[Compensation effect of re-watering after different drought stresses on source-sink metabolism during tuber expansion period of potato.] / 马铃薯块茎膨大期不同程度干旱后复水的源库补偿效应.

The compensation effect of re-watering after drought has been widely reported in various crops during different growth stages. It is considered as an important self-regulation mechanism for plants to resist abiotic stresses and also an efficient utilization of limited water resource. In this study, two rounds of re-watering after drought treatments were carried out during tuber expansion period of potato, to investigate the drought threshold of potato and explore the potential mechanisms of compensation effect with source-sink aspect. We used virus-free plantlets of "Atlantic" potato as experimental materials. Four treatments were included: sufficient water supply (W), re-watering after mild drought (D1-W), re-watering after medium drought (D2-W) and re-watering after severe drought (D3-W). The results showed that potato yield exhibited an over-compensation effect after two rounds of D1-W treatment, with water use efficiency and yield being increased by 17.5% and 6.3%, respectively, compared with the sufficient water supply. D2-W treatment had no significant effect on potato yield, but water use efficiency was increased by 8.4%, indicating a near-equivalent compensation effect. On the contrary, D3-W treatment did not show any compensation effect in yield. In addition, leaf chlorophyll content, net photosynthetic rate, and leaf area were all reduced after drought treatment, indicating a reduction in "source" size and activity. After re-watering, D1-W and D2-W treatments showed over-compensation and compensation effects through improving source supply capacity. Meanwhile, re-watering after moderate drought increased the sink activity through significantly enhancing the activities of key enzymes in tubers (sink), thus increased the average weight of tubers. In conclusion, re-watering after moderate drought stress during potato tuber expansion period had compensation and over-compensation effects on both source and sink, and thus could compensate for the drought-induced yield loss and improve water use efficiency.

Overexpressing Arabidopsis ABF3 increases tolerance to multiple abiotic stresses and reduces leaf size in alfalfa.

Arabidopsis ABSCISIC ACID-RESPONSIVE ELEMENT-BINDING FACTOR 3 (ABF3), a bZIP transcription factor, plays an important role in regulating multiple stress responses in plants. Overexpressing AtABF3 increases tolerance to various stresses in several plant species. Alfalfa (Medicago sativa L.), one of the most important perennial forage crops worldwide, has high yields, high nutritional value, and good palatability and is widely distributed in irrigated and semi-arid regions throughout the world. However, drought and salt stress pose major constraints to alfalfa production. In this study, we developed transgenic alfalfa plants (cv. Xinjiang Daye) expressing AtABF3 under the control of the sweetpotato oxidative stress-inducible SWPA2 promoter (referred to as SAF plants) via Agrobacterium tumefaciens-mediated transformation. After drought stress treatment, we selected two transgenic lines with high expression of AtABF3, SAF5 and SAF6, for further characterization. Under normal conditions, SAF plants showed smaller leaf size compared to non-transgenic (NT) plants, while no other morphological changes were observed. Moreover, SAF plants exhibited enhanced drought stress tolerance and better growth under drought stress treatment, which was accompanied by a reduced transpiration rate and lower reactive oxygen species contents. In addition, SAF plants showed an increased tolerance to salt and oxidative stress. Therefore, these transgenic AtABF3 alfalfa plants might be useful for breeding forage crops with enhanced tolerance to environmental stress for use in sustainable agriculture on marginal lands.

Overexpression of codA gene confers enhanced tolerance to abiotic stresses in alfalfa.

