreased the activities of enzymes. Rapid drying was better for maintaining longevity than natural (slow) drying because the former did less damage to the cell membrane than natural (slow) drying as shown in the conductivity changes. The moisture content of excised embryonic axis decreased to 11.8% when they were dried for 8 hours by silicagel. The survival percentage of these embryonic axis was 80% when they were incubated in MS+0.2 mg/L BA+2.0 mg/L NAA+500 mg/L gln+3% sucrose+0–9% agar medium. Seeds with 51.0% moisture content (rapidly dried for l0 hours by electric fan blowing) had 65% viability after 7 months wet storage with the polyethylene bag at 15℃.     

Comparison of globulin mobilization and cysteine proteinases in embryonic axes and cotyledons during germination and seedling growth of vetch (Vicia sativa L.)

Vicilin and legumin, the storage globulins of mature dry vetch (Vicia sativa L.) seeds, are found in protein bodies which are present not only in the cotyledons, but also in the radicle, axis and shoot (together, for reasons of simplicity, here called axis). When at 24 h after the start of imbibition (hai) the radicle breaks through the seed coat a major part of the globulins in the axis has already been degraded, whereas in the cotyledons globulin breakdown cannot yet be detected. Globulin mobilization starts with the degradation of vicilin. At 48 hai when globulin mobilization in the cotyledons just begins, the axis is already nearly depleted of globulins. Mobilization of storage globulin is probably brought about by a complex of different cysteine proteinases (CPRs). The papain-like CPR2 and CPR4, and the legumain-like VsPB2, together with their mRNAs, are already present in axes and cotyledons of dry seeds. This means that they must have been formed during seed maturation. Additional papain-like CPRs are formed later during germination and seedling growth. CPR4 and VsPB2 together with their corresponding mRNAs become undetectable as germination and seedling growth proceed. VsPB2 and VsPB2-mRNA are substituted by the homologous legumain-like proteinase B and its mRNA. The composition of stored and newly formed CPRs undergoes developmental changes which differ between axes and cotyledons. It is concluded that storage globulin mobilization in germinating vetch seeds is started by stored CPRs, whereas the mobilization of the bulk of globulin is predominantly mediated by CPRs which are formed de novo.     

Spatially regulated genes expressed during seed germination and postgerminative development are activated during embryogeny

Summary We investigated the control of genes expressed primarily during seed germination and postgerminative development in Brassica napus L. We identified cloned mRNA sequences which became prevalent within 1 day after the start of imbibition and were at low or undetectable levels in immature embryos, dry seeds, and leaves. Most postgermination-abundant mRNAs accumulated primarily, though not exclusively, in different parts of the seedling. Of the 14 cloned mRNAs, 8 were prevalent in cotyledons, 2 were abundant in seedling axes, and 4 were approximately equally distributed in both parts. We showed that although these mRNAs reached maximal levels in seedlings, the spatially regulated mRNAs were also detected at distinct embryonic stages; mRNAs prevalent in seedling axes accumulated primarily during early embryogenesis while cotyledon-abundant mRNA concentration increased during late embryogeny. We conclude that the temporal and spatial regulation of gene expression in seedlings reflects similarities and differences in the physiological functions of cotyledons and axes. Furthermore, the regulated expression of cotyledon-abundant genes during late embryogeny suggests that the mRNAs and possibly proteins may accumulate in preparation for subsequent seedling growth. Similarities in the accumulation of cotyledon-abundant mRNAs may indicate coordinate regulation of this gene set.Abbreviations DAF days after flowering - DAI days after the start of imbibition - HAI hours after the start of imbibition - kb kilobase(pairs)     

The Effect of Low Temperature during Imbibition on Germination Characteristics of Tetracentron sinense (Tetracentraceae) Seeds

