The Significance of the Obturator in the Control of Pollen Tube Entry into the Ovary in Peach (Prunus persica)

Changes in the obturator of the peach (Prunus persica) havebeen investigated and related to pollen tube growth in thisregion. At anthesis, the cells of the obturator are active andrich in starch reserves. Twelve days after anthesis these cellsproduce a secretion that stains for carbohydrates and for proteins.As the secretion is produced, starch vanishes from these cellsand they degenerate and collapse as callose is accumulated.Secretion is independent of pollination as it takes place ina similar fashion both in pollinated and in unpollinated flowers. Pollen tube growth along the obturator surface depends on thissecretion for, although pollen tubes reach the base of the styleseven days after pollination, they cannot grow on the obturatoruntil five days later, when the secretion is produced. Thisdiscontinuous secretion taking place at the obturator may providea mechanism that controls the entrance of pollen tubes intothe ovary in the peach. Prunus persica, peach, obturator, pollen tube     

Tomato pollen tube development and carbohydrate fluctuations in the autotrophic phase of growth

Ripe pollen has different soluble and insoluble carbohydrates in variable amounts. Pollen germination and pollen tube growth were studied in a tomato cultivar (Solanum lycopersicum L. cv. Platense) with atypical pollen among tomatoes due to its very low amount or absence of sucrose. In vitro assays were performed using a culture medium without carbohydrates to explore whether there is an autotrophic phase of pollen tube growth, and if there is, describe it, and to analyze the fluctuations of endogenous carbohydrates (soluble carbohydrates, starch, pectins, and callose). Pollen germination was fast (ca. 10 min) and a definite autotrophic phase was observed. Soluble carbohydrates and pectins showed the most substantial changes during this period, even after 10 min. A small amount of callose was observed in the ripe pollen and pollen tubes. Pectins were the most abundant pollen tube wall component. Pollen can be considered starchless; starch was not involved in the autotrophic phase of growth. Other types of substances must be connected with the carbohydrate metabolism, because the fluctuations of the different substances did not follow balanced stoichiometric relationships. Pollen germination and pollen tube elongation was sustained autotrophically, even though sucrose was absent and starch was negligible in pollen grains. The type of pollen reserves and the fast pollen tube formation could be selective advantages in this cultivar.     

Effect of Salt Stress on Viability, Germination and Endogenous Levels of Some Metabolites and Ions in Maize (Zea mays L.) Pollen

Maize plants, subjected to 0, 80, 120 and 160 meq l^–1salinity using NaCl, showed adverse effects on viability, germinationand tube growth of pollen, besides enhancing the bursting ofpollen. The endogenous levels of various metabolites in pollenwere also affected. Pollen grains from salinized plants hadmore soluble carbohydrates, free amino acids, especially proline,phenols and DNA and less starch, protein and RNA compared tothe non-saline controls. Salinity also resulted in the accumulationof ions such as Na⁺, K⁺ and Cl^– while it caused a reductionin the boron content of pollen. These metabolic disturbancespossibly lead to decreased viability, germination and tube growthof pollen thereby resulting into a reduction in reproductivecapacity of the plants under salt stress. Zea mays L., maize, pollen, viability, germination, salt stress     

Seasonal Variations in the Carbohydrates in the Xylem of Antiaris africana

The xylem of Antiaris africana contains sucrose, starch, glucose,fructose, maltose, and raffinose. Sucrose and starch are themost abundant carbohydrates. Glucose and fructose occur in relativelyequal amounts while maltose and raffinose are the least abundant.Raffinose disappears from the xylem during the dry season, justbefore leaf fall. The pattern of seasonal variation in the individualsugars and starch is similar. There is generally a peak at leaffall and a depletion of these reserves at new flush. Accumulationof carbohydrates during leaf fall occurs first in the youngestxylem (i.e. the 0–2-cm segment). The youngest xylem alsoaccumulates the greatest amount of reserve sugars and starch.The concentrations of the sugars decrease inwards until theybegin to rise after the 4–6-cm segment. There is, however,no such rise in the concentration of starch. The dry-mattercontents increase inwards from the youngest xylem until theylevel out after the 4–6-cm segment. There is a rapid fallin the sucrose and starch contents of felled A. africana. Sucrosedropped by about 65 per cent and starch by about 73 per centin the first 10 days after felling. The levels of other sugarsdecreased gradually except for glucose and fructose which initiallyrose and then fell. Glucose and maltose could still be detectedon the 68th day after felling.     

