Insect responses to plant water deficits. I. Effect of water deficits in soybean plants on the feeding preference of Mexican bean beetle larvae

Abstract. 1. We examined the preference of larvae of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), for foliage of soybean ( Glycine max [L.] Merr.) grown under several levels of water deficit. Third instar larvae were exposed simultaneously to excised foliage from plants that were either well-watered (control) or had experienced water deficits (treatment).
2. Water-deficient plants were re-watered 12 h prior to initiating feeding trials to eliminate physical differences between control and treatment foliage such as leaf water potential, diffusive resistance, relative water content, and foliage toughness.
3. Examination of the free amino acid contents of re-watered and excised foliage indicated that amino acid concentrations increased markedly in foliage grown under water deficits, and that this increase persisted during the preference tests.
4. Larvae preferred control foliage, but shifted preference to treatment foliage under mild water deficits. When the leaf water potential of water-deficient treatment foliage was lower than – 1.13 MPa or when it was more than 0.5 MPa lower than that of control foliage, larvae preferred to feed on foliage from well-watered control plants.
5. The expression of preference for well-watered control foliage was coincident with increases in the concentrations of total free amino acids and individual free amino acids in the water-deficient treatment foliage.
6. These results are inconsistent with White's (1974) hypothesis because Mexican bean beetle larvae avoid plants grown under water deficits that have increased concentrations of free amino acids.     

Sensitivity of soybean leaf development to water deficits

Abstract. Drought effects on the final leaf area of individual leaves were hypothesized to depend on the leaf developmental stage at which drought occurred. To evaluate this hypothesis, final leaf area and cell number were measured for soybean ( Glycine max (L.) Merr.) leaves that were at different stages of development when single or cyclical drought treatment was imposed. Leaf emergence rate from the meristem, as depicted by changes in the plastochron index, was not as sensitive as leaf expansion to cyclical droughts. For leaf expansion, small leaves, once they emerged from the meristem, suffered larger decreases in growth than leaves undergoing rapid leaf area expansion. Decreases in final leaf area as a result of a cyclical drought were correlated with decreases in final cell number. Decreases resulting from a single 8-d drought were dependent on the age of the leaf at the time of drought, because small leaves were found to have proportionately larger decreases in final cell number and area than larger leaves. These results indicated that age-dependent leaf responses to drought are based on the relative activity of cell division and expansion at the time stress was imposed.     

Insect responses to plant water deficits. II. Effect of water deficits in soybean plants on the growth and survival of Mexican bean beetle larvae

Abstract. 1. We examined the effect of water deficits in soybean, Glycine max [L.] Merr., on the growth and survival of Mexican bean beetle larvae, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae).
2. Larvae were reared under growth chamber, glasshouse, and field conditions on foliage from plants that were either well-watered or subjected to water deficits.
3. Larval survival, growth rate and pupal weight were reduced, and development time was increased when larvae were reared on foliage from plants subjected to water deficits. These results are contrary to White's (1974) hypothesis that water deficits in plants cause increased growth and survival of herbivorous insects.
4. Changes in foliage chemistry caused by water deficits, possibly in the concentration of free amino acids, are the most likely causes of the observed effects on growth rate and development time. However, under glasshouse and field conditions, physical changes in foliage and/or the foliage's environment that accompany water deficits are also important.     

Changes in seed water status as characterized by NMR in developing soybean seed grown under moisture stress conditions

Changes in water status of developing seeds of Soybean (Glycine max L. Merrill.) grown under different moisture stress conditions were characterized by proton nuclear magnetic resonance (NMR)- spin–spin relaxation time (T₂). A comparison of the seed development characteristics, composition and physical properties indicated that, characteristics like seed weight, seed number/ear, rate of seed filling increased with development stages but decreased with moisture stress conditions. The NMR- spin–spin relaxation (T₂) component like bound water increased with seed maturation (40–50%) but decreased with moisture stress conditions (30–40%). The changes in seed water status to increasing levels of moisture stress and seed maturity indicates that moisture stress resulted in more proportion of water to bound state and intermediate state and less proportion of water in free-state. These changes are further corroborated by significant changes in protein and starch contents in seeds under high moisture stress treatments. Thus seed water status during its development is not only affected by development processes but also by moisture stress conditions. This study strongly indicated a clear moisture stress and development stage dependence of seed tissue water status in developing soybean seeds.     

A class I chitinase from soybean seed coat.

