Low pH stress activates several genes for lateral root formation and detoxification of aluminum ions in Cotton plants

In low pH condition of soils (pH<5), Al is solubilized into a phytotoxic form Al(H2O)63+ and inhibits the plant root growth and development. Precisely, during low pH stress (e.g., pH 4.75), aluminum compound converts into its ionic form and becomes higher in level which is a limiting factor for plant root growth and seedling formation. Under aluminum (Al) toxic conditions, the organic acid transporters for example citrate and malate transporters in plasma membrane are involved in organic acid release and form non phytotoxic stable complexes with Al3+ in the rhizosphere. The study showed that, the cotton seedlings exhibited very sensitive phenotypes to low pH stress conditions due to high accumulation of ionic Al stress, the seedlings displayed retarded primary, secondary root growth and small cotyledons. These results indicated that cotton plants are susceptible to low pH condition.. As a whole without fine divisions the root system becomes corraloid in structure which will be having squat secondary roots. Plant has developed a natural defense mechanism in order to combat this unfavorable environment. Expression profile and Al complexation with organic acid exudates studies clearly revealed that both GhALMT1 and GhALS3 genes are involved in Al3+detoxification mechanisms. The remarkable expression was detected for GhALS3 under both low pH and aluminum stress condition in comparison to wild type untreated control whereas GhALMT1 expression was only activated under Al3+ stress condition. Our study, displayed enhanced citrate and malate excretion values in the wild type plants which are treated with Al and H+ stress. Thus, it can be clearly mentioned that GhALMT1 and GhALS3 is playing a significant role in low pHstress tolerance of cotton plant

In Vivo Assessment of Cold Tolerance through Chlorophyll-a Fluorescence in Transgenic Zoysiagrass Expressing Mutant Phytochrome A.

Chlorophyll-a fluorescence analysis provides relevant information about the physiology of plants growing under abiotic stress. In this study, we evaluated the influence of cold stress on the photosynthetic machinery of transgenic turfgrass, Zoysia japonica, expressing oat phytochrome A (PhyA) or a hyperactive mutant phytochrome A (S599A) with post-translational phosphorylation blocked. Biochemical analysis of zoysiagrass subjected to cold stress revealed reduced levels of hydrogen peroxide, increased proline accumulation, and enhanced specific activities of antioxidant enzymes compared to those of control plants. Detailed analyses of the chlorophyll-a fluorescence data through the so-called OJIP test exhibited a marked difference in the physiological status among transgenic and control plants. Overall, these findings suggest an enhanced level of cold tolerance in S599A zoysiagrass cultivars as reflected in the biochemical and physiological analyses. Further, we propose that chlorophyll-a fluorescence analysis using OJIP test is an efficient tool in determining the physiological status of plants under cold stress conditions

Phenotypic differences between non-transgenic (NT) and transgenic plants expressing wild-type oat PhyA (PhyA) in the above panel and control plants carrying only vector with a <i>BAR</i> gene for herbicide resistance (HR) and transgenic plants expressing mutant PhyA (S999A-PhyA-18) in the lower panel.

<p>This photograph was taken in late October 2014 at Jeju National University experimental plots, Jeju, South Korea.</p

Radar plot with a series of parameters derived from JIP-test analyses of the experimental fluorescence OJIP transients.

<p>This plot depicts possible differences in the structure and function of the photosynthetic apparatus under different conditions; PhyA plants under normal conditions (PhyA-Con) as closed blue diamonds, PhyA plants under cold stress (PhyA-Cold) as open red squares, S599A-2-14 plants under normal conditions (S599A-2-14-Con) as closed green triangles, S599A-2-14 plants under cold stress (S599A-2-14-Cold) as pink crosses, S599A-2-18 plants under normal conditions (S599A-2-18-Con) as closed blue squares, S599A-2-18 plants under cold stress (S599A-2-18-Cold) as closed brown circles, non-transgenic plants under normal conditions (NT-Con) as closed black squares and non-transgenic plants under cold stress (NT-Cold) are depicted as open yellow circles. The deviation of the behavior pattern from the regular polygon demonstrates the fractional impact, compared to the untreated plants of the corresponding treatment. Details of each parameter are discussed in the Results section.</p

Formulae and glossary of terms used by the JIP-test (modified after Strasser et al. 2004).

