Identification of genes associated with kernel size in almond [Prunus dulcis (Mill.) D.A. Webb] using RNA-Seq

Plant Growth Regulation - Almond is a stone fruit crop belonging to the Rosaceae family, cultivated in the temperate region of the world for its high nutritive valued fruits. In today’s...     

Ecophysiological responses of almond (Prunus dulcis) seedlings to cadmium stress

Almond (Prunus dulcis L.) seedlings were exposed to 0, 25, 50, 100 and 150 μM of CdCl₂ in a solution culture under controlled conditions. The effects of cadmium (Cd) exposure on almond seedlings growth, stomatal architecture, gas exchange and physiological parameters were investigated. Under cadmium stress conditions, significant decrease in fresh and dry weight, length of shoot and chlorophyll content were observed. Stomatal conductance, transpiration and net photosynthetic rates were generally depressed by Cd stress, despite stomatal frequency values and stomatal pore size remained unchanged. Exposure to Cd severely restricted the starch content and increased soluble sugars.     

Looking into flowering time in almond (Prunus dulcis (Mill) D. A. Webb): the candidate gene approach

Blooming time is one of the most important agronomic traits in almond. Biochemical and molecular events underlying flowering regulation must be understood before methods to stimulate late flowering can be developed. Attempts to elucidate the genetic control of this process have led to the identification of a major gene (Lb) and quantitative trait loci (QTLs) linked to observed phenotypic differences, but although this gene and these QTLs have been placed on the Prunus reference genetic map, their sequences and specific functions remain unknown. The aim of our investigation was to associate these loci with known genes using a candidate gene approach. Two almond cDNAs and eight Prunus expressed sequence tags were selected as candidate genes (CGs) since their sequences were highly identical to those of flowering regulatory genes characterized in other species. The CGs were amplified from both parental lines of the mapping population using specific primers. Sequence comparison revealed DNA polymorphisms between the parental lines, mainly of the single nucleotide type. Polymorphisms were used to develop co-dominant cleaved amplified polymorphic sequence markers or length polymorphisms based on insertion/deletion events for mapping the candidate genes on the Prunus reference map. Ten candidate genes were assigned to six linkage groups in the Prunus genome. The positions of two of these were compatible with the regions where two QTLs for blooming time were detected. One additional candidate was localized close to the position of the Evergrowing gene, which determines a non-deciduous behaviour in peach.     

Microfluorometry of pectic materials in the dehiscence zone of almond (Prunus dulcis [Mill.] DA Webb) fruits

We examined the middle lamella and the primary and secondary walls in almond pericarp dehiscence zone cells using a fluorescent cytochemical method which permitted specific, quantitative detection of pectic cell wall materials. Glycol methacrylate-embedded sections were stained with coriphosphine and pectin-specific fluorescent emissions at 630 nm were quantified using green excitation (546 nm). Examination of sectioned material extracted with purified pecto-lytic enzyme preparations was used to demonstrate the relative specificity of the staining reaction for pectic substances.     

Photosynthesis performance in sweet almond [<Emphasis Type="Italic">Prunus dulcis</Emphasis> (Mill) D. Webb] exposed to supplemental UV-B radiation

Due to anthropogenic influences, solar UV-B irradiance at the earth’s surface is increasing. To determine the effects of enhanced UV-B radiation on photosynthetic characteristics of Prunus dulcis, two-year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-B_c), 4.42 (UV-B₁), 7.32 (UV-B₂) and 9.36 (UV-B₃) kJ m⁻² d⁻¹. Effects of UV-B stress on a range of chlorophyll (Chl) fluorescence parameters (FPs), Chl contents and photosynthetic gas-exchange parameters were investigated. UV-B stress promoted an increase in minimal fluorescence of dark-adapted state (F₀) and F₀/F_m, and a decrease in variable fluorescence (F_v, F_v/F_m, F_v/F₀ and F₀/F_m) due to its adverse effects on photosystem II (PSII) activity. No significant change was observed for maximal fluorescence of dark-adapted state (F_m). Enhanced UV-B radiation caused a significant inhibition of net photosynthetic rate (P _N) at UV-B₂ and UV-B₃ levels and this was accompanied by a reduction in stomatal conductance (g _s) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increased UV-B stress. In general, adverse UV-B effects became significant at the highest tested radiation dose 9.36 kJ m⁻² d⁻¹. The most sensitive indicators for UV-B stress were F_v/F₀, Chl a content and P _N. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis.     

