The roles of ascorbic acid and glutathione in symptom alleviation to SA-deficient plants infected with RNA viruses.

Salicylic acid (SA) is required for plant systemic acquired resistance (SAR) to viruses. However, SA-deficient plants adapt to RNA virus infections better, which show a lighter symptom and have less reactive oxygen species (ROS) accumulation. The virus replication levels are higher in the SA-deficient plants during the first 10 days, but lower than the wild-type seedlings after 20 dpi. The higher level of glutathione and ascorbic acid (AsA) in SA-deficient plants may contribute to their alleviated symptoms. Solo virus-control method for mortal viruses results in necrosis and chlorosis, no matter what level of virus RNAs would accumulate. Contrastingly, early and high-dose AsA treatment alleviates the symptom, and eventually inhibits virus replication after 20 days. ROS eliminators could not imitate the effect of AsA, and could neither alleviate symptom nor inhibit virus replication. It suggests that both symptom alleviation and virus replication control should be considered for plant virus cures.

Mg-protoporphyrin, haem and sugar signals double cellular total RNA against herbicide and high-light-derived oxidative stress.

Cellular total RNA level is usually stable, although it may increase gradually during growth or seed germination, or decrease gradually under environmental stresses. However, we found that plant cell RNA could be doubled within 48 h in response to herbicide-induced Mg-protoporphyrin and heme accumulation or a high level of sugar treatment. This rapid RNA multiplication is important for effective cellular resistance to oxidative stress, such as high-light and herbicide co-stress conditions, where the plastid-signalling defective mutant gun1 shows an apparent phenotype (more severe photobleaching). Hexokinase is required for sugar-induced RNA multiplication. While both sugar and Mg-protoporphyrin IX require plastid protein GUN1 and a nuclear transcription factor ABI4, haem appears to function through an independent pathway to control RNA multiplication. The transcription co-factor CAAT binding protein mediates the rapid RNA multiplication in plant cells in all the cases.

A broad-spectrum, efficient and nontransgenic approach to control plant viruses by application of salicylic acid and jasmonic acid.

Plant viruses cause many diseases that lead to significant economic losses. However, most of the approaches to control plant viruses, including transgenic processes or drugs are plant-species-limited or virus-species-limited, and not very effective. We introduce an application of jasmonic acid (JA) and salicylic acid (SA), a broad-spectrum, efficient and nontransgenic method, to improve plant resistance to RNA viruses. Applying 0.06 mM JA and then 0.1 mM SA 24 h later, enhanced resistance to Cucumber mosaic virus (CMV), Tobacco mosaic virus (TMV) and Turnip crinkle virus (TCV) in Arabidopsis, tobacco, tomato and hot pepper. The inhibition efficiency to virus replication usually achieved up to 80-90%. The putative molecular mechanism was investigated. Some possible factors affecting the synergism of JA and SA have been defined, including WRKY53, WRKY70, PDF1.2, MPK4, MPK2, MPK3, MPK5, MPK12, MPK14, MKK1, MKK2, and MKK6. All genes involving in the synergism of JA and SA were investigated. This approach is safe to human beings and environmentally friendly and shows potential as a strong tool for crop protection against plant viruses.

Light regulation to chlorophyll synthesis and plastid development of the chlorophyll-less golden-leaf privet.

Ligustrum vicaryi L. is a hybrid of Ligustrum ovalifolium Hassk. var. aureo-marginatum and Ligustrum vulgale L., and displays a chlorophyll-less phenotype. Therefore it is widely used as a horticultural shrub because of its golden-color leaves. Its putative mechanism, light responses, chlorophyll synthesis and plastid development were studied. L. vicaryi has a higher level of 5-aminolevulinic acid (ALA), but lower levels of chlorophylls compared with L. quihoui. The yellowish phenotype of L. vicaryi upper leaves could be attributed to their hampered conversion from chlorophyllide into chlorophyll a. Despite the enhanced ALA level and the decreased thylakoid stacking in plastids, L. vicaryi golden leaves contain normal levels of Lhcb transcripts and photosystem apoproteins. Furthermore, reactive oxygen species (ROS) accumulation is almost the same in L. vicaryi and L. quihoui. The golden leaves often turn green and the contents of chlorophylls increase with decreasing light intensity. Dynamic changes of chlorophyll-synthesis-system under the light transition were also analyzed.

Difference of physiological characters in dark green islands and yellow leaf tissue of Cucumber mosaic virus (CMV)-infected Nicotiana tabacum leaves.

Dark green islands (DGIs) are a common symptom of plants systemically infected with the mosaic virus. DGIs are clusters of green leaf cells that are free of virus but surrounded by yellow leaf tissue that is full of virus particles. In Cucumber mosaic virus (CMV)-infected Nicotiana tabacum leaves, the respiration and photosynthesis capabilities of DGIs and yellow leaf tissues were measured. The results showed that the cyanide-resistant respiration was enhanced in yellow leaf tissue and the photosynthesis was declined, while in DGIs they were less affected. The activities of the oxygen-scavenging enzymes catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) in infected leaves were significantly higher than those in the healthy leaves, and the enzyme activities in DGIs were always lower than in the yellow leaf tissues. Reactive oxygen species (ROS) staining showed that the hydrogen peroxide content in yellow leaf tissues was apparently higher than that in DGIs, while the superoxide content was on the contrary. Formation of DGIs may be a strategy of the host plants resistance to the CMV infection.

Phosphorylation of photosynthetic antenna protein CP29 and photosystem II structure changes in monocotyledonous plants under environmental stresses.

Kinetic studies of protein dephosphorylation in thylakoid membranes showed that the minor light-harvesting antenna protein CP29 could be phosphorylated in barley (C3) and maize (C4) seedlings, but not in spinach under water [Liu, W. J., et al. (2009) Biochim. Biophys. Acta 1787, 1238-1245], salt, or cold stress [Pursiheimo, S., et al. (2003) Plant Cell Environ. 26, 1995-2003], suggesting that phosphorylation of CP29 is a general phenomenon in monocots, but not in dicots under environmental stresses. Abscisic acid (ABA), reactive oxygen species (ROS), salicylic acid (SA), jasmonic acid (JA), ethylene (ET), NO, and the scavenger of H(2)O(2) had weak effects on CP29 phosphorylation. However, three protein kinase inhibitors, U0126, W7, and K252a (for mitogen-activated protein kinase, Ca(2+)-dependent protein kinase, and Ser/Thr protein kinases, respectively), decrease the level of CP29 phosphorylation in barley apparently under environmental stresses. Therefore, these three protein kinases are involved in CP29 phosphorylation. We also found that most CP29 phosphorylation was accompanied by its lateral migration from granum membranes to stroma-exposed thylakoid regions, and the instability of PSII supercomplexes and LHCII trimers under environmental stresses.