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To study the mechanisms of drought inhibiting photosynthesis and the role of PAs and ethylene, the photosynthetic rate (Pn), the maximal photochemical efficiency of PSII (Fv/Fm), the intercellular CO2 concentration (Ci), photorespiratory rate (Pr), the amount of chlorophyll (chl), antioxidant enzyme activity, ethylene levels, RuBPC (ribulose-1,5-bisphosphate carboxylase) activity and endogenous polyamine levels of pakchoi were examined, and an inhibitor of S-adenosylmethionine decarboxylase (SAMDC) and an inhibitor of ethylene synthesis and spermidine (Spd) were used to induce the change of endogenous polyamine levels. The results show that drought induced a decrease in Pn and RuBPC activity, an increase in the intercellular CO2 concentration (Ci), but no change in the actual photochemical efficiency of PSII (ΦPSII), and chlorophyll content. In addition, drought caused an increase in the free putrescine (fPut), the ethylene levels, a decrease in the Spd and spermine (Spm) levels, and the PAs/fPut ratio in the leaves. The exogenous application of Spd and amino oxiacetic acid (AOAA, an inhibitor of ethylene synthesis) markedly reversed these drought-induced effects on polyamine, ethylene, Pn, the PAs/fPut ratio and RuBPCase activity in leaves. Methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of SAMDC resulting in the inability of activated cells to synthesize Spd and Spm, exacerbates the negative effects induced by drought. These results suggest that the decrease in Pn is at least partially attributed to the decrease of RuBPC activity under drought stress and that drought inhibits RuBPC activity by decreasing the ratio of PAs/fPut and increasing the release of ethylene., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

Camelina (Camelina sativa) and rapeseed (Brassica napus) are well-established oil-seed crops with great promise also for biofuels. Both are cold-tolerant, and camelina is regarded to be especially appropriate for production on marginal lands. We examined physiological and biochemical alterations in both species during cold stress treatment for 3 days and subsequent recovery at the temperature of 25°C for 0, 0.25, 0.5, 1, 2, 6, and 24h, with particular emphasis on the post-translational regulation of the plasma membrane (PM) H(+)-ATPase (EC3.6.3.14). The activity and translation of the PM H(+)-ATPase, as well as 14-3-3 proteins, increased after 3 days of cold stress in both species but recovery under normal conditions proceeded differently. The increase in H(+)-ATPase activity was the most dramatic in camelina roots after recovery for 2h at 25°C, followed by decay to background levels within 24h. In rapeseed, the change in H(+)-ATPase activity during the recovery period was less pronounced. Furthermore, H(+)-pumping increased in both species after 15min recovery, but to twice the level in camelina roots compared to rapeseed. Protein gel blot analysis with phospho-threonine anti-bodies showed that an increase in phosphorylation levels paralleled the increase in H(+)-transport rate. Thus our results suggest that cold stress and recovery in camelina and rapeseed are associated with PM H(+)-fluxes that may be regulated by specific translational and post-translational modifications., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Chinese flowering cabbage is one of the main leafy vegetables produced in China. They have a rapid leaf yellowing due to chlorophyll degradation after harvest that limits their marketing. In the present study, leaf senescence of the cabbages was manipulated by ethylene and 6-benzyl aminopurine (6-BA) treatment to investigate the correlation of leaf senescence and chlorophyll degradation related to gene expression/activities in the darkness. The patterns of several senescence associated markers, including a typical marker, the expression of senescence-associated gene SAG(12), demonstrated that ethylene accelerated leaf senescence of the cabbages, while 6-BA retarded this progress. Similar to the trends of BrSAG(12) gene expression, strong activation in the expression of three chlorophyll degradation related genes, pheophytinase (BrPPH), pheophorbide a oxygenase (BrPAO) and red chlorophyll catabolite reductase (BrRCCR), was detected in ethylene treated and control leaves during the incubation, while no evident increase was recorded in 6-BA treated leaves. The overall dynamics of Mg-dechelatase activities in all treatments displayed increasing trends during the senescence process, and a delayed increase in the activities was observed for 6-BA treated leaves. However, chlorophyllase activity as well as the expression of BrChlase1 and BrChlase2 decreased with the incubation in all treatments. Taken together, the expression of BrPPH, BrPAO and BrRCCR, and the activity of Mg-dechelatase was closely associated with the chlorophyll degradation during the leaf senescence process in harvested Chinese flowering cabbages under dark conditions., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