We generated transgenic alfalfa plants (Medicago sativa L. cv. Xinjiang Daye) expressing a bacterial codA gene in chloroplasts under the control of the SWPA2 promoter (referred to as SC plants) and evaluated the plants under various abiotic stress conditions. Three transgenic plants (SC7, SC8, and SC9) were selected for further characterization based on the strong expression levels of codA in response to methylviologen (MV)-mediated oxidative stress. SC plants showed enhanced tolerance to NaCl and drought stress on the whole plant level due to induced expression of codA. When plants were subjected to 250 mM NaCl treatment for 2 weeks, SC7 and SC8 plants maintained higher chlorophyll contents and lower malondialdehyde levels than non-transgenic (NT) plants. Under drought stress conditions, all SC plants showed enhanced tolerance to drought stress through maintaining high relative water contents and increased levels of glycinebetaine and proline compared to NT plants. Under normal conditions, SC plants exhibited increased growth due to increased expression of auxin-related IAA genes compared to NT plants. These results suggest that the SC plants generated in this study will be useful for enhanced biomass production on global marginal lands, such as high salinity and arid lands, yielding a sustainable agricultural product.

Transgenic alfalfa plants expressing AtNDPK2 exhibit increased growth and tolerance to abiotic stresses.

In this study, we generated and evaluated transgenic alfalfa plants (Medicago sativa L. cv. Xinjiang Daye) expressing the Arabidopsis nucleoside diphosphate kinase 2 (AtNDPK2) gene under the control of the oxidative stress-inducible SWPA2 promoter (referred to as SN plants) to develop plants with enhanced tolerance to various abiotic stresses. We selected two SN plants (SN4 and SN7) according to the expression levels of AtNDPK2 and the enzyme activity of NDPK in response to methyl viologen (MV)-mediated oxidative stress treatment using leaf discs for further characterization. SN plants showed enhanced tolerance to high temperature, NaCl, and drought stress on the whole-plant level. When the plants were subjected to high temperature treatment (42 °C for 24 h), the non-transgenic (NT) plants were severely wilted, whereas the SN plants were not affected because they maintained high relative water and chlorophyll contents. The SN plants also showed significantly higher tolerance to 250 mM NaCl and water stress treatment than the NT plants. In addition, the SN plants exhibited better plant growth through increased expression of auxin-related indole acetic acid (IAA) genes (MsIAA3, MsIAA5, MsIAA6, MsIAA7, and MsIAA16) under normal growth conditions compared to NT plants. The results suggest that induced overexpression of AtNDPK2 in alfalfa will be useful for increasing biomass production under various abiotic stress conditions.

Enhanced tolerance of transgenic potato plants expressing choline oxidase in chloroplasts against water stress.

BACKGROUND: Glycinebetaine, whose biosynthesis could be catalyzed by choline oxidase (COD), is an extremely efficient compatible solute for scavenging oxidative stress-inducing molecules and protecting the photosynthetic system in plants. To study the effects of the codA transgene for choline oxidase on the drought resistance and recovery, a transgenic potato cultivar (SC) bearing codA gene and a non-transgenic (NT) control cultivar were raised in pots under moderate and severe drought stress. The experiment was constituted by a two-day-pretreatment with 20% PEG and a four-day-water stress combined with two-day-recovery treatment. RESULTS: Under the four-day-water stress, plants were provided with normal water condition, 10% or 20% polyethylene glycol. The results of pretreatment showed an expression of codA gene in transgenic potato and an accumulation of glycine betaine (GB); leaf water potential was higher in SC than in NT. In the stress-recovery-treatment, SC showed stronger antioxidant ability, more efficient photosynthetic system, higher chlorophyll content, lower malondialdehyde content and better recovery from water deficit stress than NT. CONCLUSION: Although this work concentrated on the short-term water stress and recover treatments on transgenic potato plants with the over-expression of CodA gene and its control line. The datas shows that the exogenous codA gene provided potato a stronger drought resistance and recovery ability.

Enhanced salt stress tolerance in transgenic potato plants expressing IbMYB1, a sweet potato transcription factor.

