Research For The Influential Mechanism Of Light Intensity On Photosynthetic Characteristics And Its Products Of Chinese Yam(Dioscorea Opposita Thunb.)

As a kind of C₃plant,photosynthetic efficiency of Chinese yam may be an important factor leading to its growth and development,and Rubisco carboxylase is one of the key enzymes in the process of photosynthesis.In this study,Dahechangyu Yam was used as material,and the growth environment of two different light transmitters T1（30%-45%FL）and T2（60%-75%FL）were set up under full light intensity.The leaf morphology,photosynthetic characteristics and related indexes of starch accumulation in tuber of yam were analyzed under different light intensity.The open reading frame（ORF）of yam Rubisco carboxylase gene was cloned by RT-PCR and bioinformatics analysis was performed.Transient expression vector was constructed and gene subcellular localization was performed.The expression patterns of Rubisco carboxylase gene in tubers at different developmental stages and under different light intensities were analyzed,and the correlation between the photase and related physiological indexes and expression levels was analyzed.The aim was to analyze the physiological mechanism of yam’s response to different light intensity,to understand the effect of light intensity on Rubisco carboxylase gene expression,and to clarify the relationship between light intensity and photosynthetic efficiency of yam and tuber starch synthesis.The main findings are as follows:（1）Light intensity had significant effect on the leaf characters of Chinese yam.With the decrease of light intensity,leaf length,leaf width and leaf area increased and were positively correlated with shading rate.Stomatal density was negatively correlated with light intensity,and stomatal opening changed significantly.The thickness of the leaves and the thickness of the upper epidermis also decreased significantly.The palisade tissue cells fused with each other and became thicker.The arrangement of spongy tissue cells was sparse.The results showed that under the condition of low light intensity,the light absorption area of Chinese yam could be increased by changing the leaf morphology and structure,so as to improve the photosynthesis of Chinese yam,so as to deal with the adverse effects on growth under the condition of low light.（2）The variation of light intensity has a significant effect on the photosynthetic rate.Net photosynthetic rate,transpiration rate and stomatal conductance all decreased with the decrease of light intensity,but there was no significant change in intercellular CO₂concentration.The content of chlorophyll increased significantly and the activities of Rubisco carboxylase and Rubisco activase decreased significantly.（3）The change of light intensity affected the enlargement of tuber,and the length,diameter and weight per plant decreased with the decrease of light intensity.The contents of starch,sucrose and reducing sugar decreased with the decrease of light intensity,the activities of amylase,starch synthetase and sucrose synthesis related enzymes decreased,the contents of soluble total sugar and soluble protein increased with the decrease of light intensity,so as to improve the adaptability to the environment.The results showed that low light could reduce the activities of enzymes related to starch synthesis and sugar metabolism,and the level of enzyme activity would affect the metabolic process of starch and sugar,thus affecting the accumulation of starch in tuber.（4）The ORF length of Rubisco carboxylase gene（Do Rbc L）was 1752bp and encoded 583 amino acids.Compared with the amino acid sequences of 11plants such as jujube,it was found that the amino acid sequences of Do Rbc L of Yam and Dioscorea zingensis were relatively similar.Transient expression in tobacco leaf epidermal cells showed that Do Rbc L protein in yam was localized in chloroplasts.The expression of Do Rbc L gene was tissue specific,and the expression level was the highest in leaves,and the expression level of Do Rbc L gene was significantly decreased after shading.