Autophagy contributes to various cellular processes, including innate immunity, development, and programmed cell death (PCD) in multicellular organisms. In plants, autophagy plays roles in recycling of proteins and metabolites including lipids, and is involved in many physiological processes, such as abiotic and biotic stress responses. Furthermore, rice mutants defective in autophagy showed sporophytic male sterility and reduced accumulation of lipids and starch in pollen grains at the flowering stage and exhibited reduced pollen germination activity, indicating crucial roles of autophagy during plant reproductive development. An in vivo imaging system has been established to analyze the dynamics of autophagy in rice as well as in cultured tobacco cells using GFP-ATG8, a marker of autophagosomes. In the present study, we review the spatiotemporal dynamics of autophagic fluxes in plant cells and discuss their possible significance in PCD and metabolic regulation, with particular focus on plant reproductive development.

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The regulation of intracellular events is of critical importance in proliferating cells. These events may be altered by signaling molecules linked through cell-cycle regulatory mechanisms. Recent advances have linked the calcium ion (Ca²⁺) with the progression of the cell cycle through interphase and the different phases of mitosis. However, there has been little explanation on the fundamental relationship of calcium signals and their associated receptors with the interphase subphases. In the present study, to clarify this possible relationship, we investigated how calcium signaling and its associated purinergic receptors are related to the cell cycle between the nucleoplasm and cytoplasm in cultured G₁-interphase cells of HeLa.S-Fucci2 and fucci/mouse fibroblasts. Ratiometric fluorescence and reverse transcriptase polymerase chain reaction (RT-PCR) techniques were employed to assess the intracellular Ca²⁺ concentrations ([Ca²⁺]_i) and the expression of purinergic and inositol trisphosphate receptors, respectively. The results obtained revealed the existence of two distinct subcellular increases in [Ca²⁺]_i in a single individual G₁-phase cell, suggesting variations between the early and late G₁-phases of the cell cycle. In addition to the Ca²⁺ wave, the RT-PCR results indicated variability in the purinergic receptors and inositol 1,4,5-trisphosphate receptor subtypes within G₁-phase cells. Based on these results, we propose that receptor expression and calcium signals are functionally distinct within individual interphase subphases.

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