In this paper, the effects of low temperature, soil moisture and freezing time on the germination of Tetracentron sinense Oliv. seeds were studied by simulating wild environment conditions, and the factors influencing the natural regeneration of Tsinense population were discussed. The results are as follows: (1) The imbibition process of Tsinense seed can be divided into four stages, the water absorbing capacity of Tsinense seed after imbibition would increase with the increase of soil moisture, and the seeds would be fully imbibed under the condition of 30% soil moisture; (2) The germination rate, germination force and water content of Tsinense seed increased with the increase of storage time, and the vigor index gradually decreased after increasing before; (3) At different low temperature, the germination rate of Tsinense seed reached the highest when the soil moisture is 20% or 30%; (4) When treated at 20% soil moisture for 2-4 days or 21-28 days, 0℃ is best for the germination rate of Tsinense seed; when treated at 30% soil moisture for 14-28 days, -7℃ is best fort he germination rate of Tsinense seed; (5) When treated at the same condition of freezing time, the germination rate of seeds in fallen leaves had no significant difference with the decrease of low temperature; under the same condition of low temperature (0℃ low temperature except), the germination rate increased after frozen 28 days. The results showed that there is no significant influence of low temperature during imbibition on germination characteristics of Tetracentron sinense seeds and indicating that low temperature during imbibition is not the main factor influencing the natural regeneration of Tsinense population.     

Protein Synthesis During Rehydration, Germination and Seedling Growth of Naturally and Precociously Matured Soybean Seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo andaccumulate several non-storage, soluble polypeptides duringnatural and precocious seed maturation. These polypeptides havepreviously been coined ‘maturation polypeptides’.The objective of this study was to determine the fate of maturationpolypeptides in naturally and precociously matured soybean seedsduring rehydration, germination, and seedling growth. Developingsoybean seeds harvested 35 d after flowering (mid-development)were precociously matured through controlled dehydration, whereasnaturally matured soybean seeds were harvested directly fromthe plant. Seeds were rehydrated with water for various timesbetween 5 and 120 h. Total soluble proteins and proteins radio-labelledin vivo were extracted from the cotyledons and embryonic axesof precociously and naturally matured and rehydrated seed tissuesand analyzed by one-dimensional PAGE and fluorography. The resultsindicated that three of the maturation polypeptides (21, 31and 128 kDa) that had accumulated in the maturing seeds (maturationpolypeptides) continued to be synthesized during early stagesof seed rehydration and germination (5–30 h after imbibition).However, the progression from seed germination into seedlinggrowth (between 30 and 72 h after imbibition) was marked bythe cessation of synthesis of the maturation polypeptides followedby the hydrolysis of storage polypeptides that had been synthesizedand accumulated during seed development. This implied a drasticredirection in seed metabolism for the precociously maturedseeds as these seeds, if not matured early, would have continuedto synthesize storage protein reserves. Glycine max (L.) Merr, soybean, cotyledons, maturation, germination/seedling growth     

A study of seed lots of peas (Pisum sativum L.) differing in predisposition to pre-emergence mortality in soil

In three seed lots the condition of the cotyledons was found to be important in denning seeds predisposed to pre-emergence mortality. Such seeds readily exuded materials into seed-steep water, were rapidly infected by Pythium spp. and showed intensely stained cotyledons after being in solutions of tetrazolium chloride. In soil, infection of the cotyledons was found to occur before infection of the seedling axis and occurred in normal seed if disks of cotyledon material were placed in the soil next to the seed.
It is suggested that cotyledons influence predisposition by either increasing exudation around the seed and stimulating the fungal pathogen or by acting as a food base for the fungal hyphae which infect and kill the seedling axis.     

Tolerance of coffee (Coffea spp.) seeds to ultra-low temperature exposure in relation to calorimetric properties of tissue water, lipid composition, and cooling procedure

The effect of exposure to ultra-low temperature (liquid nitrogen, LN) on viability of seeds desiccated to various water contents was investigated in 9 coffee species. Three groups of species could be distinguished based on seed survival after LN exposure. In group 1 species, no seedling production could be obtained after LN exposure due to endosperm injury. In group 2 species, recovery was very low or nil after rapid cooling, and only moderate after slow cooling. In group 3 species, very high percentages of seedling development were observed after both rapid and slow cooling. A high interspecific variability for the high moisture freezing limit was observed within the species of groups 2 and 3, since it ranged from 0.14 to 0.26 g H₂O g⁻¹ dry weight. A very highly significant correlation was found for those species between the unfreezable water content, as determined from DSC analysis, and the high moisture freezing limit of their seeds. No significant correlation was found between seed lipid content, which varied from 9.8 to 34.6% dry weight, and survival after LN exposure. However, a negative relationship was found between seed unfreezable water content and lipid content. Interspecific differences in fatty acid composition of seed lipids resulted in a high variability in the percentage of unsaturated fatty acids, which ranged from 28.7 to 54.4% among the 9 species studied. For all species studied, a highly significant correlation was found between the percentage of unsaturated fatty acids and the percentage of seedling recovery after rapid or slow cooling.