Abstract:
Among the rubber producing plant species, Hevea brasiliensis Muell. Arg., commonly
known as rubber tree, is almost the sole source of natural rubber. Currently, the rubber
industry of Sri Lanka contributes about 1.0 % of the GDP being one of the major income
sources of the agriculture sector. Over the past decades, the rubber yield has been
significantly increased due to the introduction of high yielding clones. However, the latex
production is seriously affected by tapping panel dryness (TPD), a physiological disorder,
which ultimately results in decline or complete cessation of latex production and causes
15 % to 20 % yield loss worldwide annually. In Sri Lanka, yield loss due to TPD is
increasing at an alarming rate. It is hypothesized that TPD is caused by tapping induced
oxidative stress resulted from over exploitation. Under oxidative stress, plants generally
increase the production of free radical scavenging or antioxidant enzymes such as,
superoxide dismutase (SOD), catalase (CAT) and peroxidase (APX). At present, the cause
of TPD is not clear. Therefore, this study was started with the objectives of studying the
role of antioxidant genes on TPD. The expression differences of antioxidant genes in both
TPD affected and healthy trees of RRISL 2001 rubber clone were analyzed using semi
quantitative RT-PCR. Gene specific primers designed to span exon junctions were used for
PCR amplifications and the amplified products were visualized on ethidium bromide
stained agarose gels. The band intensities were determined by visually. The results
showed that the expression of the rubber SOD gene is highly down-regulated in TPD
affected trees compared to that of healthy trees. Whereas, the CAT gene is slightly upregulated in TPD affected tress leading to conclude that rubber SOD gene might play an
important role in TPD. Moreover, our results support to the hypothesis that TPD is caused
by inefficient scavenging of reactive oxygen species due to defects in antioxidant system of
some rubber trees.