Protein extracts from soybean (Glycine max [L.] Merr) seed hulls were fractionated by isoelectric focusing and SDS-PAGE analysis and components identified by peptide microsequencing. An abundant 32 kDa protein possessed an N-terminal cysteine-rich hevein domain present in class I chitinases and in other chitin-binding proteins. The protein could be purified from seed coats by single step binding to a chitin bead matrix and displayed chitinase activity by an electrophoretic zymogram assay. The corresponding cDNA and genomic clones for the chitinase protein were isolated and characterized, and the expression pattern determined by RNA blot analysis. The deduced peptide sequence of 320 amino acids included an N-terminal signal peptide and conserved chitin-binding and catalytic domains interspaced by a proline hinge. An 11.3 kb EcoRI genomic fragment bearing the 2.4 kb chitinase gene was fully sequenced. The gene contained two introns and was flanked by A+T-rich tracts. Analysis by DNA blot hybridization showed that this is a single or low copy gene in the soybean genome. The chitinase is expressed late in seed development, with particularly high expression in the seed coat. Expression was also evident in the late stages of development of the pod, root, leaf, and embryo, and in tissues responding to pathogen infection. This study further illustrates the differences in protein composition of the various seed tissues and demonstrates that defence-related proteins are prevalent in the seed coat.     

Hourglass cell development in the soybean seed coat

Background and Aims

Hourglass cells (HGCs) are prominent cells in the soybean seed coat, and have potential use as ‘phytofactories’ to produce specific proteins of interest. Previous studies have shown that HGCs initiate differentiation at about 9 d post-anthesis (dpa), assuming their characteristic morphology by 18 dpa. This study aims to document the structural changes in HGCs during this critical period, and to relate these changes to the concurrent development of a specific soybean peroxidase (SBP) encoded by the Ep gene.

Methods

Pods were collected from plants at specific growth stages. Fresh material was processed for analysis of Ep peroxidase activity. Tissues were processed for scanning and transmission electron microscopy, as well as extracted for western blotting. A null variety lacking expression of Ep peroxidase was grown as a control.

Key Results and Conclusions

At 9 dpa, HGCs are typical undifferentiated plant cells, but from 12–18 dpa they undergo rapid changes in their internal and external structure. By 18 dpa, they have assumed the characteristic hourglass shape with thick cell walls, intercellular air spaces and large central vacuoles. By 45 dpa, all organelles in HGCs have been degraded. Additional observations indicate that plasmodesmata connect all cell types. SBP activity and SBP protein are detectable in the HGC before they are fully differentiated (approx. 18 dpa). In very early stages, SBP activity appears localized in a vacuole as previously predicted. These results increase our understanding of the structure and development of the HGC and will be valuable for future studies aimed at protein targeting to components of the HGC endomembrane systems.     

Role of nitrogen assimilation in seed development of soybean

A nondestructive acetylene reduction assay for nitrogenase activity of soybean (Glycine max L. Merr) field plots is presented. Plots consisted of 120 × 150 × 30 centimeter boxes containing 65 plants. The plants were grown in a medium grade sand under controlled nutrient, moisture, and root temperature conditions. Acetylene at a concentration of 10 milliliters per liter was circulated through manifolds in the chambers; equilibration required 5 minutes, and activity was linear with time. Optimum growth and assay environments resulted in activity of 70 micromoles ethylene per plant per hour. Plant development and yield were comparable to soil-grown companion plots.

The well accepted hypothesis that developing seeds deprive the nodules of carbohydrate was not substantiated. The nondestructive acetylene reduction profile did not decline until 30 days after the onset of seed development (R-5). This result was consistent with reports from the literature which indicated that 60% of seasonal nitrogen was fixed after R-5. Further, a high correlation shown between integrated seasonal acetylene reduction and yield (r = 0.999) suggested a cooperative relationship between the roots and shoot. A reduction in source:sink ratio (60% defoliation) after R-5 had no effect on acetylene reduction. This showed that neither an increase in sink demand by the pods nor a carbon shortage during podfill decreased dinitrogen fixation. A conceptual model relating seed growth with carbon and nitrogen assimilation is proposed.

