Journal of Experimental Botany

Published by Oxford University Press

Online ISSN: 1460-2431


Print ISSN: 0022-0957


The historical perspective of dryland agriculture: Lessons learned from 10 000 years of wheat cultivation
  • Article
  • Full-text available

February 2007


495 Reads




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.

Energetics and the evolution of carnivorous plants-025EFDarwin's 'most wonderful plants in the world'

February 2009


420 Reads

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.

Development of β‐1,3‐glucanase activity in germinated tomato seeds

August 2000


84 Reads

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 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.

Fig. 1. Genomic DNA digested with EcoRI, separated by agarose gel electrophoresis and hybridized on gels blots with a full-length Hg30C02 (JF896103) DIG-labelled cDNA probe. BCN, beet cyst nematode (H. schachtii); SCN, soybean cyst nematode (H. glycines); RKN, root-knot nematode (M. incognita); AT, A. thaliana. At least five copies of 30C02 are present in H. schachtii and a single copy is present in H. glycines. No hybridization signal was detected in M. incognita or A. thaliana genomic DNA. M, DIG-labelled DNA marker.
Fig. 2. A 98% predicted amino acid sequence identity between the 30C02 protein expressed in the parasitic life stages (within host plant roots) of both H. schachtii (JF896102) and H. glycines (JF896103), was determined using the Clustal W program (Thompson et al., 1994); the underlined sequence represents the predicted secretion signal peptide motif (Bendtsen et al., 2004). Identical amino acids are indicated by asterisks.
Fig. 3. Expression of the gene encoding the 30C02 effector protein in cyst nematodes. (A) Micrograph of a mRNA in situ hybridization of a DIG-labelled probe of Hg30C02 specifically within the single enlarged dorsal oesophageal gland cell of a cyst nematode third-stage juvenile (J3) that was excised from a host root. (B) Quantitative expression of Hs30C02 within the developmental life stages of the beet cyst nematode H. schachtii determined by qRT-PCR. The relative fold-change values were calculated using the 2−ΔΔCT method (Livak and Schmittgen, 2001) and represent changes in mRNA level in nematode pre-parasitic J2 (pre-J2), late parasitic J2 (late J2), J3, and J4 relative to that of eggs (pre-J2). The H. schachtii actin gene (AY443352) was used as an internal control to normalize gene expression levels for all samples.
Fig. 4. Constitutive expression of Hg30C02 in transgenic A. thaliana increases plant susceptibility to infection by the beet cyst nematode H. schachtii. (A) RT-PCR confirmed the expression of Hg30C02 without signal peptide in transgenic Arabidopsis lines L1-5 and L2-1 compared with WT control, and RT-PCR amplification of expressed Hg30C02 with signal peptide from transgenic lines L6-3 and L13-12 in the absence (–RT) and presence (+RT) of reverse transcriptase, respectively. (B) A significant (*, P≤0.05) increase in the mean number of H. schachtii females per plant was observed in the roots of transgenic Arabidopsis lines that expressed Hg30C02 compared with females developed on the WT control plants. (C) No significant (P≤0.05) difference in root infection (gall number) by the root-knot nematode M. incognita was observed in roots of the same Hg30C02 transgenic Arabidopsis lines compared with WT plants.
Fig. 5. Protein–protein interactions of Hs30C02 with the Arabidopsis β-1,3-endoglucanase (AT4G16260) in yeast and onion cells. (A) Yeast two-hybrid interaction between Hg30C02 and AT4G16260 Arabidopsis β-1,3-endoglucanase visualized by differential growth on non-selective medium (SD/–Trp/–Leu) and on selective medium (SD/–DQO). Only yeast cells containing the β-1,3-endoglucanase prey plus the 30C02 bait (upper right) or the positive control (+C) interaction of CV40 plus LamC (upper left) grew on the selective medium. No interaction of the Arabidopsis β-1,3-endoglucanase with the empty vector control (–C1) or LamC (–C2), or interaction of 30C02 with empty vector control (–C3), was detected on the selective medium. (B) The interaction between Hg30C02 and AT4G16260 Arabidopsis β-1,3-endoglucanase proteins within a transformed onion epidermal cell visualized by bifluorescence complementation. (C) A bright-field image of the onion epidermal cells presented in (B). The images in (B) and (C) were taken 24 h after transformation of onion cells by particle bombardment. (This figure is available in colour at JXB online.)


