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Plants have evolved various strategies to sense and respond to saline environments, which severely reduce plant growth and limit agricultural productivity. Alteration to the cell wall is one strategy that helps plants adapt to salt stress. However, the physiological mechanism of how the cell wall components respond to salt stress is not fully understood. Here, we show that expression of XTH30, encoding xyloglucan endotransglucosylase-hydrolase30, is strongly up-regulated in response to salt stress in Arabidopsis. Loss-of-function of XTH30 leads to increased salt tolerance and overexpression of XTH30 results in salt hypersensitivity. XTH30 is located in the plasma membrane and is highly expressed in the root, flower, stem, and etiolated hypocotyl. The NaCl-induced increase in xyloglucan (XyG)-derived oligosaccharide (XLFG) of the wild type is partly blocked in xth30 mutants. Loss-of-function of XTH30 slows down the decrease of crystalline cellulose content and the depolymerization of microtubules caused by salt stress. Moreover, lower Na+ accumulation in shoot and lower H2O2 content are found in xth30 mutants in response to salt stress. Taken together, these results indicate that XTH30 modulates XyG side chains, altered abundance of XLFG, cellulose synthesis, and cortical microtubule stability, and negatively affecting salt tolerance.

Water deficit is a key limiting factor that affects the growth, development and productivity of crops. It is vital to understand the mechanisms by which plants respond to drought stress. Here an N-acetylglutamate kinase gene, ZmNAGK, was cloned from maize (Zea mays). ZmNAGK was expressed at high levels in maize leaves and at lower levels in root, stem, female flower and male flower. The expression of ZmNAGK was significantly induced by PEG, NaCl, ABA, brassinosteroid and H2O2. The ectopic expression of ZmNAGK in tobacco resulted in higher tolerance to drought compared to plants transformed with empty vector. Further physiological analysis revealed that overexpression of ZmNAGK could enhance the activities of antioxidant defense enzymes, and decrease malondialdehyde content and leakage of electrolyte in tobacco under drought stress. Moreover, the ZmNAGK transgenic tobacco accumulated more arginine and nitric oxide (NO) than control plants under drought stress. In addition, the ZmNAGK transgenic tobaccos activated drought responses faster than vector-transformed plants. These results indicate that ZmNAGK can play a vital role in enhancing drought tolerance by likely affecting the arginine and NO accumulation, and ZmNAGK could be involved in different strategies in response to drought stress.

BackgroundWe previously developed several strategies to engineer plants to produce cost-efficient biofuels from plant biomass. Engineered Arabidopsis plants with low xylan and lignin content showed normal growth and improved saccharification efficiency under standard growth conditions. However, it remains to be determined whether these engineered plants perform well under drought stress, which is the primary source of abiotic stress in the field.ResultsUpon exposing engineered Arabidopsis plants to severe drought, we observed better survival rates in those with a low degree of xylan acetylation, low lignin, and low xylan content compared to those in wild-type plants. Increased pectic galactan content had no effect on drought tolerance. The drought-tolerant plants exhibited low water loss from leaves, and drought-responsive genes (RD29A, RD29B, DREB2A) were generally up-regulated under drought stress, which did not occur in the well-watered state. When compared with the wild type, plants with low lignin due to expression of QsuB, a 3-dehydroshikimate dehydratase, showed a stronger response to abscisic acid (ABA) in assays for seed germination and stomatal closure. The low-lignin plants also accumulated more ABA in response to drought than the wild-type plants. On the contrary, the drought tolerance in the engineered plants with low xylan content and low xylan acetylation was not associated with differences in ABA content or response compared to the wild type. Surprisingly, we found a significant increase in galactose levels and sugar released from the low xylan-engineered plants under drought stress.ConclusionsThis study shows that plants engineered to accumulate less lignin or xylan are more tolerant to drought and activate drought responses faster than control plants. This is an important finding because it demonstrates that modification of secondary cell walls does not necessarily render the plants less robust in the environment, and it shows that substantial changes in biomass composition can be achieved without compromising plant resilience.

