Abstract
Although huanglongbing (HLB) is a devastating citrus disease, improved tolerant cultivars, such as Sugar Belle (SB) mandarin, have been identified. To understand the responses that HLB-affected SB undergoes, we compared 14 CO 2 fixation, carbohydrate export, phloem callose accumulation, relative expression of plant defense activators, and anatomical changes between healthy and infected SB trees versus susceptible Pineapple (PA) sweet orange. Eight- to ten-week-old leaves of infected SB showed a 2.5-fold increase in 14 CO 2 fixation and a 13% decrease in 14 C-carbohydrate export, whereas HLB-affected PA presented a decrease of 33 and 50%, respectively. The mean distance of a callose deposit to its closest neighbor was 36% smaller in infected SB versus healthy, whereas in HLB-affected PA, it was 33% higher. Expression of papain-like cysteine proteases (PLCPs) was upregulated in SB but downregulated in PA. Infected SB showed minor alterations in the number of xylem vessels, a 16% larger xylem vessel lumen area, and a 14% increase in the proportional area of the xylem. In contrast, PA showed a 2.4-fold increase in the xylem vessel number and a 2% increase in the proportional xylem area. Three complementary mechanisms of tolerance in SB are hypothesized: (i) increased carbohydrate availability induced by greater CO 2 fixation, mild effect in carbohydrate export, and local accumulation of callose in the phloem; (ii) activation of defense response via upregulation of PLCPs, and (iii) increased investment in the xylem structure. Thus, phloem and xylem modifications seem to be involved in SB tolerance.
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Claims 14
Claim · model-written summary
Infected SB leaves had a 2.5-fold increase in carbon fixation.
Verbatim
e0“Eight- to ten-week-old leaves of infected SB showed a 2.5-fold increase in 14 CO 2 fixation”
e1“Sugar Belle (SB) mandarin”
Claim · model-written summary
Infected SB leaves had a 13% decrease in carbohydrate export.
Verbatim
e0“a 13% decrease in 14 C-carbohydrate export”
e1“Eight- to ten-week-old leaves of infected SB”
e2“Sugar Belle (SB) mandarin”
Claim · model-written summary
HLB-affected PA had a 33% decrease in carbon fixation.
- Taxon
- Pineapple
Ananas comosuse2 - Outcome
- 14 CO 2 fixatione1
- Direction
- decreasee0
- Value
- 33e0
- Qualifier
- HLB-affectede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HLB-affected PA presented a decrease of 33 and 50%, respectively”
e1“14 CO 2 fixation and a 13% decrease in 14 C-carbohydrate export”
e2“Pineapple (PA) sweet orange”
Claim · model-written summary
HLB-affected PA had a 50% decrease in carbohydrate export.
- Taxon
- PineappleAnanas comosuse2
- Outcome
- 14 C-carbohydrate exporte1
- Direction
- decreasee0
- Value
- 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HLB-affected PA presented a decrease of 33 and 50%, respectively”
e1“14 C-carbohydrate export”
e2“Pineapple (PA) sweet orange”
Claim · model-written summary
Nearest-neighbor callose deposit distance was 36% smaller in infected SB.
Verbatim
e0“The mean distance of a callose deposit to its closest neighbor was 36% smaller in infected SB versus healthy”
e1“Sugar Belle (SB) mandarin”
Claim · model-written summary
Nearest-neighbor callose deposit distance was 33% higher in HLB-affected PA.
- Taxon
- PineappleAnanas comosuse2
- Outcome
- mean distance of a callose deposit to its closest neighbore1
- Direction
- highere0
- Value
- 33%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in HLB-affected PA, it was 33% higher”
e1“The mean distance of a callose deposit to its closest neighbor”
e2“Pineapple (PA) sweet orange”
Claim · model-written summary
PLCP expression rose in SB.
Verbatim
e0“Expression of papain-like cysteine proteases (PLCPs) was upregulated in SB”
e1“Sugar Belle (SB) mandarin”
Claim · model-written summary
PLCP expression fell in PA.
- Taxon
- PineappleAnanas comosuse1
- Gene
- papain-like cysteine proteases (PLCPs)e0
- Outcome
- Expression of papain-like cysteine proteases (PLCPs)e0
- Direction
- downregulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Expression of papain-like cysteine proteases (PLCPs) was upregulated in SB but downregulated in PA”
e1“Pineapple (PA) sweet orange”
Claim · model-written summary
Infected SB showed minor changes in xylem vessel number.
Verbatim
e0“Infected SB showed minor alterations in the number of xylem vessels”
e1“Sugar Belle (SB) mandarin”
Claim · model-written summary
Infected SB had a 16% larger xylem vessel lumen area.
Verbatim
e0“a 16% larger xylem vessel lumen area”
e1“Infected SB showed minor alterations”
e2“Sugar Belle (SB) mandarin”
Claim · model-written summary
Infected SB had a 14% increase in proportional xylem area.
Verbatim
e0“a 14% increase in the proportional area of the xylem”
e1“Infected SB showed minor alterations”
e2“Sugar Belle (SB) mandarin”
Claim · model-written summary
PA had a 2.4-fold increase in xylem vessel number.
- Taxon
- PineappleAnanas comosuse1
- Outcome
- xylem vessel numbere0
- Direction
- increasee0
- Value
- 2.4-folde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PA showed a 2.4-fold increase in the xylem vessel number”
e1“Pineapple (PA) sweet orange”
Claim · model-written summary
PA had a 2% increase in proportional xylem area.
- Taxon
- PineappleAnanas comosuse2
- Outcome
- proportional xylem areae0
- Direction
- increasee0
- Value
- 2%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a 2% increase in the proportional xylem area”
e1“PA showed a 2.4-fold increase”
e2“Pineapple (PA) sweet orange”
Claim · model-written summary
The authors hypothesize that carbohydrate availability, defense activation and xylem investment contribute to SB tolerance.
Verbatim
e0“Three complementary mechanisms of tolerance in SB are hypothesized: (i) increased carbohydrate availability induced by greater CO 2 fixation, mild effect in carbohydrate export, and local accumulation of callose in the phloem; (ii) activation of defense response via upregulation of PLCPs, and (iii) increased investment in the xylem structure”
e1“Sugar Belle (SB) mandarin”