Survival of <i>M</i>. <i>persicae</i> on <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants.

<p><i>M</i>. <i>persicae</i> survival on (A) local and (B) systemic leaves of WT tobacco plants. <i>M</i>. <i>persicae</i> survival on (C) local and (D) systemic leaves of NahG tobacco plants. Values represent the mean survival of aphids ± standard error.</p

Fecundity of <i>M</i>. <i>persicae</i> on <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants.

<p><i>M</i>. <i>persicae</i> fecundity on local and systemic leaves of (A) WT and (B) NahG tobacco plants. Values represent the mean number of newborn nymphs per female ± standard error. ^** indicates significant differences (<i>P</i> ≤ 0.01) relative to the controls.</p

Quantification of SA hormone levels in <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants.

<p>SA levels in (A) local and (B) systemic leaves of WT plants and in (C) local and (D) systemic leaves of NahG plants after 10, 15, and 20 days of <i>B</i>. <i>tabaci</i> nymphs infestation. Values represent the mean ng SA per g fresh weight (FW) ± standard error. ^**indicates significant differences (<i>P</i> ≤ 0.01) relative to the controls.</p

Infestation by <i>B</i>. <i>tabaci</i> nymphs on defense enzyme activity levels of WT and NahG tobacco plants.

<p>Each value represents the average (± SE) of four replicates. The different capital letters in each of the column indicate significant differences among local and systemic leaves of treated plants in activity levels of each defense enzyme (<i>P</i> < 0.05). The different lowercase letters at each of the rows indicate significant differences between WT and NahG plants in activity levels of each defense enzyme (<i>P</i> < 0.05).</p><p>Infestation by <i>B</i>. <i>tabaci</i> nymphs on defense enzyme activity levels of WT and NahG tobacco plants.</p

<i>M</i>. <i>persicae</i> survival on <i>B</i>. <i>tabaci</i> nymph-infested plants.

<p><i>M</i>. <i>persicae</i> survival on (A) local and (B) systemic leaves of <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants. Values represent the mean survival of aphids ± standard error.</p

Antioxidant Enzyme Responses Induced by Whiteflies in Tobacco Plants in Defense against Aphids: Catalase May Play a Dominant Role

<div><p>Background</p><p><i>Bemisia tabaci</i> MEAM1 (Middle East-Asia Minor 1) feeding alters antioxidative enzyme activity in some plant species. Infestation of <i>B</i>. <i>tabaci</i> nymphs decreases <i>Myzus persicae</i> performance on systemic, but not local leaves of tobacco plants. However, it is unclear if <i>B</i>. <i>tabaci</i> nymphs induced antioxidant activities contributing to the aphid resistance.</p><p>Methodology/Principal Findings</p><p>We investigated the relationship between antioxidants induced by nymphs of <i>B</i>. <i>tabaci</i> feeding on tobacco and aphid resistance. The activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and the concentration of hydrogen peroxide (H₂O₂) were assayed in tobacco leaves at different feeding times following infestation of <i>B</i>. <i>tabaci</i> nymphs. The infestation altered the activities of CAT and POD, but had no significant effect on SOD activity. The highest CAT activity was observed at 15 d after infestation. This was 98.2% greater than control systemic leaves, but 32.6% lower than the control in local leaves. Higher POD activity was recorded in local vs. systemic leaves after 15 d of infestation. POD activity was 71.0% and 112.9% higher in local and systemic leaves, respectively, than in the controls. The changes of CAT, but not POD or SOD activity were correlated to levels of aphid resistance. H₂O₂ levels were higher in local than in systemic leaves in contrast to CAT activity. <i>Tobacco curly shoot virus</i> mediated virus-induced gene silencing was employed to determine if CAT activation was involved in the aphid resistance induced by <i>B</i>. <i>tabaci</i> nymphs. <i>B</i>. <i>tabaci</i> induced CAT activity decreased when the <i>Cat1</i> expression was silenced. The performance assay indicated that <i>Cat1</i> silencing made <i>B</i>. <i>tabaci</i> infested plants a more suitable host for aphids than infested control plants. The aphid survival rate was reduced by 40.4% in infested control plants, but reduced by only 26.1% in <i>Cat1</i>-silenced plants compared to uninfested controls. Also, qPCR results showed that silencing of <i>Cat1</i> led to the suppression of the <i>B</i>. <i>tabaci</i> mediated <i>PR-2a</i> expression.</p><p>Conclusions/Significance</p><p>Aphid resistance in plants infested with <i>B</i>. <i>tabaci</i> nymphs is associated with enhanced antioxidant activities in which CAT may play a dominant role. This resistance probably acted via interactions with SA-mediated defense responses.</p></div

Quantification of H₂O₂ levels in <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants.

<p>H₂O₂ levels in (A) local and (B) systemic leaves of tobacco plants after 5, 10, 15, and 20 days of <i>B</i>. <i>tabaci</i> nymphs infestation. Values represent the mean μmol H₂O₂ per g fresh weight (FW) ± standard error. Paired means with the same letter are not significantly different (P > 0.05).</p

SOD activity levels in tobacco plants infested with <i>B</i>. <i>tabaci</i> nymphs.

<p>SOD activity levels in (A) local and (B) systemic leaves of tobacco plants after 5, 10, 15, and 20 days of <i>B</i>. <i>tabaci</i> nymphs infestation. Values represent the mean unit per mg protein ± standard error. Paired means with the same letter are not significantly different (P > 0.05).</p

Infestation by <i>B</i>. <i>tabaci</i> nymphs on relative expression of <i>Cat1</i> in tobacco plants.

<p>Relative expression of <i>Cat1</i> on systemic and local leaves of (A) empty vector injected and (B) <i>Cat1</i>-silenced plants. Values represent the mean expression levels of <i>Cat1</i> ± standard error. (C) CAT activity on systemic and local leaves of <i>Cat1</i>-silenced tobacco plants. Paired means with the same letter are not significantly different (P > 0.05).</p

Relative expression of <i>PR-2a</i> on <i>B</i>. <i>tabaci</i> nymph-infested tobacco plants.

<p>Relative expression of <i>PR-2a</i> on local and systemic leaves of (A) empty vector injected and (B) <i>Cat1</i>-silienced tobacco plants. Values represent the mean <i>PR</i> gene expression levels ± standard error. Paired means with the same letter are not significantly different (P > 0.05).</p