Changes in the formation of the lignified cell wall within a twenty-four hour period

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The purpose of this paper is to determine the sequence of the formation of the lignified cell wall and to confirm the hypothesis expressed previously on the alternate deposition of cellulose and lignin in a 24-hour period. In this connection, the inner surface of the cell wall of the fibre cells from the youngest wood ofPopulus nigra L. ‘Italica’ taken during a typical summer day in two-hours’ intervals was investigated electron microscopically. The fine structure of the inner surface of the growing secondary cell walls was found to change regularly within 24 hours and to be determined by the structure of the components just being deposited. Cellulose and lignin were identified unambiguously, hemicelluloses could not be identified by their structure. The cellulose was characterised by the parallel microfibrillar structure; lignin was detected as an amorphous deposition. The identified structural components are being deposited separately in certain intervals of the day cycle: cellulose in the afternoon hours (12 a. m. – 6 p. m.) and lignin after midnight (0 – 4 a.m.); in the morning hours (6–10 a.m.), neither lignin nor cellulose are deposited, however, the structure of the cellulose formed previously rises as a microrelief under the amorphous layer. The alternate deposition of both structural components corresponds to variations of the biophysical and biochemical condition of the cells observed in the cambial zone during 24 hours. This periodicity appears to be autonomous and affected only partly by environmental factors. The results confirm the presumption that each lamella of the secondary wall consists of a cellulosic and a non-cellulose (lignin) part. Lignin permeates through the cellulosic part formed previously, impregnates it and cements it to the preceding lamella.