Fragment size does not matter when you are well connected: effects of fragmentation on fitness of coexisting gypsophiles

Most habitat fragmentation studies have focused on the effects of population size on reproductive success of single species, but studies assessing the effects of both fragment size and connectivity, and their interaction, on several coexisting species are rare. In this study, we selected 20 fragments along two continuous gradients of size and degree of isolation in a gypsum landscape in central Spain. In each fragment, we selected 15 individuals of each of three dominant gypsophiles (Centaurea hyssopifolia, Lepidium subulatum and Helianthemum squamatum, 300 plants per species, 900 plants in total) and measured several reproductive traits: inflorescence number, fruit set, seed set and seed mass. We hypothesised that plant fitness would be lower on small and isolated fragments due to an interaction between fragment size and connectivity, and that response patterns would be species-specific. Overall, fragment size had very little effect on reproductive traits compared to that of connectivity. We observed a positive effect of fragment connectivity on C. hyssopifolia fitness, mediated by the increased seed predation in plants from isolated fragments, resulting in fewer viable seeds per capitulum and lower seed set. Furthermore, seed mass was lower in plants from isolated fragments for both C. hyssopifolia and L. subulatum. In contrast, few reproductive traits of H. squamatum were affected by habitat fragmentation. We discuss the implications of species-specific responses to habitat fragmentation for the dynamics and conservation of gypsum plant communities. Our results highlight the complex interplay among plants and their mutualistic and antagonistic visitors, and reinforce the often-neglected role of habitat connectivity as a key component of the fragmentation process.

Physiology of pepper fruit and the metabolism of antioxidants: chloroplasts, mitochondria and peroxisomes

BACKGROUND AND AIMS

Pepper (Capsicum annuum) contains high levels of antioxidants, such as vitamins A and C and flavonoids. However, information on the role of these beneficial compounds in the physiology of pepper fruit remains scarce. Recent studies have shown that antioxidants in ripe pepper fruit play a key role in responses to temperature changes, and the redox state at the time of harvest affects the nutritional value for human consumption. In this paper, the role of antioxidant metabolism of pepper fruit during ripening and in the response to low temperature is addressed, paying particular attention to ascorbate, NADPH and the superoxide dismutase enzymatic system. The participation of chloroplasts, mitochondria and peroxisomes in the ripening process is also investigated.

SCOPE AND RESULTS

Important changes occur at a subcellular level during ripening of pepper fruit. Chloroplasts turn into chromoplasts, with drastic conversion of their metabolism, and the role of the ascorbate-glutathione cycle is essential. In mitochondria from red fruits, higher ascorbate peroxidase (APX) and Mn-SOD activities are involved in avoiding the accumulation of reactive oxygen species in these organelles during ripening. Peroxisomes, whose antioxidant capacity at fruit ripening is substantially affected, display an atypical metabolic pattern during this physiological stage. In spite of these differences observed in the antioxidative metabolism of mitochondria and peroxisomes, proteomic analysis of these organelles, carried out by 2-D electrophoresis and MALDI-TOF/TOF and provided here for the first time, reveals no changes between the antioxidant metabolism from immature (green) and ripe (red) fruits.

CONCLUSIONS

Taken together, the results show that investigation of molecular and enzymatic antioxidants from cell compartments, especially chloroplasts, mitochondria and peroxisomes, is a useful tool to study the physiology of pepper fruit, particularly in the context of expanding their shelf-life after harvest and in maintaining their nutritional value.

Bicolored display of Miconia albicans fruits: Evaluating visual and physiological functions of fruit colors

PREMISE OF THE STUDY

Most bird-dispersed fruits are green when unripe and become colored and conspicuous when ripe, signaling that fruits are ready to be consumed and dispersed. The color pattern for fruits of Miconia albicans (Melastomataceae), however, is the opposite, with reddish unripe and green ripe fruits. We (1) verified the maintenance over time of its bicolored display, (2) tested the communicative function of unripe fruits, (3) tested the photoprotective role of anthocyanins in unripe fruits, and (4) verified whether green ripe fruits can assimilate carbon.

