Wheat is one of the founder crops of Western agriculture. This study reconstructs agronomic conditions, potential yields, and kernel weight in the beginnings of cultivation of domesticated free-threshing wheat, c. 8000 BC. The carbon and nitrogen stable isotope compositions and the dimensions of fossil grains of naked wheat (Triticum aestivum/durum) were analysed. Samples were collected in Tell Halula and Akarçay Tepe, two Neolithic archaeological sites from the Middle Euphrates (the claimed core area for wheat domestication). The samples analysed include the oldest reported remains of naked wheat. Consistently wetter conditions but lower kernel weights were found in the Neolithic compared with the present day. Besides, the estimated yields were clearly beyond what is expected from the gathering of wild stands of cereals. Patterns of phenotypic adaptation achieved by wheat after its diffusion through the Mediterranean were also assessed. On the one hand, the study looked at variation in morphophysiological traits as related to local climate in a set of 68 durum wheat landraces from the Middle Euphrates. On the other hand, an assessment was made of regional adaptation around the Mediterranean Basin in a set of 90 landraces, traditional varieties, and modern cultivars from different origins by characterizing agronomic and morphophysiological variability. Significant relationships were observed between phenotypic variation among landraces from the Middle Euphrates and both minimum temperatures and the ratio of precipitation to potential evapotranspiration of the sites of origin. In addition, consistent differences in grain yield, plant structure, and water status were found among genotypes following both north-south and east-west gradients across the Mediterranean. These differences are associated with contrasting environmental and selection pressures.
Carnivory has evolved independently at least six times in five angiosperm orders. In spite of these independent origins, there is a remarkable morphological convergence of carnivorous plant traps and physiological convergence of mechanisms for digesting and assimilating prey. These convergent traits have made carnivorous plants model systems for addressing questions in plant molecular genetics, physiology, and evolutionary ecology. New data show that carnivorous plant genera with morphologically complex traps have higher relative rates of gene substitutions than do those with simple sticky traps. This observation suggests two alternative mechanisms for the evolution and diversification of carnivorous plant lineages. The 'energetics hypothesis' posits rapid morphological evolution resulting from a few changes in regulatory genes responsible for meeting the high energetic demands of active traps. The 'predictable prey capture hypothesis' further posits that complex traps yield more predictable and frequent prey captures. To evaluate these hypotheses, available data on the tempo and mode of carnivorous plant evolution were reviewed; patterns of prey capture by carnivorous plants were analysed; and the energetic costs and benefits of botanical carnivory were re-evaluated. Collectively, the data are more supportive of the energetics hypothesis than the predictable prey capture hypothesis. The energetics hypothesis is consistent with a phenomenological cost-benefit model for the evolution of botanical carnivory, and also accounts for data suggesting that carnivorous plants have leaf construction costs and scaling relationships among leaf traits that are substantially different from those of non-carnivorous plants.
Laminarin‐hydrolysing activity developed in the endosperm of tomato (Lycopersicon esculentum) seeds following germination. The enzyme was basic (pI>10) and the apparent molecular mass was estimated to be 35 kDa by
SDS‐PAGE. It was specific for linear β‐1,3‐glucan substrates. Laminarin was hydrolysed by the enzyme to yield a mixture of
oligoglucosides, indicating that the enzyme had an endo‐action pattern. Thus, the enzyme was identified as β‐1,3‐ endoglucanase
(EC 184.108.40.206). The activity of the enzyme developed in the endosperm after radicle protrusion (germination) had occurred and
the enzyme activity was localized exclusively in the micropylar region of the endosperm where the radicle had penetrated.
When the lateral endosperm region, where no induction of the enzyme occurred, was wounded (cut or punctured), there was a
marked enhancement of β‐1,3‐glucanase activity. Thus the post‐germinative β‐1,3‐glucanase activity in the micropylar endosperm
portion might be brought about by wounding resulting from endosperm rupture by radicle penetration.
Phytoparasitic nematodes secrete an array of effector proteins to modify selected recipient plant cells into elaborate and
essential feeding sites. The biological function of the novel 30C02 effector protein of the soybean cyst nematode, Heterodera glycines, was studied using Arabidopsis thaliana as host and the beet cyst nematode, Heterodera schachtii, which contains a homologue of the 30C02 gene. Expression of Hg30C02 in Arabidopsis did not affect plant growth and development but increased plant susceptibility to infection by H. schachtii. The 30C02 protein interacted with a specific (AT4G16260) host plant β-1,3-endoglucanase in both yeast and plant cells, possibly
to interfere with its role as a plant pathogenesis-related protein. Interestingly, the peak expression of 30C02 in the nematode and peak expression of At4g16260 in plant roots coincided at around 3–5 d after root infection by the nematode, after which the relative expression of At4g16260 declined significantly. An Arabidopsis At4g16260 T-DNA mutant showed increased susceptibility to cyst nematode infection, and plants that overexpressed At4g16260 were reduced in nematode susceptibility, suggesting a potential role of host β-1,3-endoglucanase in the defence response
against H. schachtii infection. Arabidopsis plants that expressed dsRNA and its processed small interfering RNA complementary to the Hg30C02 sequence were not phenotypically different from non-transformed plants, but they exhibited a strong RNA interference-mediated
resistance to infection by H. schachtii. The collective results suggest that, as with other pathogens, active suppression of host defence is a critical component
for successful parasitism by nematodes and a vulnerable target to disrupt the parasitic cycle.
Cellodextrins (CD), water-soluble derivatives of cellulose composed of β-1,4 glucoside residues, have been shown to induce
a variety of defence responses in grapevine (Vitis vinifera L.) cells. The larger oligomers of CD rapidly induced transient generation of H2O2 and elevation in free cytosolic calcium, followed by a differential expression of genes encoding key enzymes of the phenylpropanoid
pathway and pathogenesis-related (PR) proteins as well as stimulation of chitinase and β-1,3 glucanase activities. Most of
these defence reactions were also induced by linear β-1,3 glucans (βGlu) and α-1,4 oligogalacturonides (OGA) of different
degree of polymerization (DP), but the intensity of some reactions induced by CD was different when compared with βGlu and
OGA effects. Moreover, desensitization assays using H2O2 production showed that cells treated with CD remained fully responsive to a second application of OGA, suggesting a different
mode of perception of these oligosaccharides by grape cells. None of CD, βGlu, or OGA induced HSR gene expression nor did
they induce cell death. In accordance with elicitor activity in grapevine cells, CD-incubated leaves challenged with Botrytis cinerea also resulted in a significant reduction of the disease. Data suggest that CD could operate via other distinct reaction pathways
than βGlu and OGA. They also highlight the requirement of a specific DP for each oligosaccharide to induce the defence response.
Root holoparasitic angiosperms, like Orobanche spp, completely lack chlorophyll and totally depend on their host for their supply of nutrients. O. crenata is a severe constraint to the cultivation of legumes and breeding for resistance remains the most economical, feasible, and
environmentally friendly method of control. Due to the lack of resistance in commercial pea cultivars, the use of wild relatives
for breeding is necessary, and an understanding of the mechanisms underlying host resistance is needed in order to improve
screening for resistance in breeding programmes. Compatible and incompatible interactions between O. crenata and pea have been studied using cytochemical procedures. The parasite was stopped in the host cortex before reaching the
central cylinder, and accumulation of H2O2, peroxidases, and callose were detected in neighbouring cells. Protein cross-linking in the host cell walls appears as the
mechanism of defence, halting penetration of the parasite. In situ hybridization studies have also shown that a peroxidase and a β-glucanase are differently expressed in cells of the resistant
host (Pf651) near the penetration point. The role of these proteins in the resistance to O. crenata is discussed.
