Conserved cellular patterning in the mesophyll of rice leaves.

The mesophyll cells of grass leaves, such as rice, are traditionally viewed as displaying a relatively uniform pattern, in contrast to the clear distinctions of palisade and spongy layers in typical eudicot leaves. This quantitative analysis of mesophyll cell size and shape in rice leaves reveals that there is an inherent pattern in which cells in the middle layer of the mesophyll are larger and less circular and have a distinct orientation of their long axis compared to mesophyll cells in other layers. Moreover, this pattern was observed in a range of rice cultivars and species. The significance of this pattern with relation to potential photosynthetic function and the implication of the widespread use of middle layer mesophyll cells as typical of the rice leaf have been investigated and discussed.

Increasing amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology.

The determination of starch granule morphology in plants is poorly understood. The amyloplasts of wheat endosperm contain large discoid A-type granules and small spherical B-type granules. To study the influence of amyloplast structure on these distinct morphological types, we isolated a mutant in durum wheat (Triticum turgidum) defective in the plastid division protein PARC6, which had giant plastids in both leaves and endosperm. Endosperm amyloplasts of the mutant contained more A- and B-type granules than those of the wild-type. The mutant had increased A- and B-type granule size in mature grains, and its A-type granules had a highly aberrant, lobed surface. This morphological defect was already evident at early stages of grain development and occurred without alterations in polymer structure and composition. Plant growth and grain size, number and starch content were not affected in the mutants despite the large plastid size. Interestingly, mutation of the PARC6 paralog, ARC6, did not increase plastid or starch granule size. We suggest TtPARC6 can complement disrupted TtARC6 function by interacting with PDV2, the outer plastid envelope protein that typically interacts with ARC6 to promote plastid division. We therefore reveal an important role of amyloplast structure in starch granule morphogenesis in wheat.