METHODS

Using a paired experiment, we tested whether detection of ripe fruits was higher on infructescences with unripe and ripe fruits compared with infructescences with only ripe fruits. We also measured and compared gas exchange, chlorophyll a fluorescence, and heat dissipation of covered (to prevent anthocyanin synthesis) and uncovered ripe and unripe fruits.

KEY RESULTS

Although the bicolored display was maintained over time, unripe fruits had no influence on bird detection and removal of ripe fruits. Ripe and unripe fruits did not assimilate CO2, but they respired instead.

CONCLUSIONS

Since the communicative function of unripe fruits was not confirmed, seed dispersers are unlikely to select the display with bicolored fruits. Because of the absence of photosynthetic activity in ripe and unripe fruits and enhanced photoprotective mechanisms in ripe fruits rather than in unripe fruits, we could not confirm the photoprotective role of anthocyanins in unripe fruits. As an alternative hypothesis, we suggest that the bicolored fruit display could be an adaptation to diversify seed dispersal vectors instead of restricting dispersal to birds and that anthocyanins in unripe fruits may have a defense role against pathogens.

Roles of Ethylene Production and Ethylene Receptor Expression in Regulating Apple Fruitlet Abscission

Apple (Malus × domestica) is increasingly being considered an interesting model species for studying early fruit development, during which an extremely relevant phenomenon, fruitlet abscission, may occur as a response to both endogenous and/or exogenous cues. Several studies were carried out shedding light on the main physiological and molecular events leading to the selective release of lateral fruitlets within a corymb, either occurring naturally or as a result of a thinning treatment. Several studies pointed out a clear association between a rise of ethylene biosynthetic levels in the fruitlet and its tendency to abscise. A direct mechanistic link, however, has not yet been established between this gaseous hormone and the generation of the abscission signal within the fruit. In this work, the role of ethylene during the very early stages of abscission induction was investigated in fruitlet populations with different abscission potentials due either to the natural correlative inhibitions determining the so-called physiological fruit drop or to a well-tested thinning treatment performed with the cytokinin benzyladenine. A crucial role was ascribed to the ratio between the ethylene produced by the cortex and the expression of ethylene receptor genes in the seed. This ratio would determine the final probability to abscise. A working model has been proposed consistent with the differential distribution of four receptor transcripts within the seed, which resembles a spatially progressive cell-specific immune-like mechanism evolved by apple to protect the embryo from harmful ethylene.

Tomato Glutamate Decarboxylase Genes SlGAD2 and SlGAD3 Play Key Roles in Regulating γ-Aminobutyric Acid Levels in Tomato (Solanum lycopersicum)

Tomato (Solanum lycopersicum) can accumulate relatively high levels of γ-aminobutyric acid (GABA) during fruit development. However, the molecular mechanism underlying GABA accumulation and its physiological function in tomato fruits remain elusive. We previously identified three tomato genes (SlGAD1, SlGAD2 and SlGAD3) encoding glutamate decarboxylase (GAD), likely the key enzyme for GABA biosynthesis in tomato fruits. In this study, we generated transgenic tomato plants in which each SlGAD was suppressed and those in which all three SlGADs were simultaneously suppressed. A significant decrease in GABA levels, i.e. 50-81% compared with wild-type (WT) levels, was observed in mature green (MG) fruits of the SlGAD2-suppressed lines, while a more drastic reduction (up to <10% of WT levels) was observed in the SlGAD3- and triple SlGAD-suppressed lines. These findings suggest that both SlGAD2 and SlGAD3 expression are crucial for GABA biosynthesis in tomato fruits. The importance of SlGAD3 expression was also confirmed by generating transgenic tomato plants that over-expressed SlGAD3. The MG and red fruits of the over-expressing transgenic lines contained higher levels of GABA (2.7- to 5.2-fold) than those of the WT. We also determined that strong down-regulation of the SlGADs had little effect on overall plant growth, fruit development or primary fruit metabolism under normal growth conditions.

