Study On The Mechanism Of Tapping Panel Dryness In Hevea Brasiliensis

The Tapping Panel Dryness(TPD) disease results in tremendous damage of latex production in rubber tree plantations.In previous study, the result of PSORT (Prediction of Protein Localization Sites) suggests that HbMybl may encode a nuclear protein. The results of protein domain prediction indicate that there may be a N-glycosylation site, three cAMP- and cGMP-dependent protein kinase phosphorylation sites, a Protein kinase C phosphorylation site, nine Casein kinase II phosphorylation sites, five N-myristoylation sites, an Amidation site and an ATP/GTP-binding site. Its deduced amino acid sequence shows similarities 59% with F16M14.2 and presents a common DNA binding motif with F16M14.2, Ibbf, Ibbfl, Mybltf and MybSti. The results of Northern analysis indicated that HbMybl was expressed significantly higher in healthy trees than in TPD trees and it was expressed highest in bark (near cambium) and lowest in leaf. Moreover; HbMybl was expressed far lower in the latex of the tapping line than in those of far from the tapping line. Those facts indicated that the level of expression HbMybl maybe related to TPD of Hevea brasiliensis.To test whether TPD is programmed cell death (PCD) in rubber tree, we extracted DNA from healthy and TPD rubber tree bark. The electrophoresis map showed that the DNA from TPD rubber tree bark had a typical "DNA ladder", on the contrary the DNA from healthy rubber tree bark were intact(Fig.l). Cells undergoing programmed cell death display characteristic morphological changes such as the cleavage of genomic DNA into internucleosomal 180~200bp fragments that referred to as "DNA ladder". The DNA from TPD rubber tree bark showing typical "DNA ladder" suggests that TPD in rubber tree bark is PCD.TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling) is the most established method for the detection of PCD-specific DNA strand breaks in single cells. It is more sensitive and special to PCD DNA strand breaks than non-apoptotic DNA breaks. To test whether TPD is programmed cell death in rubber tree or not, the "In Situ Cell Death Detection Kit, Fluorescein" from Roche was used to detect the PCD cells in bark section of TPD trees. The results showed TPD trees had the same positive signal as the healthy trees treated with DNase I (positive control) (Fig.2A, 2B).