Table 8.

Prior and present estimates of substrate requirements for lignin biosynthesis in higher plants

Glucose requirement [g glucose (g lignin)–1]
Lignin residue:
Hydroxyphenyl	Guaiacyl	Syringyl	Notes	Reference
Previously published estimates
	2·104		1, 2, 3	Penning de Vries et al. (1974)
	1·897*		1, 2, 4	Chung and Barnes (1977)
	2·119		1, 5	Penning de Vries et al. (1983)
	2·320*		1, 2, 4	Merino et al. (1984)
2·431	2·488	2·528	4, 6	Williams et al. (1987)
1·867	1·811	1·770	4, 6, 7	Thornley and Johnson (1990)
2·078	1·981	1·912	8	Thornley and Johnson (1990)
This analysis with most efficient pathways of biosynthesis and options for polymerization, and high efficiency of respiration
2·353	2·377	2·454	Via tyrosine, 9
2·413			Via tyrosine, 9, 10
2·473	2·547	2·600	Via phenylalanine, 9
This analysis with least efficient pathways of biosynthesis and options for polymerization, but high efficiency of respiration
2·664	2·720	2·820	Via tyrosine, 9
2·784	2·891	2·967	Via phenylalanine, 9

Values shown are grams of glucose required for the biosynthesis of 1·0 g of lignin using the indicated lignin residues. For the present analysis, it was assumed that 1·0 mol sucrose is equivalent to 2·0 mol glucose (180 g mol^–1) to provide direct comparisons between the present analysis and previous publications.

Notes:

(1) Based on 37 ATP produced during complete respiratory oxidation of 1 glucose (i.e. the equivalent of Y_ATP,sucrose = 74 ATP per sucrose).

(2) Includes ATP cost of glucose import into a cell.

(3) Calculated from Table 6 in Penning de Vries et al. (1974), using the ratio 0·166 g glucose per 0·08 g lignin for carbon skeleton production (i.e. from ‘PV’ in Penning de Vries et al., 1974). The production of 0·00034 mol NADH during biosynthesis of 0·08 g lignin was assumed, and that such NADH was oxidized to produce 0·00102 mol ATP (i.e. Y_{ATP,cyt‐NADH} = 3 ATP per NADH). The total ATP requirement for biosynthesis of 0·08 g lignin was 0·00150 mol, so an additional (i.e. in addition to that produced during oxidation of the NADH formed) 0·00048 mol ATP was needed from oxidation of glucose, meaning that an additional 0·002335 g glucose was oxidized to CO₂ (assuming the ratio 37 ATP formed per glucose oxidized), for a total glucose requirement of 0·1683 g glucose per 0·08 g lignin.

(4) May exclude tool maintenance cost.

(5) Cost of glucose uptake into a cell was excluded to allow a direct comparison to present results.

(6) Based on 36 ATP produced during complete respiratory oxidation of 1 glucose (i.e. the equivalent of Y_ATP,sucrose = 72 ATP per sucrose).

(7) Assumes that polymerization reactions produce NADH. Also, Thornley and Johnson (1990) added an oxygen atom to each alcohol monomer during polymerization rather than removing a hydrogen atom, so their estimates of the molecular masses of the lignin residues exceeds that shown in Table 1 and used in other analyses (e.g. in Williams et al., 1987).

(8) Recalculated from Thornley and Johnson (1990) based on lignin residue molecular masses in Table 1.

(9) Biosynthesis from sucrose only; no input of methanol. With Y_ATP,sucrose = 60·0 ATP per sucrose, Y_{ATP,cyt‐NADH} = 1·5 ATP per NADH, and Y_{ATP,cyt‐NADPH} = 1·5 ATP per NADPH.

(10) NADH and NADPH produced in excess of that required to provide needed ATP was oxidized without producing ATP (i.e. oxidized via the alternative oxidase).

* Spruce lignin.