New candidate genes for the fine regulation of the colour of grapes

In the last decade, great progress has been made in clarifying the main determinants of anthocyanin accumulation in grape berry skin. However, the molecular details of the fine variation among cultivars, which ultimately contributes to wine typicity, are still not completely understood. To shed light on this issue, the grapes of 170 F1 progeny from the cross 'Syrah'×'Pinot Noir' were characterized at the mature stage for the content of 15 anthocyanins during four growing seasons. This huge data set was used in combination with a dense genetic map to detect genomic regions controlling the anthocyanin pathway both at key enzymatic points and at particular branches. Genes putatively involved in fine tuning the global regulation of anthocyanin biosynthesis were identified by exploring the gene predictions in the QTL (quantitative trait locus) confidence intervals and their expression profile during berry development in offspring with contrasting anthocyanin accumulation. New information on some aspects which had scarcely been investigated so far, such as anthocyanin transport into the vacuole, or completely neglected, such as acylation, is provided. These genes represent a valuable resource in grapevine molecular-based breeding programmes to improve both fruit and wine quality and to tailor wine sensory properties according to consumer demand.

The making of giant pumpkins: how selective breeding changed the phloem of Cucurbita maxima from source to sink

Despite the success of breeding programmes focused on increasing fruit size, relatively little is known about the anatomical and physiological changes required to increase reproductive allocation. To address this gap in knowledge, we compared fruit/ovary anatomy, vascular structure and phloem transport of two varieties of giant pumpkins, and their smaller fruited progenitor under controlled environmental conditions. We also modelled carbon transport into the fruit of competitively grown plants using data collected in the field. There was no evidence that changes in leaf area or photosynthetic capacity impacted fruit size. Instead, giant varieties differed in their ovary morphology and contained more phloem on a cross-sectional area basis in their petioles and pedicels than the ancestral variety. These results suggest that sink activity is important in determining fruit size and that giant pumpkins have an enhanced capacity to transport carbon. The strong connection observed between carbon fixation, phloem structure and fruit growth in field-grown plants indicates that breeding for large fruit has led to changes throughout the carbon transport system that could have important implications for how we think about phloem transport velocity and carbon allocation.

Environmental Conditions Affect Botrytis cinerea Infection of Mature Grape Berries More Than the Strain or Transposon Genotype

Effects of environment, Botrytis cinerea strain, and their interaction on the infection of mature grape berries were investigated. The combined effect of temperature (T) of 15, 20, 25, and 30°C and relative humidity (RH) of 65, 80, 90, and 100% was studied by inoculating berries with mycelium plugs. Regardless of the T, no disease occurred at 65% RH, and both disease incidence and severity increased with increasing RH. The combined effect of T (5 to 30°C) and wetness duration (WD) of 3, 6, 12, 24, and 36 h was studied by inoculating berries with conidia. At WD of 36 h, disease incidence was approximately 75% of affected berries at 20 or 25°C, 50% at 15°C, and 30 to 20% at 30 and 10°C; no infection occurred at 5°C. Under favorable conditions (100% RH or 36 h of WD) and unfavorable conditions (65% RH or 3 h of WD), berry wounding did not significantly affect disease incidence; under moderately favorable conditions (80% RH or 6 to 12 h of WD), disease incidence was approximately 1.5 to 5 times higher in wounded than in intact berries. Our data collectively showed that (i) T and RH or WD were more important than strain for mature berry infection by either mycelium or conidia and (ii) the effect of the environment on the different strains was similar. Two equations were developed describing the combined effect of T and RH, or T and WD, on disease incidence following inoculation by mycelium (R2=0.99) or conidia (R2=0.96), respectively. These equations may be useful in the development of models used to predict and control Botrytis bunch rot during berry ripening.

Do Small Canopy Gaps Created by Japanese Black Bears Facilitate Fruiting of Fleshy-Fruited Plants?

Japanese black bears often break branches when climbing trees and feeding on fruit in canopies, thereby creating small canopy gaps. However, the role of black bear-created canopy gaps has not been evaluated in the context of multiple forest dynamics. Our hypothesis was that small canopy gaps created by black bears improve light conditions, which facilitates fruiting of adult fleshy-fruited plants located beneath the gaps, and also that this chain interaction depends on interactions among the size of gaps, improved light conditions, forest layers, and life form of plants. The rPPFD, size of black bear-created canopy gaps, and fruiting/non-fruiting of fleshy-fruited plants were investigated in five forest layers beneath black-bear-created canopy gaps and closed canopies of Mongolian oak (Quercus crispula). We found that light conditions improved beneath black bear-disturbed trees with canopy gaps of large size, and the effect of improvement of light conditions was reduced with descending forest layers. Fruiting of fleshy-fruited plants, especially woody lianas and trees, was facilitated by the improvement of light conditions accompanied by an increase in the size of black-bear-created gaps. Data from this study revealed that canopy disturbance by black bears was key for improving light conditions and accelerating fruiting of fleshy-fruited trees and woody lianas in the canopy layers in particular. Therefore, our hypothesis was mostly supported. Our results provide evidence that Japanese black bears have high potential as ecosystem engineers that increase the availability of resources (light and fruit in this study) to other species by causing physical state changes in biotic materials (branches of Q. crispula in this study).