Occurrence of mono- or disaccharides and polysaccharide reserves in mature pollen grains

 Pollen from 13 species of gymnosperms and angiosperms was studied for soluble and insoluble carbohydrates at dispersal. Starch reserves stored during pollen development give rise to carbohydrates at maturity. Combinations of different types of carbohydrates in mature pollen may depend on the extent of starch hydrolysis. An inverse relationship was found between the extent of starch hydrolysis and sucrose content. If the starch was scarcely de-polymerized, the cytoplasm had very low levels of soluble sugars and none of the periodic acid-Schiff (PAS)-positive material as found in pollen not subject to high dehydration (Cucurbita pepo L., Zea mays L.). After total or partial starch hydrolysis, insoluble PAS-positive oligo/polysaccharides were found in the cytoplasm associated with much soluble sugar, and the pollen grains were dehydrated at dispersal as in Typha latifolia L., Chamaerops humilis L., Trachycarpus excelsa Wendl., and other specimens. Intermediate levels of starch and soluble sugars, together with cytoplasmic PAS-positive material, characterized species with dehydrated pollen such as Pinus halepensis Miller. Carbohydrates may be related to pollen longevity, which largely depends on the abundance of sucrose, which is known to protect membrane integrity. The relationship between PAS-positive material and pollen viability is unclear at present. Received: 30 July 1996 / Revision accepted: 18 December 1996     

Ultrastructural Modifications of Plastids and Starch Metabolism during the Microsporogenesis of Ophrys lutea (Orchidaceae)

Ultrastructure of plastids has been studied throughout microsporogenesisof Ophrys lutea Cav. (Orchidaceae). A typical dedifferentiation/redifferentiationcycle of plastids was observed. At prophase I, plastids of pre-meiocytesgradually lost starch and separated the meiocytes through cytomicticchannels. At meiosis, plastids dedifferentiated to protoplastsand redifferentiated in young microspores. During pollen grainformation and maturation a cycle of starch accumulation/degradationoccurred; the mature pollen grain is starchless. Results arediscussed in terms of genetic inheritance following haploidnuclear state and in terms of carbohydrate metabolism. Plastids, starch, microsporogenesis, ultrastructure, Ophrys lutea, Orchidaceae     

Types and meaning of pollen carbohydrate reserves

During pollen development, soluble carbohydrates of sporophytic origin may be consumed immediately, polymerized to form starch reserves or intine, or transformed into other molecules. Disregarding intine, in mature pollen there are three different types of carbohydrates: (1) polysaccharides such as starch in amyloplasts or polysaccharides in cytoplasmic vesicles, (2) disaccharides such as sucrose and (3) monosaccharides such as glucose and fructose. At dispersal, pollen may be partly or slightly dehydrated, or not dehydrated at all. Partly dehydrated pollen has the capacity to lose or acquire water within limits without detriment to its viability. Slightly and non-dehydrated pollen is vulnerable to water loss and quickly becomes inviable. In partly dehydrated of pollen the carbohydrates consist of cytoplasmic polysacharides and sucrose; in slightly and non-dehydrated pollen these are absent or in low concentrations but there may be reserves of cytoplasmic callose. Starch, glucose and fructose are found in both types. It is postulated that cytoplasmic carbohydrates and sucrose are involved in protecting pollen viability during exposure and dispersal.     

