Pigment comparison and expression of chlorophyll metabolism genes in yellow and green Acer palmatum leaves

Exterior leaf color is an important trait for ornamental foliage plants but the molecular mechanism underlying the variation in color between yellow- and green-leaf Acer palmatum Thunb. ex Murray is poorly understood. Indeed, chlorophyll (Chl) contents and gene transcriptions were very different between the yellow mutant (YM) and green wild-type (GW) leaves of this species. Here, annual variations of leaf color and pigment contents in two varieties were investigated. Then, transcript levels of six genes involved in Chl metabolism were quantitatively measured using real-time polymerase chain reaction in YM and GW leaves. Compared with GW, the color changes of YM leaves were classified into four typical periods. During the yellow leaf stage, YM showed greatly reduced Chl synthesis and a higher ratio of carotenoid (Car) to Chl than GW. These phenomena may be the main cause of yellow leaves in YM. In addition, expression levels of Chl synthesis genes (ApPORA, ApPORB, ApCAO, and ApCHLG) in YM were very low during this period. Concomitantly, the amount of transcripts of genes for Chl degradation (ApCLH1 and ApCLH2) rose significantly compared with GW. Once YM leaves turned red, the above differences between the two genotypes lessened. Overall, our results indicated that changes in Chl synthesis and degradation may play important roles leading to the yellow leaves of YM A. palmatum.