The development of blackcurrant fruit from flower to maturity: a comparative study by 3D nuclear magnetic resonance (NMR) micro-imaging and conventional histology

The development of fruits of blackcurrant (Ribes nigrum) cv. Ben Alder from flower to maturity was studied non-invasively by nuclear magnetic resonanc e (NMR) microscopy, using attached and detached fruits, and the images were compared with those from low temperature scanning electron microscopy (LTS EM) and conventional resin histology. The NMR images derived from 2-D and 3 -D datasets showed the previously unreported growth of arillar tissues to t he extent that they almost completely occlude the locular cavity, but LTSEM and resin histology revealed that no fusion occurs between the arillar tis sues and the gelatinous sheath surrounding each seed, or between the arilla r tissues and the endocarp. The discontinuities between these tissues cause magnetic inhomogenities which result in these structures being clearly res olved by gradient echo imaging sequences. During seed maturation the endosp erm changed from high (bright) to low (dark) signal intensity as lipid rese rves formed and solidified, whereas the gelatinous sheath had high signal i ntensity throughout maturation. The high lipid concentration in the seed wa s manifested by chemical shift effects in the images and the increasing vis cosity of the endosperm was reflected in the decrease in spin-lattice (T-1) relaxation times. The funiculi, throughout development of seeds, appeared in NMR images with low signal intensity and 3-D surface-rendered reconstruc tions illustrated the complexity of the spatial array of seeds and funiculi arising from parietal placentas within the loculus. All other vascular tis sues in the pericarp and placentas were resolved as a small bright core sur rounded by a dark region, within a matrix of moderate signal intensity. Con ventional microscopical studies then showed that the bright core discernibl e by NMR imaging encompassed an entire vascular bundle whereas the darker s urrounding region represented small parenchyma cells with pronounced interc ellular gas spaces. Other regions of the pericarp which included extremely large parenchyma cells, however, had fen intercellular spaces and consequen tly gave rise to brighter regions of the image.