The leaf surface of a very large number of plant species are covered by trichomes. Non-glandular trichomes are specialized
unicellular or multicellular structures that occur in many different plant species and function in xenobiotic detoxification
and protecting the plant against pest attack. By analysing the susceptibility of trichome mutants, evidence is provided that
indicates the influence of leaf trichomes on foliar fungal infections in Arabidopsis thaliana, probably by facilitating the adhesion of the fungal spores/hyphae to the leaf surface. A decreased trichome number in the
hairless Arabidopsis mutant gl1 enhances tolerance against the necrotrophic fungus Botrytis cinerea. By contrast, the try mutant shows an increased susceptibility to both fungal infection and accumulation. Trichome density does not influence infection
by the soil-borne pathogen Rhizoctonia solani. In addition, the influence of trichomes on foliar infection is supported by targeting the high-level expression of the Trichoderma harzianum α-1,3-glucanase protein to the specialized cell structures. Trichome expression of this anti-fungal hydrolase shows a significant
resistance to infection by the foliar pathogen Botrytis cinerea. Resistance to this fungus is not dependent on the constitutive induction of the salicylic or jasmonic defence signalling
pathways, but the presence of the α-1,3-glucanase protein in trichomes.
Little is known about the molecular basis for seed dormancy, after‐ripening, and radicle emergence through the covering layers
during germination. In tobacco, endosperm rupture occurs after testa rupture and is the limiting step in seed germination.
Class I β‐1,3‐glucanase (βGLU I), which is induced in the micropylar endosperm just prior to its penetration by the radicle,
is believed to help weaken the endosperm wall. Evidence is pesented here for a second site of βGLU I action during after‐ripening.
Tobacco plants were transformed with antisense βGLU I constructs with promoters thought to direct endosperm‐specific expression.
Unexpectedly, these transformants were unaffected in endosperm rupture and did not exhibit reduced βGLU I expression during
germination. Nevertheless, antisense βGLU I transformation delayed the onset of testa rupture in light‐imbibed, after‐ripened
seeds and inhibited the after‐ripening‐mediated release of photodormancy. It is proposed that βGLU I expression in the dry
seed contributes to the after‐ripening‐mediated release of seed dormancy.
The accumulation of the pathogenesis-related (PR) proteins beta-1,3-glucanase and chitinase and structural defence responses were studied in leaves of wheat either resistant or susceptible to the hemibiotrophic pathogen Septoria tritici. Resistance was associated with an early accumulation of beta-1,3-glucanase and chitinase transcripts followed by a subsequent reduction in level. Resistance was also associated with high activity of beta-1,3-glucanase, especially in the apoplastic fluid, in accordance with the biotrophic/endophytic lifestyle of the pathogen in the apoplastic spaces, thus showing the highly localized accumulation of defence proteins in the vicinity of the pathogen. Isoform analysis of beta-1,3-glucanase from the apoplastic fluid revealed that resistance was associated with the accumulation of an endo-beta-1,3-glucanase, previously implicated in defence against pathogens, and a protein with identity to ADPG pyrophosphatase (92%) and germin-like proteins (93%), which may be involved in cell wall reinforcement. In accordance with this, glycoproteins like extensin were released into the apoplast and callose accumulated to a greater extent in cell walls, whereas lignin and polyphenolics were not found to correlate with defence. Treatment of a susceptible wheat cultivar with purified beta-1,3-glucan fragments from cell walls of S. tritici gave complete protection against disease and this was accompanied by increased gene expression of beta-1,3-glucanase and the deposition of callose. Collectively, these data indicate that resistance is dependent on a fast, initial recognition of the pathogen, probably due to beta-1,3-glucan in the fungal cell walls, and this results in the accumulation of beta-1,3-glucanase and structural defence responses, which may directly inhibit the pathogen and protect the host against fungal enzymes and toxins.
(1,3;1,4)-β-D-glucans (mixed-linkage glucans) are found in tissues of members of the Poaceae (grasses), and are particularly high in barley
(Hordeum vulgare) grains. The present study describes the isolation of three independent (1,3;1,4)-β-D-glucanless (betaglucanless; bgl) mutants of barley which completely lack (1,3;1,4)-β-D-glucan in all the tissues tested. The bgl phenotype cosegregates with the cellulose synthase like HvCslF6 gene on chromosome arm 7HL. Each of the bgl mutants has a single nucleotide substitution in the coding region of the HvCslF6 gene resulting in a change of a highly conserved amino acid residue of the HvCslF6 protein. Microsomal membranes isolated
from developing endosperm of the bgl mutants lack detectable (1,3;1,4)-β-D-glucan synthase activity indicating that the HvCslF6 protein is inactive. This was confirmed by transient expression of the
HvCslF6 cDNAs in Nicotiana benthamiana leaves. The wild-type HvCslF6 gene directed the synthesis of high levels of (1,3;1,4)-β-D-glucans, whereas the mutant HvCslF6 proteins completely lack the ability to synthesize (1,3;1,4)-β-D-glucans. The fine structure of the (1,3;1,4)-β-D-glucan produced in the tobacco leaf was also very different from that found in cereals having an extremely low DP3/DP4 ratio.
These results demonstrate that, among the seven CslF and one CslH genes present in the barley genome, HvCslF6 has a unique role and is the key determinant controlling the biosynthesis of (1,3;1,4)-β-D-glucans. Natural allelic variation in the HvCslF6 gene was found predominantly within introns among 29 barley accessions studied. Genetic manipulation of the HvCslF6 gene could enable control of (1,3;1,4)-β-D-glucans in accordance with the purposes of use.
In peach (Prunus persica L. Batsch.) the degradation of the pectic compounds of the cell wall is considered to be the principal component responsible
for fruit softening. Many genes encoding enzymes acting on the different polymers of the pectic matrix have been shown to
be highly expressed during the late phases of softening, with polygalacturonase being the most important. Nevertheless, it
is known that softening starts well before the ethylene climacteric rise which occurs concomitant with the maximal expression
of the pectolytic enzymes. The cloning and characterization of PpEG4, an endo-β-1,4-glucanase (EGase) gene preferentially expressed in preclimacteric fruits, are presented here. PpEG4 belongs
to the group of EGases containing, at their carboxy-terminus, a peptide similar to the cellulose binding domain of microbial
origin. This EGase is also expressed during abscission of both leaves and fruits. The effect of exogenous ethylene treatments
on PpEG4 transcription is null in young fruits and negative in preclimacteric ones, while it is positive in abscission zones. Thus,
the expression of PpEG4 seems to be more dependent on the type of separation process rather than being influenced by a direct hormone action. The
ability of the PpEG4 regulatory sequences to drive transcription in cells undergoing separation events is also maintained in tomato, where about
3 kb of the gene promoter could drive the expression of gusA in preclimacteric fruits and in the fruit abscission zones.
Two endo‐β‐1,4‐glucanase (EGase; EC 220.127.116.11.) genes, highly expressed during ripening of the non‐climacteric strawberries
(Fragaria×ananassa Duch. cv. Chandler), were isolated. Serial promoter deletions of both genes (i.e. FaEG1 and FaEG3) fused to GUS were transiently assayed in strawberry fruits by using a technique recently developed in this laboratory. Although
differences were observed with the short fragments, GUS activity became comparable with the largest fragments of both promoters.
The apparently similar strength of the two largest promoter fragments was in contrast with previous results of Northern analyses
which demonstrated different transcripts amounts for the two genes. The inclusion of the 3′ flanking region of both genes
in the transient assays showed that, in the case of FaEG3, the 3′ region had a down‐regulating effect on the expression of GUS, and this might account for the lower amount of FaEG3 mRNA usually observed in ripe fruits compared to that of FaEG1. Downstream instability elements might be involved in such down‐regulation.
The last step of ascorbic acid (AA) biosynthesis is catalysed by the enzyme l-galactono-1,4-lactone dehydrogenase (GalLDH, EC 18.104.22.168), located on the inner mitochondrial membrane. The enzyme converts
l-galactono-1,4-lactone to ascorbic acid (AA). In this work, the cloning and characterization of a GalLDH full-length cDNA
from melon (Cucumis melo L.) are described. Melon genomic DNA Southern analysis indicated that CmGalLDH was encoded by a single gene. CmGalLDH mRNA accumulation was detected in all tissues studied, but differentially expressed during fruit development and seed germination.
