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Mitogen-activated protein kinases (MAPKs) play important roles in signal transduction pathways responding to various stresses. In this study, we described the molecular characteristics of six MAPK genes (MaMAPK1, MaMAPK2, MaMAPK3, MaMAPK4, MaMAPK5 and MaMAPK6) cloned from banana (Musa acuminate L. AAA group, cv. Cavendish) using a RACE-PCR-based strategy. The predicted molecular masses of these MAPKs ranged from 43.0 to 70.1 kDa and their pIs ranged from 5.67 to 9.32. At the amino acid level, they shared high sequence similarity with MAPKs in the banana DH-Pahang (AA group) genome. Phylogenetic analysis showed that the deduced amino acid sequences of MaMAPKs also had high similarity with MAPKs of other plant species. These genes were expressed in nearly all tissues using semi-quantitative RT-PCR. All of the six MaMAPKs were induced by signal molecules in banana seedlings, such as ABA, Ethephon, MeJA and SA. The gene expressions of MaMAPK1, MaMAPK2, MaMAPK3, MaMAPK5 and MaMAPK6 were induced in resistant cultivar of banana after being inoculated with Fusarium Oxysporum f specialis (f. Sp) cubense Tropical Race 4 (Foc TR4). Our results suggest that MaMAPKs play a key role in both the development of banana seedlings and banana resistance to Foc TR4.
Plant hormones are trace organic molecules that play important roles in plant growth, development and stress resistance. 24-epibrassinolide (Br24) and strigolactones (Gr24) were reported to alleviate the toxicity of heavy metals and restrict their translocation into plants. In this study, the effects of Br24 and Gr24 with or without iron plaque (IP) induction on the uptake and accumulation of cadmium (Cd) and arsenic (As) were examined in rice seedlings exposed to 6-day treatments of 2 mg L⁻¹ Cd or 5 mg L⁻¹ As in nutrient solution. The results showed that the growth of rice seedlings was decreased by Cd or As treatment, but Br24 or Gr24 with or without IP alleviated this adverse effect. Br24 or Gr24 can improve root length, average diameter, surface area, and volume, and tip the number of roots of rice plants with or without IP. Cadmium contents in rice shoots were significantly reduced by Br24 with IP or Gr24, but Cd accumulation and translocation from root to shoot were not decreased. The interaction of Br24 or Gr24 and IP dramatically increased As contents in rice root, and reduced As translocation from root to shoot. Br24 or Gr24 with IP induction significantly increased Fe content, but decreased the contents of mineral elements (Mn, Cu and Zn) in rice plants. Our results suggested that the exogenous application of Br24 or Gr24 could be advantageous against the toxicity of Cd or As, and a potential way to effectively inhibit Cd or As uptake by rice plants.
Wheat mature seeds have large, lenticular A-type starch granules, and small, spherical B-type and irregular C-type starch granules. During endosperm development, large amyloplasts came from proplastid, divided and increased in number through binary fission from 4 to 12 days after flowering (DAF). Large starch granules formed and developed in the large amyloplast. One large amyloplast had only one large starch granule. Small amyloplasts came from the protrusion of large amyloplast envelope, divided and increased in number through envelope protrusion after 12 DAF. B-type starch granules formed and developed in small amyloplast from 12 to 18 DAF, C-type starch granules formed and developed in small amyloplast after 18 DAF. Many B- and C-type starch granules might form and develop in one small amyloplast. The amyloplast envelopes were asynchronously degraded and starch granules released into cell matrix when amyloplasts were full of starch granules. Apparent amylose contents of large starch granules were higher than that of small starch granules, and increased with endosperm development. The swelling powers and crystallinity of large starch granule were lower than that of small starch granules, and decreased with endosperm development. Small starch granules displayed broader gelatinization temperature ranges than did large starch granules.
Fritillaria unibracteata is a classic perennial alpine herb. In this study, we examined it's responses to shading (SH) and nitrogen addition (NA), as well as its correlation with internal C-N balance to detect how it adjusted to the changes of habitat conditions. Randomized block experiment was carried out in the field in Chuanbeimu Research Station in Songpan County, Sichuan Province, China (32°09′54″N, 103°38′36″E, altitude 3300 m a.s.l.). Two growing seasons after NA and SH, Fritillaria unibracteata's total plant biomass decreased significantly, with the proportion of biomass allocated to aboveground significantly increased. In addition, in this study, under both SH and NA treatments, Fritillaria unibracteata increased its biomass allocation to above-ground, which consisted with optimal partitioning theory. Moreover, Fritillaria unibracteata's biomass allocation was significantly correlated with its internal C-N status, regardless of nitrogen and light condition. We conclude that Fritillaria unibracteata optimizes its biomass allocation between root and shoot by adjusting its internal C-N balance, which would not be changed by the specialized resource storage organ-bulb.
The source and composition of dissolved organic matter (DOM) are important drivers of its biogeochemical role in aquatic environments. Different land use types may alter DOM amount and composition in freshwaters. Here, water samples were collected from the outlets of 16 subcatchments within mixed land use patterns in the South Tiaoxi River in Eastern China. Dissolved organic carbon (DOC), DOM absorption coefficient (α350), and fluorescence spectrum were measured. These 16 subcatchments were grouped into four clusters with different land use features: natural forest land, planted forest land (Phyllostachys praecox, a bamboo species), cropland, and residential land. Two humic-like and two protein-like fluorescent components were identified using parallel factor analysis (PARAFAC). DOC concentrations were the lowest in natural forest land dominated subcatchments as compared to other land uses with intensive anthropogenic activities, so did α350 and fluorescent intensities of different components. Protein-like fluorescence was more pronounced for the subcatchments dominated by residential land, while terrestrial humic-like fluorescence was the most abundant component for the subcatchments dominated by the other three land use types. The relationships between the percentage of cropland and that of fluorescence fraction appear to be a threshold response, indicating that effects on DOM composition varied with agricultural activity patterns. The reservoir would have a positive effect on DOM amount and the percentage of protein-like fluorescence associated with autochthonous activities. This study in general shows the impact of anthropogenic land use patterns on the amount and composition of DOM in headwater streams, which may affect ecosystem function and health of aquatic environments.
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