The interaction of the novel 30C02 cyst nematode effector protein with a plant Beta-1,3-endoglucanase may suppress host defence to promote parasitism

March 2012


427 Reads


Chunying Li


Tarek Hewezi




Eric L Davis
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.

Fig. 2. The effect of antisense bGLU I transformation on the timecourse of bGLU I induction during germination of after-ripened homozygous seed. (A) The incidence of testa rupture expressed as a percentage scored with time after the start of imbibition in continuous light in control medium. Homozygous, monogenic S 2 seed populations of independent bGLU I-antisense lines TGAG2-24 (bGLU I promoter) and TKAG4-31 (Cat1 promoter) and of empty-vector line TCIB1-2 were used. (B) The incidence of endosperm rupture. (C) The accumulation of bGLU enzyme activities expressed in pkat mg À1 protein. (D) The accumulation of the 1.6 kb bGLU I mRNA expressed as arbitrary PhosphoImager units per seed. The signals detected and quantified by RNA-blot hybridization using additional seed samples from the experiment described in (A) are corrected for RNA loading based on the 18S ribosomal RNA signals. (A-C) Mean values "SE of two samples each with 100-150 seeds are presented (30 h one sample); SE-values F2.0% and F0.01 pkat mg À1 protein are not drawn.
Table 2 . Effect of after-ripening on endosperm rupture and photodormancy of sense and antisense bGLU I seeds
Fig. 1. Schematic representation of antisense class I β‐1,3‐glucanase (βGLU I) expression vectors used for tobacco transformation. Transcriptional fusions of the castor bean Cat1 promoter (PCat1), the tobacco βGLU I B gene (Glb) full length promoter (1.7 kb PGlb), and the truncated proximal Glb promoter (0.5 kb PGlb) with a 1.3 kb βGLU I cDNA in reverse orientation and the CaMV 35S terminator (T35S) constitute the antisense βGLU I constructs of pKAG4, pGAG2 and pGAG3, respectively. The empty‐vector pCIB200 was used to generate control transformants. The chimeric neomycin phosphotransferase gene (NPTII) confers kanamycin resistance and is under the control of the nopaline synthase promoter (PNOS) and terminator (TNOS). The right (RB) and left (LB) T‐DNA borders are indicated.
Antisense-transformation reveals novel roles for class I β-1,3-glucanase in tobacco seed after-ripening and photodormancy

October 2001


174 Reads

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.

Elicitor and resistance-inducing activities of -1,4 cellodextrins in grapevine, comparison with -1,3 glucans and -1,4 oligogalacturonides

February 2007


295 Reads

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.

Leaf hairs influence phytopathogenic fungus infection and confer an increased resistance when expressing a Trichoderma -1,3-glucanase

February 2006


303 Reads

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.

Protein cross-linking, peroxidase and β-1,3-endoglucanase involved in resistance of pea against Orobanche crenata

February 2006


61 Reads

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.

Effects of beta-1,3-glucan from Septoria tritici on structural defence responses in wheat

October 2009


452 Reads

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.

Functional characterization of barley betaglucanless mutants demonstrates a unique role for CslF6 in (1,3;1,4)- -D-glucan biosynthesis

September 2011


245 Reads

(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.