The aim of this experiment, conducted under greenhouse conditions, was to assess the influence of various H(2)SeO(3) concentrations added to soil (0.05, 0.15, and 0.45mMkg(-1)) on selenium and adenosine triphosphate (ATP) content, and on the activity of the ascorbate-glutathione cycle enzymes in green parts of wheat and oilseed rape. Selenium uptake by the test plants was found to vary, with content increasing from one developmental stage to the next over four stages of the developmental cycle. At the lowest H(2)SeO(3) dose (0.05mMkg(-1)), the wheat plants took up much more selenium than did the oilseed rape plants, while the amount of selenium taken up at higher doses (0.15 and 0.45mMkg(-1)) was markedly higher in rape. The increasing Se content in the wheat to about 10mgkg(-1) (in the dark) and to about 16mgkg(-1) (in the light) was accompanied by a concurrent increase in the ATP content, which remained unchanged in the light-exposed plants, while clearly decreasing in those kept in the dark. On the other hand, the ATP content of the light-exposed oilseed rape was maintained at a stable level to about 10mg Sekg(-1), following which ATP content was observed to decrease. In contrast, the tendency for the ATP content to decrease appeared immediately in the dark. The increasing plant selenium concentration was accompanied by decreased APX activity in wheat, increased activity in oilseed rape, no major change in the dehydroascorbate reductase (DHAR) activity in oilseed rape and a slight increase in wheat to about 8mg Sekg(-1), followed by a reduction. The glutathione reductase (GR) activity in wheat differed from the activity of DHAR; an increase in the selenium content to about 8mgkg(-1) was accompanied by a distinct reduction, while a significant increase was observed at higher selenium contents; in oilseed rape, the activity was observed to increase slightly within a narrow range of selenium contents (up to 5mgkg(-1)), and to decrease thereafter.

The effect of selenium (Se) on rape (Brassica napus) seedlings subjected to cadmium (Cd) stress was studied in vitro by investigating plant growth and changes in fatty acid composition, activity of antioxidative enzymes and DNA methylation pattern. Physiological experiments were carried out on seedlings cultured for 2 weeks on Murashige-Scoog (MS) media with Cd concentrations of 0, 400 and 600 microM, and on corresponding media supplied with Se (2 microM). Exposure to increasing Cd concentrations reduced the fresh weight of the upper part (hypocotyls+cotyledons) of the seedlings more strongly than that of the root system, which was accompanied by higher Cd accumulation in these tissues. In the upper part, Cd exposure led to significant changes in the biochemical parameters: fatty acid unsaturation of plasmalemma decreased, the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPOX) diminished and that of ascorbate peroxidase (APX) increased. In contrast, the roots showed an increase in fatty acid unsaturation and in the activity of antioxidative enzymes. In both parts of rape seedlings H(2)O(2) level and lipid peroxidation increased. Se addition to medium considerably reversed the Cd-induced decrease in fresh mass as well as the changes in lipid unsaturation and peroxidation. Se applied separately or in combination with Cd did not significantly affect the activity of antioxidative enzymes in the roots, but diminished it in the upper part. Moreover, the presence of Se in medium prevented changes in the DNA methylation pattern triggered in rape seedlings by high Cd concentrations. Two possible mechanisms for the action of Se were considered: (1) removal of Cd from metabolically active cellular sites, and (2) reduction of oxygen radicals.

During zygotic embryogenesis of turnip-tops (Brassica rapa L. cv. Rapa), the polygalacturonase activity (PG; EC 3.2.1.15), measured as a decrease in viscosity of polygalacturonic acid, reached a high when the desiccation process in the seeded silique was triggered and the valves had lost more than 70-75% of their moisture (45-50 DPA). The PG activity was not detected in any phases of developing seeds. This work also characterizes a cDNA with an open reading frame of 1303 bp and that codes for a putative PG called BrPG1. This falls into the category of clade-B, which includes PG related to shattering and abscission processes. The deduced BrPG1 sequence predicted a 434-residue-long precursor protein (46.7kDa) with a transit peptide sequence 23 amino acids long. A molecular mass of 44.3 kDa was calculated for the mature form of BrPG1, which showed high sequence similarity to PGA1 (97%) of B. napus (X98373) and ADPG1 (87%) of Arabidopsis thaliana (AJ002532). All conserved amino acids at the catalytic site of PGs belonging to clade-B were preserved on BrPG1. This BrPG1 gene was specifically expressed in the silique valves of turnip-tops and was temporally expressed at the beginning of its desiccation.