Study On Mechanism Of Leaf Color Variation Of Pseudosasa Japonica F. Akebonosuji

Most bamboos show green color in nature, however, some of them mutate at different growth stages and further show colorful (yellow, white, purple, red, brown or other unique colors) strips, patches or spots on their shoots, culms and leaves, respectively. Those colorful mutant add more ornamental value to bamboos. Pseudosasa japonica cv. Akebonosuji is a typical representative with varying leaf color, whose unique variation type of leaf color may indicate a special regulation approach. In this dissertation, we focus on mechanism of its unsteady color variation in leaves, and hope to provide important theoretical support and reference for similar research, and to provide basic technical support for ornamental bamboo cultivation. Main results are as follows:Basic biological indicators (including chlorophyll content, the culm height, ground stems, internodes, each branch leaf number, leaf length and width) in white leaf bamboo were significantly lower than those in green leaves (P<0.05), while most of these indicators are not significantly different between striped leaves and in green leaves (P<0.05), but excepting ground stems and leaf number. Under natural conditions, green leaf (GL) has a stable phenotype, the unstable phenotype with stripes on striped leaf (SL) can be revealed on re-greening of albino leaf (AL). However, the SPAD value of AL can significantly increased up to level of GL after 12 months of growth. Features of P. japonica cv. Akebonosuji leaf under tissue culture condition are consistent with those under the natural conditions. Notably, stripy leaf can be maintained by application of cytokinins.Determination of precursors in chlorophyll biosynthetic pathway indicated that, content of coproporphyrin III in AL and white part in SL were 38% and 51.7% higher than that in GL. But relative content of Proto IX, a downstream product after coproporphyrin III, were only 16.4% and 5.91% (P<0.05) of that in GL respectively. Furthermore, the total chlorophyll content in AL is only 2.7% in GL. From these we inferred, the process of protoporphyrin IX to chlorophyll is blocked in chlorophyll biosynthesis in AL or striped leaves. On the other hand, Chla/b value in AL was significantly lower than GL, and Catoid/Chla+b value in AL was significantly higher than GL, indicating that AL was a chl a-deficiency type mutant.Different blade types of parameters with chlorophyll fluorescence from excitation instrument analyse indicated that, the light reaction center parameter ABS/RC, TRO/RC, ETO/RC were significantly higher than GL in AL, but there is no significant difference in re-green leaves with GL. The reaction central density parameter and φPo, φEo,Φo, PIABS were significantly higher than AL in GL. And after re-greening, AL was still significantly lower than the green leaves. Therefore, PSII performance degradation is due to the degradation of electron transport activity after QA in mosaic leaves, thedegradation of PSI donor sideperformance causePSI performance degradation. Epidermal cells have no significant difference between AL and GL during leafdevelopment. But mesophyll plastids have developmental disorders, which cannot be converted into functional chloroplasts.Transcriptome feature analysis of GL and AL indicated there are 1160 and 1356 differentially expressed genes (DEGs) respectively. Of these,248 DEGs were differentially expressed between two lines. According to expression pattern, nine significant clusters (p< 0.05) were classified for 248 DEGs genes, among which,6 clusters harboring 188 DEGs exhibited the common higher expression in AL, compared with GL.Gene Ontology analysis indicated that the higher-expressed genes in AL were functionally enriched in stress response and tetrapyrrole binding, implying their response to the chlorophyll-deficiency. Co-expression analysis of these DEGs represented a complex regulatory network involved in the chlorophyll-deficiency in AL. Among these, ELIPs gene is a candidate gene inducing variation of leaf color. It keeps a highly expression status during stage 2- stage 5, and resulted in expression change with genes related to development, stress resistance, oxido-reduction and senescence.In summary, the specific expression pattern with ELIPs gene during leaf development of Pseudosasa japonica f.Akebonosuji, can cause the abnormal assembly of thylakoid membrane, and the later block of chlorophyll, expression changes of these genes, and finally affect conversion from plastid to chlorophyll, performance reduction of light system, and the variation of leaf color.