Fig. 1. The PpEG4 gene. (A) Restriction map and structure of the PpEG4 gene. The sequence encompassing the EGase protein consists of nine exons (numbers over solid blocks) and eight introns (connecting line between blocks). In blue are indicated the exons coding for the part of the protein corresponding to the ‘classical’ 53–57 kDa EGases while in green are indicated the c . 110 aa corresponding to the C-ter extra peptide containing the CBD (depicted in purple). 5 9 and 3 9 untranslated regions (UTR) are represented by the horizontal open arrows. The five light blue blocks in the 5 9 untranscribed region represent regions of high homology with the promoter of the strawberry FaEG3 gene. The green oval on the same level represents a putative ERE (E4 type). Some common restriction enzyme sites are indicated above the gene structure over a ruler which shows the size, in base pairs, of the sequenced fragment of peach genomic DNA which contains PpEG4 . (B) Structure of the PpEG4-30 promoter deletion construct, fused to the GUS-INT reporter gene, used for the PpEG4 promoter analysis in tomato. The length is calculated from the starting ATG. (C) Alignment of the deduced amino acid sequences of 12 cellulose-binding domains (CBD): 11 putative CBDs from higher-plant EGases (PpEG4, strawberry FaEG3, pear PC-EG2, tomato cel8, three arabidopsis and four rice proteins deduced from genomic sequences), and one CBD from a microbial protein (i.e. the Dictyostelium discoideum celB). Dashes in the sequences have been introduced by the program ClustalW to optimize the alignment. Black boxes show the conserved tryptophans while shaded boxes and white boxes indicate conserved and identical amino acid residues, respectively. The 578 Y residue of OS_CAE03241.2 is red-highlighted because it is in the position of an otherwise conserved W. A conserved potential Asn glycosylation site (N-X-S/T) in the plant CBDs is shown by a red box. 
Fig. 2. Expression analyses of the PpEG4 gene during fruit development and ripening (stages S1 to S4). The expression of PpEG4 is compared with that of the ACO-1 gene to show its increase in the preclimacteric phase (late S3, here S3II) followed by a decrease during the ripening phase (S4I and S4II), that is when high amounts of ethylene are produced by the fruit. Arabic numerals on the top indicate days after full bloom. In each lane 10 l g of total RNA have been loaded. The panel at the bottom of the figure shows ethidium bromide staining of RNA used to check equal loading in each lane. 
Fig. 3. Effect of hormone treatments on the expression of PpEG4 in fruits at different stages of development and ripening. RNA (10 l g lane ÿ 1 ) has been extracted from fruits frozen either immediately after harvest or after treating them with either ethylene or an auxin analogue (NAA) or leaving them in air for 48 h. In the middle part of the figure the expression of a peach PG gene is shown as a well-characterized example of expression of an ethylene- inducible gene. The panel at the bottom of the figure shows ethidium bromide staining of RNA used to check equal loading in each lane. 
Fig. 4. Involvement of PpEG4 in the abscission process. Abscission zones of leaves (AZ) have been collected either in early autumn (left panels, to investigate PpEG4 expression during natural abscission) or early summer (middle panels, to investigate PpEG4 expression during ethylene-induced abscission). Autumn AZs have been sampled either from non-abscising (NA) or from abscising (A) leaves while summer AZs have either been activated to abscise with ethylene (ET) or not (C, control). The expression of PpEG4 in abscission zones of fruits (AZ3) at the S3 stage has been monitored in AZ3s of explants treated either with ethylene (ET) or NAA, or left in air (Air) for 48 h. The basal expression in AZ3s of fruits at harvest time is shown in the control sample (C). The expression of PpEG4 is compared with that of PpEG1 , already described as the EGase mainly involved in the abscission process in peach. An RNA sample from fruits at the S3II stage has been loaded to allow a comparison of the PpEG4 expression in the two cell separation processes. The panel at the bottom of the figure shows ethidium bromide staining of RNA used to check equal loading in each lane. 
Fig. 5. Histochemical analysis of tomato plants transformed with the PpEG4-30 promoter fragment. (A) Fruit at the immature green. (B) Fruit at the breaker stage. (C) Fruit at the breaker stage + 8 d stage (red fruit). 
PpEG4 is a peach endo- -1,4-glucanase gene whose expression in climacteric peaches does not follow a climacteric pattern

February 2006


186 Reads

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.

Fig. 1. GUS activity measured in protein extracts obtained from strawberries transformed at the pink stage with constructs harbouring different promoter deletions of FaEG1 (top) and FaEG3 (bottom). The different promoter fragments used in each construct are depicted on the left; the indicated bp length is meant from the starting ATG. Also putative cis elements are marked (G-box; AGL3: box recognized by Agamous-like proteins; Dof1 and Dof2: box recognized by Dof transcription factors). In the various experiments the GUS activity (expressed as nmol MU min ±1 m g ±1 protein) was normalized to the luciferase activity (expressed as pmol of luciferase in 1 m g of protein) measured in the same protein extract. The activities measured with the strawberry promoter fragments were expressed as a percentage of the activity obtained with the CaMV 35S promoter, set arbitrarily to 100%. EA: endogenous activity (i.e. GUS activity measured in fruits transformed only with a luciferase gene). All values are the average of four independent experiments. Bars represent standard errors. 
Fig. 2. GUS 
Fig. 3. GUS activity measured in proteins extracted from strawberries transformed at the white stage with different constructs (i.e. pEG1-30 and pEG3-30, respectively). The GUS activity (expressed as nmolMU min ±1 m g ±1 protein) was normalized to luciferase activity (expressed as 
Isolation and promoter analysis of two genes encoding different endo- -1,4-glucanases in the non-climacteric strawberry1

February 2003


103 Reads

Two endo‐β‐1,4‐glucanase (EGase; EC 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.

