Saline-induced changes of epicuticular waxy layer on the Puccinellia tenuiflora and Oryza sativa leave surfaces

BACKGROUND: The epicuticular waxy layer of plant leaves enhances the extreme environmental stress tolerance. However, the relationship between waxy layer and saline tolerance was not established well. The epicuticular waxy layer of rice (Oryza sativa L.) was studied under the NaHCO3 stresses. In addition, strong saline tolerance Puccinellia tenuiflora was chosen for comparative studies. RESULTS: Scanning electron microscope (SEM) images showed that there were significant changes in waxy morphologies of the rice epicuticular surfaces, while no remarkable changes in those of P. tenuiflora epicuticular surfaces. The NaHCO3-induced morphological changes of the rice epicuticular surfaces appeared as enlarged silica cells, swollen corns-shapes and leaked salt columns under high stress. Energy dispersive X-ray (EDX) spectroscopic profiles supported that the changes were caused by significant increment and localization of [Na(+)] and [Cl(-)] in the shoot. Atomic absorption spectra showed that [Na(+)]shoot/[Na(+)]root for P. tenuiflora maintained stable as the saline stress increased, but that for rice increased significantly. CONCLUSION: In rice, NaHCO3 stress induced localization and accumulation of [Na(+)] and [Cl(-)] appeared as the enlarged silica cells (MSC), the swollen corns (S-C), and the leaked columns (C), while no significant changes in P. tenuiflora.

Improving the short-chain fatty acids production of waste activated sludge stimulated by a bi-frequency ultrasonic pretreatment.

Short-chain fatty acids (SCFAs) are the most important intermediate in the waste activated sludge (WAS) fermentation process. This work explored a novel approach to improve the SCFAs production from WAS. Experimental results showed that the disintegration and acidification of WAS were enhanced markedly by using bi-frequency (28+40 kHz) ultrasonic pretreatment compared with mono-frequency (28 kHz and 40 kHz) ultrasonic pretreatments. After 28+40 kHz ultrasonic pretreatment, the SCOD concentration increased from original 363 mg COD l-1 to 10810 mg COD l-1 which was 1.53-fold and 1.44-fold of the values obtained with 28kHz and 40kHz ultrasonic pretreatments, respectively. The maximum SCFAs production reached 7587 mg COD l-1 in the 28+40 kHz test which was respectively 1.25-fold and 1.31-fold of that in the 28kHz (6053 mg COD l-1) and 40 kHz (5809 mg COD l-1) tests. This was the highest SCFAs production obtained so far using WAS, pretreated by ultrasonic technology, as the renewable carbon source. SCFAs composition analysis revealed there was more acetic acid (3992 mg COD l-1, accounted for 52.6% of the total SCFAs) for the 28+40 kHz ultrasonic pretreatment which was beneficial to many subsequent bioprocesses.