Genotypic Differences in the Production and Partitioning of Carbohydrates Between Roots and Shoots of Wheat Grown under Zinc or Manganese Deficiency

The partitioning of soluble carbohydrates and starch betweenroots and shoots was investigated in wheat genotypes differingin Zn or Mn efficiency. The plants were grown for 11 d in achelate-buffered nutrient solution with sufficient or deficientZn and Mn supply. The Zn-efficient cultivar Warigal had a greatershoot fresh weight under sufficient Zn compared with the Zn-inefficientcultivar Durati. When supplied with sufficient Zn, Warigal hada greater concentration and content of soluble carbohydratesin roots and shoots in comparison with Durati. Under deficientZn supply, Durati had a greater concentration and content ofstarch in roots and shoots compared with Warigal. In an experimentwith varying supply of Mn, the Mn-efficient genotype C8MM hada greater shoot fresh weight than the Mn-inefficient cultivarBayonet under sufficient or deficient Mn supply. The concentrationof soluble carbohydrates in roots and shoots was decreased bydeficient Mn supply in C8MM but not in Bayonet. Starch accumulatedin the roots of Bayonet under deficient Mn supply. The resultssuggest that synthesis of carbohydrates is decreased under Zndeficiency, while they are preferentially partitioned to theroots to increase growth and thus the surface area availablefor Zn uptake. In the case of Mn deficiency, carbohydrate productionwas limited, but partitioning between roots and shoots was notaltered.Copyright 1997 Annals of Botany Company Carbohydrate; deficiency; manganese; assimilate partitioning; starch; Triticum aestivum; zinc     

Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Pollen of the palm Trachycarpus fortunei was kept at 25°C and relative humidities (RH) of 20, 55 and 98%. Changes in viability, water content and carbohydrates were measured over 2–17 days. Water content remained almost constant at 20 and 50% RH and increased dramatically at 98%. Pollen viability and germination rate remained almost constant over 14 days at 20% RH and decreased to about 2% after 7–9 days at 55% and to even less at 98% RH. Although the three experimental conditions were constant, qualitative and quantitative variations in pollen carbohydrates were recorded, even after pollen had lost its viability. The quantities of mono-, di- and polysaccharides varied with the period of pollen storage at the various RH. The greatest changes in glucose, fructose and sucrose content were recorded at 55 and 98% RH. At these relative humidities, maximum glucose and fructose content and minimum sucrose content occurred at maximum water content. Starch was not present in mature pollen but appeared and peaked after 7–9 days of pollen storage at 55 and 98%. Appearance of starch coincided with an increase in pectin content. PAS-positive cytoplasmic polysaccharides showed an increasing trend at 20% RH. A relation was found between pollen viability, water content and monosaccharide content. Pollen viability and germination capacity remained high at 20% RH for 14 days. At this relative humidity, pollen water, glucose and fructose contents remained almost constant, while sucrose reached its maximum value. The fluctuations of more complex carbohydrates (starch, pectins and PAS-positive cytoplasmic polysaccharides) were less easy to interpret. Changes observed under experimental conditions could simulate processes occurring in nature during pollen presentation and dispersal.     

Seasonal Changes of the Metabolites in the Leaves, Bark and Xylem Tissues of Olive Tree (Olea europaea. L) II. Carbohydrates

Seasonal changes of starch and soluble carbohydrates in leaves,bark and xylem tissues of olive tree were examined during acomplete annual cycle. Leaf starch and soluble carbohydrateswere detected at high levels during the spring and autumn metabolicallyactive periods. The low level of leaf starch in combinationwith the drastic reduction of soluble carbohydrates and mannitol,defined the summer period of the low metabolic state of thetree. The low leaf starch level in conjunction with the risensoluble carbohydrate levels in leaves in winter were associatedwith cold acclimation processes. The bark and xylem tissueswere performing as starch deposition sites, and differencesin the extent of starch accumulation in these tissues were detectedduring the seasons. The starch fluctuations in bark and xylemwere discussed in relation to the translocation of metabolitesand other physiological processes. Mannitol, the most abundantleaf carbohydrate, was examined in relation to the reducingsugars exported to the bark. The bark mannitol was examinedin conjunction with the sucrose, glucose and starch levels inthe maturing bark tissues and was correlated to the low wintertemperatures. During the winter there was a drastic reductionof mannitol circulation from the bark to xylem. Olive tree, Olea europaea, L, carbohydrates     