Molecular characterization and expression studies during melon fruit development and ripening of L-galactono-1,4-lactone dehydrogenase

September 2004


662 Reads

The last step of ascorbic acid (AA) biosynthesis is catalysed by the enzyme l-galactono-1,4-lactone dehydrogenase (GalLDH, EC, 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.

Multiple forms of endo-1,4- -glucanases in the endosperm of Euphorbia heterophylla L.

October 2003


32 Reads

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.

Reduction of inositol (1,4,5)-trisphosphate affects the overall phosphoinositol pathway and leads to modifications in light signaling and secondary metabolism in tomato plants

January 2012


588 Reads

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.

Phylogenetic and molecular analysis of the ribulose-1,5-bisphosphate carboxylase small subunit gene family in banana

February 2007


207 Reads

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.

Increased fructose 1,6-bisphosphate aldolase in plastids enhances growth and photosynthesis of tobacco plants

February 2012


255 Reads

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 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 plants.

Fig. 1. RT-PCR determination of specific mRNAs for FBPase (a),
Fig. 3. FBPase (a), NADP-MDH (b), Trx f (c), Trx m (d ) and total
Fig. 5. FBPase (a), NADP-MDH (b),Trx f (c), Trx m (d ), and total protein (e), as well as FBPase (f, g) and NADP-MDH (h) activities of upper petioled leaflets of pea plants grown for 10 d under normal Fig. 4. RT-PCR determination of specific mRNAs for FBPase (a), temperature (25/20 °C day/night gradient) and low light (100 mmol m−2 s−1 PAR) (NTLL), normal temperature and high light NADP-MDH (b), Trx f (c), and Trx m (d) in upper petioled leaflets of pea plants grown for 10 d under normal temperature (25/20 °C (2500 mmol m−2 s−1 PAR) (NTHL), high temperature (35/30 °C day/night gradient) and low light (HTLL), high temperature and high day/night gradient) and low light (100 mmol m−2 s−1 PAR) (NTLL), normal temperature and high light (2500 mmol m−2 s−1 PAR) (NTHL), light (HTHL), low temperature (15/10 °C day/night gradient) and low light (LTLL), and low temperature and high light (LTHL). (a-d) were high temperature (35/30 °C day/night gradient) and low light (HTLL), high temperature and high light (HTHL), low temperature (15/10 °C measured by ELISA with the corresponding specific antibodies, and (e) by Bradford. FBPase activity was determined at pH 8.8 under nonday/night gradient) and low light (LTLL), and low temperature and high light (LTHL). Bars represent percentages in relation to the highest reducing conditions (f ) or at pH 7.9 in the presence of DTT (g), whereas DTT-dependent NADP-MDH activity (h) was measured at value (on fresh weight basis), and are the means (±SE ) of two measures on each of two independent experiments. Top insets are alkaline pH 8.0, as stated in the Materials and methods. Bars represent percentages in relation to the highest value (on a fresh weight basis), phosphatase stains of one of the agarose electrophoresis transfers on nylon membranes of digoxygenin-labelled PCR-amplified specific and are the means (±SE) of two measures on each of two independent experiments. DNAs.
Fig. 6. Electron micrograph of ultrathin sections of upper-leaf mesophyll from 10-d-old pea plants grown under normal conditions
Expression of thioredoxins f and m, and of their targets fructose‐1,6‐bisphosphatase and NADP‐malate dehydrogenase, in pea plants grown under normal and light/temperature stress conditions

August 2000


92 Reads

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.

Fig. 2. FBPase expression in wild type (ws) and A. thaliana transformants. Expression was determined by RT-PCR (bottom panel) and the signals were quantified and normalized using UBQ10 expression as a control (top panel, arbitrary units). PCR products were visualized in the agarose gel by ethidium bromide staining. Results are the means of five individual plants. 
Table 3 . Carbohydrate content of the whole rosette of untransformed control and anti-FBPase plants grown in air
Fig. 4. Carbohydrate content in whole Arabidopsis thaliana rosette. Levels of sucrose (A) and ratio sucrose/starch (B) were determined 3 h after the beginning of the light period. Results are means of five individual plants.
Increased sucrose level and altered nitrogen metabolism in Arabidopsis thaliana transgenic plants expressing antisense chloroplastic fructose-1,6-bisphosphatase

January 2005


217 Reads

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.

