Abstract:A study was conducted to determine the effects of UV-B on seedling growth and chloroplast ultrastructure of Psychotria rubra, Schefflera octophylla, Archidendron clypearia, Pterospermum heterophyllum, Sapium discolor and Albizia lebbeck. The seeds of these species were collected from Nature Reserves in Guangdong, and the seedlings were grown in growth cabinets programmed for a 28/20℃ light/dark temperature regime and a 12 h photoperiod. The 15-day-old seedlings were exposed to visible light (23μmol m-2s-1) supplemented with 7.2 kJ m-2d-1 or 14.4 kJ m-2d-1， or without UV-B radiation (contro1) for 30 and 60 days． Results demonstrated that UV-B radiation inhibited the growth of main roots and stems，decreased the number of lateral roots and leaf number as well as leaf area．UV—B radiation damaged membrane of leaf cells，particularly the structure of chloroplast membrane．Affected symptoms varied with plant species．Under UV-B radiation，the plasma membrane in Schefflera octophylla was contracted and corrugated， and separated from cell wal1． Chloroplast in S．octophylla and Pterospermum heterophyllum was dilated and even broken， the thylakoid dilated and adhered．In A rchidendron clypearia the mitochondria appeared to be cavitate．Starch grains in chloroplast in A．clypearia and Pterospermum heterophylla were increased， and the black particles in chloroplast in Schefflera octophyUa and Sapium discolor were also increased， and appeared on mitochondrial membrane of S．octophylla.
