Photosynthetic mechanism of maize yield under fluctuating light environments in the field.

The photosynthetic mechanism of crop yields in fluctuating light environments in the field remains controversial. To further elucidate this mechanism, we conducted field and simulation experiments using maize (Zea mays) plants. Increased planting density enhanced the light fluctuation frequency and reduced the duration of daily high light, as well as the light-saturated photosynthetic rate, biomass, and yield per plant. Further analysis confirmed a highly significant positive correlation between biomass and yield per plant and the duration of photosynthesis related to daily high light. The simulation experiment indicated that the light-saturated photosynthetic rate of maize leaves decreased gradually and considerably when shortening the daily duration of high light. Under an identical duration of high light exposure, increasing the fluctuation frequency decreased the light-saturated photosynthetic rate slightly. Proteomic data also demonstrated that photosynthesis was mainly affected by the duration of high light and not by the light fluctuation frequency. Consequently, the current study proposes that an appropriate duration of daily high light under fluctuating light environments is the key factor for greatly improving photosynthesis. This is a promising mechanism by which the photosynthetic productivity and yield of maize can be enhanced under complex light environments in the field.

Do rapid photosynthetic responses protect maize leaves against photoinhibition under fluctuating light?

Plants in their natural environment are often exposed to fluctuating light because of self-shading and cloud movements. As changing frequency is a key characteristic of fluctuating light, we speculated that rapid light fluctuation may induce rapid photosynthetic responses, which may protect leaves against photoinhibition. To test this hypothesis, maize seedlings were grown under fluctuating light with various frequencies (1, 10, and 100 cycles of fluctuations/10 h), and changes in growth, chlorophyll content, gas exchange, chlorophyll a fluorescence, and P700 were analyzed carefully. Our data show that though the growth and light-saturated photosynthetic rate were depressed by rapidly fluctuating light, photosynthesis induction was clearly speeded up. Furthermore, more rapid fluctuation of light strikingly reduced the chlorophyll content, while thermal dissipation was triggered and enhanced. The chlorophyll a fluorescence induction kinetics and P700 absorption results showed that the activities of both photosystem II and photosystem I decreased as the frequency of the fluctuating light increased. In all treatments, the light intensities of the fluctuating light were kept constant. Therefore, rapid light fluctuation frequency itself induced the acceleration of photosynthetic induction and the enhancement of photoprotection in maize seedlings, which play important roles in protecting photosynthetic apparatus against fluctuating high light to a certain extent.

Chemical constituents from Morinda citrifolia and their inhibitory activities on proliferation of synoviocytes in vitro / 中国中药杂志

The chemical constituents from the stems and leaves of Morinda citrifolia were isolated and purified by column chromatography methods with silica gel, ODS, Sephadex LH-20 and preparative high performance liquid chromatography(HPLC). The structures of the isolated compounds were identified by physicochemical properties and spectroscopic analysis, as well as comparisons with the data reported in literature. 17 compounds were isolated from the 90% ethanol extract of the stems and leaves of M. citrifolia, and were identified as 9,10-dihydroxy-4, 7-megastigmadien-3-one(1), 5,12-epoxy-6,9-hydroxy-7-megastigmen-3-one(2), fukinone(3), β-eudesmol(4), sarmentol F(5), 4, 5-dihydroblumenol A(6), 3-hydroxy-β-ionone(7), aristol-8-en-1-one(8), ergosta-7-en-3β-ol(9), ergosta-7-ene-3β,5α,6β-triol(10),(22E)-5α,8α-epidioxyergosta-6,22-dien-3β-ol(11), olivil(12), 4-epi-larreatricin(13), chushizisin Ⅰ(14), rabdosia acid A(15), glycerol monolinoleate(16) and(9Z,12Z,15Z)-2,3-dihydroxypropyl octadeca-trienoate(17). All compounds were isolated from M. citrifolia for the first time. All isolated compounds were evaluated for their anti-rheumatoid arthritis activities via examining their inhibitory activities on the proliferation of synoviocytes in vitro using MTS met-hod. Compounds 1-11 showed significant anti-rheumatoid arthritis activities, displaying the inhibitory effects on the proliferation of MH7 A synovial fibroblast cell with the IC_(50) values ranging from(38.69±0.86) to(203.45±1.03) μmol·L~(-1).