Plant hormones and oxidative stress in Hevea brasiliensis

Plant hormones are naturally occurring organic substances that are produced within the plant at low concentrations which regulate the growth and metabolism. It was observed that over-harvesting latex through high intensity tapping had a direct effect on the endogenous hormone levels in rubber plants. This could induce the development of oxidative stress leading to several complex physiological disorders including tapping panel dryness (TPD). During oxidative stress, the levels of stress hormones increased and the growth hormones decreased in the bark tissue. Both ethylene (ET) and abscisic acid (ABA) concentrations were high in trees that are exposed to oxidative stress. The levels of hydrogen peroxide (H2O2) and its scavenging enzyme, peroxidase (Px), present in healthy trees were appeared to be capable of scavenging the H2O2 molecule produced in the tissue. Hence, the minimum stress response was noticed in the bark tissues of normal trees. The regular wounding of the bark tissues for harvesting latex cannot be avoided in rubber trees. But, the amount of Px produced in the bark tissue was inadequate to detoxify the H2O2 produced under certain physiological state of the tree (TPD) and thus leading to oxidative stress. Accumulation of malondealdehyde (MDA) was evidenced as the peroxidative damage occurred in the bark tissues of stressed trees. The tissue cyanide (CN) level was very high in stressed trees due to the low levels of CN scavenging enzyme, β-cyanolalanine synthase (β-CAS). Trees under oxidative stress had increased levels of stress hormone in the bark tissue and hence, the low levels of growth hormones and high levels of stress hormones in the soft bark tissue would have caused disorders in the cellular differentiation and metabolism in the laticiferous tissues of Hevea trees limiting the production leading to significant crop loss

Cloning and expression of hmgr1 gene from Hevea brasiliensis

Biosynthesis of natural rubber (cis-1,4-polyisoprene) takes place through mevalonate pathway in Hevea. The enzyme 3-hydroxy- 3-methyl glutaryl-CoA reductase (HMGR), which catalyses the synthesis of mevalonate from HMG-CoA is a key regulatory enzyme in this pathway. This study aimed to clone and express hmgr1 gene, in order to obtain the HMGR protein in vitro and to further use this protein as a marker for yield potential in Hevea. For this purpose, mRNA was isolated from the latex of Hevea (clone RRII 105). cDNA was synthesized and PCR amplification of coding region of hmgr1 was performed using hmgr1 specific primers. The PCR amplified product (~1.8 kb) was cloned into an expression vector (pRSET-A) and transformed into E. coli (BL21DE3) cells. Protein expression in transformed cells when monitored by SDS-PAGE analysis indicated the presence of HMGR protein (61.6 kDa). The protein would be used for developing specific antibody that could be further utilized for the quantification of HMGR in different Hevea clones for screening the yield potential. The details of cloning and expression of hmgr1 are presented and discussed

Expression analysis of rubber biosynthetic pathway genes in Hevea brasiliensis

Hevea brasiliensisis, the primary commercial source of natural rubber (cis-1, 4-polyisoprene), is a fundamental raw material used for manufacturing a wide range of industrial and domestic rubber products in automobile, medical and defense industries. In Hevea, biosynthesis of rubber takes place through mevalonate pathway. Clonal variations in the productivity of rubber may be the result of variations in the activities of the enzymes involved in rubber biosynthesis in different Hevea clones. In this study, expression of 14 genes corresponding to enzymes/regulatory proteins involved in rubber biosynthesis was analyzed in high and low latex yielding clones of Hevea brasiliensis. The level of expression of HbSUT3, a sucrose transporter and enzymes related to the synthesis of rubber such as hydroxymethyl glutaryl-CoA synthase (hmgs), HMG-CoA reductase (hmgr) and mevalonate diphosphate decarboxylase (MVD) were found to be significantly higher in high rubber yielding clones compared to the low rubber yielding clones. The higher expression of these genes might result in an increased supply of IPP, the isoprenoid monomer, required for rubber biosynthesis. Expression of genes in the downstream rubber biosynthetic pathway such as FPPS, RuT and REF2 were also found to be significantly higher in high rubber yielding clones than low yielders. The results suggest that high rubber yield is associated with high expression of these genes and these genes can be used as markers for high yield potential in Hevea

Marine fisheries of Karnataka State, India

This contribution provides an overview of the marine capture fisheries off the coast of Karnataka State, India. It covers the main fisheries and fishing gears, production trends (by main species /groups and gears), assessment results and fisheries management. Marine fisheries production in the State increased from about 57,000 t/year during the 1950s to a peak of about 250,000 in 1989, declining to about 150,000 t/year by 1995. Substantive changes have been noted in dominant gears and species groups contributing to the catch between 1980-84 and 1990-95. Results of assessments indicate that many commercially important stocks are overfished, thus requiring a reduction in fishing effort