Changes in cytoplasmic carbohydrate content during Helleborus pollen presentation

Pollen grains of Helleborus foetidus and H. bocconei were exposed to low temperature treatments to simulate the natural events in pollen presentation of these two winter flowering species and to analyze the pollen carbohydrate content (glucose, fructose, sucrose and starch). In both species, cytoplasmic polysaccharides, monosaccharides and sucrose were found, while only Helleborus foetidus contained starch. Polysaccharide, sucrose and monosaccharide content varied as low temperature exposure time varied, a decrease in temperature decreases polysaccharide content and increases sucrose and monosaccharides. The relative quantities of the various types of carbohydrates were not affected by variations in the naturally occurring thermal cycles. Treatments did not greatly affect pollen viability. Although the occurrence of carbohydrates in pollen is known since many years, their function is still unclear. The findings of this research suggest a role of cytoplasmic pollen carbohydrates in resistance to low temperature exposure. The inter-conversion of carbohydrate type may be an adaptation for sustaining viability during pollen presentation that is particularly important for a winter flowering species such as Helleborus foetidus and H. bocconei .     

Studies on the Initial Biochemical Reactions in the Germination of Pollen Grains

Tritiated water (³HHO) has been used as the medium for the germinationof pollen grains of Pinus radiata D.Don (a gymnosperm), Ulexeuropaeus L., Salix caprea L. (dicotyledonous angiosperms),and Phormium tenax Forst. (a monocotyledonous angiosperm). ³H-labelledcompounds formed during the initial germination (egersis) periodhave been separated and identified to give information on themetabolism taking place.Since the earliest labelled compoundswere -aminobutyric acid, alanine, aspartic acid, and glutamicacid, it is concluded that these amino acids play an importantpart in the biochemical reactions during the early stages ofgermination. Citric acid, malic acid, and glutamine do not becomelabelled until later while carbohydrates, phosphate esters,and lipids do not appear to incorporate tritium within the firsthour of germination.The gross labelling pattern and the natureof the individually labelled metabolites, their intensity andsequence of labelling are similar for all the species investigatedexcept gorse, which showed a decrease in the intensity and thenumber of labelled metabolites with time.P. radiata pollen storedfor 3 years under vacuum or carbon dioxide has a labelling patternsimilar to freshly collected P. radiata pollen, except for aconsiderable increase in the amount of an unknown metabolite(Compound X).     

Etiolated Growth as Measure of Non-structural Biomass in Lucerne Taproots

Enzymatic hydrolysis of starch in lucerne (Medicago sativa L.)taproots is the conventional method used to determine the quantityof carbohydrates allocated to regrowth. Etiolated growth froma taproot could be used to quantify total root biomass allocatedto regrowth. This study compared concentrations of non-structuralcarbohydrates, as measured by -amylase hydrolysis of starchto glucose, to concentrations of non-structural biomass, asmeasured by etiolated growth from lucerne taproots placed inan incubator and plants in situ. The concentration of starchfrom enzymatically assayed taproots was 325 g kg^-1 expressedas glucose equivalents. Etiolated growth and weight loss byrespiration from plants grown in the incubator accounted for524 g of actual biomass per kg of root. There was 46·2g kg^-1 of N, 3·1 of P, and 33·1 of K in the etiolatedgrowth. An 88% increase in etiolated growth dry weight was observedfrom plants in situ compared to taproots placed in the incubator.Accurate quantification on non-structural biomass should notbe limited to sampling just the taproot, but must included theentire root system. Compared to determining non-structural carbohydratesby enzymatic hydrolysis of starch, the procedure used in determiningnon-structural biomass by etiolate growth gave results in unitsrelative to the plant. The use of etiolate growth also providedinformation on mineral nutrient partitioning from root to shoots,was less technically demanding, and could be applied to theentire root system.Copyright 1993, 1999 Academic Press Medicago sativa, root carbohydrates, etiolated growth, taproot     

