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Vitrification Is Essential for Anhydrobiosis in an African Chironomid, Polypedilum Vanderplanki

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Vitrification Is Essential for Anhydrobiosis in an African Chironomid, Polypedilum Vanderplanki

Minoru Sakurai et al. Proc Natl Acad Sci U S A.

Abstract

Anhydrobiosis is an extremely dehydrated state in which organisms show no detectable metabolism but retain the ability to revive after rehydration. Thus far, two hypotheses have been proposed to explain how cells are protected during dehydration: (i) water replacement by compatible solutes and (ii) vitrification. The present study provides direct physiological and physicochemical evidence for these hypotheses in an African chironomid, Polypedilum vanderplanki, which is the largest multicellular animal capable of anhydrobiosis. Differential scanning calorimetry measurements and Fourier-transform infrared (FTIR) analyses indicated that the anhydrobiotic larvae were in a glassy state up to as high as 65 degrees C. Changing from the glassy to the rubbery state by either heating or allowing slight moisture uptake greatly decreased the survival rate of dehydrated larvae. In addition, FTIR spectra showed that sugars formed hydrogen bonds with phospholipids and that membranes remained in the liquid-crystalline state in the anhydrobiotic larvae. These results indicate that larvae of P. vanderplanki survive extreme dehydration by replacing the normal intracellular medium with a biological glass. When entering anhydrobiosis, P. vanderplanki accumulated nonreducing disaccharide trehalose that was uniformly distributed throughout the dehydrated body by FTIR microscopic mapping image. Therefore, we assume that trehalose plays important roles in water replacement and intracellular glass formation, although other compounds are surely involved in these phenomena.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Contents of trehalose, protein, triacylglyceride, and water in quickly and slowly dehydrated larvae of P. vanderplanki.
Fig. 2.
Fig. 2.
Glass in anhydrobiotic larvae and their recovery after heat treatments. (A) DSC thermograms for slowly and quickly dehydrated larvae. A baseline shift of ≈60–70°C in the slowly dehydrated sample indicates the phase transition. (B) Dependence of the recovery rate after rehydration on exposure to high temperatures in slowly (filled symbols) and quickly (open symbols) dehydrated larvae. Circles and triangles show recovery after exposure to high temperature for 5 min and 1 h, respectively.
Fig. 3.
Fig. 3.
FTIR analysis of desiccated P. vanderplanki. (A) FTIR spectra of anhydrous glassy trehalose (bottom), a slowly dehydrated larva (middle), and a quickly dehydrated larva (top). Red and blue arrows indicate the characteristic 992- and 1,540-cm−1 peaks of trehalose and the amide II band of total protein, respectively. A green line indicates a region (3,800–3,000 cm−1) of O–H and N–H stretching vibration bands. (B) Temperature dependence of the maximal peak position in the region 3,800–3,000 cm−1. An inflection point (Tg) was observed in the spectrum of the slowly dehydrated larva.
Fig. 4.
Fig. 4.
Principal-component analysis of dehydrated P. vanderplanki. (A and B) FTIR spectra were decomposed into two components: P1 and P2 in slowly dehydrated larvae (A) and P1′ and P2′ in quickly dehydrated larvae (B). Shown is a region between 3,800 and 3,000 cm−1 (Fig. 3A). P1′ is likely to be a noise. (C and D) Temperature-dependent change of the score value for each principal component.
Fig. 5.
Fig. 5.
Optical and FTIR imaging data for a slowly dehydrated larva and a quickly dehydrated larva. Mapped were intensities of the characteristic 992-cm−1 peak corresponding to trehalose and 1,540-cm−1 peak corresponding to the amide II of proteins. Unequal apparent trehalose distribution due to variation in thickness of the larvae was normalized by dividing the intensity of the peak at 992 cm−1 by that of the amide II band. Spatial resolution is 12.5 × 12.5 μm. Warm colors indicate higher intensity—i.e., larger amounts of the molecule. (Scale bar: 500 μm.)
Fig. 6.
Fig. 6.
FTIR analysis for interaction between cell membrane and sugars. (A) Slowly and quickly dehydrated larvae were measured by FTIR at 30°C. In the region 1,280–1,200 cm−1, which shows asymmetric stretching vibration of Pformula imageO atomic groups, the peak position of the each band remained almost constant within the range of measured temperatures. (B) Slowly and quickly dehydrated larvae were measured by FTIR between −40°C and 50°C. In the region 2,849–2,856 cm−1, which shows symmetric CH2 stretching vibration, the peak position of the each band shifted in a temperature-dependent manner.

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