The development of fruits of blackcurrant (Ribes nigrum)
cv. Ben Alder from flower to maturity was studied
non-invasively by nuclear magnetic resonance (NMR) microscopy, using attached
and detached fruits, and the
images were compared with those from low temperature scanning electron
microscopy (LTSEM) and conventional
resin histology. The NMR images derived from 2-D and 3-D datasets showed
the previously unreported growth
of arillar tissues to the extent that they almost completely occlude the
locular cavity, but LTSEM and resin
histology revealed that no fusion occurs between the arillar tissues and
the gelatinous sheath surrounding each
seed, or between the arillar tissues and the endocarp. The discontinuities
between these tissues cause magnetic
inhomogenities which result in these structures being clearly resolved
by gradient echo imaging sequences. During
seed maturation the endosperm changed from high (bright) to low (dark)
signal intensity as lipid reserves formed
and solidified, whereas the gelatinous sheath had high signal intensity
throughout maturation. The high lipid
concentration in the seed was manifested by chemical shift effects in the
images and the increasing viscosity of the
endosperm was reflected in the decrease in spin–lattice (T1)
relaxation times. The funiculi, throughout
development of seeds, appeared in NMR images with low signal intensity
and 3-D surface-rendered
reconstructions illustrated the complexity of the spatial array of seeds
and funiculi arising from parietal placentas
within the loculus. All other vascular tissues in the pericarp and placentas
were resolved as a small bright core
surrounded by a dark region, within a matrix of moderate signal intensity.
Conventional microscopical studies
then showed that the bright core discernible by NMR imaging encompassed
an entire vascular bundle whereas
the darker surrounding region represented small parenchyma cells with pronounced
intercellular gas spaces. Other
regions of the pericarp which included extremely large parenchyma cells,
however, had few intercellular spaces
and consequently gave rise to brighter regions of the image.