Shell cracking strength in almond (Prunus dulcis [Mill.] D.A. Webb.) and its implication in uses as a value-added product

Researchers are currently developing new value-added uses for almond shells, an abundant agricultural by-product. Almond varieties are distinguished by processors as being either hard or soft shelled, but these two broad classes of almond also exhibit varietal diversity in shell morphology and physical characters. By defining more precisely the physical and chemical characteristics of almond shells from different varieties, researchers will better understand which specific shell types are best suited for specific industrial processes. Eight diverse almond accessions were evaluated in two consecutive harvest seasons for nut and kernel weight, kernel percentage and shell cracking strength. Shell bulk density was evaluated in a separate year. Harvest year by almond accession interactions were highly significant (p  0.01) for each of the analyzed variables. Significant (p  0.01) correlations were noted for average nut weight with kernel weight, kernel percentage and shell cracking strength. A significant (p  0.01) negative correlation for shell cracking strength with kernel percentage was noted. In some cases shell cracking strength was independent of the kernel percentage which suggests that either variety compositional differences or shell morphology affect the shell cracking strength. The varietal characterization of almond shell materials will assist in determining the best value-added uses for this abundant agricultural by-product.     

Embryo Sac Development in Almond [Prunus dulcis (Mill.) D. A. Webb] as Affected by Cross-, Self- and Non-pollination

Embryo sac development in ‘Nonpareil’ almond wasstudied following cross-, self- and non-pollination under fieldand greenhouse conditions. The embryo sac, which develops accordingto the Polygonum type, does not begin to differentiate untilanthesis in contrast to other Prunus spp. where a well-developedembryo sac is present at the time of flower opening. The developingmegagametophyte appears to be isolated from surrounding nucellartissue by the deposition of a ring of callose, which, as indicatedby aniline blue-induced fluorescence in the walls of nucellarcells, encloses the embryo sac during its elongation. Developmentand growth of the embryo sac following the different pollinationtreatments indicated that embryo sac development was stimulatedby the presence of compatible pollen tubes in the style andfinal elongation growth of the embryo sac was promoted by cross-pollination.Irregularities in megagametophyte development, including delayeddifferentiation of the megaspore mother cell, embryo sac abortionand lack of polar nuclei fusion and embryo sac elongation, werefrequently noted in ovules of self- and non-pollinated flowers. Almond, callose, embryo sac, megagametophyte, pollination, Prunus dulcis (Mill.) D. A. Webb.     

Molecular cloning and biochemical characterization of a lipoxygenase in almond (Prunus dulcis) seed.

We have characterized an almond (Prunus dulcis) lipoxygenase (LOX) that is expressed early in seed development. The presence of an active lipoxygenase was confirmed by western blot analysis and by measuring the enzymatic activity in microsomal and soluble protein samples purified from almond seeds at this stage of development. The almond lipoxygenase, which had a pH optimum around 6, was identified as a 9-LOX on the basis of the isomers of linoleic acid hydroperoxides produced in the enzymatic reaction. A genomic clone containing a complete lipoxygenase gene was isolated from an almond DNA library. The 6776-bp sequence reported includes an open reading frame of 4667 bp encoding a putative polypeptide of 862 amino acids with a calculated molecular mass of 98.0 kDa and a predicted pI of 5.61. Almond seed lipoxygenase shows 71% identity with an Arabidopsis LOX1 gene and is closely related to tomato fruit and potato tuber lipoxygenases. The sequence of the active site was consistent with the isolated gene encoding a 9-LOX.     

