Morphological And Photosynthetic Differences Between Heteromorphic Leaves Of Ficus Pumila L.

Heteromorphism refers to the phenomenon that mature leaves with different shapes and/or sizes appear on a same plant.The phenomenon of heteromorphism caused by environmental changes is called heterophylly,and heteroblasty is the phenomenon that heteromorphic leaves occur over the lifespan of the same plant.In principle,there is only one genotype within an individual plant,and heteromorphism could become a unique material for understanding the relationship between leaf morphological changes and adaptation.However,the existing researches mainly eye on the study of mutual adaptation between heterophylly and environmental factors,leaving a few of them focusing on ecological adaptation of heteroblasty,still less the mechanisms underlying the phenomenon.This paper chose Ficus pumila L.,a species of heteroblasty,as an example,aimed to explore adaptive significance and molecular mechanism of heteroblasty.Towards that end,we had measured the morphology,anatomical structures and photosynthetic physiological characteristics of the mature leaves on the fertile and sterile branches,and analyzed transcriptome data of buds,tender leaves and mature leaves.Main findings are as follows:1)Compared with leaves on sterile branches,the leaves on fertile branches were generally bigger,thicker and more symmetrical.Anatomy-based findings revealed that leaves on fertile and sterile branches were both typical bifacial leaves,while leaves on fertile branches featured more developed palisade tissue and spongy tissue,showing more layers of palisade and spongy cells.In addition,there was no significant difference between the cell size in the two types of leaves,indicating the number of cells accounted for the significant morphological differences between the two types of leaves.2)The positive regulatory protein AHP gene in cytokinin signal transduction pathway,the key SPR1 gene driving cell division and the key enzyme genes involved in cell wall degradation and regeneration were found significantly up-regulated at the bud stage of the leaves on fertile branches when compared with the leaves on sterile branches,which indicated that there was more active cell division at bud stage of the leaves on fertile branches.3)Significant differences had been detected in photosynthetic characters between leaves on fertile and sterile branches.The photosynthetic capacity of leaves on fertile branches was significantly higher,with higher light saturation point,greater maximum net photosynthetic rate,and more nutrients production,which might be related to higher chlorophyll content per unit area on the leaves.4)Compared with mature leaves on sterile branches,the small heat shock protein HSP gene in response to heat stress and aquaporin TIP gene are found significantly upregulated in mature leaves on fertile branches,which might account for its higher light saturation point and transpiration rate.In summary,the differentiation of leaves on fertile and sterile branches of Ficus pumila was the result of adaptation to the changes of nutrition needed during its own development.The larger and thicker leaves on fertile branches have stronger photosynthetic capacity to produce sufficient nutrients to meet the breeding needs of Ficus pumila,offering persuasive evidence for the adaptative significance of heteroblasty.In addition,findings from transcriptome analysis showed that leaf bud served as the key stage to morphological differences between these two types of leaves,and a large number of differentially expressed genes(DEGs)related to cell division and photosynthesis were identified during the development of these two types of leaves,which provides valuable genetic information for further exploring the morphological differentiation regulation mechanisms of Ficus pumila.