Beneficial Effects of Ants and Spiders on the Reproductive Value of Eriotheca gracilipes (Malvaceae) in a Tropical Savanna

Predators affect plant fitness when they forage on them and reduce the action of herbivores. Our study evaluates the complementary effects of spiders and ants that visit the extrafloral nectaries of Eriotheca gracilipes (Malvaceae) on the production of fruits and viable seeds of these savanna trees. Four experimental groups were established: control group – with free access of spiders and ants; exclusion group – spiders and ants excluded; ant group – absence of spiders; and spider group – absence of ants. The presence of ants reduced the spider richness; however, the presence of spiders did not affect the ant richness. A significantly higher number of fruits per buds were found in the presence of spiders alone or spiders and ants together (control group) compared with the absence of both predators (exclusion group). The number of seeds per fruits and seed viability were higher in the control group. This is the first study showing that spiders and ants may exert a positive and complementary effect on the reproductive value of an extrafloral nectaried plant. Mostly the impact of ants and/or spiders on herbivores is considered, whereas our study reinforces the importance of evaluating the effect of multiple predators simultaneously, exploring how the interactions among predators with distinct skills may affect the herbivores and the plants on which they forage.

The Influence of Seasonal Frugivory on Nutrient and Energy Intake in Wild Western Gorillas

The daily energy requirements of animals are determined by a combination of physical and physiological factors, but food availability may challenge the capacity to meet nutritional needs. Western gorillas (Gorilla gorilla) are an interesting model for investigating this topic because they are folivore-frugivores that adjust their diet and activities to seasonal variation in fruit availability. Observations of one habituated group of western gorillas in Bai-Hokou, Central African Republic (December 2004-December 2005) were used to examine seasonal variation in diet quality and nutritional intake. We tested if during the high fruit season the food consumed by western gorillas was higher in quality (higher in energy, sugar, fat but lower in fibre and antifeedants) than during the low fruit season. Food consumed during the high fruit season was higher in digestible energy, but not any other macronutrients. Second, we investigated whether the gorillas increased their daily intake of carbohydrates, metabolizable energy (KCal/g OM), or other nutrients during the high fruit season. Intake of dry matter, fibers, fat, protein and the majority of minerals and phenols decreased with increased frugivory and there was some indication of seasonal variation in intake of energy (KCal/g OM), tannins, protein/fiber ratio, and iron. Intake of non-structural carbohydrates and sugars was not influenced by fruit availability. Gorillas are probably able to extract large quantities of energy via fermentation since they rely on proteinaceous leaves during the low fruit season. Macronutrients and micronutrients, but not digestible energy, may be limited for them during times of low fruit availability because they are hind-gut fermenters. We discuss the advantages of seasonal frugivores having large dietary breath and flexibility, significant characteristics to consider in the conservation strategies of endangered species.

Dispersal Mutualism Incorporated into Large-Scale, Infrequent Disturbances

Because of their influence on succession and other community interactions, large-scale, infrequent natural disturbances also should play a major role in mutualistic interactions. Using field data and experiments, I test whether mutualisms have been incorporated into large-scale wildfire by whether the outcomes of a mutualism depend on disturbance. In this study a seed dispersal mutualism is shown to depend on infrequent, large-scale disturbances. A dominant shrubland plant (Arctostaphylos species) produces seeds that make up a persistent soil seed bank and requires fire to germinate. In post-fire stands, I show that seedlings emerging from rodent caches dominate sites experiencing higher fire intensity. Field experiments show that rodents (Perimyscus californicus, P. boylii) do cache Arctostaphylos fruit and bury most seed caches to a sufficient depth to survive a killing heat pulse that a fire might drive into the soil. While the rodent dispersal and caching behavior itself has not changed compared to other habitats, the environmental transformation caused by wildfire converts the caching burial of seed from a dispersal process to a plant fire adaptive trait, and provides the context for stimulating subsequent life history evolution in the plant host.

