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The effects of copper toxicity on the photosynthetic activities of Avicennia germinans was investigated using two CuSO 4 concentrations (0.062 and 0.33 M) added in Hoagland's solution in an aerated hydroponic system. Photosynthesis and chlorophyll fl uorescence were measured after 30 h of copper stress. Results obtained in this study show that increasing levels of Cu +2 of 0.062 and 0.33 M Cu +2 resulted in a general reduction of the stomatal conductance (28 and 18%, respectively) and 100% of inhibition of net photosynthesis. Additionally, at these concentrations of Cu +2, reductions of chlorophyll fl uorescence parameters were also observed. These changes suggested that the photosynthetic apparatus of Avicennia germinans was the primary target of the Cu +2 action. It is concluded that Cu +2 ions causes a drastic decline in photosynthetic gas exchange and Chlorophyll fl uorescence parameters in A. germinans leaves.

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Plants possess a wide array of potential cellular mechanisms that may be involved in the tolerance to potentially toxic elements. These mechanisms include mycorrhizal associations, heavy metals binding to cell wall, precipitation by extracellular exudates; reduction in uptake or efflux pumping of metals at the plasma membrane, chelation of metals in the cytosol by peptides such as phytochelatins, metallothionein, histidina free, proline free , and the compartmentation of metals in the vacuole by tono-plast- located transporters. This review provides a broad overview of the evidence of the involvement of each mechanism in plants' tolerance to potentially toxic metals.

In the present study, the effect of variable salinity (0, 15 and 60‰ NaCl) on photosynthetic apparatus was studied in plants (Avicennia germinans seedlings) of a salt secretor mangrove, by measuring chlorophyll fluorescence parameters and gas exchange. Plants treated with NaCl showed a decrease in the maximum net photosynthetic rate (Pn) and stomatal conductance (gs) as salinity increased from 0 to 60‰. The yield for primary photochemistry (TRo/ABS) and the efficiency with which a trapped exciton can move an electron into the electron transport chain (ETo/TRo), the performance index of Photosystem II (PIABS), and the total number of active reaction centers per absorption (RC/ABS) also decreased when exposed to the highest salinity stress (60‰). These results indicated that the main targets in PSII affected by elevated salinity were inactivation of reaction centers and inhibition of the electron transport at the acceptor side of Photosystem II.

The present study was conducted to evaluate the application of native phosphate solubilizing Bacillus sp., isolated from Prosopis juliflora rhizosphere in the biocontrol of three different Fusarium species. The native Bacillus sp., was further confirmed as B. subtilis using the Polymerase Chain Reaction (PCR). The results showed that the phosphate solubilizing ability of B. subtilis strain ALICA was tested in liquid medium with 0.5% Ca3(PO4)2, and maximum of the value of soluble phosphate was 202.02 µg/mL after 3 days of incubation. On the other hand, the growth inhibition of Fusarium solani, F. equiseti and F. oxysporum were more evident in cell-free medium filtrates with respect to dual medium with a range of percentage inhibition from 51, 66 and 47% after 5 days, respectively. Our result of the DNA-PCR amplification of the lipopeptide genes from B. subtilis strain ALICA, showed 94% identity with subtilosin and subtilisin of different Bacillus spp. This result turns B. subtilis strain ALICA into a potential alternative for the biological control of Fusarium species present in the soil of transgenic insect-resistant cotton plants in Mexico.