Anatomical and Histochemical Aspects of Bark Regeneration in Hevea brasiliensis

Abstract

Natural rubber is obtained from the bark of Hevea brasiliensis. Both virgin and renewed bark are exploited for this purpose by a process known as tapping which involves controlled wounding and excision of bark tissues. The process of bark renewal and its nature and consequences thus assume importance. Anatomical and histochemical changes encountered with tapping were the deposition of lignin and suberin in the peripheral cells, enlargement of tray cells near the cut surface and the formation of a wound periderm. In the course of development, the wound phellogen made tangential continuity with the original phellogen in the virgin bark and functioned as a single phellogen. Vascular cambial activity was enhanced due to wound stimulus and the newly differentiated sieve tubes and ray cells were larger in size. The first periderm was functional for only a short period of time, after which a new meristematic zone developed in the inner tissues. Virgin and renewed bark differed in the proportion of soft and hard bark, amount and distribution of sclereids, tannin cells and crystals.