Study of cell-differentiation and assembly of photosynthetic proteins during greening of etiolated Zea mays leaves using confocal fluorescence microspectroscopy at liquid-nitrogen temperature

Fluorescence microspectroscopy observations were used to study the processes of cell differentiation and assemblies of photosynthesis proteins in Zea mays leaves under the greening process. The observations were done at 78 K by setting the sample in a cryostat to avoid any undesired progress of the greening process during the measurements. The lateral and axial spatial resolutions of the system were 0.64 μm and 4.4 μm, respectively. The study revealed the spatial distributions of protochlorophyllide (PChld) in both the 632-nm-emitting and 655-nm-emitting forms within etiolated Zea mays leaves. The sizes of the fluorescence spots attributed to the former were larger than those of the latter, validating the assignment of the former and latter to the prothylakoid and prolamellar bodies, respectively. In vivo microspectroscopy observations of mature Zea mays leaves confirmed the different photosystem II (PS I)/photosystem I (PS II) ratio between the bundle sheath (BS) and mesophyll (MS) cells, which is specific for C4-plants. The BS cells in Zea mays leaves 1 h after the initiation of the greening process tended to show fluorescence spectra at shorter wavelength side (at around 679 nm) than the MS cells (at around 682 nm). The 679-nm-emitting chlorophyll-a form observed mainly in the BS cells was attributed to putative precursor complexes to PS I. The BS cells under 3-h greening showed higher relative intensities of the PS I fluorescence band at around 735 nm, suggesting the reduced PS II amount in the BS cells in this greening stage.