Isolation and expression analysis of LEA genes in peanut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

Late embryogenesis abundant (LEA) protein family is a large protein family that includes proteins accumulated at late stages of seed development or in vegetative tissues in response to drought, salinity, cold stress and exogenous application of abscisic acid. In order to isolate peanut genes, an expressed sequence tag (EST) sequencing project was carried out using a peanut seed cDNA library. From 6258 ESTs, 19 LEA-encoding genes were identified and could be classified into eight distinct groups. Expression of these genes in seeds at different developmental stages and in various peanut tissues was analysed by semi-quantitative RT-PCR. The results showed that expression levels of LEA genes were generally high in seeds. Some LEA protein genes were expressed at a high level in non-seed tissues such as root, stem, leaf, flower and gynophore. These results provided valuable information for the functional and regulatory studies on peanut LEA genes.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17 °C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17 °C to27 °C strongly reduced pod production, mature pod size andseeds per pod, while an increase in day temperature from 22°C to 32 °C had smaller and less consistent effects.Pod production under high night temperature was not constrainedby flower production since 27 °C at night promoted branchingand flower bud appearance. Under 32/27 °C day/night temperaturethe large reduction in pod set was due to enhanced abscissionof flower buds, flowers and young pods (< 3 cm). Flowershad the highest relative abscission followed by young pods andflower buds. Therefore, the onset of anthesis and of pod developmentwere the plant stages most sensitive to night temperature. Podslarger than 3 cm did not abscise but usually aborted and shrivelledunder high night temperature. The effects of 32/27 °C werenot due to transient water stresses and were observed even undercontinuous irrigation and mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L., cv. Tenderette     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17°C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17°C to 27°Cstrongly reduced pod production, mature pod size and seeds perpod, while an increase in day temperature from 22°C to 32°Chad smaller and less consistent effects. Pod production underhigh night temperature was not constrained by flower productionsince 27°C at night promoted branching and flower bud appearance.Under 32/27°C day/night temperature the large reductionin pod set was due to enhanced abscission of flower buds, flowersand young pods ( 3 cm). Flowers had the highest relative abscissionfollowed by young pods and flower buds. Therefore, the onsetof anthesis and of pod development were the plant stages mostsensitive to night temperature. Pods larger than 3 cm did notabscise but usually aborted and shrivelled under high nighttemperature. The effects of 32/27°C were not due to transientwater stresses and were observed even under continuous irrigationand mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L, Tenderette     

From flower to seed: identifying phenological markers and reliable growth functions to model reproductive development in the common bean (Phaseolus vulgaris L.)

The lack of dependable morphological indicators for the onset and end of seed growth has hindered modeling work in the common bean (Phaseolus vulgaris L.). We have addressed this problem through the use of mathematical growth functions to analyse and identify critical developmental stages, which can be linked to existing developmental indices. We performed this study under greenhouse conditions with an Andean and a Mesoamerican genotype of contrasting pod and seed phenotypes, and three selected recombinant inbred lines. Pods from tagged flowers were harvested at regular time intervals for various measurements. Differences in flower production and seed and pod growth trajectories among genotypes were detected via comparisons of parameters of fitted growth functions. Regardless of the genotype, the end of pod elongation marked the beginning of seed growth, which lasted until pods displayed a sharp decline in color, or pod hue angle. These results suggest that the end of pod elongation and the onset of color change are reliable indicators of important developmental transitions in the seed, even for widely differing pod phenotypes. We also provide a set of equations that can be used to model different aspects of reproductive growth and development in the common bean.     

A Flower and Pod Staging System for Soybean

Flower and pod abscission limit soybean yield. A system forquantifying flower and pod development based on the morphologicalappearance of the flower prior to and following anthesis hasbeen developed to aid in studies of pod abscission. Changesin the appearance of the corolla, primarily the banner petal,are used to distinguish the different stages of the system.External pistil dimensions have been correlated with internalfeatures for each stage of development. From anthesis to podset, pistil length and weight increase almost two- and fivefold,respectively, and ovule development progresses from unfertilizedegg cells to embryos surrounded by cellular endosperm. Pod determinedare correlated with ovule length and width and embryo cell number.Flower and pod stages can be determined in situ, thus permittingnon-destructive observation and experimental manipulation offlowers or pods without necessarily impeding their development.Stages have been identified that indicate precisely when podset occurs and when young pods cease growing and ultimatelyabscise. This system of flower and pod staging is useful instudies designed to assess effects of abiotic or biotic stressand genetic factors on pod set and abortion. Abscission, anthesis, Glycine max (L.) Merr, embryo development, pod set     

Expressed sequence tags of Chinese cabbage flower bud cDNA.

