Study On The Physiological And Biochemical Response Of Tea Under The Stress Of Lead Particles In Air And Its Rapid Spectral Nondestructive Detection

Tea is one of the three major non-alcoholic beverages in the world.It is loved by people because of its obvious health care function.About 2/3 of the global population consumes tea.As the main production area of tea,China ranks first in the world in tea production,and tea is also one of the main economic crops for export.However,in recent years,the problem of excessive lead content in tea has become more and more serious,which seriously restricts the economic benefits of tea industry in China.In this study,two common green tea varieties,Wuniuzao and Yingshuang,were subjected to aerosol stress of lead in different concentrations to simulate real air pollution.The research focuses on the pathway of lead transfer under foliar stress and the changes of microscopic morphology of tea leaves,the changes of physiological and biochemical indexes of tea leaves under different varieties and concentrations of lead stress,and the establishment of a rapid nondestructive testing model for physiological and biochemical indexes.The main research contents are as follows:(1)The pathway of lead transfer and the microscopic morphological changes of tea under leaf surface stress were studied.The content of lead in different parts(roots,stems and leaves)of tea plant under different stress time was measured by inductively coupled plasma mass spectrometry.The results showed that the content of lead in leaves of tea plant in common environment was very little,which was in line with the national standard.The content of lead in roots was much higher than that in leaves.With the increase of stress time,the content of lead in leaves of stress group was significantly higher than that in stems and roots,which indicated that there was an air-leaf absorption pathway.The stomata of leaves were studied by scanning electron microscopy and energy disperse spectroscopy.It was found that lead stress could damage the stomata of tea,and it was proved that stomata was a channel for heavy metal particles in the air to enter the plant.Through the correlation analysis of lead content in different parts,it was found that there was a significant positive correlation between the lead content in leaves and stems,which could prove that there was a way of leaf downward transport.Therefore,it can be concluded that most of the lead entering through the stomata will accumulate in the leaves,and only a small part will transfer to the lower part.Using transmission electron microscope to observe the cellular level of tea tree leaf under the stress of lead structure change,the discovery of lead stress can produce damage to tissue structure,embodied in:the lipid particles in heavy metal stress group was obviously accumulation,the chloroplast structure deformation,swelling and the internal structure of disorder,dissolved thylakoids,grana lamella structure arrangement is irregular,blurring the outer membrane,the starch particles within;The cytoplasmic volume decreased,the nuclear structure was incomplete,the nuclear membrane was blurred,and the nucleoli disappeared.(2)The changes of physiological and biochemical indexes of tea under different varieties and stress concentrations were compared.The contents of chlorophyll a,chlorophyll b,carotenoid,ascorbic acid,glutathione and moisture content in different concentrations of stress and different periods of tea were measured.It was found that with the increase of stress time,the six indexes showed significant differences:there was an obvious trend of"increase first and then decrease"in the pigment,and the increase of pigment content in the early stage of stress was due to the stress mechanism of the self pigment production system under the stress of heavy metal,but in the later stage of stress,heavy metal will destroy chloroplast and inhibit the synthesis of photosynthetic pigment;ascorbic acid and glutathione will increase rapidly in the early stage of stress to eliminate the active oxygen free radicals produced by lead stress,and the production will be inhibited in the later stage of stress;the moisture content shows the trend of"first decrease and then increase".It indicates that lead stress can seriously inhibit the water absorption of tea leaves in a certain period of time,but the later inhibition is weakened.Based on the"fingerprint peak"characteristic of Fourier Transform Infrared Spectroscopy,the changes of other physiological and biochemical indexes of tea leaves under air lead stress were analyzed semi-quantitatively.It was confirmed that lead stress could affect a variety of substances,and the resistance levels of Wuniuzao and Yingshuang were different.(3)Establish a rapid non-destructive testing model of physiological and biochemical indexes.The visible near infrared spectra of tea leaves under different varieties and concentrations of stress were collected,and the partial least square regression,support vector regression and principal component regression models of the original and different pretreatment(standard normal variate,multiplicative scatter correction,detrending and normalization)data of six biochemical indexes were established by chemometrics.On the basis of the optimal model,the characteristic wavelength is extracted by the characteristic wavelength extraction algorithm,and the characteristic wavelength model is established.Finally,the rapid detection models of six biochemical indexes were determined,the R_P~2 of which were 0.340,0.671,0.637,0.645,0.841and 0.866,respectively.Except for ascorbic acid,the characteristic wavelength model of the other five indexes is better than the full spectrum model.By extracting characteristic wavelengths,not only better results are obtained,but also the model is simplified,which is conducive to the practical application of rapid nondestructive testing model and provides a good way for tea quality supervision.