| Having a photocatalyzed characteristic, nano-anatase TiO2 under light could cause an oxidation-reduction reaction. Being a proven photocatalyst, nano-anatase TiO2 is capable of undergoing electron transfer reactions under ultraviolet light, the electron was excitated and transferred, then photogenerated electron holes in nano-anatase; the electron holes were reduced when the electron was captured by another molecule, whereas it was oxidized when it captured itself. As the characteristics, the previous researches proved that nano-anatase TiO2 improved photosynthesis and greatly promoted spinach growth, but the mechanisms of light energy absorption, distribution and transport are unclear. Therefore, we studied the effects of nano-anatase TiO2 on promoting light energy absorption and transfer in photosynthesis of spinach.The article mainly includes:1. The effects of nano-anatase TiO2 on light absorption, distribution, and conversion, and photoreduction activities of spinach chloroplast were studied by spectroscopy. The absorption peak intensity of the chloroplast was obviously increased in red and blue region, the ratio of the Soret band and Q band was higher than that of the control. The great enhancement of fluorescence quantum yield near 680 nm of the chloroplast was observed, the quantum yield under excitation wavelength of 480 nm was higher than the excitation wavelength of 440 nm. The excitation peak intensity near 440 and 480 nm of the chloroplast significantly rose under emission wavelength of 680 nm, and F480/F440 ratio was reduced. When emission wavelength was at 720 nm, the excitation peaks near 650 and 680 nm were obviously raised, and F650/F680 ratio rose. The rate of whole chain electron transport, photochemical activities of PS II DCPIP photoreduction and oxygen evolution were greatly improved, but the photoreduction activities of PS I were a little changed.2. The effects of nano-anatase TiO2 on energy transfer in PS II by spectroscopy and on oxygen evolution were studied. The results showed that nano-anatase TiO2 treatment at a suitable concentration could significantly change PS II microenvironment and increase absorbance for visible light, improve energy transfer among amino acids within PS II protein complex, and accelerate energy transport from tyrosine residue to chlorophyll a. The photochemical activity of PS II (fluorescence quantum yield) and its oxygen-evolving rate were enhanced by nano-anatase TiO2.3. The effects of nano-anatase TiO2 on the spectral responses and photochemical activities of D1/D2/Cyt b559 complex of spinach were investigated by spectroscopy. UV-Vis spectrum of D1/D2/Cyt b559 complex was blue shifted in both Soret and Q bands, and the absorption intensity was obviously increased; Resonance Raman spectrum showed four main peaks, which are ascribed to carotene, and the Raman peak intensity was obviously increased; The fluorescence emission peak was blue shifted and the intensity was increased; Nano-anatase treatment obviously accelerate the DCPIP photoreduction activity and the oxygen evolution rate. Together, the studies of the experiments showed that that nano-anatase TiO2 had bound to D1/D2/Cyt b559 complex, promoted the spectral responses, leading to the improvement of primary electron separation, electron transfer and light energy conversion of D1/D2/Cyt b559 complex.4. The improvement of spinach chloroplast photosynthesis damaged by linolenic acid was investigated. It was showed that after the addition of nanoanatase to the linolenic acid-treated chloroplast, the light absorption increased by linolenic acid could be decreased, but the excitation energy distribution from PS I to PS II was promoted, and the decrease of PS II fluorescence yield caused by linolenic acid was reduced and the inhibition of oxygen evolution caused by linolenic acid of several concentrations was decreased. It was considered that nanoanatase could combine with linolenic acid and decrease the damage of linolenic acid on the structure and function of chloroplast.5. The nano-anatase relieving the inhibition of photoreduction activity and oxygen evolution caused by linolenic acid in spinach chloroplasts was studied. The results showed that linolenic acid in various concentrations could obviously reduce the whole chain electron transport and the photoreduction activity of two photosystems, especially on the oxidative reside and reduce reside of photosystem II (PS II). After adding nano-anatase to chloroplasts treated by linolenic acid, the whole chain electron transport rate, the photoreduction activity of two photosystems, and the oxygen evolution rate were increased significantly, indicating that nano-anatase could obviously decrease the inhibition of linolenic acid on the electron transport, photoreduction activity, and oxygen evolution of spinach chloroplasts.
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