Abstract
Leaf variegation has been demonstrated to have adaptive functions such as cold tolerance. Pittosporum tobira is an ornamental plant with natural leaf variegated cultivars grown in temperate regions. Herein, we investigated the role of leaf variegation in low temperature responses by comparing variegated “Variegatum” and non-variegated “Green Pittosporum” cultivars. We found that leaf variegation is associated with impaired chloroplast development in the yellow sector, reduced chlorophyll content, strong accumulation of carotenoids and high levels of ROS. However, the photosynthetic efficiency was not obviously impaired in the variegated leaves. Also, leaf variegation plays low temperature protective function since “Variegatum” displayed strong and efficient ROS-scavenging enzymatic systems to buffer cold (10 °C)-induced damages. Transcriptome analysis under cold conditions revealed 309 differentially expressed genes between both cultivars. Distinctly, the strong cold response observed in “Variegatum” was essentially attributed to the up-regulation of HSP70/90 genes involved in cellular homeostasis; up-regulation of POD genes responsible for cell detoxification and up-regulation of FAD2 genes and subsequent down-regulation of GDSL genes leading to high accumulation of polyunsaturated fatty acids for cell membrane fluidity. Overall, our results indicated that leaf variegation is associated with changes in physiological, biochemical and molecular components playing low temperature protective function in P. tobira.
Highlights
Leaf variegation has been observed in many species of higher plants [1,2,3] and this special attractive trait has become a focus of plant breeding as it increases the economic value of ornamental plants [4]
It is well documented that the leaves of variegated plants having green/yellow sectors have impaired chloroplast biogenesis, less photosynthetic pigments in the yellow sectors and accumulate excessive levels of reactive oxygen species (ROS) [29,30]
To verify these observations in P. tobira, we analyzed the chloroplast ultrastructure in the yellow sector compared to the green sector of the variegated leaf
Summary
Leaf variegation has been observed in many species of higher plants [1,2,3] and this special attractive trait has become a focus of plant breeding as it increases the economic value of ornamental plants [4]. A mutation in the transcription factor mitochondrial transcription termination factor (mTERF) has been found to induce colorlessness in leaves of variegated fig [3] These studies have provided a deep understanding of the variegation mechanism in plants, the advantage of this trait for the good fitness or for the plant physiology is still poorly understood. Shelef et al [22] demonstrated that under lower temperatures, variegated wild type Silybum marianum leaves were significantly warmer than all-green mutants, conferring cold stress tolerance These studies showed that variegation in plants is not just a color mutation but has some physiological advantages. Some cultivars exhibit leaf variegation with yellowish or creamy white leaf margins and green interior, which have a greater aesthetic appeal and ornamental value compared to the typical all-green P. tobira. Our findings elucidate the leaf variegation mechanism in P. tobira and provide novel insights into the thermo-protective function of this important trait
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