IbMYB1, a transcription factor (TF) for R2R3-type MYB TFs, is a key regulator of anthocyanin biosynthesis during storage of sweet potatoes. Anthocyanins provide important antioxidants of nutritional value to humans, and also protect plants from oxidative stress. This study aimed to increase transgenic potatoes' (Solanum tuberosum cv. LongShu No.3) tolerance to environmental stress and enhance their nutritional value. Transgenic potato plants expressing IbMYB1 genes under the control of an oxidative stress-inducible peroxidase (SWPA2) promoter (referred to as SM plants) were successfully generated through Agrobacterium-mediated transformation. Two representative transgenic SM5 and SM12 lines were evaluated for enhanced tolerance to salinity, UV-B rays, and drought conditions. Following treatment of 100 mM NaCl, seedlings of SM5 and SM12 lines showed less root damage and more shoot growth than control lines expressing only an empty vector. Transgenic potato plants in pots treated with 400 mM NaCl showed high amounts of secondary metabolites, including phenols, anthocyanins, and flavonoids, compared with control plants. After treatment of 400 mM NaCl, transgenic potato plants also showed high DDPH radical scavenging activity and high PS II photochemical efficiency compared with the control line. Furthermore, following treatment of NaCl, UV-B, and drought stress, the expression levels of IbMYB1 and several structural genes in the flavonoid biosynthesis such as CHS, DFR, and ANS in transgenic plants were found to be correlated with plant phenotype. The results suggest that enhanced IbMYB1 expression affects secondary metabolism, which leads to improved tolerance ability in transgenic potatoes.

[Effects of water stress on protein expression and physiological properties of different genotype wheat (Triticum aestivum L.) sprouts].

With drought-resistant wheat (Triticum aestivum) cultivar Changwu 134 and drought-sensitive cultivar Zhengyin 1 as test materials, and by using -1.2 MPa PEG 6000 to treat their seeds, this paper studied the protein expression and physiological properties of the sprouts under different soil moisture conditions. SDS-PAGE analysis showed that water stress induced the production of two new proteins with molecular weights of 39.5 kDa and 23.0 kDa in Changwu 134 but not in Zhengyin 1 sprouts. Under normal water supply, the expression of the protein with molecular weight of 48.5 kDa in the sprouts of both Changwu 134 and Zhengyin 1 increased with sprout growth. This protein was preliminarily named as water-sensitive protein, due to its water-sensitivity and of newly discovered protein. The determinations of physiological properties showed that under water stress, the sprouts of drought-resistant Changwu 134 had higher root/shoot ratio and higher relative water content, but lower relative membrane permeability and lower malondlaldehyde content than those of drought-sensitive Zhengyin 1.

Analysis of antioxidant enzyme activity during germination of alfalfa under salt and drought stresses.

To understand the adaptability of alfalfa (Medicago sativa L.) to environmental stresses, we analyzed the activity of several antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT), in alfalfa shoots and roots subjected to salt and drought stresses during germination. The germination rate of six alfalfa cultivars was comparatively studied under 200 mM NaCl or 35% PEG treatment. Alfalfa Xinmu No. 1 and Northstar varieties were selected as stress-tolerant and -sensitive cultivars, respectively, and were used for further characterization. After NaCl or PEG treatment, Xinmu No. 1 showed enhanced seedling growth, compared with Northstar. Xinmu No. 1 also exhibited low levels of hydrogen peroxide (H(2)O(2)) production and lipid peroxidation, compared with Northstar. In addition, Xinmu No. 1 showed higher enzymatic activity of SOD, APX, CAT, and POD in its shoots and roots than Northstar. These results seem to indicate that Xinmu No. 1 cultivar's tolerance to salt or drought stresses during germination is associated with enhanced activity of antioxidant enzymes. This study highlights the importance of antioxidant enzymes in the establishment of alfalfa seedlings under drought and salinity conditions typical of desertification.

Overexpression of a new rice vacuolar antiporter regulating protein OsARP improves salt tolerance in tobacco.