Disruption of endosperm development: an inbreeding effect in almond (Prunus dulcis)

A homozygous self-compatible almond, originated from self-fertilization of a self-compatible genotype and producing a reasonable yield following open pollination, exhibited a very high fruit drop rate when self-pollinated. To investigate whether fruit dropping in this individual is related to an abnormal development of the embryo sac following self-fertilization, histological sections of ovaries from self and cross-pollinated flowers were observed by light microscopy. Additionally, the presence of pollen tubes in the ovary and fruit set were determined for both types of pollination. Despite pollen tubes reached the ovary after both pollinations, differences in embryo sac and endosperm development after fertilization were found. Thus, while for cross-fertilized ovules a pro-embryo and an endosperm with abundant nuclei were generally observed, most self-fertilized ovules remained in a previous developmental stage in which the embryo sac was not elongated and endosperm nuclei were absent. Although 30 days after pollination fruit set was similar for both pollination types, at 60 days it was significantly reduced for self-pollination. These results provide evidence that the high fruit drop in this genotype is the consequence of a disrupted development of the endosperm, what could be an expression of its high level of inbreeding.     

Anti-obesity potential of almond (Prunus dulcis) in experimental animals under cafeteria and atherogenic diets

Background & objectivesNatural dietary supplements are progressively getting famous to supplant synthetic substances particularly in chronic morbidities. The aim of this study was to evaluate the anti-obesity potential of almond on the normal, Cafeteria, and Atherogenic diets.Materials and methodsParameters such as change in body weight, body temperature, lipid profile, organ weights, and fat pad weights were assessed. Central Nervous System related studies (Despair Swim test and Elevated Plus maze test) were also performed to comprehend the effect of the diets, and almond on the brain. All of the experimental animals were randomly assigned to one of three diet categoriesregular, cafeteria, or atherogenic, and fed those diets for 40 days. Each diet had the control group, standard drug group and three almond groups (low dose: 50; medium dose: 100 and high dose: 200 mg/kg body weight). Body weight was recorded every alternate day. On 40th day, body temperature was measured. On day 41, lipid parameters, organ weights, fat pad weights and the CNS parameters were evaluated. ANOVA followed by Duncans Multiple Range Test were used for statistical analysis.ResultsTreatment of animals with either a low or high dose of almond as well as a standard herb prevented a rise in body weight significantly (p = 0.01) in all three diet groups. When a regular diet was replaced with a cafeteria and atherogenic diet, the serum levels of triglycerides and LDL increased significantly, while HDL levels decreased significantly. Overall, almond preparation reduced lipid parameters, organ weights, fat-pad weights, and stabilized CNS parameters substantially.Interpretation & conclusionThe almond high dose was the most effective of all the almond preparations. Our study suggests that chronic administration of almond independently reduces the body weight in experimental animals.     

Non-photochemical chlorophyll fluorescence quenching and structural rearrangements induced by low pH in intact cells of Chlorella fusca (Chlorophyceae) and Mantoniella squamata (Prasinophyceae)

We have used circular dichroism (CD) spectroscopy and chlorophyll fluorescence induction measurements in order to examine low-pH-induced changes in the chiral macro-organization of the chromophores and in the efficiency of non-photochemical quenching of the chlorophyll a fluorescence (NPQ) in intact, dark-adapted cells of Chlorella fusca (Chlorophyceae) and Mantoniella squamata (Prasinophyceae). We found that: (i) high proton concentrations enhanced the formation of chiral macrodomains of the complexes, i.e. the formation of large aggregates with long-range chiral order of pigment dipoles; this was largely independent of the low-pH-induced accumulation of de-epoxidized xanthophylls; (ii) lowering the pH led to NPQ; however, efficient energy dissipation, in the absence of excess light, could only be achieved if a substantial part of violaxanthin was converted to zeaxanthin and antheraxanthin in Chlorella and Mantoniella, respectively; (iii) the low-pH-induced changes in the chiral macro-organization of pigments were fully reversed by titrating the cells to neutral pH; (iv) at neutral pH, the presence of antheraxanthin or zeaxanthin did not bring about a sizeable NPQ. Hence, low-pH-induced NPQ in dark adapted algal cells appears to be associated both with the presence of de-epoxidized xanthophylls and structural changes in the chiral macrodomains. It is proposed that the macrodomains, by providing a suitable structure for long-distance migration of the excitation energy, in the presence of quenchers associated with de-epoxidized xanthophylls, facilitate significantly the dissipation of unused excitation energy. This revised version was published online in June 2006 with corrections to the Cover Date.     

