99. Itoh, T. and R. M. Brown, Jr. 1984.
The assembly of cellulose microfibrils in Valonia macrophysa.
The assembly of cellulose microfibrils was
investigated in artificially induced protoplasts of the alga,
Valonia macuophysa (Siphonocladales). Primary-wall microfibrils,
formed within 72 h of protoplast induction, are randomly oriented.
Secondary-wall lamellae, which are produced within 96 h after
protoplast induction, have more than three orientations of highly
ordered microfibrils. The innermost, recently deposited microfibrils
are not parallel with the cortical microtubules, thus indicating
a more indirect role of microtubules in the orientation of microfibrils.
Fine filamentous structures with a periodicity of 5.0-5.5 nm
and the dimensions of actin were observed adjacent to the plasma
membrane. Linear cellulose-terminal synthesizing complexes (TCs)
consisting of three rows, each with 30-40 particles, were observed
not only on the E fracture (EF) but also on P fracture (PF) faces
of the plasma membrane. The TC appears to span both faces of
the bimolecular leaflet. The average length of the TC is 350
nm, and the number of TCs per unit area during primary-wall synthesis
is 1 per m2 Neither paired TCs nor granule bands characteristic
of Oocystis were ob-served. Changes in TC structure and
distribution during the conversion from primary- to secondary-
wall formation have been described. Cellulose microfibril assembly
in Valonia is discussed in relation to the process among
other eukaryotic systems.