Programmed cell death (PCD) is the genetically regulated disassembly of cells, and occurs in the endosperm of cereals during seed maturation. Since PCD determines the lifetime of cells, it can affect endosperm growth and, therefore, cereal yield. However, the features and mechanisms of PCD in the developing starchy endosperm in the Poaceae remain unclear. In the present study, we investigated the characteristics of PCD in developing starchy endosperm of rice (Oryza sativa L.) by fluorescence microscopy, focusing on the spatial and temporal progress of PCD-associated responses. Cell death commenced in the central region of starchy endosperm, and then spread to the peripheral region. PCD-associated responses, such as mitochondrial membrane permeabilization and activation of the protease that cleaves the amino acid sequence VEID, showed similar spatial patterns to that of cell death, but preceded cell death. Degradation of nuclear DNA could not be detected in developing starchy endosperm by the TUNEL assay. These results indicated that PCD in developing starchy endosperm of rice proceeds via a highly organized pattern. In addition, these results suggested that PCD in developing starchy endosperm of rice is characterized by the involvement of mitochondrial signaling and the activity of a caspase-like protease that cleaves the VEID sequence.

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Some plants are able to tolerate salinity using salt glands on the leaf surface, which secrete excess salts transported into the leaves. Rhodes grass (Chloris gayana Kunth) reportedly possesses such salt glands, but the features of secretion remain unclear. In the present study, we compared the ability of Rhodes grass salt glands to secrete sodium and potassium with the aim of clarifying the preference of cations for secretion. In both whole plant experiments and detached leaf experiments, NaCl treatment increased Na + secretion and KCl treatment increased K + secretion. When the ratios of the amount of secreted ions to their concentration in the leaves were compared between Na + and K + , the ratio was greater with Na + than K + .

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Endoreduplication is the phenomenon by which cells increase their ploidy. Endoreduplication is initiated by the transition from the mitotic cell cycle to the endocycle, in which DNA replication occurs without a subsequent chromosome separation and cytokinesis, and is enhanced by endocycle reiteration. This process appears to play an important role in endosperm development, but the characteristics of endoreduplication in the endosperm of rice (Oryza sativa) remain unclear. To elucidate the features and variations of endoreduplication in rice endosperm, endoreduplication progression in the developing endosperm was compared among 10 cultivars based on flow cytometry and fluorescence microscopy. The flow cytometric analysis detected significant differences among 10 cultivars in the following three parameters: mean ploidy of all nuclei, the proportion of nuclei ≥6C (%E, an estimate of the initiation of the endocycle), and the mean ploidy of nuclei ≥6C (E6P, an estimate of the reiteration of the endocycle). However, no significant correlation between %E and E6P was observed, suggesting that the initiation and reiteration of the endocycle are independently regulated. Fluorescence microscopy revealed that the ploidy of the nuclei was higher in the intermediate region than in the central and peripheral regions of the endosperm. Cells with a higher ploidy were larger in the developing endosperm. Furthermore, the mean ploidy in the developing endosperm was significantly correlated with the mean cell size in the mature endosperm. These results indicate that endoreduplication progression in the endosperm differed significantly among the 10 rice cultivars and such differences may influence endosperm cell size.

The epidermis of wheat (Triticum aestivum L.) leaves contains trichomes that contribute to resistance to insect pests and drought tolerance. In the present study, we examined the effects of 6-benzylaminopurine (BA) and methyl jasmonate (MeJA) treatment on trichome development on the leaves of wheat cv. Norin 61 seedlings. Without phytohormone treatment, trichomes on the adaxial leaf surface were short (90 lm) and their density was low (3.6 trichomes/mm 2 ). Both BA and MeJA treatments significantly increased the density of trichomes, and there were no significant differences between the phytohormone treatments. BA treatment increased trichome length to five times as long as that in the control, whereas MeJA treatment did not significantly affect trichome length. Since BA treatment concurrently increased the DNA content of the nuclei in trichome cells, endoreduplication of the nuclei is probably involved in trichome enlargement. These results indicate that even wheat cultivars with short trichomes retain the mechanisms for trichome enlargement and stimuli such as BA application can induce increased pubescence on wheat leaves.