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1.
Many plant species can be induced to flower by responding to stress factors. The short-day plants Pharbitis nil and Perilla frutescens var. crispa flower under long days in response to the stress of poor nutrition or low-intensity light. Grafting experiments using two varieties of P. nil revealed that a transmissible flowering stimulus is involved in stress-induced flowering. The P. nil and P. frutescens plants that were induced to flower by stress reached anthesis, fruited and produced seeds. These seeds germinated, and the progeny of the stressed plants developed normally. Phenylalanine ammonialyase inhibitors inhibited this stress-induced flowering, and the inhibition was overcome by salicylic acid (SA), suggesting that there is an involvement of SA in stress-induced flowering. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T (FT) of Arabidopsis thaliana, was expressed when the P. nil plants were induced to flower under poor-nutrition stress conditions, but expression of PnFT1, another ortholog of FT, was not induced, suggesting that PnFT2 is involved in stress-induced flowering.Key words: flowering, stress, phenylalanine ammonia-lyase, salicylic acid, FLOWERING LOCUS T, Pharbitis nil, Perilla frutescensFlowering in many plant species is regulated by environmental factors, such as night-length in photoperiodic flowering and temperature in vernalization. On the other hand, a short-day (SD) plant such as Pharbitis nil (synonym Ipomoea nil) can be induced to flower under long days (LD) when grown under poor-nutrition, low-temperature or high-intensity light conditions.1–9 The flowering induced by these conditions is accompanied by an increase in phenylalanine ammonia-lyase (PAL) activity.10 Taken together, these facts suggest that the flowering induced by these conditions might be regulated by a common mechanism. Poor nutrition, low temperature and high-intensity light can be regarded as stress factors, and PAL activity increases under these stress conditions.11 Accordingly, we assumed that such LD flowering in P. nil might be induced by stress. Non-photoperiodic flowering has also been sporadically reported in several plant species other than P. nil, and a review of these studies suggested that most of the factors responsible for flowering could be regarded as stress. Some examples of these factors are summarized in 12–14
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Table 1
Some cases of stress-induced floweringStress factor | Species | Flowering response | Reference |
high-intensity light | Pharbitis nil | induction | 5 |
low-intensity light | Lemna paucicostata | induction | 29 |
Perilla frutescens var. crispa | induction | 14 | |
ultraviolet C | Arabidopsis thaliana | induction | 23 |
drought | Douglas-fir | induction | 30 |
tropical pasture Legumes | induction | 31 | |
lemon | induction | 32–35 | |
Ipomoea batatas | promotion | 36 | |
poor nutrition | Pharbitis nil | induction | 3, 4, 13 |
Macroptilium atropurpureum | promotion | 37 | |
Cyclamen persicum | promotion | 38 | |
Ipomoea batatas | promotion | 36 | |
Arabidopsis thaliana | induction | 39 | |
poor nitrogen | Lemna paucicostata | induction | 40 |
poor oxygen | Pharbitis nil | induction | 41 |
low temperature | Pharbitis nil | induction | 9, 12 |
high conc. GA4/7 | Douglas-fir | promotion | 42 |
girdling | Douglas-fir | induction | 43 |
root pruning | Citrus sp. | induction | 44 |
Pharbitis nil | induction | 45 | |
mechanical stimulation | Ananas comosus | induction | 46 |
suppression of root elongation | Pharbitis nil | induction | 7 |
2.