It is hypothesized that induction of CmGalLDH gene expression in ripening melon fruit contributes to parallel increases in the AA content and so playing a role in the
oxidative ripening process. Higher CmGalLDH message abundance in light-grown seedlings compared with those raised in the dark suggests that CmGalLDH expression is regulated by light. Finally, various stresses and growth regulators resulted in no significant change in steady
state levels of CmGalLDH mRNA in 20-d-old melon seedlings. To the authors' knowledge, this is the first report of GalLDH transcript induction in seed
germination and differential gene expression during fruit ripening.
Germinating seeds of Euphorbia heterophylla L. contain endo‐1,4‐β‐glucanases which degrade carboxymethylcellulose (CMC). The activity decreased approximately 66% in
extracts of endosperm containing isopropanol or ethanol. The endoglucanases were isolated from endosperm extracts using ammonium
sulphate fractionation followed by Sephacryl S‐100‐HR chromatography resulting in two main peaks: I and II. Peak I endoglucanase
was further purified about 15‐fold on DEAE‐Sephadex A50 and then by affinity chromatography (CF11‐cellulose). Peak II endoglucanases were further purified 10‐fold on CM‐cellulose
chromatography. The results indicated the occurrence of a 66 kDa endoglucanase (fractionated by SDS‐PAGE and visualized by
activity staining using Congo Red). Several acidic (pI 3.0 to 5.7) and basic (pI 8.5 to 10.0) forms from both peaks which
differed in their capacities for degrading CMC or xyloglucans from Copaifera langsdorffii or Hymenaea courbaril were detected.
The phosphoinositol pathway is one of the major eukaryotic signalling pathways. The metabolite of the phosphoinositol pathway,
inositol- (1,4,5) trisphosphate (InsP3), is a regulator of plant responses to a wide variety of stresses, including light, drought, cold, and salinity. It was found
that the expression of InsP 5-ptase, the enzyme that hydrolyses InsP3, also dramatically affects the levels of inositol phosphate metabolites and the secondary metabolites in transgenic tomato
plants. Tomato plants expressing InsP 5-ptase exhibited a reduction in the levels of several important inositol phosphates, including InsP1, InsP2, InsP3, and InsP4. Reduced levels of inositol phosphates accompanied an increase in the accumulation of phenylpropanoids (rutin, chlorogenic
acid) and ascorbic acid (vitamin C) in the transgenic fruits of tomato plants. The enhanced accumulation of these metabolites
in transgenic tomato plants was in direct correspondence with the observed up-regulation of the genes that express the key
enzymes of ascorbic acid metabolism (myo-inositol oxygenase, MIOX; L-galactono-γ-lactone dehydrogenase, GLDH) and phenylpropanoid metabolism (chalcone synthase, CHS1; cinnamoyl-CoA shikimate/quinate transferase, HCT). To understand the molecular links between the activation of different branches of plant metabolism and InsP3 reduction in tomato fruits, the expression of transcription factors known to be involved in light signalling was analysed
by real-time RT-PCR. The expression of LeHY5, SIMYB12, and LeELIP was found to be higher in fruits expressing InsP 5-ptase. These results suggest possible interconnections between phosphoinositol metabolism, light signalling, and secondary metabolism
in plants. Our study also revealed the biotechnological potential for the genetic improvement of crop plants by the manipulation
of the phosphoinositol pathway.
Despite being the number one fruit crop in the world, very little is known about the phylogeny and molecular biology of banana
(Musa spp.). Six banana rbcS gene families encoding the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from six different Musa spp. are presented. For a comprehensive phylogenetic study using Musa rbcS genes, a total of 57 distinct rbcS sequences was isolated from six accessions that contained different combinations of the A and B ancestral/parental genomes.
As a result, five of the six members of the rbcS gene family could be affiliated with the A and/or B Musa genomes and at least three of the six gene families most likely existed before Musa A and B genomes separated. By combining sequence data with quantitative real-time PCR it was determined that the different
Musa rbcS gene family members are also often multiply represented in each genome, with the highest copy numbers in the B genome. Expression
of some of the rbcS genes varied in intensity and in different tissues indicating differences in regulation. To analyse and compare regulatory
sequences of Musa rbcS genes, promoter and terminator regions were cloned for three Musa rbcS genes. Transient transformation assays using promoter–reporter–terminator constructs in maize, wheat, and sugarcane demonstrated
that the rbcS-Ma1, rbcS-Ma3, and rbcS-Ma5 promoters could be useful for transgene expression in heterologous expression systems. Furthermore, the rbcS-Ma1 terminator resulted in a 2-fold increase of transgene expression when directly compared with the widely used Nos terminator.
The Calvin cycle is the initial pathway of photosynthetic carbon fixation, and several of its reaction steps are suggested
to exert rate-limiting influence on the growth of higher plants. Plastid fructose 1,6-bisphosphate aldolase (aldolase, EC
22.214.171.124) is one of the nonregulated enzymes comprising the Calvin cycle and is predicted to have the potential to control
photosynthetic carbon flux through the cycle. In order to investigate the effect of overexpression of aldolase, this study
generated transgenic tobacco (Nicotiana tabacum L. cv Xanthi) expressing Arabidopsis plastid aldolase. Resultant transgenic plants with 1.4–1.9-fold higher aldolase activities than those of wild-type plants
showed enhanced growth, culminating in increased biomass, particularly under high CO2 concentration (700 ppm) where the increase reached 2.2-fold relative to wild-type plants. This increase was associated with
a 1.5-fold elevation of photosynthetic CO2 fixation in the transgenic plants. The increased plastid aldolase resulted in a decrease in 3-phosphoglycerate and an increase
in ribulose 1,5-bisphosphate and its immediate precursors in the Calvin cycle, but no significant changes in the activities
of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) or other major enzymes of carbon assimilation. Taken together,
these results suggest that aldolase overexpression stimulates ribulose 1,5-bisphosphate regeneration and promotes CO2 fixation. It was concluded that increased photosynthetic rate was responsible for enhanced growth and biomass yields of aldolase-overexpressing
The pea chloroplastic fructose-1,6-bisphosphatase (FBPase) antisense construct reduced the endogenous level of expression of the corresponding Arabidopsis thaliana gene. The reduction of foliar FBPase activity in the transformants T2 and T3 generation ranged from 20% to 42%, and correlated with lower levels of FBPase protein. FBPase antisense plants displayed
different phenotypes with a clear increase in leaf fresh weight. Measurements of photosynthesis revealed a higher carbon-assimilation
rate. Decreased FBPase activity boosted the foliar carbohydrate contents, with a shift in the sucrose:starch ratio, which
reached a maximum of 0.99 when the activity loss was 41%. Nitrate reductase activity decreased simultaneously with an increase
in glutamine synthetase activity, which could be explained in terms of ammonium assimilation regulation by sugar content.
These results suggest the role of FBPase as a key enzyme in CO2 assimilation, and also in co-ordinating carbon and nitrogen metabolism.
Thioredoxins (Trxs) f and m, as well as their targets chloroplast fructose‐1,6‐bisphosphatase (FBPase) and NADP+‐malate dehydrogenase (NADP‐MDH), displayed transcriptional expression in both photosynthetic and non‐photosynthetic organs
of pea plants (Pisum sativum L. cv. Lincoln) grown for 50 d under normal irradiance. However, whereas Trx m and both target enzymes were poorly expressed in non‐photosynthetic tissues, the content of the precursor form of the Trx
f‐specific mRNA was high in pea roots. In contrast, the translational expression of Trx f was low in this organ. The high FBPase activity in immature seeds, and the low activity of leaves, must be related to high
starch synthesis in the first, and with high sucrose formation in the second. The transcriptional expression of FBPase and
NADP+‐MDH, and to a lesser extent that of Trxs f and m, was inhibited under low irradiance in plants grown under both normal and high temperatures. Pea plants grown at low temperature
displayed a high level of mRNAs for Trxs and their targets, especially when the growth was carried out at low light. To a
lesser extent, similar behaviour was observed at the protein level. Chloroplasts of mesophyll leaf cells of pea plants grown
under saturating light, or under sub‐saturating continuous irradiance, showed broken envelopes, distorted structural elements
and disorganized starch grains, as a consequence of a photobleaching process and high starch accumulation.
