Tang Xiaomin’s research while affiliated with Guangdong Pharmaceutical University and other places

The biomass of Isodon rubescens stems is greater than that of the leaves. The stems possess a considerable surface area, although less than that of the leaves. The photosynthetic rates, light response curves and chlorophyll fluorescence characteristics of the stems were determined in this study to clarify their photosynthetic capacity and photosynthetic potential. The results showed that the I. rubescens stems possessed considerable photosynthetic capacity, although less than that of the leaves. The shape of the light response curve of the I. rubescens stem was different from that of leaf. The light response curve of stems slowly increased during the intermediate growth period. The light saturation point of the stems was significantly greater than that of the leaves. There was clear, strong light suppression in both stems and leaves. However, I. rubescens stems could effectively photosynthesize, and the stem has a high light saturation point and can adapt to intense light.

To study the source and content change of oridonin in the ice ribbons, the contents of oridonin in the ice ribbons and bleeding sap of Isodon rubescens at different times were determined with RP-HPLC. The paraffin sectioning and electron microscopy imaging were performed to study the transport channel of oridonin in the stem. The results showed that there were abundant xylem rays and perfect pit pairs in the secondary xylem of I. rubescens stems. The oridonin content in the ice ribbons of I. rubescens stems was lower than that in the stem of I. rubescens and even decreased over time. The contents of oridonin in the bleeding sap of I. rubescens stems was equal to that in second-day ice ribbons and was lower than that in first-day ice ribbons. The water in the ice ribbons of I. rubescens stems originated from water absorbed by the roots from soil. This water was transported from the roots of I. rubescens to the stem and then transferred through efficient lateral conducting tissues to the surface of the stem. The oridonin in the phloem and cortex of I. rubescens stems dissolves in water originating from the soil and freezes in the form of ice ribbons below 0 °C.

The diurnal variation of photosynthesis, light response curve and CO2 response curve in Epimedium brevicornu Maxim leaves were determined with Li-6400 photosynthesis system to evaluate the photosynthesis of E. brevicornu. Fluorescence of chlorophyll in the leaves were determined with PAM-2500 portable chlorophyll fluorescence apparatus in the study. The results showed that the midday depression of photosynthesis was very obvious in the E. brevicornu leaves. The light compensation point of E. brevicornu leaves was about 15 µmol m⁻² s⁻¹. The light saturation point of E. brevicornu leaves was below 800 µmol m⁻² s⁻¹, which was lower than the general sunlight intensity at noon in summer. The CO2 saturation point of E. brevicornu leaves was much higher than the content of CO2 in general air. E. brevicornu was a typical shade plant and could survive in very low sunlight. E. brevicornu could not endure strong sunlight and high air temperature. The net photosynthetic rate of E. brevicornu leaves linearly correlated with the content of CO2 in the leaf chamber when the content was below CO2 saturation point. E. brevicornu possessed great potential of photosynthesis.

Objectives The living stems of Isodon rubescens (Hemsley) H. Hara peels and withers when the air temperature is below 0 °C in winter. The peels and withers evidently hamper the growth of I. rubescens. This report analyses the reason that causes I. rubescens stems to peel and wither in winter. Methods The field investigation and paraffin sections of I. rubescens stems (peeled and intact) were performed. Results The results showed that I. rubescens stems extruded ice ribbons at air temperature below 0 °C. The enlarged ice ribbons separated the phloem from the xylem, burst the phloem and even the whole bark of the I. rubescens stems. Conclusions The phloem was separated from the xylem by the enlarged ice ribbons. The phloem and the whole bark of the I. rubescens stems were torn when ice ribbons appeared. The damaged stem could not transport water and nutrition to the upper section. The upper stem above the ice ribbons withered because it could not receives water and nutrition.