Cotyledons of tomato seedlings that germinated in a 20 µM AlK(SO4)2 solution remained chlorotic while those germinated in an aluminum free medium were normal (green) in color. Previously, we have reported the effect of aluminum toxicity on root proteome in tomato seedlings (Zhou et al.1). Two dimensional DIGE protein analysis demonstrated that Al stress affected three major processes in the chlorotic cotyledons: antioxidant and detoxification metabolism (induced), glyoxylate and glycolytic processes (enhanced), and the photosynthetic and carbon fixation machinery (suppressed).Key words: aluminum, cotyledons, proteome, tomatoDifferent biochemical processes occur depending on the developmental stages of cotyledons. During early seed germination, before the greening of the cotyledons, glyoxysomes enzymes are very active. Fatty acids are converted to glucose via the gluconeogenesis pathway.2,3 In greening cotyledons, chloroplast proteins for photosynthesis and leaf peroxisomal enzymes in the glycolate pathway for photorespiration are metabolized.2–4 Enzymes involved in regulatory mechanisms such as protein kinases, protein phosphatases, and mitochondrial enzymes are highly expressed.3,5,6The chlorotic cotyledons are similar to other chlorotic counterparts in that both contains lower levels of chlorophyll, thus the photosynthetic activities are not as active. In order to understand the impact of Al on tomato cotyledon development, a comparative proteome analysis was performed using 2D-DIGE following the as previously described procedure.1 Some proteins accumulated differentially in Al-treated (chlorotic) and untreated cotyledons (Fig. 1). Mass spectrometry of tryptic digestion fragments of the proteins followed by database search has identified some of the differentially expressed proteins (Open in a separate windowFigure 1Image of protein spots generated by Samspot analysis of Al treated and untreated tomato cotyledons proteomes separated on 2D-DIGE.
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Table 1
Proteins identified from tomato cotyledons of seeds germinating in Al-solutionSpot No. | Fold (treated/ctr) | ANOVA (p value) | Annotation | SGN accession |
1 | 2.34 | 0.001374 | 12S seed storages protein (CRA1) | SGN-U314355 |
2 | 2.13 | 0.003651 | unidentified | |
3 | 2.0 | 0.006353 | lipase class 3 family | SGN-U312972 |
4 | 1.96 | 0.002351 | large subunit of RUBISCO | SGN-U346314 |
5 | 1.95 | 2.66E-05 | arginine-tRNA ligase | SGN-U316216 |
6 | 1.95 | 0.003343 | unidentified | |
7 | 1.78 | 0.009219 | Monodehydroascorbate reductase (NADH) | SGN-U315877 |
8 | 1.78 | 0.000343 | unidentified | |
9 | 1.75 | 4.67E-05 | unidentified | |
12 | 1.70 | 0.002093 | unidentified | |
13 | 1.68 | 0.004522 | unidentified | |
15 | 1.66 | 0.019437 | Glutamate dehydrogenase 1 | SGN-U312368 |
16 | 1.66 | 0.027183 | unidentified | |
17 | 1.62 | 2.01E-08 | Major latex protein-related, pathogenesis-related | SGN-U312368 |
18 | −1.61 | 0.009019 | RUBisCo activase | SGN-U312543 |
19 | 1.61 | 0.003876 | Cupin family protein | SGN-U312537 |
20 | 1.60 | 0.000376 | unidentified | |
22 | 1.59 | 0.037216 | unidentified | |
0.003147 | unidentified | |||
29 | −1.56 | 0.001267 | RUBisCo activase | SGN-U312543 |
35 | 1.52 | 0.001955 | unidentified | |
40 | 1.47 | 0.007025 | unidentified | |
41 | 1.47 | 0.009446 | unidentified | |
45 | 1.45 | 0.001134 | unidentified | |
59 | −1.40 | 5.91E-05 | 12 S seed storage protein | SGN-U314355 |
61 | 1.39 | 1.96E-05 | MD-2-related lipid recognition domain containing protein | SGN-U312452 |
65 | 1.37 | 0.000608 | triosephosphate isomerase, cytosolic | SGN-U312988 |
68 | 1.36 | 0.004225 | unidentified | |
81 | 1.32 | 0.001128 | unidentified | |
82 | −1.31 | 0.001408 | 33 kDa precursor protein of oxygen-evolving complex | SGN-U312530 |
87 | 1.30 | 0.002306 | unidentified | |
89 | −1.3 | 0.000765 | unidentified | |
92 | 1.29 | 0.000125 | superoxide dismutase | SGN-U314405 |
98 | 1.28 | 0.000246 | triosephosphate isomerase, cytosolic | SGN-U312988 |
3.
4.
