Tubers, suberin layers

Suberin impregnates the walls of cork cells and in layers covers bark, tubers, roots, wound peridorm and bundle sheaths of monocotyledons to provide a protective mantle impervious to liquids and gases. The associated waxes are not as well studied as those from cutin but do exhibit certain periodicities. The hydrocarbons have a broader distribution of chain lengths than the cuticular material, a predominance of shorter carbon chains and a higher proportion of even-length chains. In addition, no single alkane predominates usually several are present in similar proportions " . 

The time course of deposition of aromatic monomers into the phenolic portion of suberin in wound-healing slices of Solanum tuberosum tubers was determined using the amount of / -hydroxybenzaldehyde and vanillin generated by alkaline nitrobenzene oxidation as a measure of aromatic deposition (85). The deposition of such phenolics into the polymer exhibited a lag period of about three days after wounding followed by several days when the deposition of phenolics increased rapidly, and subsequently the process ceased. Exogenous L-[U- C]-phenylalanine and [U- Clcinnamic acid were incorporated into the insoluble polymeric material by wound-healing slices of S. tuberosum (85). Nitrobenzene oxidation of the polymeric material derived from labeled cinnamic acid released labeled /7-hydroxybenzaldehyde and vanillin. The time course of incorporation of phenolics into the suberin polymer correlated with the time course for the deposition of aliphatic monomers into the polymer, the deposition of suberin-associated waxes into the periderm layer and the development of diffusion resistance (Fig. 6.4.12) (86). 

HHT activity was not detectable in intact potato tuber tissue but was induced upon wounding after a lag period of three days (Fig.2). The time course of induction of HHT was therefore comparable with the kinetics of accumulation of alkyl ferulates [3] and of deposition of the aliphatic components of suberin [1]. HHT activity being restricted to the outermost cell layers of the wound-healing tuber discs, the development of HHT activity was both temporally and spatially coincident with the suberization process. The... 

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