We examined the function of the rice (Oryza sativa L.) antiporter-regulating protein OsARP by overexpressing it in tobacco (Nicotiana tabacum L.). In public databases, this protein was annotated as a putative Os02g0465900 protein of rice. The OsARP gene was introduced into tobacco under the control of the cauliflower mosaic virus 35S promoter. The transformants were selected for their ability to grow on medium containing kanamycin. Incorporation of the transgene in the genome of tobacco was confirmed by PCR, and its expression was confirmed by Western blot analysis. Transgenic plants had better growth and vigor than non-transgenic plants under salt stress in vitro. Overexpression of OsARP in transgenic tobacco plants resulted in salt tolerance, and the plants had a higher rate of photosynthesis and effective PSII photon yield when compared with the wild type. The OsARP protein was localized in the tonoplast of rice plants. Transgenic plants accumulated more Na+ in their leaf tissue than did wild-type plants. It is conceivable that the toxic effect of Na+ in the cytosol might be reduced by sequestration into vacuoles. The rate of water loss was higher in the wild type than in transgenic plants under salt stress. Increased vacuolar solute accumulation and water retention could confer salt tolerance in transgenic plants. Tonoplast vesicles isolated from OsARP transgenic plants showed Na+/H+ exchange rates 3-fold higher than those of wild-type plants. These results suggest that OsARP on the tonoplasts plays an important role in compartmentation of Na+ into vacuoles. We suggest that OsARP is a new type of protein participating in Na+ uptake in vacuoles.

[Expression of ZmPIP1 subgroup genes in maize roots under water shortage].

To investigate the role of ZmPIP1-1 and ZmPIP1-2 in water uptake of roots and drought resistance of crops, semi-quantitative PCR was used to examine the expression of ZmPIP1-1 and ZmPIP1-2 in root systems of different maize genotypes under water deficit. These genotypes showed different resistance to water shortage under field conditions. The reference gene to target genes was tubulin. Maize seedlings were grown by hydroponics in a growth chamber. Water deficit was imposed on the seedlings with PEG-6000. The result showed that ZmPIP1-1 was up-regulated under water deficit in root systems of plants of the filial generation 'Hudan 4' and the mother line 'Tiansi', which were resistant to water shortage, but there was no noticeable up-regulation of ZmPIP1-1 in the root systems of the father line '803', which was sensitive to water deprivation. The result also showed that the extent of up-regulation was positively correlated with drought resistance of maize (Fig.3). On the other hand, the expression of ZmPIP1-1 showed different degrees of tendency after different duration of water stress in the root systems of the maize seedlings of different genotypes. The result showed that ZmPIP1-2 was identically expressed in three different species of maize and under different water conditions. The results support the theory that the intercellular water transport contributes to increased water uptake in root systems under water deficit by up-regulating the number of some kinds of aquaporins. The increases amount of transcripts of aquaporins is positively correlated to drought resistance of plant varieties. But not all kinds of number of aquaporins is up-regulated during water shortage, some kinds of aquaporins are identically expressed under water deficit conditions and well watered conditions.

[Drought tolerance of transgenic sweet potato expressing both Cu/Zn superoxide dismutase and ascorbate peroxidase].

Two strains, Cu/Zn SOD and APX gene transferred sweet potato (TS) and non-transgenic sweet potato (Ipomoea batatas L.) (NT), were used as experimental materials to study the drought tolerance under three different degrees of water stress: 0, -0.44 MPa, -0.78 MPa. The results showed that activities of Cu/Zn SOD and APX increased under -0.44 MPa and decreased under -0.78 MPa (Fig. 2), P(n), G(s) and leaf water content decreased, C(i) increased, then decreased under water stress (Fig. 6), but under the same PEG concentration all these indexes in the TS were higher than those in NT. The accumulation of H(2)O(2) and O(-*)(2) (Fig. 1) increased the degree of lipid peroxidation of the plasma membrane (Fig. 4), prompted the accumulation of MDA (Fig. 3), and the accumulation of TS always lower than the NT at the same PEG concentration. All the results showed that the transgenic sweet potato has a stronger ability to clean up active oxygen than the non-transgenic one, and it can keep a higher leaf water content and P(n) under water stress, so it has a stronger tolerance to drought.