Comparative Analysis Of Salt Stress-responsive Microstructure And Ultrastructure In Arabidopsis Thaliana And Thellungiella Halophila

The effects of salt stress on the microscopic and ultrastructural features between Thellungiella halophila and Arabidopsis thaliana were studied through the semi-thin sections, scanning electron microscope and transmission electron microscope. We analyzed the differences between them at the cellular and subcellular level in order to further understand the morphological changes of halophytes and non-halophytes under salt stress, and provide basic information for the mechanism of salt-tolerant plants.Results of growth and biomass shown that low concentration (50mM NaCl) inhibited the growth of A.thaliana, and high concentration (150mM NaCl) cause obvious symptoms. But T. halophila in150mM NaCl treatment did not show the stress response.300mM NaCl treatment inhibited the growth of T. halophila, but did not cause serious injury.500mM NaCl treatment caused serious damage to T. halophila, which increased with the extension of stress.Microscopic study shown that T. halophila had the characteristics of halophytes, as its higher degree of keratinization in epidermis and stomatal guard cells, more and larger intercellular spaces between the mesophyll cells, more developed main veins with numerous vessels and phloem cells compared with A. thaliana. These characteristics mean T. halophila has more advantages in terms of reduce water loss, strengthen the breathing, and accelerate the water and nutrient transport. The changes under stress included increasing the intercellular space, the number of mesophyll cells, cells layers, vessels and sieve tubes, also the size of vacuole and cell. However, T. halophila had more quickly reaction under salt stress. Volume of the mesophyll cell in T. halophila can rapidly increased to maximum (1days), but the ones in A. thaliana requires a longer time (3days). Micro structure of A. thaliana was distroyed after150mM NaCl treatment, but T. halophila changed little.Observation through scanning electron microscopy shown that the leaf surface of T. halophila and A. thaliana changed little under stress, except for stomatal characteristics. Long time and high concentration of salt treatment promoted stomatal closure. There was granular crystal precipitation surrounding stoma after rehydration. With the increasing of salt concentration and rehydration time, the number and volume of crystals increased. Energy spectrum analysis indicated that the main element of crystal was Na. This suggested that Na+could be excreted through the stoma after rehydration.Ultrastructural study on mesophyll cells by TEM suggested that:A. thaliana could recover its own morphology damages and adapt to the stress environment within3days at low concentration of50mmol·L-1. It accumulated starch grains and hydrolyzed them. Chloroplast membrane system was distorted, disordered, even disintegrated at high salt concentration of 150mmol-L-1.The injuries were more quickly,more serious and irreparable than low concentration stress. But salt stress had little effect on ultrastructure of chloroplast in T. halophila at the concentration of150mmol·L-1.The integrity of membrane structure was not destroyed, and could be able to recover by itself. At the concentration of300mmol·L-1, obviously changes took place in chloroplast. And under500mmol·L-1salt stress, membrane system had been completely destroyed. With the increasing of salt concentration and treating time, the ultrastructural changes in the two materials were similar when the concentration exceeded the plant could withstand. Just T. halophila can tolerant higher concentration of salt.