A previous study on maize F2:3 families derived from Lo964×Lo1016 highlighted one QTL in bin 1.06 (hereafter named root-yield-1.06) affecting root and agronomic traits of plants grown in well-watered (WW) and water-stressed (WS) conditions. Starting from
different F4 families, two pairs of near isogenic lines (NILs) were developed at root-yield-1.06. The objective of this study was to evaluate root-yield-1.06 effects across different water regimes, genetic backgrounds, and inbreeding levels. The NILs per se and their crosses with Lo1016 and Lo964 were tested in 2008 and 2009 near to Bologna, with the well-watered (WW) and water-stressed
(WS) treatments providing, on average, 70 mm and 35 mm of water, respectively. For NILs per se, the interactions QTL×water regime and QTL×family were negligible in most cases; the QTL additive effects across families
were significant for several traits, especially root clump weight. For NILs crosses, analogously to NILs per se, the interactions were generally negligible and the additive effects across water regimes and families were significant for
most traits, especially grain yield. A meta-analysis carried out considering the QTLs described in this and previous studies
inferred one single locus as responsible for the effects on roots and agronomic traits. Our results show that root-yield-1.06 has a major constitutive effect on root traits, plant vigour and productivity across water regimes, genetic backgrounds,
and inbreeding levels. These features suggest that root-yield-1.06 is a valuable candidate for cloning the sequence underlying its effects and for marker-assisted selection to improve yield
stability in maize.
This paper describes the ddd genes that are involved in the production of the gas dimethyl sulphide from the substrate dimethylsulphoniopropionate (DMSP),
an abundant molecule that is a stress protectant in many marine algae and a few genera of angiosperms. What is known of the
arrangement of the ddd genes in different bacteria that can undertake this reaction is reviewed here, stressing the fact that these genes are probably
subject to horizontal gene transfer and that the same functions (e.g. DMSP transport) may be accomplished by very different
mechanisms. A surprising number of DMS-emitting bacteria are associated with the roots of higher plants, these including strains
of Rhizobium and some rhizosphere bacteria in the genus Burkholderia. One newly identified strain that is predicted to make DMS is B. phymatum which is a highly unusual β-proteobacterium that forms N2-fixing nodules on some tropical legumes, in this case, the tree Machaerium lunatum, which inhabits mangroves. The importance of DMSP catabolism and DMS production is discussed, not only in terms of nutritional
acquisition by the bacteria but also in a speculative scheme (the ‘messy eater’ model) in which the bacteria may make DMS
as an info-chemical to attract other organisms, including invertebrates and other plankton.
Uptake and retranslocation of leaf‐applied radiolabelled cadmium (109Cd) was studied in three diploid (Triticum monococcum, AA), four tetraploid (Triticum turgidum, BBAA) and two hexaploid (Triticum aestivum, BBAADD) wheat genotypes grown for 9 d under controlled environmental conditions in nutrient solution. Among the tetraploid
wheats, two genotypes were primitive (ssp. dicoccum) and two genotypes modern wheats (ssp. durum). Radiolabelled Cd was applied by immersing the tips (3 cm) of mature leaf into a 109Cd radiolabelled solution. There was a substantial variation in the uptake and export of 109Cd among and within wheat species. On average, diploid wheats (AA) absorbed and translocated more 109Cd than other wheats. The largest variation in 109Cd uptake was found within tetraploid wheats (BBAA). Primitive tetraploid wheats (ssp. dicoccum) had a greater uptake capacity for 109Cd than modern tetraploid wheats (ssp. durum). In all wheats studied, the amount of the 109Cd exported from the treated leaf into the roots and the remainder of the shoots was poorly related to the total absorption.
For example, bread wheat cultivars were more or less similar in total absorption, but differed greatly in the amount of 109Cd retranslocated. The diploid wheat genotype ‘FAL‐43’ absorbed the lowest amount of 109Cd, but retranslocated the greatest amount of 109Cd in roots and remainder of shoots. The results indicate the existence of substantial genotypic variation in the uptake and
retranslocation of leaf‐applied 109Cd. This variation is discussed in terms of potential genotypic differences in binding of Cd to cell walls and the composition
of phloem sap ligands possibly affecting Cd transport into sink organs.
Intrinsic water use efficiency (WUE(intr)), the ratio of photosynthesis to stomatal conductance to water, is often used as an index for crop water use in breeding projects. However, WUE(intr) conflates variation in these two processes, and thus may be less useful as a selection trait than knowledge of both components. The goal of the present study was to determine whether the contribution of photosynthetic capacity and stomatal conductance to WUE(intr) varied independently between soybean genotypes and whether this pattern was interactive with mild drought. Photosynthetic capacity was defined as the variation in WUE(intr) that would occur if genotypes of interest had the same stomatal conductance as a reference genotype and only differed in photosynthesis; similarly, the contribution of stomatal conductance to WUE(intr) was calculated assuming a constant photosynthetic capacity across genotypes. Genotypic differences in stomatal conductance had the greatest effect on WUE(intr) (26% variation when well watered), and was uncorrelated with the effect of photosynthetic capacity on WUE(intr). Thus, photosynthetic advantages of 8.3% were maintained under drought. The maximal rate of Rubisco carboxylation, generally the limiting photosynthetic process for soybeans, was correlated with photosynthetic capacity. As this trait was not interactive with leaf temperature, and photosynthetic capacity differences were maintained under mild drought, the observed patterns of photosynthetic advantage for particular genotypes are likely to be consistent across a range of environmental conditions. This suggests that it is possible to employ a selection strategy of breeding water-saving soybeans with high photosynthetic capacities to compensate for otherwise reduced photosynthesis in genotypes with lower stomatal conductance.
In this study, it has been determined whether the arbuscular mycorrhizal (AM) symbiosis is able to alter the pattern of dehydrin
(LEA D-11 group) transcript accumulation under drought stress, and whether such a possible alteration functions in the protection
of the host plants against drought. Two dehydrin-encoding genes have been cloned from Glycine max (gmlea 8 and gmlea 10) and one from Lactuca sativa (lslea 1) and they have been analysed for their contribution to the response against drought in mycorrhizal soybean and lettuce plants.
Results with soybean plants showed that most of the treatments did not show LEA gene expression under well-watered conditions.
The higher gene expression was found in non-inoculated plants subjected to drought. Only plants singly inoculated with Bradyrhizobium japonicum showed an important level of LEA gene expression under well-watered conditions and a reduced level under drought-stress conditions.
The same results were confirmed in subsequent experiments and at the latest stage of a time-course experiment. In lettuce,
the lslea 1 gene was also induced by drought stress in all treatments. However, the level of induction was clearly higher in roots from
non-inoculated plants than in roots from the two AM treatments assayed. The overall results demonstrated that the levels of
lea transcript accumulation in mycorrhizal treatments subjected to drought were considerably lower than in the corresponding
non-mycorrhizal plants, indicating that the accumulation of LEA proteins is not a mechanism by which the AM symbiosis protects
their host plant.
