Arabidopsis VAC14 Is Critical for Pollen Development through Mediating Vacuolar Organization.

Pollen viability depends on dynamic vacuolar changes during pollen development involving increases and decreases of vacuolar volume through water and osmolite accumulation and vacuolar fission. Mutations in FAB1A to FAB1D, the genes encoding phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2]-converting kinases, are male gametophyte lethal in Arabidopsis (Arabidopsis thaliana) due to defective vacuolar fission after pollen mitosis I, suggesting a key role of the phospholipid in dynamic vacuolar organization. However, other genetic components that regulate the production of PI(3,5)P2 and its involvement in pollen germination and tube growth are unknown. Here, we identified and characterized Arabidopsis VAC14, a homolog of the yeast and metazoan VAC14s that are crucial for the production of PI(3,5)P2VAC14 is constitutively expressed and highly present in developing pollen. Loss of function of VAC14 was male gametophyte lethal due to defective pollen development. Ultrastructural studies showed that vacuolar fission after pollen mitosis I was compromised in vac14 mutant microspores, which led to pollen abortion. We further showed that inhibiting the production of PI(3,5)P2 or exogenous application of PI(3,5)P2 mimicked or rescued the pollen developmental defect of the vac14 mutant, respectively. Genetic interference and pharmacological approaches suggested a role of PI(3,5)P2 in pollen germination and tube growth. Our results provide insights into the function of VAC14 and, by inference, that of PI(3,5)P2 in plant cells.

Effects of long-term chilling on ultrastructure and antioxidant activity in leaves of two cucumber cultivars under low light.

Cucumber (Cucumis sativus L.) cv. Xintaimici (a chilling-resistant cultivar) and cv. Jinyan no. 4 (a chilling-sensitive cultivar) were subjected to two temperatures (15/15 and 25/18 degrees C) under low light (100 mumol m(-2) s(-1)) to understand the relationship between ultrastructural changes and the antioxidant abilities caused by low temperature (15/15 degrees C). We also aimed to find indicators for chilling resistance that could be used on a routine basis in breeding programs of greenhouse crops. At the 15/15 degrees C treatment, the membranes of chloroplast, mitochondrion, ER and plasma were not significantly changed in Xintaimici, whereas they were seriously affected in Jinyan no. 4. This result was consistent with the changes of malonaldehyde in chilling-stressed cucumber leaves. The antioxidant activities were changed under low temperature according to cultivar-expected resistance, relating in part to the described ultrastructural changes. The activities of superoxide dismutase (EC 1.15.1.1) and guaiacol peroxidase (EC 1.11.1.7) increased in chilling-stressed leaves of both cultivars, but the two enzymes were not responsible for the difference between cucumber cultivars. At 15/15 degrees C, contents of GSH and activities of glutathione reductase (GR, EC 1.6.4.2) increased more in leaves of Xintaimici than in those of Jinyan no. 4, while catalase (CAT, EC 1.11.1.6) activities decreased less. GSH, GR and CAT were affected by low temperature and cultivars and correlated with the difference in ultrastructure between chilling-stressed cucumber cultivars. We propose that the three antioxidants might be therefore used as biochemical indicators to screen chilling-resistant cucumber cultivars.

The effects of initial participation motivations on learning engagement in transition training for future general practitioners in rural China: perceived deterrents as mediator.

BACKGROUND: For the shortage of high-quality general practitioners (GPs) in China's rural areas, Chinese government has taken steps to encourage rural specialists to participate in transition training for future GPs. Specialists' initial participation motivations and their perceived deterrents during training may play important roles for their learning engagement in the transition training. This study aimed at revealing the relationships among the variables of initial participation motivations, perceived deterrents in training, and learning engagement. METHODS: A questionnaire survey was used in this study. A total of 156 rural specialists who participated in transition training for future GPs filled out the questionnaire, which consisted of the measurements of initial participation motivations, perceived deterrents, and learning engagement in training. The data about specialists' demographic variables were collected at the same time. RESULTS: The variance of initial escape/stimulations motivation significantly predicted the variance of learning engagement through the full mediating role of perceived deterrents in training. In addition, initial educational preparation motivations predicted the variance of learning engagement directly. CONCLUSIONS: Specialists' initial participation motivations and perceived deterrents in training played important roles for learning engagement in the transition training.