We randomly selected and partially sequenced cDNA clones from a library of Chinese cabbage (Brassica campestris L. ssp. pekinensis) flower bud cDNAs. Out of 1216 expressed sequence tags (ESTs), 904 cDNA clones were unique or nonredundant. Five hundred eighty-eight clones (48.4%) had sequence homology to functionally defined genes at the peptide level. Only 5 clones encoded known flower-specific proteins. Among the cDNAs with no similarity to known protein sequences (628), 184 clones had significant similarity to nucleotide sequences registered in the databases. Among these 184 clones, 142 exhibited similarities at the nucleotide level only with plant ESTs. Also, sequence similarities were evident between these 142 ESTs and their matching ESTs when compared using the deduced amino acid sequences. Therefore, it is possible that the anonymous ESTs encode plant-specific ubiquitous proteins. Our extensive EST analysis of genes expressed in floral organs not only contributes to the understanding of the dynamics of genome expression patterns in floral organs but also adds data to the repertoire of all genomic genes.     

Carbon Transfer and Partitioning between Vegetative and Reproductive Organs in Pisum sativum L

Assimilate partitioning was studied in the common pea (Pisum sativum L.) by feeding ¹⁴CO₂ to whole plants and measuring radioactivity in different organs 48 hours after labeling. Two experimental protocols were used. For the first, one reproductive node was darkened with an aluminum foil, to prevent photosynthesis during labeling. The aim was to study assimilate translocation among nodes. The second was carried out to assess any priority among sinks. Whole plants were shaded, during labeling, to reduce carbon assimilation. Various developmental stages between the onset of flowering and the final stage in seed abortion of the last pod were chosen for labeling. When all photosynthetic structures at the first reproductive node were darkened at any stage of development after the formation of the first flower, the first pod was supplied with assimilates from other nodes. In contrast, later developed pods, when photosynthetic structures at their node were darkened, received assimilates from other nodes only when they were beyond their final stage in seed abortion. Reducing illumination to 30% did not change distribution of assimilated carbon between vegetative and reproductive structures, nor among pods. It appears that the relative proportion of ¹⁴C allocated to any one pod, compared to other pods, depends on the dry weight of that pod as a proportion of the total reproductive dry weight. When the plant was growing actively, following the start of the reproductive phase until a few days before the end of flowering, the top of the plant (i.e., all the organs above the last opened flower) had a higher sink strength and a higher relative specific activity than pods, suggesting that it was a more competitive sink for assimilates. The pattern of assimilate distribution described here provides an explanation for pod and seed abortion.     

Defensin gene family in <Emphasis Type="Italic">Medicago truncatula:</Emphasis> structure,expression and induction by signal molecules

A large gene family encoding the putative cysteine-rich defensins was discovered in Medicago truncatula. Sixteen members of the family were identified by screening a cloned seed defensin from M. sativa (Gao et al. 2000) against the Institute for Genomic Research’s (TIGR) M. truncatula gene index (MtGI version 7). Based on the comparison of their amino acid sequences, M. truncatula defensins fell arbitrarily into three classes displaying extensive sequence divergence outside of the eight canonical cysteine residues. The presence of Class II defensins is reported for the first time in a legume plant. In silico as well as Northern blot and RT-PCR analyses indicated these genes were expressed in a variety of tissues including leaves, flowers, developing pods, mature seed and roots. The expression of these genes was differentially induced in response to a variety of biotic and abiotic stimuli. For the first time, a defensin gene (TC77480) was shown to be induced in roots in response to infection by the mycorrhizal fungus, Glomus versiforme. Northern blot analysis indicated that the tissue-specific expression patterns of the cloned Def1 and Def2 genes differed substantially between M. truncatula and M. sativa. Furthermore, the induction profiles of the Def1 and Def2 genes in response to the signaling molecules methyl jasmonate, ethylene and salicylic acid differed markedly between these two legumes.     