The hybrid Richter-110 (Vitis berlandierixVitis rupestris) has the reputation of being a genotype strongly adapted to drought. A study was performed with plants of R-110 subjected to sustained water-withholding to induce acclimation to two different levels of water stress, followed by rewatering to induce recovery. The goal was to analyse how photosynthesis is regulated during acclimation to water stress and recovery. In particular, the regulation of stomatal conductance (g(s)), mesophyll conductance to CO(2) (g(m)), leaf photochemistry (chlorophyll fluorescence and thermoluminescence), and biochemistry (V(c,max)) were assessed. During water stress, g(s) declined to 0.1 and less than 0.05 mol CO(2) m(-2) s(-1) in moderately and severely water-stressed plants, respectively, and was kept quite constant during an acclimation period of 1-week. Leaf photochemistry proved to be very resistant to the applied water-stress conditions. By contrast, g(m) and V(c,max) were affected by water stress, but they were not kept constant during the acclimation period. g(m) was initially unaffected by water stress, and V(c,max) even increased above control values. However, after several days of acclimation to water stress, both parameters declined below (g(m)) or at (V(c,max)) control values. For the latter two parameters there seemed to be an interaction between water stress and cumulative irradiance, since both recovered to control values after several cloudy days despite water stress. A photosynthesis limitation analysis revealed that diffusional limitations and not biochemical limitations accounted for the observed decline in photosynthesis during water stress and slow recovery after rewatering, both in moderately and severely stressed plants. However, the relative contribution of stomatal (SL) and mesophyll conductance (MCL) limitations changes during acclimation to water stress, from predominant SL early during water stress to similar SL and MCL after acclimation. Finally, photosynthesis recovery after rewatering was mostly limited by SL, since stomatal closure recovered much more slowly than g(m).
The nucleotide sequences of eight cDNAs encoding putative aquaporins obtained from a leaf Vitis hybrid Richter-110 cDNA library are reported. They encode proteins ranging from 249 to 287 amino acids with characteristic sequences that clearly include them within the MIP family. According to available database sequence homologies, they can be classified into four groups belonging to two subfamilies: PIP (PIP1 and PIP2) and TIP (gamma-TIP and delta-TIP). In order to elucidate the expression patterns of these putative aquaporins in the plant, specific probes were developed and tissue specific differential expression was tested by reverse Northern and compared with two reference genes (malic enzyme and glutamate dehydrogenase). Clearly, most of the putative aquaporins had higher expression in roots, whereas expression in shoot and leaves was generally weaker than the reference genes.
Endoribonuclease E (RNase E) is a regulator of global gene expression in Escherichia coli and is the best studied member of the RNase E/G ribonuclease family. Homologues are present in other bacteria but the roles
of plant RNase E/G-like proteins are not known. Arabidopsis thaliana contains a single nuclear gene (At2g04270) encoding a product with the conserved catalytic domain of RNase E/G-like proteins.
At2g04270 and the adjacent At2g04280 gene form converging transcription units with a ∼40 base overlap at their 3’ ends. Several
translation products were predicted from the analyses of At2g04270 cDNAs. An antibody raised against a recombinant A. thaliana RNase E/G-like protein recognized a 125 kDa protein band in purified chloroplast preparations fractionated by SDS-PAGE. The
125 kDa RNase E/G-like protein was detected in cotyledons, rosette and cauline leaves. T-DNA insertions in exon 6 or intron
11 of At2g04270 result in loss of the 125 kDa band or truncation to a 110 kDa band. Loss of At2g04270 function resulted in
the arrest of chloroplast development, loss of autotrophic growth, and reduced plastid ribosomal, psbA and rbcL RNA levels. Homozygous mutant plants were pale-green, contained smaller plastids with fewer thylakoids and shorter granal
stacks than wild-type chloroplasts, and required sucrose at all growth stages following germination right up to flowering
and setting seeds. Recombinant A. thaliana RNase E/G-like proteins rescued an E. coli RNase E mutant and cleaved an rbcL RNA substrate. Expression of At2g04270 was highly correlated with genes encoding plastid polyribonucleotide phosphorylase,
S1 RNA-binding, and CRS1/YhbY domain proteins.
The relative contribution of glutamate dehydrogenase (GDH) and the aminotransferase activity to mitochondrial glutamate metabolism
was investigated in dilute suspensions of purified mitochondria from potato (Solanum tuberosum) tubers. Measurements of glutamate‐dependent oxygen consumption by mitochondria in different metabolic states were complemented
by novel in situ NMR assays of specific enzymes that metabolize glutamate. First, a new assay for aminotransferase activity, based on the
exchange of deuterium between deuterated water and glutamate, provided a method for establishing the effectiveness of the
aminotransferase inhibitor amino‐oxyacetate in situ, and thus allowed the contribution of the aminotransferase activity to glutamate oxidation to be assessed unambiguously.
Secondly, the activity of GDH in the mitochondria was monitored in a coupled assay in which glutamine synthetase was used
to trap the ammonium released by the oxidative deamination of glutamate. Thirdly, the reversibility of the GDH reaction was
investigated by monitoring the isotopic exchange between glutamate and [15N]ammonium. These novel approaches show that the oxidative deamination of glutamate can make a significant contribution to
mitochondrial glutamate metabolism and that GDH can support the aminotransferases in funnelling carbon from glutamate into
the TCA cycle.
Most plant oxylipins, a large class of diverse oxygenated polyunsaturated fatty acids and their derivatives, are produced through the lipoxygenase (LOX) pathway. Recent progress in dicots has highlighted the biological roles of oxylipins in plant defence responses to pathogens and pests. By contrast, the physiological function of LOXs and their metabolites in monocots is poorly understood. Two maize LOXs, ZmLOX10 and ZmLOX11 that share >90% amino acid sequence identity but are localized on different chromosomes, were cloned and characterized. Phylogenetic analysis revealed that ZmLOX10 and ZmLOX11 cluster together with well-characterized plastidic type 2 linoleate 13-LOXs from diverse plant species. Regio-specificity analysis of recombinant ZmLOX10 protein overexpressed in Escherichia coli proved it to be a linoleate 13-LOX with a pH optimum at approximately pH 8.0. Both predicted proteins contain putative transit peptides for chloroplast import. ZmLOX10 was preferentially expressed in leaves and was induced in response to wounding, cold stress, defence-related hormones jasmonic acid (JA), salicylic acid (SA), and abscisic acid (ABA), and inoculation with an avirulent strain of Cochliobolus carbonum. These data suggested a role for this gene in maize adaptation to abiotic stresses and defence responses against pathogens and pests. ZmLOX11 was preferentially expressed in silks and was induced in leaves only by ABA, indicating its possible involvement in responses to osmotic stress. In leaves, mRNA accumulation of ZmLOX10 is strictly regulated by a circadian rhythm, with maximal expression coinciding temporally with the highest photosynthetic activity. This study reveals the evolutionary divergence of physiological roles for relatively recently duplicated genes. Possible physiological functions of these 13-LOXs are suggested.
Mesophyll conductance (gm) is now recognized as an important limiting process for photosynthesis, as it results in a significant decrease of CO2 diffusion from substomatal cavities where water evaporation occurs, to chloroplast stroma. Over the past decade, an increasing
number of studies proposed that gm can vary in the short term (e.g. minutes), but these variations are still controversial, especially those potentially induced
by changing CO2 and irradiance. In this study, gm data estimated with online 13C discrimination recorded with a tunable diode laser absorption spectrometer (TDL-AS) during leaf gas exchange measurements,
and based on the single point method, are presented. The data were obtained with three Eucalyptus species. A 50% decrease in gm was observed when the CO2 mole fraction was increased from 300 μmol mol−1 to 900 μmol mol−1, and a 60% increase when irradiance was increased from 200 μmol mol−1 to 1100 μmol mol−1 photosynthetic photon flux density (PPFD). The relative contribution of respiration and photorespiration to overall 13C discrimination was also estimated. Not taking this contribution into account may lead to a 50% underestimation of gm but had little effect on the CO2- and irradiance-induced changes. In conclusion, (i) the observed responses of gm to CO2 and irradiance were not artefactual; (ii) the respiratory term is important to assess absolute values of gm but has no impact on the responses to CO2 and PPFD; and (iii) increasing irradiance and reducing the CO2 mole fraction results in rapid increases in gm in Eucalyptus seedlings.
C5 volatile compounds, derived from fatty acids, are among the most important contributors to consumer liking of fresh tomatoes.