<p>Formulae and glossary of terms used by the JIP-test (modified after Strasser et al. 2004).</p

Estimation of ROS-scavenging enzymes activities.

<p>Specific enzyme activities of (A) APx, (B) CAT, (C) GR and (D) SOD were determined in the leaves of in non-transgenic control (NT) plants, expressing oat PhyA (PhyA) and plants expressing mutant PhyA (S599A-2-14 and S599A-2-18) subjected to cold stress. Different letters in each column indicate significant differences (<i>p≤0</i>.<i>05</i>) in between treatments after Tukey’s test (n = 5).</p

Estimation of (A) hydrogen peroxide content and (B) proline content in non-transgenic control (NT), plants expressing oat PhyA (PhyA) and plants expressing mutant PhyA (S599A-2-14 and S599A-2-18) subjected to cold stress.

<p>Different letters in each column indicate significant differences (<i>p≤0</i>.<i>05</i>) in between treatments after Tukey’s test (n = 3).</p

Schematic representation of the JIP-test expressed in terms of sequential energy fluxes from absorbance (ABS) of photons by PSII antenna, intermediate trapping flux (TR), electron transport (ET) and the reduction of the end-electron acceptors at the PS I electron acceptor side (RE) driven by PS I.

<p>Formulae and glossary of terms used by the JIP-test are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127200#pone.0127200.t001" target="_blank">Table 1</a>.</p

In Vivo Assessment of Cold Tolerance through Chlorophyll-<i>a - Fig 4 </i> Fluorescence in Transgenic Zoysiagrass Expressing Mutant Phytochrome A

<p><b>A.</b> Chlorophyll-a fluorescence kinetics of the OJIP curve of dark-adapted leaves of zoysiagrass plants. Transient curves of each line represent the average of 15 measurements per treatment. PhyA-Cold, plants expressing oat PhyA subjected to cold stress; NT-Cold, non-transgenic plants subjected to cold stress; S599A-2-14-Cold, transgenic plants expressing mutant PhyA line-14 subjected to cold stress; S599A-2-14-Con, transgenic plants expressing mutant PhyA line-14 under normal conditions; S599A-2-18-Con, transgenic plants expressing mutant PhyA line-18 under normal conditions; S599A-2-18-Cold, transgenic plants expressing mutant PhyA line-18 subjected to cold stress; NT-Con, non-transgenic plants under normal conditions; PhyA-Con, plants expressing oat PhyA under normal conditions. Fluorescence transients of NT-C, PhyA-C, and S599A (S599A-2-14-C and S599A-2-18-C) plants under cold stress conditions and their respective control plants (NT, PhyA, S599A-2-14, and S599A-2-18) maintained under greenhouse conditions are plotted with black dashes, blue triangles, green circles, blue squares, yellow circles, red squares, pink crosses, and brown circles, respectively. <b>B.</b> The L-band: Relative variable fluorescence V_OK = (F_t − F_o)/(F_k − F_o) and differences between NT, PhyA and S599A plants under normal and cold stress conditions. Curves without lines (left axis) and curves with solid symbols represent difference kinetics, ΔV_OK of plants under normal and cold stress conditions on the logarithmic scale (right vertical axis). <b>C.</b> The K-band; Double normalization of the data for NT, PhyA and S599A plants under normal and cold stress conditions at F₀ and F_J, V_OJ = (F_t–F₀)/(F_J–F₀). NT-Con/NT-Con as green diamonds; NT-Con/NT-Cold as red triangles; PhyA-Con/PhyA-Cold as brown squares; S599A-2-18-Con/S599A-2-18-Cold as purple diamonds and S599A-2-14-Con/S599A-2-14-Cold as green circles.</p