Development of the Almond Nut (Prunus dulcis (Mill.) D. A. Webb). Anatomy and Chemical Composition of Fruit Parts from Anthesis to Maturity

The growth of the fruit of two varieties of almond (Prunus dulcis(Mill.) D. A. Webb) was studid from anthesis (week 0) to maturity(week 32). The dimensions, fresh weight, moisture content, anatomyand chemical composition of the pericarp, testa, embryo, endospermand nucellus are recorded diagrarnmatically, graphically andby micrographs for one variety. Of the two ovules present atflowering only one normally developed further. By 12 weeks afterflowering the whole fruit had reached full size. The space encloscdby the pericarp was filled by nuallus until weck 10, with subsequentenlargement of both endosperm and embryo. From week 16 to week20 the embryo increased to full size with a concumnt decreasein the size of the endosperm. Sixteen weeks after flowering,the embryo began to accumulate protein and lipid, little ofwhich originated from either the nucellus or endosperm. Theembryo contained no starch or reducing sugar but up to 3% sucrosein the early stags which dtcreascd as lipid and protein increased.Starch and sucrose levels were high in the testa at week 16but subsbquently dropped, starch more rapidly than sucrose.The role of the testa in transport of metabolites to the embryois discussed. Prunus dulcis, almond, fruit development, anatomy, embryo, endosperm     

Simulation of Pulse-Amplitude-Modulated (PAM) fluorescence: Limitations of some PAM-parameters in studying environmental stress effects

Fluorescence parameters obtained during steady-state electron transport are frequently used to evaluate photosynthetic efficiency of plants. We studied the behaviour of those parameters as a function of irradiance-adapted fluorescence yields F_S and F'_M. Applied simulations showed that photochemical quenching evaluated by q_P is greatly influenced by the steady-state fluorescence level (F_S), and that its evolution is not complementary to non-photochemical quenching (q_N). On the other hand, the relative photochemical and non-photochemical quenching coefficients (q_P(rel) and q_N(rel)) proposed by Buschmann (1995) represent better the balance between the energy dissipation pathways. However, these relative parameters are also non-linearly related when the F_S level is varied. We investigated the application of a new parameter, the relative unquenched fluorescence (UQF_(rel)) which takes into account the fraction of non-quenched fluorescence yield (F_S), which is related to closed photosystem 2 reaction centres not participating in electron transport. By using computer simulations and real in vivo measurements, we found that this new parameter is complementary to q_P(rel) and q_N(rel), which may facilitate the use of PAM fluorescence as diagnostic tool in environmental studies.     

Differences in proleptic and epicormic shoot structures in relation to water deficit and growth rate in almond trees (Prunus dulcis)

Background and Aims

Shoot characteristics differ depending on the meristem tissue that they originate from and environmental conditions during their development. This study focused on the effects of plant water status on axillary meristem fate and flowering patterns along proleptic and epicormic shoots, as well as on shoot growth rates on ‘Nonpareil’ almond trees (Prunus dulcis). The aims were (1) to characterize the structural differences between proleptic and epicormic shoots, (2) to determine whether water deficits modify shoot structures differently depending on shoot type, and (3) to determine whether shoot structures are related to shoot growth rates.

Methods

A hidden semi-Markov model of the axillary meristem fate and number of flower buds per node was built for two shoot types growing on trees exposed to three plant water status treatments. The models segmented observed shoots into successive homogeneous zones, which were compared between treatments. Shoot growth rates were calculated from shoot extension measurements made during the growing season.

Key Results

Proleptic shoots had seven successive homogeneous zones while epicormic shoots had five zones. Shoot structures were associated with changes in growth rate over the season. Water deficit (1) affected the occurrence and lengths of the first zones of proleptic shoots, but only the occurrence of the third zone was reduced in epicormic shoots; (2) had a minor effect on zone flowering patterns and did not modify shoot or zone composition of axillary meristem fates; and (3) reduced growth rates, although patterns over the season were similar among treatments.

Conclusions

Two meristem types, with different latency durations, produced shoots with different growth rates and distinct structures. Differences between shoot type structure responses to water deficit appeared to reflect their ontogenetic characteristics and/or resource availability for their development. Tree water deficit appeared to stimulate a more rapid progression through ontogenetic states.     

