Changes In Cell Wall Components Research Articles

Metabolic changes in elicitor-treated bean cells. Enzymic responses associated with rapid changes in cell wall components.

Treatment of cell suspension cultures of bean (Phaseolus vulgaris c.v. Immuna) with an elicitor preparation heat-released from the cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum resulted in rapid changes in the composition of the bean cell walls. These consisted of (a) increases in phenolic material bound to the cellulosic and hemicellulosic fractions of the wall, (b) loss of material (mainly glucose) from the hemicellulosic fraction and (c) an increase in wall-associated hydroxyproline. The increases in wall-bound phenolics were preceded by (a) rapid decreases in the intracellular levels of free hydroxycinnamic acids and (b) transient increases in the extractable activities of L-phenylalanine ammonia-lyase and cinnamic acid 4-hydroxylase. 4-Hydroxycinnamic acid 3-hydroxylase activity was present at a high level in control cultures and was not induced by elicitor. Changes in the levels of cytochrome P-450, as determined by dot blot assays utilising an anti-(P-450) monoclonal antibody, paralleled the changes in cinnamic acid 4-hydroxylase activity. The accumulation of cell wall hydroxyproline was associated with rapid transient increases in the extractable activities of proline 2-oxoglutarate dioxygenase and a protein arabinosyl transferase. An hydroxyproline-rich acceptor protein of Mr 42 500 was the major protein to incorporate [3H]arabinose following elicitation of the bean cells, and the kinetics of the extent of labelling of this protein paralleled the accumulation of hydroxyproline protein in the endomembrane system. The above metabolic changes associated with cell wall components followed rapid kinetics similar to those involved in the formation of the phytoalexin kievitone in the elicited cultures [Robbins, M. P. et al. (1985) Eur. J. Biochem. 148, 563-569]. It is therefore concluded that increased 5-hydroxy-substituted isoflavonoid biosynthesis, wall-bound phenolic synthesis and synthesis of arabinosylated hydroxyproline-rich protein are all early events which are closely linked to the initial interaction between plant cell and fungal elicitor.

Some histochemical observations on leaf abscission zone inCapsicum annuum L.

The present observations were conducted on NP 46-A and Pusa jwala varieties ofCapsicum annuum L. Investigations on changes in cell wall components of the cells of leaf abscission zone associated with the process of abscission were based on specific qualitative histochemical staining procedures. It was observed that the loss of pectic and cellulosic substances preceded the separation phase of abscission from middle lamella and cell walls of the cells of separation layer of abscission zone. The abscission zone was characterized by thin cutin deposition on epidermal cells and poor lignification in vascular elements of this region. Separation of senescent part of petiole was followed by deposition of suberin in cells of some outer layers of abscission zone and by the deposition of lignin in cells of the remaining layers of abscission zone to form a protection layer on exposed part of petiole stump. Development of tyloses, tannins and calcium oxalate crystals was not found associated with abscission in the present plant material.