The Development of Tomato Root System in Relation to the Carbohydrate Status of the Whole Plant

The decrease in growth rate of the root system or complete cessationof its growth in developed, fruit-bearing tomato plants areknown phenomena. It has been suggested that a limited supplyof carbohydrates to this organ, due to its relative weaknessin competition with the flowers and developing fruitlets isthe main cause for these disorders. This theory was tested inthe present study with plants grown in an aerohydroponic systemup to the appearance of 12–13 trusses per plant, 172 dafter transplanting. The changes in the contents of carbohydratesin the various organs during this period were monitored. Theconcentrations of soluble sugars and starch in the leaves increasedwith the increase in truss number. The upper stem was foundto contain more carbohydrates than the lower stem, while nosignificant changes in the concentration of these compoundscould be detected in the roots throughout the experiment. Nevertheless,120–130 d after transplanting, the roots of the plants,bearing five to six trusses and two to three inflorescences,ceased growing and remained at the same or a slightly reducedsize for another 40–50 d. Calculations show that at thestage of five to six trusses, 38 g total soluble sugars and35 g starch were stored in the vegetative organs. Therefore,it seems unlikely that carbon deficiency caused by the competitionwith the reproductive organs (mainly developing fruits), affectedthe root growth. Instead, it is suggested that some other factoris responsible. Lycopersicon esculentumMill; carbohydrates; root growth rate; sink-source relationship; soluble sugars; starch     

Pollen starch reserves in tomato relatives: Ecophysiological implications

The presence or absence of starch in microspore development and in pollen grains was recorded in eleven wild tomato species (Solanum sect. Lycopersicon) and two close relatives (S. lycopersicoides and S. sitiens). In all the species starch started to accumulate in the early microspore bicellular stage and continued until the cytoplasm was filled. At flower anthesis, pollen grains were mostly starchless in the wild tomatoes, except in S. pennellii, which had starchy pollen. Starchy pollen is also present in the two related species. The latter two species had larger pollen grains and grow in drier environments than the other species. The heterogeneity of pollen starch content among all these species, supposed to have the same pollination mechanism, is a new finding supporting the idea that starch content and pollination mechanism do not necessarily influence each other. The presence of starchy pollen in the self‐incompatible species, which grow in the driest environments, raises questions regarding the relationship between carbohydrates content and pollen survival.     

Utilization of Exogenous Carbohydrates for Tube Growth and Starch Synthesis in Pine Pollen Suspension Cultures

Pine pollen (Pinus mugo) grown in suspension cultures readily utilize exogenous carbohydrates for tube growth and starch synthesis: these processes are not influenced by β-indolylacetic acid, gibberellic acid, kinetin and abscisic acid. It appears that the free sugars of the female gametophyte, namely sucrose, raffinose, and stachyose and their monosaccharide constituents, are the best substrates for growth and polysaccharide synthesis. The oligosaccharides are hydrolysed to their monosaccharide constituents before they are taken up. A preferential uptake of fructose is noted. Non-metabolizable sugars are not taken up. The data presented establish that tube growth, except for the initial growth phase, can be determined by the availability of exogenous carbohydrates. Measurements of some of the key enzymes in carbohydrate metabolism show that the enzymes were present in the ungerminated pollen grain, and that the enzyme activity increased severalfold during tube growth. The increase in enzyme activity was prevented if inhibitors of protein synthesis were present in the medium.     

Changes of Starch and Sorbitol in Leaves Before and After Removal of Fruits from Peach Trees