     

Expression of storage-protein genes during soybean seed development

Mature seeds of Glycine max (L.) Merr. contain two major storage proteins, a glycosylated 7S protein (conglycinin) and a non-glycosylated 11S protein (glycinin). Accumulation of these proteins and their mRNAs during seed development in cv. Provar was studied by SDS polyacrylamide gel electrophoresis and by Northern (DNA-RNA) hybridization. The 11S acidic and basic subunits and the 7S and subunits began to accumulate 18–20 d after pollination, shortly after the termination of cell division in developing cotyledons, whereas the 7S and 11S A-4 subunits were not detected until one to two weeks later, during the maturation phase of development. Messenger RNAs for 7S and 11S proteins were first detected 14–18 d after pollination, several days before the accumulation of storage proteins. Extracts from embryonic axes contained reduced levels of the 7S subunit, very little 11S protein, no detectable 7S or 11S A-4 subunits, and an additional 7S subunit not found in cotyledons. Soybean axes and cotyledons therefore differ in their synthesis of seed storage proteins.Abbreviations cDNA complimentary DNA - mRNA messenger RNA - SDS sodium dodecyl sulfate     

Tissue water relations and leaf growth of tropical corn cultivars under water deficits

Abstract This study reports on the effect of water deficit on the tissue water relations and leaf growth of six corn cultivars, growing in glasshouse conditions, in order to understand growth responses to drought of tropical corn. A mild water-stress treatment was imposed slowly; plants reached a minimum pre-dawn leaf water potential of about –1.5 MPa by day 12 after watering was withheld. Analysis of the water relation characteristics of growing leaves using the pressure–volume technique demonstrated that under water deficits all the cultivars changed their moisture-release curves compared with irrigated plants. Osmotic potential at full turgor was lowered in water-stressed plants of all the genotypes and the degree of such change was between 0.34 MPa and 0.58 MPa. Thus, turgor pressure was lost at a lower water potential in water-stressed plants than in irrigated plants of all the varieties. Volumetric elastic moduli were also increased under water deficits and the increase ranged between 10% and 141% among the cultivars. In all the genotypes, the stress imposed led to a reduction of leaf area and dry matter accumulation. Leaf expansion was very sensitive to low turgor pressure and it ceased when turgor reached 0.2 MPa. Thus, varieties able to maintain a higher degree of turgor pressure (i.e. by osmotic adjustment) under water deficits may be able to prolong leaf growth.     

Effect of water potential on seed germination

The response of seed germination to substrate water potential was determined for several plant species of the arctic tundra. Seeds were collected from Cape Thompson and Eagle Summit, Alaska and germinated on dialysis membranes over water solutions of polyethylene glycol with osmotic potentials of 0 to −6 bars. Germination did not occur with potentials below −3 bars, except for three fellfield species. Germination was delayed at lower osmotic potentials. Because the response of most species was similar, substrate water potential is probably not a factor affecting the establishment of most tundra plant species from seeds.     

Patterns of fatty acid deposition during development of soybean seed

Fatty acid deposition in developing soybean seeds of high- and low-linolenic acid cultivars show a great deal of similarity. In all cultivars, the greatest change in fatty acid content occurs during the first half of seed formation. The amount of linolenic acid is highest during the very early stage of seed formation and the relative amount decreases thereafter. Linolenic acid content in mature soybean seed is inversely proportional to that of oleic acid.     

Nutrient status and mycorrhizal enhancement of water transport in soybean

Mycorrhizal soybean (Glycine max L. Merr. var. Harosoy-63) plants have lower resistances to water transport than nonmy-corrhizal plants after 4.5 weeks of growth. Although resistances of whole plants differ by 40%, there were no differences in the resistances of stems plus leaves, indicating that the major effect of the mycorrhizae was to reduce the resistance of the roots. Since the fungitoxicant, p-chloronitrobenzene, had no effect on resistances to water transport, reduced resistances were probably not caused by a direct modification of the transport pathway by the fungus. Differences in resistance between mycorrhizal and nonmycorrhizal soybean were essentialy eliminated by the application of nutrients to the soil. Thus, lowered resistances of mycorrhizal roots growing in soil with low levels of nutrients probably resulted from the enhanced nutrient status of the plant brought about by the fungus. Mycorrhizal infection increased growth at both low and high nutrient levels.     

Leaf expansion of four sunflower (Helianthus annuus L) cultivars in relation to water deficits. I. Patterns during plant development

Abstract. The influence of a slow stress and recovery cycle on the pattern of leaf expansion in four diverse sunflower cultivars ( Helianthus annuus L. cvs. Hysun 31, Havasupai, Hopi and Seneca) was studied in a glasshouse. Stress had no significant effect on the time of flower bud emergence and anthesis, or on final leaf number, but delayed the appearance of leaves at high insertions in all cultivars except Hysun 31.
Leaf expansion was markedly reduced as the predawn leaf water potential decreased from −0.35 to −0.60 MPa, and the predawn turgor pressure decreased from 0.3 to 0.2 MPa, and expansion ceased at a predawn leaf water potential of about −1.0 MPa, i.e. when the predawn turgor pressure reached zero.
The leaves most reduced in final size when water was withheld were those at the insertions which grew the most rapidly in unstressed plants. The maximum reduction in final leaf size of 25–35% was similar in all cultivars and was due to retardation of the rate of leaf expansion: the duration of leaf expansion was actually increased by stress. However, leaves that were initiated during stress, but emerged after rewatering, had final leaf areas at least equal to those in the unstressed plants: in the cultivar Seneca, the final size of leaves of high insertion was significantly greater in stressed than unstressed plants, whereas in the three other cultivars the final leaf sizes were similar in both treatments. All four cultivars examined adjusted osmotically to the same degree, but leaf water potentials in one, Seneca, increased more rapidly after rewatering than in the other three, and this may have contributed to the greater relative leaf size in the leaves of high insertion in this cultivar.     