A dynamic role for sterols in embryogenesis of Pisum sativum

Molecular roles of sterols in plant development remain to be elucidated. To investigate sterol composition during embryogenesis, the occurrence of 25 steroid compounds in stages of developing seeds and pods of Pisum sativum was examined by GC-MS analysis. Immature seeds containing very young embryos exhibited the greatest concentrations of sterols. Regression models indicated that the natural log of seed or pod fr. wt was a consistent predictor of declining sterol content during embryonic development. Although total sterol levels were reduced in mature embryos, the composition of major sterols sitosterol and campesterol remained relatively constant in all 12 seed stages examined. In mature seeds, a significant decrease in isofucosterol was observed, as well as minor changes such as increases in cycloartenol branch sterols and campesterol derivatives. In comparison to seeds and pods, striking differences in composition were observed in sterol profiles of stems, shoots, leaves, flowers and flower buds, as well as cotyledons versus radicles. The highest levels of isofucosterol, a precursor to sitosterol, occurred in young seeds and flower buds, tissues that contain rapidly dividing cells and cells undergoing differentiation. Conversely, the highest levels of stigmasterol, a derivative of sitosterol, were found in fully-differentiated leaves while all seed stages exhibited low levels of stigmasterol. The observed differences in sterol content were correlated to mRNA expression data for sterol biosynthesis genes from Arabidopsis. These findings implicate the coordinated expression of sterol biosynthesis enzymes in gene regulatory networks underlying the embryonic development of flowering plants.     

Functional analysis of <Emphasis Type="Italic">SlEZ1</Emphasis> a tomato <Emphasis Type="Italic">Enhancer of zeste</Emphasis> (<Emphasis Type="Italic">E(z))</Emphasis> gene demonstrates a role in flower development

The Enhancer of Zeste (E(z)) Polycomb group (PcG) proteins, which are encoded by a small gene family in Arabidopsis thaliana, have been shown to participate to the control of flowering and seed development. For the time being, little is known about the function of these proteins in other plants. In tomato E(z) proteins are encoded by at least two genes namely SlEZ1 and SlEZ2 while a third gene, SlEZ3, is likely to encode a truncated non-functional protein. The analysis of the corresponding mRNA demonstrates that these two genes are differentially regulated during plant and fruit development. We also show that SlEZ1 and SlEZ2 are targeted to the nuclei. These results together with protein sequence analysis makes it likely that both proteins are functional E(z) proteins. The characterisation of SlEZ1 RNAi lines suggests that although there might be some functional redundancy between SlEZ1 and SlEZ2 in most plant organs, the former protein is likely to play specific function in flower development.     

The Effects of Primates and Squirrels on Seed Survival of a Canopy Tree,Afzelia quanzensis,in Arabuko‐Sokoke Forest,Kenya1

I examined the fate of seeds from ten focal trees of Afzelia quanzensis (Leguminosae), a canopy tree in the Arabuko‐Sokoke, Kenya. The study was conducted for one fruiting season, between August 1990 and July 1991. Yellow baboons (Papio cynocephalus), Syke's monkeys (Cercopithecus albogularis), sun squirrels (Heliosciurus rufobrachium), and bush squirrels (Paraxerus palliatus) were all observed to interact with A. quanzensis seeds at various stages of pod development. Baboons and squirrels consumed high percentages of seeds when they were still immature, but the seeds were still unavailable to Syke's monkeys at this stage. Baboons bit open the hard green pods and squirrels gnawed through the pods to extract the immature seeds (hereafter referred to as seed predation), but monkeys were unable to open the pods. Upon maturity, the pods opened slightly, revealing red arils that were sought by baboons, monkeys, and squirrels. Monkeys removed the highest percentage of mature seeds from these pods. These mammal dispersers ate the arils from the mature seeds and discarded the viable part that germinates (hereafter referred to as seed dispersal). My data indicate that baboons and squirrels are seed predators while monkeys are seed dispersers of A. quanzensis.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.     

The Cryptochrome Gene Family in Pea Includes Two Differentially Expressed <Emphasis Type="Italic">CRY2</Emphasis> Genes

The cryptochromes are a family of blue light photoreceptors that play important roles in the control of plant development. We have characterised the cryptochrome gene family in the model legume garden pea (Pisum sativum L.). Pea contains three expressed cryptochrome genes; a single CRY1 orthologue, and two distinct CRY2 genes that we have termed CRY2a and CRY2b. Genomic southern blots indicate that there are unlikely to be more CRY genes in pea. Each of the three genes encodes a full-length CRY protein that contains all the major domains characteristic of other higher plant cryptochromes. Database searches have identified Medicago truncatula expressed sequence tags (ESTs) corresponding to all three genes, whereas only a single CRY2 is represented in EST collections from the more distantly related legumes soybean and Lotus japonicus. The proteins encoded by the pea and Medicago CRY2b genes are distinguished from other CRY2 proteins by their shorter C-terminus. Expression analyses have identified marked differences in the regulation of the three genes, with CRY2b expression in particular distinguished by high-amplitude diurnal cycling and rapid repression in seedlings transferred from darkness to blue light.