Increased endogenous indole-3-acetic acid:abscisic acid ratio is a reliable marker of Pinus massoniana rejuvenation.

Pinus massoniana is a recalcitrant tree species for rooting in vitro. We rejuvenated 26-year-old P. massoniana trees by successive grafting. Rooting rates of rejuvenated shoots were > 83.1% after rooting induction. We compared endogenous levels of indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellins (GAs) and zeatin-riboside (ZR), and the rhizogenesis ability of axillary shoots of mature and rejuvenated materials in vitro, i.e., somaplants and grafts. Enhancement of the rooting ability of mature materials in vitro following somatic embryogenesis or repeated grafting onto juvenile rootstocks was accompanied by increased IAA and GAs levels, and by decreased ABA levels in scions used as starting material for micropropagation in vitro. Successive subcultures did not influence the rooting ability of shoots from untreated mature material. Rooting ability of shoots in vitro, however, gradually increased with subculture frequency during repeated subculturing in grafting materials. The IAA:ABA ratio in shoots in vitro after grafting five times, and consequently capable of root organogenesis, was higher than in shoots of untreated mature material incapable of root organogenesis in vitro. A high IAA:ABA ratio was detected in scions of somaplants that were capable of rooting in vitro despite subculture times. We found that the endogenous IAA:ABA ratio is a reliable marker for the recovery of root organogenesis in vitro after rejuvenating treatments for mature P. massoniana trees.

[Analysis on the tendency of practical dust exposure year and the out-of-dust rate among coalminers].

It is important to study the practical dust exposure year and out-of-dust rate for the evaluation of dust level and to predict pneumoconiosis incidence in coal miners. A Retrospective Cohort Study was carried out on the calculation of practical dust exposure year and the out-of-dust rate among coal miners employed during 1958-1988 in a mine. The results showed that job variety had a strong effect on dust exposure year and that out-of-dust rate beared relationship to the years of employment. It can be estimated that the percentage of coalminers who were employed in 1975-1979 with dust exposure year reached 20 years would be less than 30%, and that those being employed after 1980 would be even lesser.