Fig. 1. Root clumps of the two NILs families (no. 1 and no. 4) grown under water-stressed (WS) conditons. 
Table 1 . Main sources of variation in the ANOVA of trials concerning NILs per se and NILs crosses
Table 2 . NILs per se: mean values of the three trials across the two families for the investigated traits
Characterization of root-yield-1.06, a major constitutive QTL for root and agronomic traits in maize across water regimes

August 2010


123 Reads

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.

Fig. 2. Relatedness of DddD proteins. The tree was derived from BLAST pairwise alignments at the NCBI BLAST website. The groupings of the different bacterial species and strains in the three branches, ‘A’, ‘B’, and ‘C’ are discussed in the text.
Fig. 3. Location of genes in the dddD regions of different Ddd + 
Johnston AWB, Todd JD, Sun L, Nikolaidou-Katsaridou MN, Curson ARJ, Rogers R.. Molecular diversity of bacterial production of the climate changing gas, dimethyl sulphide, a molecule that impinges on local and global symbioses. J Exp Bot 59: 1059-1067

February 2008


327 Reads

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.

Fig. 1. The relationship between the accumulation of 109Cd in roots and shoots in different genotypes of diploid, tetraploid and hexaploid wheats grown for 9 d in nutrient solution. Radiolabelled Cd was applied when the plants were 7‐d‐old, and continued for a 42 h period. Data represent mean of five replicates.
Uptake and retranslocation of leaf-applied cadmium (Cd-109) in diploid, tetraploid and hexaploid wheats

March 2000


95 Reads

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.

Fig. 1. Northern blot of total RNA (15 l g) from soybean roots. Treatments are designed as NI, non-inoculated controls; Br, Bradyrhizobium japonicum ; Gm, Glomus mosseae ; Gm+Br, G. mosseae plus B. japonicum ; Gi, Glomus intraradices ; Gi+Br, G. intraradices plus B. japonicum . Plants were either well-watered (ww) or drought-stressed (ds) for 10 d. The lower panel shows a representative example of the amount of 26S rRNA loaded for each treatment (methylene blue staining). Histogram shows the relative gene expression (after normalization to rRNA) presented as a percentage of the value for droughted non-inoculated plants. 
Fig. 2. Northern blot of total RNA (15 l g) from soybean roots. Plants were harvested 5, 12, 20, or 35 d after inoculation (dai). Treatments are designed as NI, non-inoculated controls; Br, Bradyrhizobium japonicum ; Gm+Br, G. mosseae plus B. japonicum . Plants were either well-watered (ww) or drought-stressed (ds) for 10 d. The lower panel shows a representative example of the amount of 26S rRNA loaded for each treatment (methylene blue staining). Histogram shows the relative gene expression (after normalization to rRNA) presented as a percentage of the value for droughted non-inoculated plants. 
Fig. 3. Northern blot of total RNA (10 l g) from soybean nodules. Treatments are designed as Br, Bradyrhizobium japonicum and Gm+Br, G. mosseae plus B. japonicum . Plants were either well-watered (ww) or drought-stressed (ds) for 10 d. The lower panel shows the amount of 26S rRNA loaded for each treatment (methylene blue staining). Histogram shows the relative gene expression (after normalization to rRNA) presented as a percentage of the value for droughted non-inoculated plants. 
Fig. 4. Northern blot of total RNA (15 l g) from lettuce roots. Treatments are designed as NI, non-inoculated controls; Gm, Glomus mosseae ; Gi, Glomus intraradices ; Plants were either well-watered (ww) or drought-stressed (ds) for 10 d. The lower panel shows the amount of 26S rRNA loaded for each treatment (methylene blue staining). Histogram shows the relative gene expression (after normalization to rRNA) presented as a percentage of the value for droughted non-inoculated plants. 
Evaluation of the role of genes encoding for dehydrin proteins (LEA D-11) during drought stress in arbuscular mycorrhizal Glycine max and Lactuca sativa plants

August 2005


182 Reads

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.

Independent variation in photosynthetic capacity and stomatal conductance leads to differences in intrinsic water use efficiency in 11 soybean genotypes before and during mild drought

February 2011


788 Reads

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.

Photosynthesis limitations during water stress acclimation and recovery in the drought-adapted Vitis hybrid Richter-110 (V. berlandieri×V. rupestris)

May 2009


455 Reads

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).

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