Sketch of the experimental setup for quantitative phase tomography: a multilayer monochromator selects the photons with an energy close to 21 keV from the synchrotron radiation emitted by an insertion device. A high-resolution detector system records Fresnel diffraction patterns at varying distances with respect to the sample. During the tomographic scan that is acquired in air and at room temperature, the specimen is rotated around the vertical axis.

Architecture of an Arabidopsis seed. Shown are a longitudinal virtual slice (A) and a transverse virtual slice (B) through the same seed, 0.3 μm thick, reconstructed by quantitative phase tomography, along with their schematic representations (D and E). Part of the slice in B, viewed at higher magnification, is shown in F with a duplication (G) with white lines to indicate the cell boundaries. For comparison, a classical light microscopic observation of a transverse section of a resin-embedded open-coat seed is shown (C), brought to a similar orientation and scale as the virtual slice shown in B. With the exception of the coat openings, the schematic representation (E) is applicable to the classical microscopic observation (C). The key components are marked as follows: aleu, aleuron; cot, cotyledon; hyp, hypocotyl; ra, radicle; asm, apical shoot meristem; sc, seed coat; cor, cortex; end, endodermis; epi, epidermis; pv, provasculature.

3D rendering of single cells. (A) A mesophyll cell. (B) A palisade cell. Higher-density structures in the cells are classified and colored according to their volume such that green and red correspond, respectively, to the smallest and largest cell structure. (C) Equivalent radii of the structures in the mesophyll cell, arranged in ascending order. An animated 3D image of the mesophyll cell, corresponding to varying angles of view, can be seen in Movie 1, which is published as supporting information on the PNAS web site.

3D rendering of intercellular air space in the hypocotyl (A) and in a cotyledon (B) and air space in cotyledon at higher magnification (C). Animated 3D images of the void network can be seen in Movies 2 and 3, which are published as supporting information on the PNAS web site.