Methanol fixation for scanning electron microscopy of plants

Changes and biotransformation mechanism of main functional compounds during kombucha fermentation by the pure cultured tea fungus

Kombucha was fermented by the pure cultured tea fungus, and the changes of functional compounds and their transformation were explored. After fermentation, the contents of total polyphenols, total flavonoids, quercetin, kaempferol and catechins respectively enhanced by 77.14%, 69.23%, 89.11%, 70.32% and 45.77% compared with the control, while flavonol glycosides reduced by 38.98%. The bioavailability of polyphenols and flavonoids respectively increased by 29.52% and 740.6%, and DPPH and ABTS respectively increased by 43.81% and 35.08% compared with the control. Correlation analysis showed that microorganisms and the antioxidant activity were highly positive correlation with total polyphenols, total flavonoids, EGC, EC, EGCG, ECG, quercetin and kaempferol, and negative correlation with kaempferol-3-glucoside. The constructed models confirmed that organic acids were more likely to damage the structure of tea leaves, and enzymes (polygalacturonidase and tannase) and solvents (acids, alcohols and esters) had a synergistic effect on the biotransformation of functional compounds.

Appressed, directed and silicified trichomes of the kudzu climbing vine

Kudzu (Pueraria montana var. lobata) is becoming one of the most prevalent climbing vines in urban forests. Here, surface characteristics of kudzu leaves and stems are investigated using field-emission scanning electron microscopy and X-ray microanalysis. The leaf and stem surfaces were characterized by different types of trichomes. No adhesive pads, modified hooks or tendrils were found on kudzu vines. Trichomes on the leaves and stems of kudzu could be categorized into (i) complex bulbous glandular trichomes and (ii) needle-shaped nonglandular trichomes (NSNGTs). Two morphotypes of the nonglandular trichomes were present on the stems: (i) long hairy nonglandular trichomes and (ii) short NSNGTs. The leaf trichomes were appressed and oriented in an uphill direction, whereas the stem trichomes were appressed and oriented in a downhill direction. This opposite trichome orientation appears to facilitate climbing and prohibits slipping of kudzu vines through differential friction between the plants and the kudzu vines. X-ray microanalysis revealed a distinct accumulation of silicon in the leaf and stem trichomes. These results suggest that appressed, directed and silicified trichomes may contribute to the twining behavior of kudzu vines.

Chemical fixation creates nanoscale clusters on the cell surface by aggregating membrane proteins

Chemical fixations have been thought to preserve the structures of the cells or tissues. However, given that the fixatives create crosslinks or aggregate proteins, there is a possibility that these fixatives create nanoscale artefacts by aggregation of membrane proteins which move around freely to some extent on the cell surface. Despite this, little research has been conducted about this problem, probably because there has been no method for observing cell surface structures at the nanoscale. In this study, we have developed a method to observe cell surfaces stably and with high resolution using atomic force microscopy and a microporous silicon nitride membrane. We demonstrate that the size of the protrusions on the cell surface is increased after treatment with three commonly used fixatives and show that these protrusions were created by the aggregation of membrane proteins by fixatives. These results call attention when observing fixed cell surfaces at the nanoscale.

Atomic force microscopy imaging shows that cell fixation can lead to unwanted aggregation of membrane proteins.

Biological applications of the NanoSuit for electron imaging and X-microanalysis of insulating specimens

Field emission scanning electron microscopy (FESEM) is an essential tool for observing surface details of specimens in a high vacuum. A series of specimen procedures precludes the observations of living organisms, resulting in artifacts. To overcome these problems, Takahiko Hariyama and his colleagues proposed the concept of the "nanosuit" later referred to as "NanoSuit", describing a thin polymer layer placed on organisms to protect them in a high vacuum in 2013. The NanoSuit is formed rapidly by (i) electron beam irradiation, (ii) plasma irradiation, (iii) Tween 20 solution immersion, and (iv) surface shield enhancer (SSE) solution immersion. Without chemical fixation and metal coating, the NanoSuit-formed specimens allowed structural preservation and accurate element detection of insulating, wet specimens at high spatial resolution. NanoSuit-formed larvae were able to resume normal growth following FESEM observation. The method has been employed to observe unfixed and uncoated bacteria, multicellular organisms, and paraffin sections. These results suggest that the NanoSuit can be applied to prolong life in vacuo and overcome the limit of dead imaging of electron microscopy.