Pollination system and the effect of inflorescence size on fruit set in the deceptive orchid Cephalanthera falcata

Larger inflorescences in reward-producing plants can benefit plants by increasing both pollinator attraction and the duration of visits by individual pollinators. However, ultimately, inflorescence size is determined by the balance between the benefits of large inflorescences and the increased cost of geitonogamy. At present, little is known about the relationship between inflorescence size and fecundity in deceptive plants. Given that pollinators are likely to leave inflorescences lacking rewards quickly, it seems unlikely that longer pollinator visits and the risk of geitonogamy would be strong selective pressures in these species, which indicates that pollinator attraction might be the most important factor influencing their inflorescence size. Here we examined the pollination ecology of the deceptive orchid Cephalanthera falcata in order to clarify the effects of inflorescence size on the fruit set of this non-rewarding species. Field observations of the floral visitors showed that C. falcata is pollinated by the andrenid bee Andrena aburana, whilst pollination experiments demonstrated that this orchid species is neither autogamous nor apogamous, but is strongly pollinator dependent. Three consecutive years of field observations revealed that fruit set was positively correlated with the number of flowers per inflorescence. These results provide strong evidence that the nectarless orchid C. falcata benefits from producing larger inflorescences that attract a greater number of innate pollinators. Large inflorescences may have a greater positive effect on fruit set in deceptive plants because a growing number of studies suggest that fruit set in reward-producing plants is usually unaffected by display size.

It's Not Easy Being Blue: Are There Olfactory and Visual Trade-Offs in Plant Signalling?

Understanding the signals used by plants to attract seed disperses is a pervasive quest in evolutionary and sensory biology. Fruit size, colour, and odour variation have long been discussed in the controversial context of dispersal syndromes targeting olfactory-oriented versus visually-oriented foragers. Trade-offs in signal investment could impose important physiological constraints on plants, yet have been largely ignored. Here, we measure the reflectance and volatile organic compounds of a community of Malagasy plants and our results indicate that extant plant signals may represent a trade-off between olfactory and chromatic signals. Blue pigments are the most visually-effective--blue is a colour that is visually salient to all known seed dispersing animals within the study system. Additionally, plants with blue-reflecting fruits are less odiferous than plants that reflect primarily in other regions of the colour spectrum.

Sugar demand of ripening grape berries leads to recycling of surplus phloem water via the xylem

We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink-driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought-induced berry shrinkage. Rewatering accelerated berry growth and sugar accumulation concurrently with leaf photosynthetic recovery. Interrupting phloem flow through the peduncle prevented the increase in berry growth after rewatering, but interrupting xylem flow did not. Nevertheless, xylem flow in ripening berries, but not berry size, remained responsive to root or shoot pressurization. A mass balance analysis on ripening berries sampled in the field suggested that phloem water inflow may exceed growth and transpiration water demands. Collecting apoplastic sap from ripening berries showed that osmotic pressure increased at distinct rates in berry vacuoles and apoplast. Our results indicate that the decrease in xylem inflow at the onset of ripening may be a consequence of the sink-driven increase in phloem inflow. We propose a conceptual model in which surplus phloem water bypasses the fruit cells and partly evaporates from the berry surface and partly moves apoplastically to the xylem for outflow.

Fruit calcium accumulation coupled and uncoupled from its transpiration in kiwifruit

