Characterization of a lignified secondary phloem fibre-deficient mutant of jute (Corchorus capsularis)

Abstract

Background and aims: High lignin content of lignocellulose jute fibre does not favour its utilization in making finer fabrics and other value-added products. To aid the development of low-lignin jute fibre, this study aimed to identify a phloem fibre mutant with reduced lignin.

Methods: An x-ray-induced mutant line (CMU) of jute (Corchorus capsularis) was morphologically evaluated and the accession (CMU 013) with the most undulated phenotype was compared with its normal parent (JRC 212) for its growth, secondary fibre development and lignification of the fibre cell wall.

Key results: The normal and mutant plants showed similar leaf photosynthetic rates. The mutant grew more slowly, had shorter internodes and yielded much less fibre after retting. The fibre of the mutant contained 50 % less lignin but comparatively more cellulose than that of the normal type. Differentiation of primary and secondary vascular tissues throughout the CMU 013 stem was regular but it did not have secondary phloem fibre bundles as in JRC 212. Instead, a few thin-walled, less lignified fibre cells formed uni- or biseriate radial rows within the phloem wedges of the middle stem. The lower and earliest developed part of the mutant stem had no lignified fibre cells. This developmental deficiency in lignification of fibre cells was correlated to a similar deficiency in phenylalanine ammonia lyase activity, but not peroxidase activity, in the bark tissue along the stem axis. In spite of severe reduction in lignin synthesis in the phloem cells this mutant functioned normally and bred true.

Conclusions: In view of the observations made, the mutant is designated as deficient lignified phloem fibre (dlpf). This mutant may be utilized to engineer low-lignin jute fibre strains and may also serve as a model to study the positional information that coordinates secondary wall thickening of fibre cells.

Fig. 1. Phenotype of the normal (JRC 212) and mutants (CMU). A, The stem segments (m, middle; b, bottom) of (i) CMU 010, (ii) CMU 011, (iii) CMU 012, (iv) CMU 013 and (v) CMU 014. B, Portions of (i) JRC 212 and (ii) CMU 013 plants. CMU 013 shows undulation in the main axis, petiole and lamina.

Fig. 2. Increase in plant height of JRC 212 and CMU 013 between 45 and 75 d from sowing. LSD P < 0·01 for genotype = 2·47, genotype × days = 1·75.

Fig. 3. Transverse sections of the stem segments of JRC 212 (A, C and E) and CMU 013 (B, D and F). A and B, Upper portions; C and D, middle portions; E and F, lower portions. pp, Bundles of primary phloem fibre cells; sp, wedge of secondary phloem; xy, secondary xylem; c, cambium. Note the deeply stained fibre bundles (fb) in the wedge of JRC 212. Bar = 100 µm.

Fig. 4. Nature of CMU 013 and JRC 212 plants after retting. A, A bunch of CMU 013 plants showing the upper fibrous and lower non‐fibrous portions. B, Magnified lower portions. Note (i) the corky nature of CMU 013 and (ii) the fibrous nature of JRC 212.

Fig. 5. Phloroglucinol stained cells in the secondary phloem wedges at the middle portion of JRC 212 (A) and CMU 013 (B–D). Bar = 10 µm.