Photosynthetic Characteristics of Clerodendrum trichotomum Thumb. Responses to Drought, Salt and Water-logging Stresses

In order to reveal the photosynthetic characteristics of C. trichotomum responses to drought, salt and water-logging stresses, one-year-old potted seedlings were taken as materials, and the several stresses including natural drought, submergence stress, water-logging and different salt treatments （0.2%, 0.4%, 0.6% and 0.8% NaCl） were carried out on August 15, 2012. The morphological and photosynthetic characteristics were observed and determined. The results showed that adverse enviromental stress had a significant effect on the morphological changes and photosynthetic characteristics of C. trichotomum. On the 14th day after natural drought, the leaves wilted and could not recovery at night, and 60% of the seedlings could recover after re-watering. From the 7th day to the 10th day after submergence stress treatment, the 2nd and the 3rd leaves at the base of 60% seedling turned yellow and the lenticels were observed. At the early stage of water-logging stress, white lenticels appeared at the base of seedlings, and the leaves wilted, chlorina and fallen off on the 8th day. A large number of leaves fallen off under 0.6% NaCl or more salt stress, and even the whole plant died. The chlorophyll content, net photosynthetic rate （Pn） and transpiration rate （Tr） decreased gradually with the stress process, such as 8 days after natural drought, less than 0.4% salt stress and water-logging stress, but the changes were not significant compared with those of the control. With the increase of the stress intensity and the prolonged time, the changes of photosynthetic index were significant. All the results indicated that C. trichotomum had a certain degree of tolerance to drought, water and salt, but it was not suitable for living, in water-logging condition for a long time.

Submergence induced changes of molecular species in membrane lipids in Arabidopsis thaliana

The composition of membrane lipids is sensitive to environmental stresses.Submergence is a type of stress often encountered by plants.However,how the molecular species of membrane lipids respond to submergence has not yet been characterised.In this study,we used a lipidomic approach to profile the molecular species of membrane lipids in whole plants of Arabidopsis thaliana that were completely submerged for three days.The plants survived one day of submergence,after which,we found that the total membrane lipids were only subtly decreased,showing significant decreases of monogalactosyldiacylglycerol(MGDG)and phosphatidylcholine(PC)and an increase of phosphatidic acid(PA);however,the basic lipid composition was retained.In contrast,three days of submergence caused plants to die,and the membranes deteriorated via the rapid loss of 96% of lipid content together with a 229% increase in PA.The turnover of molecular species from PG and MGDG to PA indicated that submergenceinduced lipid changes occurred through PA-mediated degradation.In addition,molecular species of extraplastidic PG degraded sooner than plastidic ones,lyso-phospholipids exhibited various patterns of change,and the double-bond index(DBI)remained unchanged until membrane deterioration.Our results revealed the unique changes of membrane lipids upon submergence and suggested that the major cause of the massive lipid degradation could be anoxia.

Contribution of Antioxidative Enzymes and Anoxia Responsive Genes to Submergence Tolerance in Rice: A Review

Flooding/submergence of rice fields is a severe problem in South and South-East Asia, affecting more than 20 million hectares of rice every year. Submergence creates hypoxic or anoxic condition causing poor germination, seedling establishment,and enormous yield loss. Standing water in the field from weeks to months also leads to significant yield losses when large part of aerial tissues is under water. For flash flooding, a rice variety FR1A3 with tolerant gene(SUB1A) was identified. SNORKEL1 and SNORKEL2 have been identified for their ability to survive deep-water flooding by rapid elongation. Submergence stress has also been reported to adversely affect cell division and damage cellular and organelle membranes. Research on antioxidative enzymes response and genes that confer tolerance to prolonged flooding is in progress. Here we review the different anoxia responsive genes and the potential involvement of antioxidative enzymes, such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, which occur in cells of rice plant exposed to submergence stress.