Accumulation of Ca in several fleshy fruit is often supposed to depend, among others, by climatic variables driving fruit transpiration. This study tests the whole causal chain hypothesis: VPD → fruit transpiration → Ca accumulation. Also there are evidences that relationship between fruit transpiration and Ca content is not always clear, hence the hypothesis that low VPD reduces the fraction of xylemic water destined to transpiration was tested by examining the water budget of fruit. Attached fruits of Actinidia deliciosa were subjected to Low (L) and High (H) VPD. Their transpiration was measured from early after fruit-set to day 157 after full bloom (DAFB). Fruits were picked at 70, 130 and 157 DAFB for Ca and K determinations and for water budget analysis. Cumulative transpired water was ∼ 70 g and ∼ 16 g H2O f(-1) in HVPD and LVPD, respectively. Calcium accumulated linearly (R(2) = 0.71) with cumulative transpiration when VPD was high, while correlation was weaker (R(2) = 0.24) under LVPD. Under low VPD the fraction of xylem stream destined to transpiration declined to 40-50%. Results suggest that Ca accumulation is coupled to cumulative transpiration under high VPD because under that condition cumulative transpiration equals xylem stream (which carry the nutrient). At LVPD, Ca gain by fruit is uncoupled from transpiration because ∼ 60% of the xylemic water is needed to sustain fruit growth. Results will apply to most fruits (apples, tomatoes, capsicum, grapes etc.) since most suffer Ca deficiency disorders and grow in changing environments with variable VPD, also they could be supportive for the implementation of fruit quality models accounting also for mineral compositions and for a reinterpretation of certain field practices aimed at naturally improve fruit Ca content.

Fruit calcium accumulation coupled and uncoupled from its transpiration in kiwifruit

Accumulation of Ca in several fleshy fruit is often supposed to depend, among others, by climatic variables driving fruit transpiration. This study tests the whole causal chain hypothesis: VPD → fruit transpiration → Ca accumulation. Also there are evidences that relationship between fruit transpiration and Ca content is not always clear, hence the hypothesis that low VPD reduces the fraction of xylemic water destined to transpiration was tested by examining the water budget of fruit. Attached fruits of Actinidia deliciosa were subjected to Low (L) and High (H) VPD. Their transpiration was measured from early after fruit-set to day 157 after full bloom (DAFB). Fruits were picked at 70, 130 and 157 DAFB for Ca and K determinations and for water budget analysis. Cumulative transpired water was ∼ 70 g and ∼ 16 g H2O f(-1) in HVPD and LVPD, respectively. Calcium accumulated linearly (R(2) = 0.71) with cumulative transpiration when VPD was high, while correlation was weaker (R(2) = 0.24) under LVPD. Under low VPD the fraction of xylem stream destined to transpiration declined to 40-50%. Results suggest that Ca accumulation is coupled to cumulative transpiration under high VPD because under that condition cumulative transpiration equals xylem stream (which carry the nutrient). At LVPD, Ca gain by fruit is uncoupled from transpiration because ∼ 60% of the xylemic water is needed to sustain fruit growth. Results will apply to most fruits (apples, tomatoes, capsicum, grapes etc.) since most suffer Ca deficiency disorders and grow in changing environments with variable VPD, also they could be supportive for the implementation of fruit quality models accounting also for mineral compositions and for a reinterpretation of certain field practices aimed at naturally improve fruit Ca content.

Impedance of the grape berry cuticle as a novel phenotypic trait to estimate resistance to Botrytis cinerea

Warm and moist weather conditions during berry ripening provoke Botrytis cinerea (B. cinerea) causing notable bunch rot on susceptible grapevines with the effect of reduced yield and wine quality. Resistance donors of genetic loci to increase B. cinerea resistance are widely unknown. Promising traits of resistance are represented by physical features like the thickness and permeability of the grape berry cuticle. Sensor-based phenotyping methods or genetic markers are rare for such traits. In the present study, the simple-to-handle I-sensor was developed. The sensor enables the fast and reliable measurement of electrical impedance of the grape berry cuticles and its epicuticular waxes (CW). Statistical experiments revealed highly significant correlations between relative impedance of CW and the resistance of grapevines to B. cinerea. Thus, the relative impedance Z_rel of CW was identified as the most important phenotypic factor with regard to the prediction of grapevine resistance to B. cinerea. An ordinal logistic regression analysis revealed a R²_McFadden of 0.37 and confirmed the application of Z_rel of CW for the prediction of bunch infection and in this way as novel phenotyping trait. Applying the I-sensor, a preliminary QTL region was identified indicating that the novel phenotypic trait is as well a valuable tool for genetic analyses.

Do seed VLCFAs trigger spongy tissue formation in Alphonso mango by inducing germination?

