Photosynthate allocation and productivity of latex vessels inHevea brasiliensis

Abstract

Manipulations of production systems in rubber tree which were intended to improve sucrose translocation in tapped bark resulted in an increase of latex sucrose and of latex production and reduced the incidence of nonyielding laticiferous tissue. This was achieved by shortening the tapping cut from full to half spiral, by changing the descending direction into an ascending mode of tapping or by annual change-over of tapping panel allowing for a longer time the regeneration of bark removed above the location of the cut. The increase of latex yield did not result in a significant decrease in the growth of tr~es over a period of three years.Clonal differences in nonyielding bark appeared to be related to differences in sucrose depletion by tapping. In clone PB 235 which exhibited low latex sucrose, a reduction of tapping frequency resulted in an increase in sucrose level and in a decrease of bark "dryness" tending to an increase in total yield.The tapping manipulations examined did not affect latex flow characteristics such as the plugging index of latex vessels and the bursting index of lutoids. The results stress the importance of photosynthate allocation for the physiology of laticiferous system productivity and indicate the possibilities of improving assimilate economy in rubber trees.Hevea latex, the rubber containing cytosol of latex vessels (ARCHER et al. 1963, DICKENSON 1965) is commercially extracted by controlled cutting of secondary phloem tissue of the trunk, known as tapping, which is practised at regular time intervals, normally twice a week. The yielding peculiarities of the rubber tree thus consist in that the economical product is continuously removed from the site of its formation and its analysis makes it possible to examine metabolic factors of productivity.Saccharides are supplied to latex vessels as sucrose (TvP:~ and RESING 1968, TUPff 1985) and its utilization in latex metabolism is limited by the activity of latex invertase which in turn is strongly pH dependent (Tvrff 1969). The tapping results in a decrease of sucrose content in the latex (BEALING and GHUA 1972, TuP~: 1973a) which indicates that the sucrose exported and utilized in latex metabolism is not fully replaced by translocated sucrose. The sucrose depletion is genotype dependent (TuP~ 1973b, Low

Sucrose importation into laticifers of Hevea brasiliensis, in relation to ethylene stimulation of latex production

“…Laticifers are regarded as a strong sink for sucrose and need to be adequately supplied exogenously with sucrose to meet their high carbon and energy demands (Tupy, 1973;Eschbach et al, 1986;Silpi et al, 2007). Based on a few circumstantial observations, active transport across the plasma membrane of laticifers had been hypothesized as the main route of sugar uptake.…”

Ethrel® stimulant increases the activity of soluble invertase isoforms in rubber tree (Hevea brasiliensis) bark tissues

“…In this study, it was observed that most of soluble sugars (TSS) were comprised of reducing sugars, which indicated that sucrose hydrolysis by invertase isoforms were present in that tissue which led increased hexose availability for glycolytic route and consequently enabled greater IPP production. Work with sucrose ( 14 C) application in tapping panel resulted radioactivity appearance in cytosolic fraction of latex that was collected, and process was enhanced by Ethel ® stimulation (Eschbach et al, 1986). In general, latex production in rubber tree bark is related to regeneration of new latex quantities and depends on frequency at which tapping is performed.…”

Agronomic Performance of Hevea brasiliensis Muell. Arg. Clone IRCA 331 Grown in Southwestern Côte d'Ivoire

“…The physiological profile, through sucrose, inorganic phosphorus, thiol group and latex dry rubber content is taken into account as secondary criteria in order to assess the influence of the intensity of rubber biosynthesis metabolism. The physiological profile also helps to determine the ability of clones to bear tapping and hormonal stimulation related stress [16,17,18,19,20]. The clones received by Côte d'Ivoire in international exchanges with rubber tree research institutes are tested directly in LSCT.…”