Changes in contents of nonstructural carbohydrates in leaves,as well as some characteristics of leaves before and after fruitremoval, were investigated in potted peach (Prunus persica L.)trees. Leaf area and dry mass per unit leaf area (SLW) at thefruit-maturation stage decreased with increasing numbers ofpeaches per tree, whereas the chlorophyll content per unit areain leaves of fruiting trees increased. The chlorophyll contentdecreased more rapidly upon removal of fruit than that in leavesof fruiting trees. The starch content per unit dry mass in leavesof fruiting trees at the fruit-maturation stage was lower thanthat in leaves of non-fruiting trees. Starch accumulated significantlyin leaves within 1 d of removal of fruit during the fruit-maturationstage and continued to increase thereafter. The accumulationof starch after removal of fruit occurred more rapidly thanthe decrease in chlorophyll content. Reducing and non-reducingsugars (total sugars) per unit dry mass in the leaves were higherin fruiting trees than in non-fruiting trees. After fruit removal,the total sugar content of leaves increased temporarily andthen gradually decreased. The sorbitol content per unit freshmass in leaves of fruiting trees during the fruit-maturationstage was slightly higher than that in leaves of non-fruitingtrees. One day after removal of fruit, the sorbitol contentincreased in parallel with the accumulation of starch and remainedhigh. The sucrose content of leaves did not change markedlyupon removal of fruit. Prunus persica L.; peach leaves; nonstructural carbohydrate; starch and sorbitol; fruit removal     

Do Sprouting Tree Species on Erosion-prone Sites Carry Large Reserves of Resources?

Saplings ofEuptelea polyandra were studied to determine whethertree species found on unstable hillslopes of temperate, old-growthforests in Japan carry substantial storage materials for sproutingreplacement genets, as is the case with resprouter species offire-prone areas. Concentrations (% d. wt basis) of carbohydrates(starch, sucrose, glucose and fructose) contained in roots,stems and leaves were measured in summer and winter.E. polyandrasaplings were compared with those ofQuercus serrata (a frequentlysprouting tree), and those ofMallotus japonicus andIdesia polycarpa(rarely sprouting trees) in the same forest. Total concentrationsof carbohydrates (the sum of starch, sucrose, glucose and fructose)in roots were lowest inE. polyandra in both summer and winter.In addition,E. polyandra had a lower ratio of root biomass tototal plant biomass thanQ. serrata , but similar to that ofthe non-sprouting species,M. japonicus andI. polycarpa . Onthe other hand, the total concentration of carbohydrates inthe above-ground parts were similar in the four species in bothsummer and winter. These results indicate thatE. polyandra hadless long-term storage resources to implement sprouting, inspite of its apparent effectiveness in sprouting. We proposehypotheses to explain the reason whyE. polyandra stores a relativelysmall amount of resources for sprouting. Carbohydrate concentration; Euptelea polyandra Sieb. et Zacc; ground-surface disturbance; Idesia polycarpa Maxim; Mallotus japonicus (Thunb.) Muell. Arg.; Quercus serrata Thunb.; resprouter; root dry weight ratio; soluble sugars; sprouting; starch     

Pollen-pistil interaction in kiwifruit (Actinidia deliciosa; Actinidiaceae)

The pollen-pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life-span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.     

Characteristics of the Photosynthetic Metabolism of Carbon in Deuterated Chlorella ellipsoidea C-27

The photosynthetic metabolism of carbon in fully deuteratedcells of Chlorella ellipsoidea C-27 (D-Chlorella), obtainedby culture in medium prepared with 100 mol% D₂O, was characterizedby examining the activities of several enzymes and the levelsof metabolic regulators in a comparison with those of ordinarycells (H-Chlorella). The cellular content of starch in D-Chlorellawas more than twice that in H-Chlorella, whereas those of sucroseand glucose were significantly lower in D-Chlorella. Deuterationof Chlorella caused marked alterations in the activities ofenzymes involved in starch metabolism. There was a significantdecrease in the activity of phosphorylase, a catabolic enzyme,and a significant increase in the activity of starch synthase,an anabolic enzyme. These alterations are probably responsiblefor the increase in the amount of starch in cells. By contrast,no marked changes were observed in the activities of enzymesand the levels of metabolic inhibitors that are involved inthe synthesis of sucrose. It seems likely, therefore, that thedecrease in the amount of sucrose in D-Chlorella was causedmainly by a deficiency in sources of carbon in the cytoplasm,as a consequence of an increase in levels of starch in chloroplasts. (Received May 13, 1992; Accepted December 1, 1992)