Spongy tissue is a physiological disorder in Alphonso mango caused by the inception of germination-associated events during fruit maturation on the tree, rendering the fruit inedible. Inter-fruit competition during active fruit growth is a major contributing factor for the disorder which leads to reduced fat content in spongy tissue affected fruits. This study was, therefore, carried out to determine the possible association between seed fats and ST formation. The study of the fat content during fruit growth showed that it increased gradually from 40 percent fruit maturity. At 70 percent maturity, however, there was a sudden increase of fat content of whole fruit, leading to acute competition and resulting in differential allocation of resources among developing fruits. As a result, the seed in spongy-tissue-affected mature ripe fruit showed a marked drop in the levels of fats and the two very long chain fatty acids (VLCFAs), tetracosanoic acid and hexacosanoic acid together with an increase of linolenic acid and a fall in oleic acid contents, which are known to be key determinants for the initiation of pre-germination events in seed. Subsequently, a rise in the level of cytokinin and gibberellins in ST seed associated with a fall in abscisic acid level clearly signalled the onset of germination. Concurrently, a significant reduction in the ratio of linolenic acid/linoleic acid in pulp led to the loss of membrane integrity, cell death and the eventual formation of spongy tissue. Based on the above, it is concluded that a significant reduction in the biosynthesis of VLCFAs in seeds during fruit growth might trigger pre-germination events followed by a cascade of biochemical changes in the pulp, leading to lipid peroxidation and membrane injury in pulp culminating in ST development. Thus, this study presents crucial experimental evidence to highlight the critical role played by VLCFAs in inducing ST formation in Alphonso mango during the pre-harvest phase of fruit growth.

Butterfly pollination in Pteroglossa (Orchidaceae, Orchidoideae): a comparative study on the reproductive biology of two species of a Neotropical genus of Spiranthinae

Spiranthinae orchids are known for being self-compatible and offering nectar as a reward. Although data on their pollinators are scarce, members of this tribe are mostly pollinated by bees, hummingbirds and moths. Some of them even reproduce through facultative self-pollination. Nothing is known about the pollinators and reproduction system in Pteroglossa. Based on records on flowering phenology, floral morphology, reward production, pollinators and breeding system, this paper aims to study the reproductive biology of two Pteroglossa spp. Both species offer nectar as a resource and are pollinated exclusively by diurnal Lepidoptera at the studied areas. Nectar is produced by two glandular nectaries, and is stored in a spur. Pollinaria possess a ventrally adhesive viscidium that is deposited on the basal portion of butterfly proboscides. Both species are self-compatible but pollinator-dependent. The reproductive success is low when compared to other Spiranthinae. Although no evident mechanical barrier to avoid self-pollination or geitonogamy was identified, the erratic behavior of the butterflies, with their infrequent visits to only one flower per inflorescence, contributes to an increased fruit set produced through cross-pollination. The presence of ventrally adhesive viscidia in Spiranthinae is responsible for greater pollinator diversity when compared to bee-pollinated Goodyerinae with dorsally adhesive viscidia, adapted to attach to bee mouthparts.

Analysis of xyloglucan endotransglycosylase/hydrolase (XTH) genes and diverse roles of isoenzymes during persimmon fruit development and postharvest softening

Xyloglucan endotransglycosylase/hydrolase (XTH) enzymes have played a role in the remodeling of cell wall hemicelluloses. To investigate the function of XTHs in persimmon (Diospyros kaki L.) fruit development and postharvest softening, five cDNAs (DkXTH1 to DkXTH5), whose putative proteins contained the conserved DEIDFEFLG motif of XTH, were cloned. Real time quantitative PCR analysis revealed that DkXTH1, DkXTH4, and DkXTH5 peaked in immature expanding fruit, and their higher expression was observed along with higher fruit firmness in cold-treated fruit or firmer cultivar fruit during storage. The opposite gene expression patterns were observed in DkXTH2 and DkXTH3, which reached maxima concomitance with pronounced fruit softening. Meanwhile, the xyloglucan endotransglycosylase (XET) enzymes play important roles in both the rapid growth and ripening of persimmon fruit. Furthermore, the recombined DkXTH1 and DkXTH2 proteins showed significant XET activity without any detected XEH activity. However, the XET activity of recombined DkXTH2 protein had a higher affinity for small acceptor molecules than that of recombined DkXTH1 protein. The former might prefer to participate in cell wall restructuring, and the latter is more inclined to participate in cell wall assembly. Besides, DKXTH proteins could function by targeting to the cell wall under regulation of a signal peptide. The data suggested that individual DKXTHs could exhibit different patterns of expression, and the encoded products possessed specific enzymatic properties conferring on their respective functions in growth and postharvest softening of persimmon fruit.