Unstable expression of a soybean gene during seed coat development

Summary The R gene of soybean is involved in anthocyanin synthesis in the seed coat, and its r-m allele conditions a variegated distribution of black spots and/or concentric rings of pigment superimposed on an otherwise brown seed coat. We describe an unusual feature of r-m that causes expression at the R locus to switch between active and inactive phases both somatically and germinally. Non-heritable somatic changes of the allele produce single plants containing mixtures of seed with different coat colors (black+striped or brown+striped). Heritable changes of the r-m allele are manifested in progeny plants which produce all black seed or all brown seed. Surprisingly, subsequent generations from revertant sublines show continued instability of the allele such that brown revertants (r*/r*) or homozygous black seed revertants (R*/R*) can give rise to striped or striped+black-seeded plants. Thus, the revertants produced by the r-m allele are not stable but interconvert between all three forms (R*, r*, and r-m) at detectable frequencies. Mutability of the r-m allele in a different genetic background has also been found after inter-crossing various soybean genotypes.     

Genome-wide identification and characterization of novel microRNAs in seed development of soybean

MicroRNAs (miRNAs) are important and ubiquitous regulators of gene expression in eukaryotes. However, the information about miRNAs population and their regulatory functions involving in soybean seed development remains incomplete. Base on the Dicer-like1-mediated cleavage signals during miRNA processing could be employed for novel miRNA discovery, a genome-wide search for miRNA candidates involved in seed development was carried out. As a result, 17 novel miRNAs, 14 isoforms of miRNA (isomiRs) and 31 previously validated miRNAs were discovered. These novel miRNAs and isomiRs represented tissue-specific expression and the isomiRs showed significantly higher abundance than that of their miRNA counterparts in different tissues. After target prediction and degradome sequencing data-based validation, 13 novel miRNA–target pairs were further identified. Besides, five targets of 22-nt iso-gma-miR393h were found to be triggered to produce secondary trans-acting siRNA (ta-siRNAs). Summarily, our results could expand the repertoire of miRNAs with potentially important functions in soybean.     

Quantification of soybean seed germination response to seed deterioration under PEG-induced water stress using hydrotime concept

This experiment was arranged to investigate the ability of hydrotime model (θ_H) for estimating soybean seed germination (cv. ‘JK’) under different accelerated aging periods (AAP, 0, 24, 48, and 72 h) at each of the following water potentials (ψ, 0, ??0.12, ??0.24, and ??0.36 MPa). Results indicated that both germination percentage (GP) and germination rate (GR) significantly influenced by ψ, AAP, and their interactions (P?<?0.01). GP and GR decreased by 62.6 and 47.3% with longer AAP from 0 to 72 h and by 90.7 and 81.5% with lower ψ from zero to ??0.36 MPa as compared to the control, respectively. Therefore, the effect of ψ on GP and GR was more than AAP. The θ_H value was constant (~?6.71 MPa h^?1) till 50.6 h AAP and then linearly declined with the rate of 0.1545 MPa h^?1 per hour increase in AAP until 72 h (~?50% lower than its initial value). The ψ_b(50) value was ? 0.343 MPa in the control and then increased (became more positive) by ~?70% until 72 h AAP (? 0.104 MPa). In general, GP and GR of soybean declined with the increasing ψ_b(50) which can be due to cell membrane damage and reduce the activity of enzymes and organelles during AAP. Based on our findings, the θ_H model could describe well these relationships and their parameters can nicely be used for simulating soybean seed germination under this condition.     

温度及种子含水量对剪枝栎实象和青冈象卵发育的影响

剪枝栎实象Mechoris ursulu和青冈象Curculio megadens是危害多种壳斗科植物坚果的重要害虫,在长期与寄主的相互作用中已进化出相应的反防御策略.了解两种象甲与植物间的相互关系,可有助于对其进行科学防治.本文通过温度等因子对具有相近生态位的剪枝栎实象和青冈象卵发育影响的比较研究,探讨产卵于寄主组织...