| Acid soil accounts for30%of the total arable soil all around the world. In China, acid soil distributes throughout15provinces, consisting of approximately22.7%of the total land area. Aluminum (Al)-toxicity at low pH (4.5) is the main stress fector that causes inhibition in plant growth and thus, seriously restricts the sustainable development of agriculture. It is imperative to control this increasing problem by adapting some suitable strategies. As a new kind of signal molecule, hydrogen sulfide (H2S) has been proved to regulate a variety of plant physiological processes under biotic stress. In the present study, oilseed rape(Brassica napus L. cv. Zheshuang758) was used to investigate whether exogenous H2S has any alleviating role on Al-exposed B. napus plants. For this purpose, three levels (0,0.1and0.3mM) of A1were applied at both germinating and seedling stages with or without application of0.3mM H2S donor, sodium hydrosulfide (NaHS). Biological accumulation, Al concentration, reactive oxygen species (ROS), antioxidants scavenging system and ultrastructural changes were studied in order to understand the mechanism of exogenous H2S to Al-toxicity. The main findings of the study were as follows:1. Laboratory experiments demostrated that Al stress decreased the seedling growth and the activities of antioxidant enzymes which could be illustrated by increased level of malondialdehyde (MDA), hydrogen peroxide (H2O2) and Al concentration in B. napus shoots. Exogenously applied H2S reduced the MDA and H2O2levels in the leaves and roots of B. napus seedlings. Moreover, antioxidants enzymes (APX, CAT, SOD, POD and GR) elevated their activities significantly with exogenous application of H2S under Al stress. The microscopic examination confirmed that higher level of Al completely impaired leaf mesophyll and root tip cells. The chloroplast was spongy shaped with dissolved thylakoid membranes and a number of starch grains. Root tip cells showed visible symptoms under Al-toxicity such as deposition of Al in vacuole and disruption of whole cell organelles. Under pretreatment of exogenous H2S, cell structures were improved and presented a clean mesophyll cell and chloroplast possessing well developed thylakoid membranes as well as less number of starch grains. A number of modifications could be observed in root tip cell i.e. mature mitochondria, long endoplasmic reticulum as well as golgibodies were observed under the combined application of H2S and AL2. Greenhouse hydroponic experiments indicated that exogenously applied H2S ameliorated the growth of plant under Al stress which can be illustrated by the recovery of growth indicators such as root length and biomass. It might be closely correlated with a substantial decrease of Al contents in leaves and roots of B. napus. The addition of H2S not only improved the photosynthesis partly by increasing the content of chlorophyll, but also reduced the oxidative stress injury induced by A1stress through activating antioxkiants scavenging system. Meanwhile, exogenous H2S improved the cell structure and displayed a clean mesophyll and root tip cells compared with Al alone. The chloroplast with developed thylakoid membranes could be found in the micrographs. A number of modifications could be observed in root tip cell i.e. mitochondria, long endoplasmic reticulum, as well as golgibodies with combined application of H2S and ALOn the basis of these findings, it can be concluded that exogenous application of H2S under Al stress, improved the plant growth, photosynthetic parameters, biochemical and ultrastructural changes in leaves and roots of B. napus. Thus, exogenous H2S has a promotive role that could improve B. napus plants adaptability to Al toxiity and enhance its survivability under Al stress. |
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