Effects of lead stress on the growth, physiology, and cellular structure of privet seedlings

<div><p>In this study, we investigated the effects of different lead (Pb) concentrations (0, 200, 600, 1000, 1400 mg kg^-1 soil) on the growth, ion enrichment in the tissues, photosynthetic and physiological characteristics, and cellular structures of privet seedlings. We observed that with the increase in the concentrations of Pb, the growth of privet seedlings was restricted, and the level of Pb ion increased in the roots, stem, and leaves of the seedlings; however, most of the ions were concentrated in the roots. Moreover, a decreasing trend was observed for chlorophyll a, chlorophyll b, total chlorophyll, net photosynthesis (Pn), transpiration rate (Tr), stomatal conductance (Gs), sub-stomatal CO₂ concentration (Ci), maximal photochemical efficiency (Fv/Fm), photochemical quenching (qP), and quantum efficiency of photosystem II (ΦPSII). In contrast, the carotene levels, minimum fluorescence (F₀), and non-photochemical quenching (qN) showed an increasing trend. Under Pb stress, the chloroplasts were swollen and deformed, and the thylakoid lamellae were gradually expanded, resulting in separation from the cell wall and eventual shrinkage of the nucleus. Using multiple linear regression analysis, we found that the content of Pb in the leaves exerted the maximum effect on the seedling growth. We observed that the decrease in photosynthetic activation energy, increase in pressure because of the excess activation energy, and decrease in the transpiration rate could result in maximum effect on the photosynthetic abilities of the seedlings under Pb stress. Our results should help in better understanding of the effects of heavy metals on plants and in assessing their potential for use in bioremediation.</p></div

Effect of lead concentrations in the soil on the lead concentrations in <i>Ligustrum lucidum</i> seedlings.

<p>(a) root, (b) stem, (c) leaf. Vertical bars indicate means ± SD, n = 3. ANOVA values with different letters are significantly different (<i>P</i> < 0.05).</p

Linear correlations between the dry weight (DW), photosynthetic function (Pn), and their influencing factors in <i>Ligustrum lucidum</i> seedlings under lead stress.

<p>Linear correlations between the dry weight (DW), photosynthetic function (Pn), and their influencing factors in <i>Ligustrum lucidum</i> seedlings under lead stress.</p

Effects of lead stress on the growth, physiology, and cellular structure of privet seedlings - Fig 4

<p><b>Variation in the Net Photosynthetic Rate (Pn; a), Stomatal Conductance (gs; b), Intracellular CO</b>_<b>2</b><b>Concentration (Ci; c), and Transpiration Rate (Tr; d) of <i>Ligustrum lucidum</i> Seedlings under Lead Stress.</b> Vertical bars in the figure indicate means ± SD, n = 5. Different letters indicate significant differences at <i>P</i> < 0.05.</p

Effects of lead stress on the growth, physiology, and cellular structure of privet seedlings - Fig 3

<p><b>Variations in the Contents of Total Chlorophyll (a), Chlorophyll a (b), Chlorophyll b (c), and Carotenoids (d) in <i>Ligustrum lucidum</i> Seedlings under Lead Stress.</b> Vertical bars in the figure indicate means ± SD, n = 3. Different letters indicate a significant difference at <i>P</i> < 0.05.</p

Effects of lead stress on the growth, physiology, and cellular structure of privet seedlings - Fig 5

<p><b>Effects of Lead Stress on the Initial fluorescence (F</b>_<b>0</b><b>; a), Maximum Photochemical Efficiency (F</b>_<b>v</b><b>/F</b>_<b>m</b><b>; b), Photochemical Quenching (qP; c), Nonphotochemical Quenching (qN; d), and Quantum Yield (ΦPSII; e) of <i>Ligustrum lucidum</i> Seedlings.</b> Vertical bars in the figure indicate means ± SD, n = 5. Different letters indicate significant differences at <i>P</i> < 0.05.</p

Multiple linear regression analyses of biomass accumulation and photosynthetic functions in <i>Ligustrum lucidum</i> seedlings under lead stress conditions, considering the factors that influence the photosynthesis and chlorophyll fluorescence indices.

<p>Multiple linear regression analyses of biomass accumulation and photosynthetic functions in <i>Ligustrum lucidum</i> seedlings under lead stress conditions, considering the factors that influence the photosynthesis and chlorophyll fluorescence indices.</p

Ranking of candidate reference genes in order of their expression stability as calculated by BestKeeper.

<p>Note: Expression stability and ranking of 10 reference genes as calculated by Bestkeeper in all samples (A), different ages (B), different tissue types (C), cold-treated (D), heat-treated (E), NaCl-treated (F), PEG-treated (G), ABA-treated (H). Descriptive statistics of 10 candidate genes based on their coefficient of variance (CV) and standard deviation (SD) of Ct values were determined using the whole data set, and all Ct values were analyzed as a total data set. Reference genes are identified as the most stable genes (those with the lowest coefficient of variance and standard deviation; CV±SD).</p

Determination of the optimal number of reference genes for normalization by pairwise variation (V) using geNorm.

<p>Determination of the optimal number of reference genes for normalization by pairwise variation (V) using geNorm.</p

Effects of aspect and size class of layering module on clonal reproduction of <i>Nitraria tangutorum</i>.

<p>RatRs and DenAR represent the rate of ramet sprouting (%) (A and B)and density of adventitious root formation points (number/cm) (C and D), respectively. BioLm represents the layering biomass; Open bars (A and C) are grand means of four aspect sections across two size classes of layering. Grayscale bars (B and D) are means of the four aspect sections and two size classes of layering; the error bars represent standard errors of the means; the letters above the error bar are the groupings from Duncan's multiple range tests. Bars followed by different letters are significantly different at <i>P</i> = 0.05.</p