Despite their important roles in flavour, the genes responsible for C5 volatile synthesis have yet to be identified. This
work shows that their synthesis is catalysed in part by a 13-lipoxygenase (LOX), TomloxC, the same enzyme responsible for
synthesis of C6 volatiles. C5 synthesis is independent of hydroperoxide lyase (HPL); moreover, HPL knockdown significantly
increased C5 volatile synthesis. This LOX-dependent, HPL-independent pathway functions in both fruits and leaves. Synthesis
of C5 volatiles increases in leaves following mechanical wounding but does not increase in response to infection with Xanthomonas campestris pv. vesicatoria. Large reductions in C5 and C6 volatiles in antisense TomloxC knockdown plants were observed but those reductions did not alter the development of disease symptoms, indicating that these
volatiles do not have an important defensive function against this bacterial pathogen.
Understanding of the control of metabolic pathways in plants requires direct measurement of the metabolic turnover rate. Sugar
phosphate metabolism, including the Calvin cycle, is the primary pathway in C3 photosynthesis, the dynamic status of which has not been assessed quantitatively in the leaves of higher plants. Since the
flux of photosynthetic carbon metabolism is affected by the CO2 fixation rate in leaves, a novel in vivo 13C-labelling system was developed with 13CO2 for the kinetic determination of metabolic turnover that was the time-course of the 13C-labelling ratio in each metabolite. The system is equipped with a gas-exchange chamber that enables real-time monitoring
of the CO2 fixation rate and a freeze-clamp that excises a labelled leaf concurrently with quenching the metabolic reactions by liquid
nitrogen within the photosynthesis chamber. Kinetic measurements were performed by detecting mass isotopomer abundance with
capillary electrophoresis-tandem mass spectrometry. The multiple reaction monitoring method was optimized for the determination
of each compound for sensitive detection because the amount of some sugar phosphates in plant cells is extremely small. Our
analytical system enabled the in vivo turnover of sugar phosphates to be monitored in fresh tobacco (Nicotiana tabacum) leaves, which revealed that the turnover rate of glucose-1-phosphate (G1P) was significantly lower than that of other sugar
phosphates, including glucose-6-phosphate (G6P). The pool size of G1P is 12 times lower than that of G6P. These results indicate
that the conversion of G6P to G1P is one of the rate-limiting steps in the sugar phosphate pathway.
Using 13C-NMR, methyl-β-D-glucopyranoside (MeG) was characterized as a major compound in the leaves of the alpine herb Geum montanum L. MeG continuously accumulated during the life span of G. montanum leaves, and accounted for up to 20% of the soluble carbohydrates in aged overwintering leaves, without being reallocated
during senescence. Incubating intact plant tissues, culture cells, and purified organelles with 13C-labelled substrates showed that MeG was synthesized in the cytosol of cells, directly from glucose and methanol molecules.
There was no contribution of the C-1 pathway. MeG was subsequently stored in the vacuole without being re-exported to the
cytoplasm. All the dicots tested contained the enzymatic machinery permitting MeG synthesis from methanol and glucose, but
the plants accumulating this compound at concentrations higher than 1 μmol g−1 wet wt were mainly members of the Rosaceae family belonging to the Rosoideae subfamily. It is suggested that the synthesis
of MeG may contribute to reduce the accumulation in the cytoplasm of methanol and its derived compounds.
13C discrimination in organic matter with respect to atmospheric CO2 (Δ13C) is under tight genetic control in many plant species, including the pedunculate oak (Quercus robur L.) full-sib progeny used in this study. Δ13C is expected to reflect intrinsic water use efficiency, but this assumption requires confirmation due to potential interferences
with mesophyll conductance to CO2, or post-photosynthetic discrimination. In order to dissect the observed Δ13C variability in this progeny, six genotypes that have previously been found to display extreme phenotypic values of Δ13C [either very high (‘high Δ’) or low (‘low Δ’) phenotype] were selected, and transpiration efficiency (TE; accumulated biomass/transpired
water), net CO2 assimilation rate (A), stomatal conductance for water vapour (gs), and intrinsic water use efficiency (Wi=A/gs) were compared with Δ13C in bulk leaf matter, wood, and cellulose in wood. As expected, ‘high Δ’ displayed higher values of Δ13C not only in bulk leaf matter, but also in wood and cellulose. This confirmed the stability of the genotypic differences
in Δ13C recorded earlier. ‘High Δ’ also displayed lower TE, lower Wi, and higher gs. A small difference was detected in photosynthetic capacity but none in mesophyll conductance to CO2. ‘High Δ’ and ‘low Δ’ displayed very similar leaf anatomy, except for higher stomatal density in ‘high Δ’. Finally, diurnal
courses of leaf gas exchange revealed a higher gs in ‘high Δ’ in the morning than in the afternoon when the difference decreased. The gene ERECTA, involved in the control of water use efficiency, leaf differentiation, and stomatal density, displayed higher expression
levels in ‘low Δ’. In this progeny, the variability of Δ13C correlated closely with that of Wi and TE. Genetic differences of Δ13C and Wi can be ascribed to differences in stomatal conductance and stomatal density but not in photosynthetic capacity.
Phloem is a central conduit for the distribution of photoassimilate, nutrients, and signals among plant organs. A revised
technique was used to collect phloem sap from small woody plants in order to assess changes in composition induced by water
deficit and flooding. Bled phloem sap δ13C and sugar concentrations were compared to δ13C of bulk material, soluble carbon extracts, and the neutral sugar fraction from leaves. Amino acid composition and inorganic
ions of the phloem sap was also analysed. Quantitative, systematic changes were detected in phloem sap composition and δ13C in response to altered water availability. Phloem sap δ13C was more sensitive to changes of water availability than the δ13C of bulk leaf, the soluble carbon fraction, and the neutral soluble fraction of leaves. Changes in water availability also
resulted in significant changes in phloem sugar (sucrose and raffinose), inorganic nutrient (potassium), and amino acid (phenylalanine)
concentrations with important implications for the maintenance of phloem function and biomass partitioning. The differences
in carbohydrate and amino acid composition as well as the δ13C in the phloem, along with a new model system for phloem research, offer an improved understanding of the phloem-mediated
signal, nutrient, and photoassimilate transduction in relation to water availability.
Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid‐state 13C‐NMR spectroscopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C‐1 or C‐4
with 13C‐isotope was incorporated into the cell‐wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled
with d‐[1‐13C]glucose and, by exploiting the differences in rotating‐frame and spin‐spin proton relaxation, a small signal was detected
which was assigned to Xyl of XGs with rigid glucan backbones. After labelling seedlings with d‐[4‐13C]glucose and using a novel combination of spin‐echo spectroscopy with proton spin relaxation‐editing, signals were detected
that had 13C‐spin relaxations and chemical shifts which were assigned to partly‐rigid XGs surrounded by mobile non‐cellulosic polysaccharides.
Although quantification of these two mobility types of XG was difficult, the results indicated that the partly‐rigid XGs were
predominant in the cell walls. The results lend support to the postulated new cell‐wall models in which only a small proportion
of the total surface area of the cellulose microfibrils has XG adsorbed on to it. In these new models, the partly‐rigid XGs
form cross‐links between adjacent cellulose microfibrils and/or between cellulose microfibrils and other non‐cellulosic polysaccharides,
such as pectic polysaccharides.