Loquat fruit ripening is associated with root depletion. Nutritional and hormonal control

In woody species, it is known that there is a competition for nutrients, water and carbohydrates between root and fruit-shoot systems, however the influence of root development on fruit quality has received little attention. This research aims to identify the network of mechanisms involved in loquat (Eriobotrya japonica Lindl.) fruit ripening in connection with root activity. The study includes root growth rate measurements paralleling the ongoing fruit developmental stages, photosynthate translocation to the root by using (13)CO2 tracing, and nitrogen fractions (N-NH4(+), N-NO3(-), and N-proteinaceous) as well as their upward translocation to the fruit. The role of hormones (IAA, zeatin and ABA) in regulating the responses is also addressed. The experiment was conducted during two consecutive years on adult and 3-year-old loquat trees from early fruit developmental stage (10% of final size, 701 BBCH scale) to fully developed fruit colour (809 BBCH scale). This approach revealed that root development depends on the growing fruit sink strength, which reduces carbohydrates translocation to the roots and prevents them for further elongation. A nitrate accumulation in roots during the active fruit growth period takes place, which also contributes to slowing elongation and paralleled reduced ammonium and proteinaceous nitrogen concentrations. Concomitantly, the concentration of IAA and zeatin were lowest while that of ABA was highest when root exhibited minimum elongation. The depletion in zeatin and nitrogen supply by the roots paralleling the high ABA transport to the fruit allowed for colour break. These results suggest that loquat fruit changes colour by reducing root growth, as fruit increases sugars and ABA concentrations and reduces nitrogen and zeatin concentrations.

High light decreases xylem contribution to fruit growth in tomato

Recently, contradicting evidence has been reported on the contribution of xylem and phloem influx into tomato fruits, urging the need for a better understanding of the mechanisms involved in fruit growth. So far, little research has been performed on quantifying the effect of light intensity on the different contributors to the fruit water balance. However, as light intensity affects both transpiration and photosynthesis, it might be expected to induce important changes in the fruit water balance. In this study, tomato plants (Solanum lycopersicum L.) were grown in light and shade conditions and the fruit water balance was studied by measuring fruit growth of girdled and intact fruits with linear variable displacement transducers combined with a model-based approach. Results indicated that the relative xylem contribution significantly increased when shading lowered light intensity. This resulted from both a higher xylem influx and a lower phloem influx during the daytime. Plants from the shade treatment were able to maintain a stronger gradient in total water potential between stem and fruits during daytime, thereby promoting xylem influx. It appeared that the xylem pathway was still functional at 35 days after anthesis and that relative xylem contribution was strongly affected by environmental conditions.

Xenia and metaxenia in grapes: differences in berry and seed characteristics of maternal grape cv. 'Narince' (Vitis vinifera L.) as influenced by different pollen sources

Literature investigations indicate that the grapes have quite complex fertilisation biology. This complexity necessitates extensive investigations to obtain reliable knowledge for both well-organised hybridisation studies and maximising grape yield. Therefore, this study was conducted to investigate the influences of self-, free- and cross-pollination on berry and seed characteristics in grape. Five different pollination treatments were applied to 'Narince', the most widely known and popular white wine grape in Turkey. Pollen tests indicated that all the cultivars had satisfactory in vitro pollen viability percentages. Free-pollination produced a significantly higher percentage berry set. Among the pollinizers, the use of pollen of 'Thompson Seedless' and 'Cardinal' varieties resulted in higher berry set percentage in 'Narince'. The free-pollination was also superior in giving the highest weight, length and width of the berry, as well as number of seeds per berry. These findings revealed that there were strong xenial and metaxenial effects in the studied grape cultivars. Among the pollinizer cultivars, the most effective pollinator was 'Thompson Seedless'. Hence, for better berry set and quality, the use of 'Thompson Seedless' as a pollinizer may be an attractive option in both grape production and breeding studies.