On Ecophysiological Adaptation Of Dioscorea Zingiberensis To Light Intensities And Its Mechanism

This dissertation includes the adaptation of ecological differentiation, long-term acclimation and short-term responses ofDioscorea zingiberensis to light intensities.The adaptation of ecological differentiation of D. zingiberensis to light intensity leads to the differentiation of 3 ecotypes. The three ecotypes DZTL, DZTM and DZTH adapt low, medium and high light intensities respectively. This conclusion is supported by the following proofs, (a) The 3 ecotypes DZTL, DZTM and DZTH grew well respectively under low (LLX40umol m'V1), medium (MLX240fimol m'V1) and high light (HLX700umoI m'V1), with their highest amount of biomass. (b) The electron transport rates (ETR) of chloroplast samples of the 3 ecotypes grown under identical medium light condition, measured with oxygen electrode, increase in order of DZTL, DZTM and DZTH. (c) DZTL grown under LL had its highest maximal quantum yield (MQY), while DZTH grown under HL had its highest MQY. (d) An analysis of 77 K fluorescence spectra showed that DZTL in steady photosynthesis had more excitation energy in photosystem two (PSH) than other two ecotypes. SDS electrophoresis of chloroplast protein showed that DZTL had more PSII than DZTM and DZTH, while DZTH had more PSI than DZTL. Based on the change of energy distribution between two photosystems in state transition, it is inferred that although DZTL has a lot of LHCI1 with low ratio of mobile peripheral LHC1I; in contrast DZTH has less LHCII with high ratio of mobile peripheral LHCII, when both ecotypes were grown under identical conditions, (e) Measurement of the content of Rubisco (measured with rocket immunoelectrophoresis), soluble sugar, protein, and malondialdehyde, and activity of peroxidase suggested that DZTH could be classified as a sun-plant, and DZTL as a shade plant (f)The difference among the lipid compositions of the three ecotypes are significant; the content of saturated fatty acids of DZTL, DZTM and DZTH decreases successively, so does the content of Cl6:ltrans of DZTL, DZTM and DZTH. (g)The carotenoids/chlorophyll ratios of DZTL, DZTM and DZTH were 1: 6.27, 1: 2.86 and 1:2.1 respectively. And the total xanthophylls/ ^-carotene ratios of DZTL, DZTM and DZTH were 1:8.29, 1:4.68 and 1:3.78. (h)Micrographs of chloroplast ultrastructure of the three ecotypes grown under identical light conditions show that the number of grana in each section of chloroplast increases in order of DZTL, DZTM and DZTH, but thylakoid number of each granum of DZTL, DZTM and DZTH decreases in order. The total number of grana thylakoids is almost the same in the three ecotypes. And the grana of DZTL are much wider than those of DZTH.Long-term acclimation of the wild type DZTL to light intensity was investigated. (l)The ETRs of DZTL increase with growth light intensities in certain range, but decrease when growth light intensity was 270 umol m'V. The effective quantum yields (EQY) of the leaves under extreme weak light (l.Sumol m'V1) and strong light are lower than those under light of 10-55umol m~V. (2) The photorespiration of intact leaves, measured with a stable isotope ratio mass spectrometer, increases with growth light intensity. (3) Excitation energy, measured at 77 K, distributes in PSH mainly in plants grown under low light (lOumol m'V1); when plants grown under 55-270 umol m'V 1 of light intensity, the excitation energy in PS11 increases with growth light intensity. This may beone of the reasons why DZTL can not grow well under high light. (4) With increment of growth light intensity, the stacking index of thylakoids becomes smaller and smaller, and both grana number in each chloroplast and thylakoid number in each grana decrease significantly. (5)Under lower light (30-55 umol m"V), DZTL leaves have much higher concentration of soluble sugar than under 10 and 270 umol m'V1 of light. (6)Under 10 and 270 umol m'V1 of light, malondialdehyde content is higher than those under 30, 55 and 100 umol m'V1 of light; and activity of peroxidase is positively related to growth light intensity. (?)Chlorophyll content in...