The objective of this study was to evaluate the effect of deficit irrigation on intrinsic water use efficiency (A/g(s)) and carbon isotope composition (delta13C) of two grapevine cultivars (Moscatel and Castelão), growing in a commercial vineyard in SW Portugal. The study was done in two consecutive years (2001 and 2002). The treatments were full irrigation (FI), corresponding to 100% of crop evapotranspiration (ETc), rain-fed (no irrigation, NI), and two types of deficit irrigation (50% ETc): (i) by supplying the water either to one side of the root system or to the other, which is partial rootzone drying (PRD), or (ii) dividing the same amount of water by the two sides of the root system, the normal deficit irrigation (DI). The water supplied to the PRD treatment alternated sides approximately every 15 d. The values of predawn leaf water potential (Psi(pd)) and the cumulative integral of Psi(pd) (S(Psi)) during the season were lower in 2001 than in the 2002 growing season. Whereas differences in Psi(pd) and S(Psi) between PRD and DI were not significantly different in 2001, in 2002 (a dryer year) both cultivars showed lower values of S(Psi) in the PRD treatment as compared with the DI treatment. This suggests that partial rootzone drying may have a positive effect on water use under dryer conditions, either as a result of better stomatal control and/or reduced vigour. The effects of the water treatments on delta13C were more pronounced in whole grape berries and pulp than in leaves. The delta13C of pulp showed the best correlation with intrinsic water use efficiency (A/g(s)) as well as with S(Psi). In spite of the better water status observed in PRD compared with DI in the two cultivars in 2002, no statistical differences between the two treatments were observed in A/g(s) and delta13C. On the other hand, they showed a higher delta13C compared with FI. In conclusion, it is apparent that the response to deficit irrigation varies with the environmental conditions of the particular year, the driest conditions exacerbating the differences among treatments. The highest values of delta13C found in the pulp of NI vines in Castelão compared with Moscatel suggest different sensitivities to water deficits in the two cultivars, as was empirically observed.
Mesophyll conductance to CO2 (gm) limits carbon assimilation and influences carbon isotope discrimination (Δ) under most environmental conditions. Current
work is elucidating the environmental regulation of gm, but the influence of gm on model predictions of Δ remains poorly understood. In this study, field measurements of Δ and gm were obtained using a tunable diode laser spectroscope coupled to portable photosynthesis systems. These data were used to
test the importance of gm in predicting Δ using the comprehensive Farquhar model of Δ (Δcomp), where gm was parameterized using three methods based on: (i) mean gm; (ii) the relationship between stomatal conductance (gs) and gm; and (iii) the relationship between time of day (TOD) and gm. Incorporating mean gm, gs-based gm, and TOD-based gm did not consistently improve Δcomp predictions of field-grown juniper compared with the simple model of Δ (Δsimple) that omits fractionation factors associated with gm and decarboxylation. Sensitivity tests suggest that b, the fractionation due to carboxylation, was lower (25‰) than the value commonly used in Δcomp (29‰) and Δsimple (27‰). These results demonstrate the limits of all tested models in predicting observed juniper Δ, largely due to unexplained
offsets between predicted and observed values that were not reconciled in sensitivity tests of variability in gm, b, or e, the day respiratory fractionation.
To integrate the complex physiological responses of plants to stress, natural abundances (δ) of the stable isotope pairs 15N/14N and 13C/12C were measured in 30 genotypes of wild barley (Hordeum spontaneum C. Koch.). These accessions, originating from ecologically diverse sites, were grown in a controlled environment and subjected
to mild, short‐term drought or N‐starvation. Increases in total dry weight were paralleled by less negative δ13C in shoots and, in unstressed and droughted plants, by less negative whole‐plant δ13C. Root δ15N was correlated negatively with total dry weight, whereas shoot and whole‐plant δ15N were not correlated with dry weight. The difference in δ15N between shoot and root varied with stress in all genotypes. Shoot–root δ15N may be a more sensitive indicator of stress response than shoot, root or whole‐plant δ15N alone. Among the potentially most productive genotypes, the most stress‐tolerant had the most negative whole‐plant δ15N, whether the stress was drought or N‐starvation. In common, controlled experiments, genotypic differences in whole‐plant
δ15N may reflect the extent to which N can be retained within plants when stressed.
In Japanese pear, the application of GA3+4 during the period of rapid fruit growth resulted in a marked increase in pedicel diameter and bigger fruit at harvest. To elucidate the relationship between pedicel capacity and fruit growth and to determine the main factor responsible for larger fruit size at harvest, fruit growth and pedicel vascularization after GA application were examined and the carbohydrate fluxes were monitored in a spur unit by non-invasive techniques using 13C tracer. Histological studies of fruit revealed that GA increased the cell size of the mesocarp but not the cell number and core size. The investigation of carbon partitioning showed that an increase in the specific rate of carbohydrate accumulation in fruit or the strength of fruit should be responsible for an increase of fruit weight in GA-treated trees. Observation of pedicel vascularization showed that an increase in pedicel cross-sectional area (CSA) by GA application mainly resulted from phloem and xylem CSA, but it is unlikely that an increase in the transport system is the direct factor for larger fruit size. Therefore, it can be concluded that larger fruit size resulting from GA application during the period of rapid fruit growth caused an increase in the cell size of the mesocarp and increased carbon partitioning to the fruit. Although GA is closely involved with pedicel vascularization, it seems that photosynthate accumulation in fruit is limited by the sink strength of fruit rather than by the transport capacity of the pedicel.
The role of fructans from leaf sheaths for the refoliation of Lolium perenne after severe defoliation was assessed by following the fate of 13C‐fructose supplied to leaf sheaths at the time of defoliation. At the end of the 4 h labelling period on defoliated plants,
77% of the 13C incorporated was still located in leaf sheaths. Only 4% and 0.9% were, respectively, allocated to stem and roots, while
18% was imported by the growing leaves where 13C was allocated first to the proximal part of the leaf growth zone (0–10 mm). In all tissues, the most highly 13C‐labelled carbohydrates was not fructose but sucrose. In leaf sheaths, 13C‐loliose was produced. In the leaf growth zone (0–20 mm), fructans were simultanously synthesized from 13C entering the leaves and degraded. The export of 13C from leaf sheaths continued during the first day of regrowth but stopped afterwards. There was no net loss of C from 13C‐fructose over the first 2 d of regrowth. The role of fructans and loliose is discussed as well as the physiological mechanisms
contributing to defoliation tolerance in L. perenne.
High-resolution 13C MAS NMR spectroscopy was used to profile a range of primary and secondary metabolites in vivo in intact whole seeds of eight different conifer species native to North America, including six of the Pinaceae family and
two of the Cupressaceae family. In vivo 13C NMR provided information on the total seed oil content and fatty acid composition of the major storage lipids in a non-destructive
manner. In addition, a number of monoterpenes were identified in the 13C NMR spectra of conifer seeds containing oleoresin; these compounds showed marked variability in individual seeds of Pacific
silver fir within the same seed lot. In imbibed conifer seeds, the 13C NMR spectra showed the presence of considerable amounts of dissolved sucrose presumed to play a protective role in the desiccation-tolerance
of seeds. The free amino acids arginine and asparagine, generated as a result of storage protein mobilization, were detected
in vivo during seed germination and early seedling growth. The potential for NMR to profile metabolites in a non-destructive manner
in single conifer seeds and seed populations is discussed. It is a powerful tool to evaluate seed quality because of its ability
to assess reserve accumulation during seed development or at seed maturity; it can also be used to monitor reserve mobilization,
which is critical for seedling emergence.
In ongoing investigations of the role of the signal transduction pathway in tree–pathogen interactions, four complete and
two partial 14‐3‐3 cDNAs have been isolated which are members of a gene family. Comparisons of DNA sequences reveal a high
degree of identity among the cDNAs, and, in some cases, higher than 75% sequence similarity with previously published sequences.
Sequence analysis at the amino acid level uncovered potential phosphorylation sites, some of which were identical among the
proteins, and some of which varied. Treatment of trees with chitosan, jasmonates or by wounding of leaves, caused increases
in the levels of 14‐3‐3 mRNA transcripts. Since jasmonates and chitosan are signal transducers of defence reactions in plants,
these results suggest a possible role for 14‐3‐3 proteins in the pathogen defence response of deciduous trees. Effects of
elicitors on transcription of the pal gene were also monitored. Pal is a well‐characterized, pathogen response‐related gene.
Proteins of the 14-3-3 family regulate a divergent set of signalling pathways in all eukaryotic organisms. In this study,
several cDNAs encoding 14-3-3 proteins were isolated from a cotton fibre cDNA library. The Gh14-3-3 genes share high sequence homology at the nucleotide level in the coding region and at the amino acid level. Real-time quantitative
RT-PCR analysis indicated that the expression of these Gh14-3-3 genes is developmentally regulated in fibres, and reached their peak at the stage of rapid cell elongation of fibre development.
