A test of biotic interactions among two alpine plant species in Australia

This study examines the extent to which interactions among two common alpine/subalpine plant species and their neighbours at the Bogong High Plains in southern Australia are characterized by competition or facilitation. The two target species were Celmisia pugioniformis (Asteraceae) and Carex breviculmis (Cyperaceae). Biotic interactions were examined using vegetation removal manipulations over three growing seasons at five sites across the altitudinal range of tall alpine herbfield communities. Observations recorded growth and mortality. Results for C. pugioniformis clearly indicated facilitation as a dominant process across all sites and seasons. Plants that had their neighbours removed tended to perform worse than plants that had their neighbours left intact. Growth observations for Ca. breviculmis were less clear, but again suggested facilitation. Mortality was distinctly higher among Ca. breviculmis individuals that had their neighbours removed relative to those with neighbours left intact. Results collectively suggest the removal of neighbours acts to reduce growth and increase mortality in C. pugioniformis and Ca. breviculmis throughout the altitudinal range of tall alpine herbfields at the Bogong High Plains. Facilitative and competitive interactions need to be recognized in efforts aimed at mitigating climate change‐associated impacts on the ecology of alpine plant communities. The extent to which biotic interactions may exacerbate or buffer abiotic change is difficult to predict, emphasizing the need for ecological monitoring.     

The effect of barban on shoot formation in tobacco callus cultures

Shoot formation in tobacco callus was completely inhibited bythe presence of barban in the media during the first 2 daysof culture. Callus transferred to media containing barban from4th to the 12th day showed progressively less inhibition. Similarresults were obtained with GA₃. ¹Present address: Biology Department, Chung Chi College, TheChinese Univ. of Hong Kong, Shatin, N.T., Hong Kong ²Present address: Plant Hormone & Regulator Pioneering ResearchLab., U.S. Dept. Agric, Crops Res. Div., Beltsville, Md., U.S.A. (Received April 21, 1970; )     

The unconventional P‐loop NTPase OsYchF1 and its regulator OsGAP1 play opposite roles in salinity stress tolerance

YchF proteins are a group of mysterious but ubiquitous unconventional G‐proteins found in all kingdoms of life except Archaea. Their functions have been documented in microorganisms, protozoa and human, but those of plant YchF homologues are largely unknown. Our group has previously shown that OsYchF1 and its interacting protein, OsGAP1, play opposite roles in plant defense responses. OsGAP1 was found to stimulate the GTPase/ATPase activities of OsYchF1 and regulate its subcellular localization. In this report, we demonstrate that both OsYchF1 and OsGAP1 are localized mainly in the cytosol under NaCl treatment. The ectopic expression of OsYchF1 in transgenic Arabidopsis thaliana leads to reduced tolerance towards salinity stress, while the ectopic expression of OsGAP1 has the opposite effect. Similar results were also obtained with the Arabidopsis homologues, AtYchF1 and AtGAP1, by using AtGAP1 overexpressors and underexpressors, as well as an AtYchF1‐knockdown mutant. OsYchF1 and OsGAP1 also exhibit highly significant effects on salinity‐induced oxidative stress tolerance. The expression of OsYchF1 suppresses the anti‐oxidation enzymatic activities and increases lipid peroxidation in transgenic Arabidopsis, and leads to the accumulation of reactive oxygen species (ROS) in tobacco BY‐2 cells, while the ectopic expression of OsGAP1 has the opposite effects in these two model systems.