Thermonastic leaf movements: a synthesis of research with Rhododendron

Thermonastic leaf movements in Rhododendron L. occur in response to freezing temperatures. These movements are composed of leaf curling and leaf angle changes that are distinct leaf movements with different responses to climatic factors. Leaf angle is controlled by the hydration of the petiole, as affected by soil water content, atmospheric vapour pressure, and air temperature. In contrast, leaf curling is a specific response to leaf temperature, and bulk leaf hydration has little effect. The physiological cause of leaf curling is not well understood, but the mechanism must lie in the physiology of the cell wall and/or regional changes in tissue hydration. Available evidence suggests that intercellular freezing is not a cause of leaf curling.
Manipulation experiments demonstrate that changes in leaf orientation in Rhododendron most likely serve to protect the leaves from membrane damage due to high irradiance and cold temperatures. In particular, the pendent leaves protect the chloroplast from photoinhibition. Leaf curling may serve to slow the rate of thaw following freezing, a common phenomenon in the Appalachian mountains of the U.S. The thermonastic leaf movements have a greater importance to plants in a dim environment because the potential impact to canopy carbon gain is greater than in high light environments.
These leaf movements have several implications for horticultural management. There seems to be a trade-off between water stress tolerance and freezing stress tolerance by leaf movements. Thermonastic leaf movements may be a major mechanism of cold stress tolerance in Rhododendron species. The actual physiological cause of leaf movement has not been elucidated and many more species need to be evaluated to verify the general importance of leaf movements to Rhododendron ecology and evolution.     

马醉木二萜成分及其乙酰胆碱酯酶抑制活性研究

为研究马醉木叶中的二萜成分及其乙酰胆碱酯酶抑制活性,该研究根据薄层色谱显色特征,使用硅胶、MCI和半制备高效液相等色谱技术对其进行分离与纯化,并通过波谱数据(NMR和MS)分析且结合文献报道数据进行对比,鉴定了所得化合物的结构,同时采用Ellman法首次对其乙酰胆碱酯酶抑制活性进行评价。结果表明:从马醉木叶中分离并鉴定了8个二萜化合物,分别是pierisformoside F(1)、3-epi-grayanotoxin XVIII(2)、3-epi-grayanotoxin B(3)、asebotoxin-X(4)、pierisformosin B(5)、asebotoxin Ⅲ(6)、rhodojaponin Ⅲ(7)和pierisformosin C(8)。其中,化合物1为首次从该植物中分离得到,化合物8表现出乙酰胆碱酯酶抑制活性。综上表明,马醉木中含有丰富的二萜成分和活性成分。该研究结果丰富了马醉木的化学成分多样性,为其后续综合开发和利用提供了一定的理论依据,也为寻求更多的活性成分提供了借鉴。     

Grayanoside C,a new diterpene glucoside from Leucothoe grayana

A new diterpene glucoside has been isolated from Leucothoe grayana. Its structure was elucidated by X-ray diffraction analysis of a dehydrated product of the aglycone and conversion of the same to leucothol A.     

DNA barcoding of Gaultheria L.in China (Ericaceae: Vaccinioideae)

Four DNA barcoding loci,chloroplast loci rbcL,matK,trnH-psbA,and nuclear locus internal transcribed spacer (ITS),were tested for the accurate discrimination of the Chinese species of Gaultheria by using intraspecific and interspecific pairwise P-distance,Wilcoxon signed rank test,and tree-based analyses.This study included 186 individuals from 89 populations representing 30 species.For all individuals,single locus markers showed high levels of sequencing universality but were ineffective for species resolvability.Polymerase chain reaction amplification and sequencing were successful for all four loci.Both ITS and matK showed significantly higher levels of interspecific species delimitation than rbcL and trnH-psbA.A combination ofmatK and ITS was the most efficient DNA barcode among all studied regions,however,they do not represent an appropriate candidate barcode for Chinese Gaultheria,by which only 11 out of 30 species can be separated.Loci rbcL,matK,and trnH-psbA,which were recently proposed as universal plant barcodes,have a very poor capacity for species separation for Chinese Gaultheria.DNA barcodes may be reliable tools to identify the evolutionary units of this group,so further studies are needed to develop more efficient DNA barcodes for Gaultheria and other genera with complicated evolutionary histories.