PubMed · 14839422
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H GOUGEROT, P BLUM, GRUPPER, G HALLEZ, IZARD. [Orange man].. https://pubmed.ncbi.nlm.nih.gov/14839422/
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The protein p12 accumulates in leaves of trees with citrus blight (CB), a serious decline of unknown cause. The function of p12 is not known, but sequence analysis indicates it may be related to expansins. In studies to determine the function of p12, sense and antisense constructs were used to make transgenic Carrizo citrange using an Agrobacterium-mediated transformation system. Homogeneous beta-glucuronidase+ (GUS+) sense and antisense transgenic shoots were regenerated using kanamycin as a selective agent. Twenty-five sense and 45 antisense transgenic shoots were in vivo grafted onto Carrizo citrange for further analyses. In addition, 20 sense and 18 antisense shoots were rooted. The homogeneous GUS+ plants contained either the p12 sense or antisense gene (without the intron associated with the gene in untransformed citrus) as shown by PCR and Southern blotting. Northern blots showed the expected RNA in the sense and antisense plants. A protein of identical size and immunoreactivity was observed in seven of nine sense plants but not in nine antisense or non-transgenic plants. At the current stage of growth, there are no visual phenotypic differences between the transgenic and non-transgenic plants. Selected plants will be budded with sweet orange for field evaluation for resistance or susceptibility to CB and general rootstock performance.
Phytophthora citrophthora causes serious losses in Citrus fruits through brown rot lesion. The effect of infection with P. citrophthora on Citrus sinensis (cv. Valencia Late) fruits was studied, with particular reference to the levels of the flavanones hesperidin and isonaringin and the polymethoxyflavones sinensetin, nobiletin, tangeretin, and heptamethoxyflavone, because flavonoids are most probably involved as natural defense or resistance mechanisms in this genus. Changes in the levels of these flavonoids were detected after infection. The hesperidin and isonaringin contents fell by 13 and 67%, respectively, whereas the contents of their corresponding aglycons, hesperetin and naringenin, increased, suggesting the hydrolyzing effect of this fungus on the glycosylated flavanones. The heptamethoxyflavone, nobiletin, sinensetin, and tangeretin levels increased by 48, 28, 26, and 24%, respectively. The in vitro study revealed that these compounds acted as antifungal agents, the most active being the aglycons (naringenin and hesperetin), followed by the polymethoxyflavones and flavanone glycosides. The participation of these flavonoids in the defense mechanism of this Citrus species is discussed.
Interstocks improve the growth and salt resistance of lemon (Citrus limon (L.) Burm. f.) trees, but their effects on orange (Citrus sinensis (L.) Osbeck) trees are unknown. We grew 'Cleopatra' mandarin (CM) seedlings, budded trees of 'Salustiano' orange (SAO) on CM, 'Valencia Late' orange (VLO) on CM (VLO/CM), and interstock trees VLO/SAO/CM in pots of sand watered with nutrient solution containing 5 (control) or 50 mM NaCl for 12 weeks. Plants were harvested on six successive occasions and the time trends in relative growth rate (RGR) and its components were estimated by fitting a Richards function regression to the harvest data. At low and high salinities, the VLO/SAO/CM combination had higher mean RGR than VLO/CM. Under control conditions, the increase in RGR caused by the interstock was the result of an increase in leaf mass fraction (LMF; leaf dry mass/plant dry mass ratio). Increases in net assimilation rate on a leaf mass basis (NARm) and LMF contributed equally to the increase in RGR in saline conditions, their growth response coefficients being 0.52 and 0.48, respectively. The structural modifications, specific leaf area (SLA) and leaf area ratio (LAR; leaf area:plant dry mass ratio), had a slight influence on the reduction in RGR by salinity. However, NARm had a large influence on RGR, except in CM. The interstock-induced mechanism increased biomass allocation to the assimilatory organs and, under saline conditions, increased Cl- and Na+ allocations to roots. Thus, the flux of ions to the leaves was either delayed or reduced or both. The dilution of imported ions by foliar growth reduced ion concentrations in leaves, resulting in higher NARm, which together with higher LMF, increased RGR.