Furthermore, overexpression of Gh14-3-3a, Gh14-3-3e, and Gh14-3-3L in fission yeast promoted atypical longitudinal growth of the host cells. Yeast two-hybrid analysis revealed that the interaction
between cotton 14-3-3 proteins is isoform selective. Through yeast two-hybrid screening, 38 novel interaction partners of
the six 14-3-3 proteins (Gh14-3-3a, Gh14-3-3e, Gh14-3-3f, Gh14-3-3g, Gh14-3-3h, and Gh14-3-3L), which are involved in plant
development, metabolism, signalling transduction, and other cellular processes, were identified in cotton fibres. Taking these
data together, it is proposed that the Gh14-3-3 proteins may participate in regulation of fibre cell elongation. Thus, the
results of this study provide novel insights into the 14-3-3 signalling related to fibre development of cotton.
The members of the 14-3-3 isoform family have been shown to be developmentally regulated during animal embryogenesis, where they take part in cell differentiation processes. 14-3-3 isoform-specific expression patterns were studied in plant embryogenic processes, using barley (Hordeum vulgare L.) microspore embryogenesis as a model system. After embryogenesis induction by stress, microspores with enlarged morphology showed higher viability than non-enlarged ones. Following microspore culture, cell division was only observed among the enlarged microspores. Western blot and immunolocalization of three barley 14-3-3 isoforms, 14-3-3A, 14-3-3B and 14-3-3C were carried out using isoform-specific antibodies. The level of 14-3-3C protein was higher in enlarged microspores than in non-enlarged ones. A processed form of 14-3-3A was associated with the death pathway of the non-enlarged microspores. In the early embryogenesis stage, 14-3-3 subcellular localization differed among dividing and non-dividing microspores and the microspore-derived multicellular structures showed a polarized expression pattern of 14-3-3C and a higher 14-3-3A signal in epidermis primordia. In the late embryogenesis stage, 14-3-3C was specifically expressed underneath the L(1) layer of the shoot apical meristem and in the scutellum of embryo-like structures (ELSs). 14-3-3C was also expressed in the scutellum and underneath the L(1) layer of the shoot apical meristem of 21 d after pollination (DAP) zygotic embryos. These results reveal that 14-3-3A processing and 14-3-3C isoform tissue-specific expression are closely related to cell fate and initiation of specific cell type differentiation, providing a new insight into the study of 14-3-3 proteins in plant embryogenesis.
Protein phosphorylation is key to the regulation of many proteins. Altered protein activity often requires the interaction
of the phosphorylated protein with a class of ‘adapters’ known as 14‐3‐3 proteins. This review will cover aspects of 14‐3‐3
interaction with key proteins of carbon and nitrogen metabolism such as nitrate reductase, glutamine synthetase and sucrose‐phosphate
synthase. It will also address 14‐3‐3 involvement in signal transduction pathways with emphasis on the regulation of plant
metabolism. To date, 14‐3‐3 proteins have been identified and studied in many diverse systems, yielding a plethora of data,
requiring careful analysis and interpretation. Problems such as these are not uncommon when dealing with multigene families.
The number of isoforms makes the question of redundancy versus specificity of 14‐3‐3 proteins a crucial one. This issue is
discussed in relation to structure, function and expression of 14‐3‐3 proteins.
The vacuolar H(+)-ATPase (V-ATPase) is a key enzyme that controls the electrochemical proton potential across endomembranes. Although evidence suggests that V-ATPase is important for photo-morphogenesis, little is known about short-term regulation of V-ATPase upon initiation of the photo-morphogenetic programme by exposure of dark-grown plants to light. In this study, etiolated coleoptiles were given a short blue light treatment and V-ATPase characteristics were determined. The effectiveness of the light treatment was assessed by means of fusicoccin binding to the plasma membrane; this increased 5-fold. The short light treatment also induced a 2-fold to 3-fold increase in the hydrolytic activity of V-ATPase. Members of the 14-3-3 protein family are involved in both blue light perception and the subsequent activation of the P-type ATPase. We provide evidence that 14-3-3 proteins specifically interact with the catalytic A-subunit of the V-ATPase. First, the isolated V1-part of the V-ATPase co-purifies with 14-3-3 on a gel filtration column. Secondly, in an overlay experiment, 14-3-3 interacts with a 68 kDa band that was identified as the V1 A-subunit by mass spectrometry. Thirdly, in 14-3-3 affinity chromatography, both A- and B-subunits of the catalytic moiety of the V-ATPase were identified by matrix-assisted laser desorption ionization tandem time of flight mass spectrometry (MALDI TOF/TOF MS) as 14-3-3-interacting proteins. It was shown that the A-subunit can be phosphorylated in vitro by a tonoplast-bound kinase, whose properties are affected by blue light. Taken together, the data show that besides the P- and F-type H(+)-ATPases, the V-type H(+)-ATPase also interacts with 14-3-3 proteins.
To monitor site‐specific phosphorylation of spinach leaf nitrate reductase (NR) and binding of the enzyme to 14‐3‐3 proteins,
serum antibodies were raised that select for either serine 543 phospho‐ or dephospho‐NR. The dephospho‐specific antibodies
blocked NR phosphorylation on serine 543. The phospho‐specific antibodies prevented NR binding to 14‐3‐3s, NR inhibition by
14‐3‐3s, NR dephosphorylation on serine 543, and did not precipitate 14‐3‐3s together with NR. Together, this confirms that
14‐3‐3s bind to NR at hinge 1 after it has been phosphorylated on serine 543. The amounts of individual NR forms were determined
in leaf extracts by immunoblotting and immunoprecipitation. The phosphorylation state of NR on serine 543 increased 2–3‐fold
in leaves upon a light/ dark transition. Before the transition, one‐third of NR was already phosphorylated on serine 543 but
was not bound to 14‐3‐3s. Phosphorylation of serine 543 seems not to be enough to bind to 14‐3‐3s in leaves.
The 14-3-3 proteins specifically bind a number of client proteins to influence important pathways, including flowering timing
via the photosensory system. For instance, 14-3-3 proteins influence the photosensory system through interactions with Constans
(CO) protein. 14-3-3 associations with the photosensory system were further studied in this investigation using 14-3-3 T-DNA
insertion mutants to study root and chloroplast development. The 14-3-3 μ T-DNA insertion mutant, 14-3-3μ-1, had shorter roots than the wild type and the difference in root length could be influenced by light intensity. The 14-3-3
ν T-DNA insertion mutants also had shorter roots, but only when grown under narrow-bandwidth red light. Five-day-old 14-3-3
T-DNA insertion and co mutants all had increased root greening compared with the wild type, which was influenced by light wavelength and intensity.
However, beyond 10 d of growth, 14-3-3μ-1 roots did not increase in greening as much as wild-type roots. This study reveals new developmental roles of 14-3-3 proteins
in roots and chloroplasts, probably via association with the photosensory system.
14N-NMR and 31P-NMR have been used to monitor the in vivo pH in roots, stems, and needles from seedlings of Norway spruce, a typical ammonium-tolerant plant. The vacuolar and cytoplasmic
pH measured by 31P-NMR was found to be c. pH 4.8 and 7.0, respectively, with no significant difference between plants growing with ammonium or nitrate as the N-source.
The 1H-coupled 14 resonance is pH-sensitive: at alkaline pH it is a narrow singlet line and below pH 4 it is an increasing multiplet line with
five signals. The pH values in ammonium-containing compartments measured by 14N-NMR ranged from 3.7 to 3.9, notably lower than the estimated pH values of the Pi pools. This suggests that, in seedlings of Norway spruce, ammonium is stored in vacuoles with low pH possibly to protect
the seedlings against the toxic effects of ammonium () or ammonia (NH3). It was also found that concentrations of malate were 3–6 times higher in stems than in roots and needles, with nitrate-grown
plants containing more malate than plants grown with ammonium.