Water deficit is a key limiting factor that affects the growth, development and productivity of crops. It is vital to understand the mechanisms by which plants respond to drought stress. Here an N-acetylglutamate kinase gene, ZmNAGK, was cloned from maize (Zea mays). ZmNAGK was expressed at high levels in maize leaves and at lower levels in root, stem, female flower and male flower. The expression of ZmNAGK was significantly induced by PEG, NaCl, ABA, brassinosteroid and H2O2. The ectopic expression of ZmNAGK in tobacco resulted in higher tolerance to drought compared to plants transformed with empty vector. Further physiological analysis revealed that overexpression of ZmNAGK could enhance the activities of antioxidant defense enzymes, and decrease malondialdehyde content and leakage of electrolyte in tobacco under drought stress. Moreover, the ZmNAGK transgenic tobacco accumulated more arginine and nitric oxide (NO) than control plants under drought stress. In addition, the ZmNAGK transgenic tobaccos activated drought responses faster than vector-transformed plants. These results indicate that ZmNAGK can play a vital role in enhancing drought tolerance by likely affecting the arginine and NO accumulation, and ZmNAGK could be involved in different strategies in response to drought stress.

As the major resource of reactive oxygen species (ROS), the NADPH oxidases (Rbohs) have been shown to play important roles in plant cells under normal growth and stress conditions. Although many family members of Rbohs were studied, little is known about the function of RbohI in Arabidopsis thaliana. Here, we report that exogenous ABA application decreases RbohI expression and mannitol significantly increases RbohI expression at transcript level. The RbohI transcripts were strongly detected in dry seeds and roots. The loss-of-function mutant rbohI exhibited sensitivity to ABA and mannitol stress during germination. Furthermore, the lateral root growth of rbohI was severely inhibited after treatment with mannitol stress. Overexpression of RbohI in Arabidopsis significantly improves the drought tolerance. Moreover, more H2O2 accumulated in RbohI overexpressors than in wild type plants in response to mannitol stress. Our conclusion is that AtRbohI functions in drought-stress response in Arabidopsis thaliana.

Calcium/calmodulin-dependent protein kinase (CCaMK) has been shown to play an important role in abscisic acid (ABA)-induced antioxidant defense and enhance the tolerance of plants to drought stress. However, its downstream molecular events are poorly understood. Here, we identify a NAC transcription factor, ZmNAC84, in maize (Zea mays), which physically interacts with ZmCCaMK in vitro and in vivo. ZmNAC84 displays a partially overlapping expression pattern with ZmCCaMK after ABA treatment, and H2O2 is required for ABA-induced ZmNAC84 expression. Functional analysis reveals that ZmNAC84 is essential for ABA-induced antioxidant defense in a ZmCCaMK-dependent manner. Furthermore, ZmCCaMK directly phosphorylates Ser-113 of ZmNAC84 in vitro, and Ser-113 is essential for the ABA-induced stimulation of antioxidant defense by ZmCCaMK. Moreover, overexpression of ZmNAC84 in tobacco (Nicotiana tabacum) can improve drought tolerance and alleviate drought-induced oxidative damage of transgenic plants. These results define a mechanism for ZmCCaMK function in ABA-induced antioxidant defense, where ABA-produced H2O2 first induces expression of ZmCCaMK and ZmNAC84 and activates ZmCCaMK. Subsequently, the activated ZmCCaMK phosphorylates ZmNAC84 at Ser-113, thereby inducing antioxidant defense by activating downstream genes.

Composite stiffened panels always have defects at the bonding surface in preparation,which accelerates the debonding of the interface between skin and stringer,greatly affects the bearing capacity of the structure. The model of stiffened panel with prefabricated debonding at the interface of stiffened strip and skin was established with both cohesive zone model（ CZM）and virtual crack closure technique（ VCCT） in ABAQUS,and the rationality of model was verified by experiments. The distribution of energy release rate in prefabricated debonding leading edge was given and the effect of debonding position and area on stiffness and carrying capacity was analyzed. The results indicate that the contribution of type II energy release rate to damage initiation is the greatest; the bearing capacity of the prefabricated debonding structure is stronger than that is in the middle when it is located in outside; the carrying capacity of the structure decrease with the increase of prefabricated debonding area.

