Abstract
Anthocyanins belong to the group of flavonoid compounds broadly distributed in plant species responsible for attractive colors. In black rice (Oryza sativa L.), they are present in the stems, leaves, stigmas, and caryopsis. However, there is still no scientific evidence supporting the existence of compartmentalization and trafficking of anthocyanin inside the cells. In the current study, we took advantage of autofluorescence with anthocyanin’s unique excitation/emission properties to elucidate the subcellular localization of anthocyanin and report on the in planta characterization of anthocyanin prevacuolar vesicles (APV) and anthocyanic vacuolar inclusion (AVI) structure. Protoplasts were isolated from the stigma of black and brown rice and imaging using a confocal microscope. Our result showed the fluorescence displaying magenta color in purple stigma and no fluorescence in white stigma when excitation was provided by a helium–neon 552 nm and emission long pass 610–670 nm laser. The fluorescence was distributed throughout the cell, mainly in the central vacuole. Fluorescent images revealed two pools of anthocyanin inside the cells. The diffuse pools were largely found inside the vacuole lumen, while the body structures could be observed mostly inside the cytoplasm (APV) and slightly inside the vacuole (AVI) with different shapes, sizes, and color intensity. Based on their sizes, AVI could be grouped into small (Ф < 0.5 um), middle (Ф between 0.5 and 1 um), and large size (Ф > 1 um). Together, these results provided evidence about the sequestration and trafficking of anthocyanin from the cytoplasm to the central vacuole and the existence of different transport mechanisms of anthocyanin. Our results suggest that stigma cells are an excellent system for in vivo studying of anthocyanin in rice and provide a good foundation for understanding anthocyanin metabolism in plants, sequestration, and trafficking in black rice.
Highlights
Anthocyanin is a subcategory of flavonoid compounds found in plants providing numerous functions in Human bodies and plants themselves
Anthocyanin is found at the different developmental stages in various tissues and organs, such as caryopsis, leaves blade, leaves sheath, internodes, stems ligules, apiculus, and stigmas and can be visualized with naked eyes or under a microscope
Using nondestructive cell isolation and modern microscopy techniques, we examined the rice stigma’s protoplast containing anthocyanins and obtained images of anthocyanin distribution inside the cells
Summary
Anthocyanin is a subcategory of flavonoid compounds found in plants providing numerous functions in Human bodies and plants themselves. Some scientific studies, such as animal models and human clinical trials, revealed that anthocyanins have potential antioxidant and antimicrobial properties [1], they are effective in supporting glucose homeostasis in the treatment of diabetes [2], cardiovascular diseases [3,4], and can prevent tumor and cancer [5,6,7] They possess anti-carcinogenic and anti-inflammation properties [8], improve visual and neurological health, and offer protection against various non-communicable diseases [9]. These properties have raised the research interest in agriculture, health science, and commerce significantly
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