Pavan Umate 《Plant signaling & behavior》2011,6(3):335-338
The enzymes called lipoxygenases (LOXs) can dioxygenate unsaturated fatty acids, which leads to lipoperoxidation of biological membranes. This process causes synthesis of signaling molecules and also leads to changes in cellular metabolism. LOXs are known to be involved in apoptotic (programmed cell death) pathway, and biotic and abiotic stress responses in plants. Here, the members of LOX gene family in Arabidopsis and rice are identified. The Arabidopsis and rice genomes encode 6 and 14 LOX proteins, respectively, and interestingly, with more LOX genes in rice. The rice LOXs are validated based on protein alignment studies. This is the first report wherein LOXs are identified in rice which may allow better understanding the initiation, progression and effects of apoptosis, and responses to bitoic and abiotic stresses and signaling cascades in plants.Key words: apoptosis, biotic and abiotic stresses, genomics, jasmonic acid, lipidsLipoxygenases (linoleate:oxygen oxidoreductase, EC 1.13.11.-; LOXs) catalyze the conversion of polyunsaturated fatty acids (lipids) into conjugated hydroperoxides. This process is called hydroperoxidation of lipids. LOXs are monomeric, non-heme and non-sulfur, but iron-containing dioxygenases widely expressed in fungi, animal and plant cells, and are known to be absent in prokaryotes. However, a recent finding suggests the existence of LOX-related genomic sequences in bacteria but not in archaea.1 The inflammatory conditions in mammals like bronchial asthama, psoriasis and arthritis are a result of LOXs reactions.2 Further, several clinical conditions like HIV-1 infection,3 disease of kidneys due to the activation of 5-lipoxygenase,4,5 aging of the brain due to neuronal 5-lipoxygenase6 and atherosclerosis7 are mediated by LOXs. In plants, LOXs are involved in response to biotic and abiotic stresses.8 They are involved in germination9 and also in traumatin and jasmonic acid biochemical pathways.10,11 Studies on LOX in rice are conducted to develop novel strategies against insect pests12 in response to wounding and insect attack,13 and on rice bran extracts as functional foods and dietary supplements for control of inflammation and joint health.14 In Arabidopsis, LOXs are studied in response to natural and stress-induced senescence,15 transition to flowering,16 regulation of lateral root development and defense response.17The arachidonic, linoleic and linolenic acids can act as substrates for different LOX isozymes. A hydroperoxy group is added at carbons 5, 12 or 15, when arachidonic acid is the substrate, and so the LOXs are designated as 5-, 12- or 15-lipoxygenases. Sequences are available in the database for plant lipoxygenases (EC:1.13.11.12), mammalian arachidonate 5-lipoxygenase (EC:1.13.11.34), mammalian arachidonate 12-lipoxygenase (EC:1.13.11.31) and mammalian erythroid cell-specific 15-lipoxygenase (EC:1.13.11.33). The prototype member for LOX family, LOX-1 of Glycine max L. (soybean) is a 15-lipoxygenase. The LOX isoforms of soybean (LOX-1, LOX-2, LOX-3a and LOX-3b) are the most characterized of plant LOXs.18 In addition, five vegetative LOXs (VLX-A, -B, -C, -D, -E) are detected in soybean leaves.19 The 3-dimensional structure of soybean LOX-1 has been determined.20,21 LOX-1 was shown to be made of two domains, the N-terminal domain-I which forms a β-barrel of 146 residues, and a C-terminal domain-II of bundle of helices of 693 residues21 (Fig. 1). The iron atom was shown to be at the centre of domain-II bound by four coordinating ligands, of which three are histidine residues.22Open in a separate windowFigure 1Three-dimensional structure of soybean lipoxygenase L-1. The domain I (N-terminal) and domain II (C-terminal) are indicated. The catalytic iron atom is embedded in domain II (PDB ID-1YGE).21This article describes identification of LOX genes in Arabidopsis and rice. The Arabidopsis genome encodes for six LOX proteins23 (www.arabidopsis.org) (Locus Annotation Nomenclature A* B* C* AT1G55020 lipoxygenase 1 (LOX1) LOX1 859 98044.4 5.2049 AT1G17420 lipoxygenase 3 (LOX3) LOX3 919 103725.1 8.0117 AT1G67560 lipoxygenase family protein LOX4 917 104514.6 8.0035 AT1G72520 lipoxygenase, putative LOX6 926 104813.1 7.5213 AT3G22400 lipoxygenase 5 (LOX5) LOX5 886 101058.8 6.6033 AT3G45140 lipoxygenase 2 (LOX2) LOX2 896 102044.7 5.3177