Effects of secretions of the mucus gland of Sirex Noctilio on biochemical systems in Pinus Radiata, and some physicochemical properties of the mucus
Creators: name: Wong, LK
Publisher: name: University Of Tasmania
Year: 2023

description: The mucus secretion of S.noctilio induces a series of degradative changes in the tissues of P.radiata needles, which result in chlorosis and desiccation, and ultimtely death. Dramatic changes are recorded in the respiratory rate and mode, and activities of amylase and peroxidase, in tissues which develop severe symptoms. These changes are associated with the destruction of chloroplasts, excessive loss of moisture and necrosis of food conducting elements. Basic similarities between changes caused by s.noctilio mucus, and natural and induced senescence of other plant foliage are discussed, It is also suggested that plant hormones confer a degree of resistance to the effects of Sirex mucus. Some physiological and biochemical changes (e.g., respiration and chlorophyll) are almost immediate upon treatment of P.radiata with autoclaved mucus. This is partly due to the faster uptake of autoclaved mucus solution which is also less viscous than raw mucus solution, Raw mucus has an estimated molecular weight of 60,000 - 100,000. In an aqueous solution, it undergoes slow spontaneous disaggregation with loss of viscosity to yield dialysable subunits of molecular weight 2,000 - 6,000, which are physiologically active, Rapid disaggregations are brought about by treatment with moderate concentrations of `NaCl`, `KCl`, or `CaCl_2`, or by heating, but not with urea, The presence of amylase, esterase, acid phosphatase, phenoloxidase and proteolytic enzyme activities in native mucus may be partly responsible for the process of \natural disaggregation. The mucus appears to be a fairly homogeneous polysaccharide - protein complex with properties of both a neutral and an acid polysaccharide. The acidic polysaccharide bears close similarities to mammalian hyaluronic acid in its reactions to histochemical stains. Thus it reacts with basic dyes at pH 3 - 7 it is orthochromatic in toluidine blue red in acridine orange blue - green in alcian blue and its reactions with alcian blue appears to be mediated through its carboxyl groups however it shows high resistance to mammalian hyaluronidase. Two major polysaccharide - protein complexes both with physiological activities are separated f'rom DEAE - Sephadex using autoclaved mucus. The first complex is eluted in 0.1 - 0.4 M `NaCl` and appears to be a collageneous type of sulphated glycoprotein consisting mainly of fucose galactose glucosamine and galacturonic acid. The second complex is eluted in 0.5 - 0.9 M `NaCl` and appears to be a conjugate of sulphated glycoprotein and hyaluronate type of acid mucopolysaccharide. A total of five hexoses (i.e. rhamnose fucose mannose glucose and galactose) 1 two hexuronic acids (i.e glucuronic acid and galacturonic acid) and two hexosamines (i.e. glucosamine and galactosamine) are present. The mucus secretion of S.noctilio is compared with extracellular secretions of microbes which also induce senescence of their host plants. A brief study of mucus secretions from two other siricids i.e. Urocerus gigas and Xeris spectrum reveals the presence of protein and carbohydrate but these secretions do not induce foliar senescence of P.radiata and probably indicates a high specificity of wasp to host tree species."