Liposomal membranes. XIV. Fusion of liposomal membranes induced by polyisoprenoids as monitored by fluorescence quenching method

Fusion of the single-walled liposomes of egg phosphatidylcholine as induced by the polyisoprenoids such as solanesol, trans-ethyl decaprenoate (EDP), coenzyme Q10, and dolichol has been investigated adopting the fluorescence quenching method. Relative efficiency of the polyisoprenoids employed on the induced fusion of liposomes was a sequence of solanesol less than or equal to EDP much less than CoQ10, dolichol, which was consistent with the result previously obtained by the dye-release method.     

Prediction of leaf nitrogen from early season samples and development of field sampling protocols for nitrogen management in Almond (Prunus dulcis [Mill.] DA Webb)

Background and aim

Protocols for leaf sampling in deciduous tree crops are commonly executed too late in the season and do not adequately consider field variability to be effectively used to guide N management. The goal of this study was to develop improved sampling strategies to optimize nitrogen management in deciduous tree crops.

Method

Leaf nutrient concentration from individual trees in four mature commercial orchards was collected (n =1148) for three consecutive seasons to develop nitrogen prediction models and to estimate the distribution of N values in orchards in July. Spatial variance analysis was used to determine optimal sampling strategies.

Results

Leaf nitrogen concentration in summer can be predicted (r²?=?0.9) from the leaf N and B concentration in spring with the sum of K, Ca, and Mg equivalents. Mean field leaf nutrient concentration can be obtained by collecting one pooled sample per management zone composed of 30 trees each of which are at least 30 m apart. Using these methods the percentage of trees with leaf N above the recommended July critical value can be predicted accurately.

Conclusions

Optimized methods for sample collection and models to predict mid-season leaf N from early season samples can be used to improve N management in deciduous tree crops.     

Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. III. Chlorophyll fluorescence at 77 K

Photoinhibition in Lemna gibba L. was studied by interpreting chlorophyll fluorescence characteristics at 77 K on the basis of the bipartite model of Butler and co-workers (Butler 1978). Application of this analysis to chloroplasts (isolated from plants before and after exposure to a photosynthetic photon flux density of 1 750 μmol m⁻² s⁻¹ at 3°C for 2 h) revealed that photoinhibition had the following effect on primary events in photosynthesis. Firstly, the fluorescence of PS II increased (44%) in the state of open traps (F_o) and decreased (32%) in the state of closed traps (F_m). It is suggested, that the F_o-decrease reflects increased quenching by radiationless decay, both effects occurring at PS II reaction centers. Secondly, the rate constant for transfer of excitation energy from PS II to PS I (k_T(μ→J)) increased by 34%. However, in the state of closed traps, the flux of excitation energy via this transfer process decreased, most likely because of increased quenching by radiationless decay at PS II reaction centers. Thirdly, the probability for fluorescence from PS I decreased (19%). This indicates increased quenching by radiationless decay.     

Differential response to paraquat induced oxidative stress in two rice cultivars on antioxidants and chlorophyll a fluorescence

The responses of antioxidative system and photosystem II photochemistry of rice (Oryza sativa L.) to paraquat induced oxidative stress were investigated in a chilling-tolerant cultivar Xiangnuo no. 1, and a chilling-susceptible cultivar, IR-50. Electrolyte leakage and malondialdehyde (MDA) content of Xiangnuo no. 1 were little affected by paraquat, but they increased in IR-50. After paraquat treatment, superoxide dismutase (SOD) activity remained high in Xiangnuo no. 1, while it declined in IR-50. Activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) declined with oxidative stress in both cultivars, but Xiangnuo no. 1 had higher GR activity than IR-50. Under paraquat induced oxidative stress, ascorbic acid (AsA) and reduced glutathione (GSH) concentrations remained high in Xiangnuo no. 1, but decreased in IR-50. The results indicated that higher activities of SOD and GR and higher contents of AsA and GSH in Xiangnuo no. 1 under paraquat induced oxidative stress were associated with its tolerance to paraquat, while paraquat induced damage to IR-50 was related to decreased activities of SOD, APX and GR and contents of AsA and GSH. F _v/F _m, Φ _PSII, and qP remained high in Xiangnuo no. 1, while they decreased greatly in IR-50 under paraquat induced oxidative stress.