as multi-spar composite box has been used for many airplanes,in order to assure structure security,it is necessary to study the mechanical properties of multi-spar composite box. Aiming at the buckling and postbuckling problems,buckling behavior and damage process of multi-spar composite box under bending-shearing load is researched in this paper. A self-defined nonlinear degradation rule was presented to simulate the propagation of the interface elements which were discretized with solid elements. In this model,the onset and propagation of damage can be predicted by quadratic failure criteria and mixed-mode strain energy release rate criteria respectively. cohesive elements are used to simulate the adhesive layer between skin and flange.composite structures were discretized with continuum shell elements. In this paper,a failure algorithm based upon Puck’s failure theory has been developed. Based on ABAQUS,a material degradation rule of composite was presented. The process of damage initiation,propagation and failure of the stiffened composite panels was simulated in detail. At last,a good agreement between tests and numerical prediction was observed.

The progressive damage analysis technique was studied by using finite element method and test validation of the repaired aircraft wing composite panel with discrete-source damage. Firstly,an analysis model adopting the two dimensional LaRC05 and B-K failure criteria was established to indentify the initial damage of composite ply and interface. Then,a user defined subroutine UMAT of material failure criteria and degradation rule based on commercial software ABAQUS was programmed and the load carrying capacity of the repaired aircraft wing composite panel was analyzed. The numerical results indicated that: the FEM analysis method presented in this paper was viable for the large-scale bolted repair structure. The comparison between analysis and test indicates that the load carrying capacity and failure mode of numerical results agree well with test results. The errors of predicted load carrying capacity are within 5%.

Since the wing is the principle bearing structure of aircraft,wing skin is repaired by using mechanically fastened joints. In this paper,scheme design,experimental verification,finite element analysis and design improvement investigation of aircraft composite wing panel with discrete-source damage were carried out. Firstly,the specimen with discrete-source damage and the repaired which used fastened joint repair method were designed and manufactured. Experimental verification of scheme design was performed. Load-carrying capacity of the repaired specimen increases about 124%,compared to the unrepaired,which fully meet the design requirements. Then,for further analysis,two different specimens’ FEM models were established.The results showed that the initial repaired scheme was conservative,and the cost of structure weight was increased. Finally,three improved design configurations were proposed,and the load-carrying capacity of configuration II increased by 4. 7%,its structure weight decreased by 3. 9%. This repaired scheme provides reference for the repair design of aircraft composite wing panel with discrete-source damage.

Fastened joint repair is a main repair method for composite structure with advantages of easy disassembling,high load transferring capacity. It is important to evaluate the residual strength in repair design process. In this paper,the tensile load bearing capacity of metal riveted repair laminates were evaluated by numerical simulation using progressive failure analysis method. Laminate was modeled using shell element whereas the fasteners were modeled by beam elements. MPC technique was adopt to simulate the constraint between fastener and hole. The USDFLD subroutine was used to degrade material stiffness by multi-lever manner while damage occurred. The failure analysis results including failure mode,failure load are in good agreement with test results. The errors of predicted failure loads are with 6%,which shows the proposed method is helpful to composite fastened joint repair design.

The heating process of the polymer composite reinforced by buckypaper was simulated with the finite element model. FLUENT was used to analyze how the thickness of buckypaper affect the temperature distribution, the changes of the temperature with time and the heating rate during heating. The maximum and average temperature of the composites decrease when the thickness of the buckypaper increase, whereas the minimum temperature on the samples have the opposite trend. The heating rate of the average temperature of the composites reinforced by the buckypaper with the thickness of 1.2 mm is faster than those of 0.4 mm and 0.8 mm. The temperature distribution of the polymer composites reinforced by the buckypaper is more uniform as the thickness of the buckypaper increase.

FLUENT was used to analyze how the bending cycles of buckypaper affects the temperature distribution, the changes of the temperature with time and the heating rate during heating. The typical temperature decreases with the increase of bending cycles of the buckypaper. The typical temperature increases with the increase of heating power. The temperature distribution of the polymer composites is more uniform with the increase of bending cycles of buckypaper. The difference of the maximum and minimum temperature of the composites increases linearly with the increase of heating power. The average temperature of the composites when reaching the stable state increase as the bending cycles of buckypaper decrease. The difference of the maximum and minimum temperature of the composites decreases with the increase of the bending cycles.